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Abstract This LPG Gas Sensor (MQ6), ideal sensor for use to detect the presence of a dangerous LPG leak in your Home, car or in a service station, storage tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a visual indication of the Combustible Gas / LPG concentration. The sensor has excellent sensitivity combined with a quick repsonse time. The sensor can also sense iso-butane, propane, LNG and cigarette smoke. This LPG Gas Sensor can be used to make wireless Gas leak detector in home security system This project is High Sensitivity to LPG, iso-butane, propane. This also can sense to alcohol and smoke, but with poor sensitivity. This project is designed to detect the LPG from 100parts per million (PPM) to 10,000 PPM. Whenever LPG is detected, the sensor produces the output voltage, which is depended on the amount of gas leakage. This voltage drives the transistor into saturation region. A buzzer is connected to produce audible alert signal. This project uses regulated 5V, 750mA power supply for charging the battery. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/18V step down transformer.

Diagram

Gas Conversion

Approvals LPG Bulk Transport Auto LPG Dispensing Stations Gas Conversion ALDS Installation About Auto LPG Trademark

1. ADVANTAGES OF LPG ON PETROL ?
LPG has an anti knocking power which is comparable with Gasoline and superior to Diesel. The oil drain period of car running on Auto LPG will increase and it will also extend the life of spark plug as Auto LPG is a clean fuel. Adulteration or spilling or theft is not possible LPG reaches the engine in pure form resulting in an improved air / fuel mixture and enables refined combustion. There is hardly any discharge of co(Carbon mono oxide ) as compared to petrol and diesel since the exhaust fumes contains less harmful substance. The CO emissions are around 80% less than petrol and 40 % less than diesel. Hydrocarbon emissions are 60 % less than petrol and 50 % less than diesel. Nitrous Oxide emissions are around 80 % less than petrol and 90 % less than diesel. Carbon dioxide which contributes to global warming is less in LPG. Existing fuel system is retained which can work as an option and thus increases the flexibility of the usage

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of the mode of fuel.

2. IS IT LEGAL?
LPG as motor fuel is now legal, with the amendment of all statutory regulations, such as CMV Act, CMV Rules, LPG Control Order etc. vehicles owners have to use only approved brand of kits (Type approvals now being granted by the testing agencies) and get the vehicle R.C.book endorsed by the local R.T.O The retro - fitment of LPG kits can be carried out only by authorized workshops approved by RTO and Transport Dept.

3. GAS & PETROL CAN WORK IN THE SAME ENGINE
Yes, LPG like CNG can be used in bi-fuel mode for which selector switch is erected on dashboard,to activate Solenoid valve of either MS or LPG.

4.DUEL FUEL SYSTEM ?
As stated above,you can start and run the car with either gas or petrol by using an electronic change over switch provided on dashboard.

5. SAFETY ?
The LPG Conversion Kit have large number of inherent safety features and is also manufactured, tested and installed as per highest international standards. It is thus safe in all the ways to convert the vehicle using LPG Conversion kit. To understand this better certain facts are to be given due consideration fixed Auto LPG Tanks are made as per BIS Standards to meet all safety requirements. A tank can normally burst only in the event of a fire in a car where the surrounding temperature exceeds atleast 400o - 500o degree centigrade which again never happens in a car due the presence of pressure relieving devices. The tanks fitted with multifunction valve with large number of safety fittings like Safety

Relief Valve, Excess Flow Valve. ROV's fusible plug fitted on it.

6. WHERE IS THE TANK PLACED IN THE CAR?
It is fixed in the luggage space of your car. It is fastened with metal strap so that it doesnot move while the car is running. As per BIS code it has to be permenantely fitted tank an should be integral part of vehicle ( As per BIS 14899 for fuel tank container and as per LPG control order) 7. WILL AN EXCESS LOAD OF TANK AFFECT MY CAR SUSPENSION? No a car is designed to carry sufficient load. This is similar to carrying a passenger with luggage. Moreover, the weight of empty LPG tank of 60 Ltrs. capacity of weights not more than 20 kgs.

8. HOW WILL I KNOW THAT I SHOULD REFILL, THE GAS ?
The content gauge on the multivalve and the indicator on the switch mounted on the dash board shows the level of LPG inside the tank.

9. HOW MUCH MILEAGE DO I GET FROM LPG ?
1 Ltr of LPG will give approx .0.8 to 0.9 time mileage as petrol. For Eg : If a car on a petrol runs for 10 Km the same will run for 8-9Km with 1 Ltr of LPg considering the lower coast of LPG 40 % coast of savings could be expected.

10. WILL IT AFFECT MY CATALYTIC CONVERTOR ?
No it will not damage any part of the engine or fuel system.There is no lead in LPG

11. HOW IS ITS PERFORMANCE ?

Very low emissions, no smoke no compromise on the pick up.

12. IN THE EVENT OF ANY LEAKAGE WILL IT EXPLODE ?
As explained earlier the fuel tanks have several pressure relieving devices to avert any blast or explosions. This is demonstrated in Bonfire tests, where in the car is set on fire. the leaked product from the vent will get out from the rear tyre, but even after prolonged fire there are no explosions occurring due to the provison of pressure relieving devices.

13. IN A SMALL CAR LIKE MARUTI WILL IT NOT OCCUPY MY LUGGAGE SPACE ?.
A Smaller tank is fitted in small cars to facilitate easy removal of Stepny Torroidal tanks (in the shape of a tyre) can also be installed which help to save luggage room. Alternatively small tanks 36 Liters are available to conserve the space

14. WILL THERE BY ANY SMELL IN THE PASSENGER CABIN ?
Ethyl Mercaptan is added in 20 PPM to Auto LPG to detect the leakage. This is a safety feature. At the time of installation approved leakage test is done and a leakage free installation is ensured.

15. WHAT IS THE PRICE OF THE CONVERSION KIT
For carburetor Cars Rs. 23,000/- including installation /fittling charges.

16. PROCEDURES FOR APPROVAL WITH R.T.O ?
On getting your vehicle converted with an approved LPG conversion kit, the Retro-fitment Centre will facilitate the endorsement in the vehicle R.C.Book by the local R.T.O this endorsement permits legal use of the kit in your vehicle .

17. CAN WE USE CNG KITS AND TANKS ON LPG FUEL ? - NOThe properties and characteristics of CNG and LPG are different. The safety and other devices are set for a particular pressure of LPG. There is no fill limiter in case of CNG tanks as it meant for the Services of Gas. The fill connections are also different for LPG and CNG. Hence, not advisable to use CNG kits for LPG Service.

IS AUTO LPG SAFE?
YES, LPG is absolutely safe and in fact safer than petrol

The gas is stored in the vehicle in liquid form and contained in an Auto LPG Tank. The Tank is designed from special low carbon steel. Tests and practical experiences have shown that LPG can only ignite or cause a fire if it leaks and spreads at tight area and then it is ignited. Such a situation does not arise in automobile as the engine compartment is open to air and any leaked gas will escape. Moreover, these are the same kits as used in European countries. If the Autogas system and tanks were not safe would the large number of car users in America, Australia and Europe where there are stringent safety norms have changed their vehicles to run on Autogas? What you have to do is to ensure that you use a good quality approved kit as these kits undergo rigorous tests ensure safety, also ensure that you have the kit fitted by an approved Retro fitment Center.

1.1 INTRODUCTION This project is microcontroller based project. A Gas sensor is used to Detect dangerous gas leaks in the kitchen or near the gas heater. This unit detects 300 to 5000ppm of Natural Gas. Ideal to detect dangerous gas leaks in the kitchen. Sensor can be easily configured as an alarm unit. The sensor can also sense LPG and Coal Gas. Ideal sensor for use to detect the presence of a dangerous LPG leak in your car or in a service station, storage tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a visual indication of the LPG concentration. The sensor has excellent sensitivity combined with a quick response time. detected is messaged to the authorized person using cellular network called GSM. In this project there are mainly two units, GSM modem and microcontroller unit.GSM modem can be configured by standard GSM AT command set for sending and receiving SMS and getting modem status. Depending upon the Gas sensor output microcontroller can send message to the authorized person and also depending upon the message received the microcontroller unit will control the devices and acknowledges the device status to the user as SMS. 1.2. SOFTWARE & HARDWARE REQUIREMENTS a) SOFTWARE REQUIREMENTS  Keil software programming using assembly language  Flash magic b) HARDWARE REQUIREMENTS  Gas sensor  Microcontroller  LCD display  GSM  MAX 232 GAS SENSOR 2.1. GAS SENSOR: A NATURAL GAS SENSOR is an electronic device which Detect dangerous gas leaks in the kitchen or near the gas heater. This unit detects 300 to 5000ppm of Natural Gas. Ideal to detect dangerous gas leaks in the kitchen. Sensor can be easily configured as an alarm unit. The sensor can also sense LPG and Coal Gas. A LPG SENSOR Ideal sensor for use to detect the presence of a dangerous LPG leak in your car or in a service station, storage tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a visual indication of the LPG concentration. The sensor has excellent sensitivity combined with a quick response time. The sensor can also sense iso-butane, propane, LNG and cigarette smoke. FEATURES: • High sensitivity to LPG, iso-butane, propane • Small sensitivity to alcohol, smoke. • Fast response . . Stable and long life • Simple drive circuit

2.2 NATURAL/LPG GAS SENSOR: STRUCTURE AND CONFIGURATION: Sensor composed by micro AL2O3 ceramic tube, Tin Dioxide (SnO2) sensitive Layer , measuring electrode and heater are fixed into a crust made by plastic and stainless steel net. The heater provides necessary work conditions for work of sensitive components. The enveloped MQ-5 have 6 pin ,4 of them are used to fetch signals, and other 2 are used for providing heating current. They are used in gas leakage detecting equipments in family and industry, are suitable for detecting of LPG, natural gas , town gas, avoid the noise of alcohol and cooking fumes and cigarette smoke. The gas sensor gives 12v to 16 v output when triggered and this output voltage is given to the microcontroller using NPN transistor BC547.The gas sensor output is taken across he HS1527 OTP Encoder, HS1527 It can reduce any code collision and unauthorized code scanning possibilities. Natural gas is an energy source that is commonly used in homes for cooking, heating, and Water heating. It is primarily composed of methane. (Methane is a highly flammable chemical compound consisting of one carbon atom surrounded by four hydrogen atoms.) Although it only happens rarely, a natural gas leak can sometimes occur inside the home. A natural gas leak can be dangerous because it increases the risk of fire or explosion. Your local gas company works hard to provide adequate warning in the event of a gas leak. Because methane—and therefore, natural gas—does not have any odor, the gas company adds a warni“rottenegg” smell (mercaptan or a similar sulfur-based compound) that can be easily detected by most people. However, people who have a diminished sense of smell may not be able to rely upon this safety mechanism. If you have a concern about your ability to smell the additive that signals a gas leak, you need to see a physician and use a different safety signal. A gas detector can be an important tool to help protect you and your family. PRECAUTIONS TO BE TAKEN WHEN GAS LEAKAGE DETECTED: What to do if your gas detector alerts you to a natural gas leak 1. Leave the house immediately. 2. DO NOT make calls from your home. Phones are capable of producing a spark, which could start a fire or explosion. Contact your local gas utility company or call 911 from a phone outside and away from your home. 3. DO NOT light a match or other combustible material. Likewise, DO NOT turn any light switches on or off, and DO NOT plug or unplug electrical appliances such as a television or vacuum cleaner. These activities also can produce a spark that could start a fire or explosion. 4. Do not re-enter the house until the gas company finds the source of the leak and corrects it. 2.3 SOURCES OF NATURAL GAS SENSORS: 1. Leaks from gas appliances, heating systems, and water heaters 2. Leaks from interior natural gas piping systems 3. Migration of natural gas indoors from leaks in outdoor piping systems

Gas Sensors

Share: Our organization is reckoned as a trusted trader and exporter of Gas Sensors. Our range of Gas Sensors includes Flammable Gas & Smoke Sensor MQ-2, Alcohol Gas Sensor MQ-3, Methane CNG Gas Sensor - MQ-4, LPG & Natural GAS Sensor MQ- 5, LPG Gas Sensor (MQ6), Carbon Monoxide Sensor ( MQ-7), Semiconductor Sensor MQ135 and MQ303A Alcohol Sensor. The technologically advanced product range is fitted with advanced sensors and components. We make sure that the products are thoroughly tested on their quality parameters before these get delivered to the clients. Our range encompasses: Flammable Gas & Smoke Sensor MQ-2

We are engaged in offering Flammable Gas & Smoke Sensors that can detect the presence of combustible gas and smoke at concentrations from 300 to 10,000 ppm. Owing to its simple analog voltage interface, the sensor requires one analog input pin from the microcontroller. The product can detect the presence of the smoke and send the output in form of analog signals. Our range can function at temperature ranging from -20 to 50°C and consume less than 150 mA at 5 V.

Send Enquiry Alcohol Gas Sensor MQ-3

Functioning similar to common breath-analyzer, Alcohol Gas Sensor can detect the concentration of alcohol in breath. The range is appreciated for high sensitivity and fast response time. On the basis of alcohol concentration, the sensor provides analog resistive output. Further, due to the simple design of the product, it requires only one resistor to detect and process the result. Given below are few highlighting features of our products:
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5V DC or 5V AC Requires heater voltage Operation Temperature: -10 to 70 degrees C Heater consumption: less than 750mW Dimensions: 16.8mm diameter 9.3 mm height without the pins

Send Enquiry Methane CNG Gas Sensor - MQ-4

Available with heater coil with 5V, load resistance and ADC output, Methane CNG Gas Sensor is reckoned for its high sensitivity and fast response time. Our range is suitable for sensing natural gas (composed of mostly Methane [CH4]) concentrations in the air. It can ascertain natural gas concentrations ranging between 200 and 10000 ppm. The product is easy to install and can be used in conjunction with breakout boards.

Send Enquiry LPG & Natural GAS Sensor MQ- 5

In order to ensure optimum safety and security, our clients can rely on our range of LPG & Natural GAS Sensors. It can be easily installed for detecting presence of LPG, natural gas, fumes, cigarette smoke and town gas. The reliable and durable sensor is provided with simple drive circuit. Some highlighting features of our products are:
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High sensitivity to LPG, natural gas, town gas Small sensitivity to alcohol & smoke Fast response Stable working life

Send Enquiry LPG Gas Sensor (MQ6)

Extensively used in homes, cars, service stations and storage tanks, LPG Gas Sensor can be easily installed into an alarm unit. The equipment provides visual indication of the combustible gas or LPG concentration. It can sense iso-butane, propane, LNG and cigarette smoke. We hold expertise in offering wireless gas leak detectors for home security systems. Given below are few highlighting features of our products:
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High Sensitivity Small sensitivity to alcohol, smoke Detection range from 100 - 10,000 ppm isobutane propane Fast response time <10s Simple drive circuit Heater voltage: 5.0V Dimensions: 18mm Diameter: 17mm High excluding pins Pins - 6mm high

The application areas of our products are given below:
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Gas leak detection system Gas leak alarm Fire/Safety detection system Gas detector

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We bring forth for our clients Carbon Monoxide Sensors that provide output in the form of analog signal. The product finds usage in sensing carbon monoxide concentrations (PPM) in the air. It can measure CO concentrations ranging from 20 to 2000 ppm. The drive circuit contains a voltage divider, which requires heater coil with 5V DC or AC, a load resistance, and output source such as ADC or a simple OPAMP comparator.

Send Enquiry Semiconductor Sensor MQ135

With the implementation of latest technology and quality tested components, our vendors offer Semiconductor Sensor MQ135. The product has high sensitivity to ammonia, sulfide and benze steam, smoke and other harmful gases. Easy to install and maintain, the product is used for the following applications:
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Domestic air pollution detector Industrial air pollution detector Portable air pollution detector

Some other features of our products are highlighted below:
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High sensitivity to ammonia, sulfide and benzene Long life and low cost

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Simple drive circuit

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Our expertise enables us to offer MQ303A semiconductor sensors. The portable detector can be used to offer good sensitivity and fast response to alcohol. We make sure that the products are thoroughly tested for their quality and reliability before these get delivered to the clients. Given below are some striking features of our products:
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High sensitivity Fast response and resume Long life and low cost Mini size

Relay
From Wikipedia, the free encyclopedia Jump to: navigation, search This article is about the electrical component. For other uses, see Relay (disambiguation). This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2009)

Automotive-style miniature relay, dust cover is taken off A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

Contents
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1 Basic design and operation 2 Types

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2.1 Latching relay 2.2 Reed relay 2.3 Mercury-wetted relay 2.4 Polarized relay 2.5 Machine tool relay 2.6 Ratchet relay 2.7 Contactor relay 2.8 Solid-state relay 2.9 Solid state contactor relay 2.10 Buchholz relay 2.11 Forced-guided contacts relay 2.12 Overload protection relay 3 Pole and throw 4 Applications 5 Relay application considerations o 5.1 Derating factors o 5.2 Undesired arcing 6 Protective relays 7 Railway signalling 8 History 9 See also 10 References 11 External links

o o o o o o o o o o o o

[edit] Basic design and operation

Simple electromechanical relay.

Small "cradle" relay often used in electronics. The "cradle" term refers to the shape of the relay's armature. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing. When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components. Some automotive relays include a diode inside the relay case. Alternatively, a contact protection network consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil is designed to be energized with alternating current (AC), a small copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase current which increases the minimum pull on the armature during the AC cycle.[1] A solid-state relay uses a thyristor or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting

diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits.

[edit] Types
[edit] Latching relay

Latching relay with permanent magnet A latching relay has two relaxed states (bistable). These are also called "impulse", "keep", or "stay" relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remanent core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that one coil consumes power only for an instant, while it is being switched, and the relay contacts retain this setting across a power outage. A remanent core latching relay requires a current pulse of opposite polarity to make it change state.

[edit] Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid. Reed relays can switch faster than larger relays, require only little power from the control circuit, but have low switching current and voltage ratings. In addition, the reeds can become magnetized over time, which makes them stick 'on' even when no current is present; changing the orientation of the reeds with respect to the solenoid's magnetic field will fix the problem.

Top, middle: reed switches, bottom: reed relay

[edit] Mercury-wetted relay
A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less) where the mercury reduces the contact resistance and associated voltage drop, for low-current signals where surface contamination may make for a poor contact, or for high-speed applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are now rarely used. See also mercury switch.

[edit] Polarized relay
A polarized relay placed the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay.
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External links o Schematic diagram of a polarized relay used in a teletype machine.

[edit] Machine tool relay
A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normallyclosed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications. A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with a relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions (relay logic). The principle of relay logic is based on relays which energize

and de-energize associated contacts. Relay logic is the predecessor of ladder logic, which is commonly used in Programmable logic controllers.

[edit] Ratchet relay
This is again a clapper type relay which does not need continuous current through its coil to retain its operation.

[edit] Contactor relay
A contactor is a very heavy-duty relay used for switching electric motors and lighting loads, although contactors are not generally called relays. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor.[2] Such devices are often used for motor starters. A motor starter is a contactor with overload protection devices attached. The overload sensing devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for use where noise is a chief concern.

[edit] Solid-state relay

Solid state relay with no moving parts

25 A or 40 A solid state contactors A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This voltage drop limited the amount of current a given SSR could handle. The minimum voltage drop for such a relay is equal to the voltage drop across one transistor (~0.6-2.0 volts), and is a function of the material used to make the transistor (typically silicon). As transistors improved, higher current SSR's, able to handle 100 to 1,200 Amperes, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients.

[edit] Solid state contactor relay
A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

[edit] Buchholz relay
A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil.

[edit] Forced-guided contacts relay
A forced-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forced-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".

[edit] Overload protection relay
Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings.[3] One type of electric motor overload protection relay is operated by a heating element in series with the electric motor. The heat generated by the motor current heats a bimetallic strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

[edit] Pole and throw

Circuit symbols of relays. (C denotes the common terminal in SPDT and DPDT types.) Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways:
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Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact. NO contacts can also be distinguished as "early-make" or NOEM, which means that the contacts will close before the button or switch is fully engaged. Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact. NC contacts can also be distinguished as "late-break" or NCLB, which means that the contacts will stay closed until the button or switch is fully disengaged. Change-over (CO), or double-throw (DT), contacts control two circuits: one normallyopen contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact ("break before make"). If this type of contact utilizes a "make before break" functionality, then it is called a Form D contact.

The following designations are commonly encountered:
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SPST – Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity. SPDT – Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

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DPST – Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. The poles may be Form A or Form B (or one of each). DPDT – Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

The "S" or "D" may be replaced with a number, indicating multiple switches connected to a single actuator. For example 4PDT indicates a four pole double throw relay (with 14 terminals). EN 50005 are among applicable standards for relay terminal numbering; a typical EN 50005compliant SPDT relay's terminals would be numbered 11, 12, 14, A1 and A2 for the C, NC, NO, and coil connections, respectively.

[edit] Applications
Relays are used to and for:
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Amplify a digital signal, switching a large amount of power with a small operating power. Some special cases are: o A telegraph relay, repeating a weak signal received at the end of a long wire o Controlling a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers, o Controlling a high-current circuit with a low-current signal, as in the starter solenoid of an automobile, Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),

A DPDT AC coil relay with "ice cube" packaging
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Isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors to conserve energy,

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Logic functions. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using normally closed contacts. The Ladder programming language is often used for designing relay logic networks. o The application of Boolean Algebra to relay circuit design was formalized by Claude Shannon in A Symbolic Analysis of Relay and Switching Circuits o Early computing. Before vacuum tubes and transistors, relays were used as logical elements in digital computers. See electro-mechanical computers such as ARRA (computer), Harvard Mark II, Zuse Z2, and Zuse Z3. o Safety-critical logic. Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery. Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed. Vehicle battery isolation. A 12v relay is often used to isolate any second battery in cars, 4WDs, RVs and boats. Switching to a standby power supply.

[edit] Relay application considerations

A large relay with two coils and many sets of contacts, used in an old telephone switching system.

Several 30-contact relays in "Connector" circuits in mid 20th century 1XB switch and 5XB switch telephone exchanges; cover removed on one Selection of an appropriate relay for a particular application requires evaluation of many different factors:
 

  







    

Number and type of contacts – normally open, normally closed, (double-throw) Contact sequence – "Make before Break" or "Break before Make". For example, the old style telephone exchanges required Make-before-break so that the connection didn't get dropped while dialing the number. Rating of contacts – small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15 000 V Operating lifetime, useful life - the number of times the relay can be expected to operate reliably. There is both a mechanical life and a contact life; the contact life is naturally affected by the kind of load being switched. Coil voltage – machine-tool relays usually 24 VAC, 120 or 250 VAC, relays for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few milliamperes Coil current - including minimum current required to operate reliably and minimum current to hold. Also effects of power dissipation on coil temperature at various duty cycles. Package/enclosure – open, touch-safe, double-voltage for isolation between circuits, explosion proof, outdoor, oil and splash resistant, washable for printed circuit board assembly Operating environment - minimum and maximum operating temperatures and other environmental considerations such as effects of humidity and salt Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB post soldering cleaning, which is removed once assembly is complete. Mounting – sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment Switching time – where high speed is required "Dry" contacts – when switching very low level signals, special contact materials may be needed such as gold-plated contacts

       

Contact protection – suppress arcing in very inductive circuits Coil protection – suppress the surge voltage produced when switching the coil current Isolation between coil contacts Aerospace or radiation-resistant testing, special quality assurance Expected mechanical loads due to acceleration – some relays used in aerospace applications are designed to function in shock loads of 50 g or more Accessories such as timers, auxiliary contacts, pilot lamps, test buttons Regulatory approvals Stray magnetic linkage between coils of adjacent relays on a printed circuit board.

There are many considerations involved in the correct selection of a control relay for a particular application. These considerations include factors such as speed of operation, sensitivity, and hysteresis. Although typical control relays operate in the 5 ms to 20 ms range, relays with switching speeds as fast as 100 us are available. Reed relays which are actuated by low currents and switch fast are suitable for controlling small currents. As for any switch, the current through the relay contacts (unrelated to the current through the coil) must not exceed a certain value to avoid damage. In the particular case of high-inductance circuits such as motors other issues must be addressed. When a power source is connected to an inductance, an input surge current which may be several times larger than the steady current exists. When the circuit is broken, the current cannot change instantaneously, which creates a potentially damaging spark across the separating contacts. Consequently for relays which may be used to control inductive loads we must specify the maximum current that may flow through the relay contacts when it actuates, the make rating; the continuous rating; and the break rating. The make rating may be several times larger than the continuous rating, which is itself larger than the break rating.

[edit] Derating factors
Control relays should not be operated above rated temperature Type of load % of rated value because of resulting increased degradation and fatigue. Resistive 75 Common practice is to derate 20 degrees Celsius from the Inductive 35 maximum rated temperature limit. Relays operating at rated Motor 20 load are also affected by their environment. Oil vapors may greatly decrease the contact tip life, and dust or dirt may cause Filament 10 the tips to burn before their normal life expectancy. Control Capacitive 75 relay life cycle varies from 50,000 to over one million cycles depending on the electrical loads of the contacts, duty cycle, application, and the extent to which the relay is derated. When a control relay is operating at its derated value, it is controlling a lower value of current than its maximum make and break ratings. This is often done to extend the operating life of the control relay. The table lists the relay derating factors for typical industrial control applications.

[edit] Undesired arcing

Main article: Arc suppression Without adequate contact protection, the occurrence of electric current arcing causes significant degradation of the contacts in relays, which suffer significant and visible damage. Every time a relay transitions either from a closed to an open state (break arc) or from an open to a closed state (make arc & bounce arc), under load, an electrical arc can occur between the two contact points (electrodes) of the relay. The break arc is typically more energetic and thus more destructive. The heat energy contained in the resulting electrical arc is very high (tens of thousands of degrees Fahrenheit), causing the metal on the contact surfaces to melt, pool and migrate with the current. The extremely high temperature of the arc cracks the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This very activity causes the material in the contacts to degrade quickly, resulting in device failure. This contact degradation drastically limits the overall life of a relay to a range of about 10,000 to 100,000 operations, a level far below the mechanical life of the same device, which can be in excess of 20 million operations.[4]

[edit] Protective relays
Main article: protective relay For protection of electrical apparatus and transmission lines, electromechanical relays with accurate operating characteristics were used to detect overload, short-circuits, and other faults. While many such relays remain in use, digital devices now provide equivalent protective functions.

[edit] Railway signalling

Part of a relay interlocking using UK Q-style miniature plug-in relays.

UK Q-style signalling relay and base. Railway signalling relays are very big and cumbersome compared to the mostly small voltages (less than 120 V) and currents (perhaps 100 mA) that they switch. Contacts are widely spaced to prevent dangerous flashovers and short circuits over a lifetime that may exceed fifty years. BR930 series plug-in relays are widely used on railways following British practice. These are 120 mm high, 180 mm deep and 56 mm wide and weigh about 1400 g, and can have up to 16 separate contacts, say 12 make and 4 break contacts. Since rail signal circuits must be highly reliable, special techniques are used to detect and prevent failures in the relay system. To protect against false feeds, double switching relay contacts are often used on both the positive and negative side of a circuit, so that two false feeds are needed to cause a false signal. Not all relay circuits can be proved so there is reliance on construction features such as carbon to silver contacts to resist lightning induced contact welding and to provide AC immunity. Opto-isolators are also used in some instances with railway signalling, especially where only a single contact is to be switched. Signalling relays and their circuits come in a number of schools, including:
   

British American German France

American signaling relays are the origin of the 19 inch rack.

[edit] History
A simple device, which we now call a relay, was included in the original 1840 telegraph patent[5] of Samuel Morse. The mechanism described acted as a digital amplifier, repeating the telegraph signal, and thus allowing signals to be propagated as far as desired. This overcame the problem of limited range of earlier telegraphy schemes. The earlier ‗relay‘ or ‗repeater‘ of Edward Davy of 1837/1838 was used in his electric telegraph

LPG Leakage Alarm

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Step-up and step-down transformers
So far, we've observed simulations of transformers where the primary and secondary windings were of identical inductance, giving approximately equal voltage and current levels in both circuits. Equality of voltage and current between the primary and secondary sides of a transformer, however, is not the norm for all transformers. If the inductances of the two windings are not equal, something interesting happens:
transformer v1 1 0 ac 10 sin rbogus1 1 2 1e-12 rbogus2 5 0 9e12 l1 2 0 10000 l2 3 5 100 k l1 l2 0.999 vi1 3 4 ac 0 rload 4 5 1k .ac lin 1 60 60 .print ac v(2,0) i(v1) .print ac v(3,5) i(vi1) .end freq v(2) 6.000E+01 1.000E+01 freq 6.000E+01 v(3,5) 9.962E-01

i(v1) 9.975E-05 i(vi1) 9.962E-04

Primary winding Secondary winding

Notice how the secondary voltage is approximately ten times less than the primary voltage (0.9962 volts compared to 10 volts), while the secondary current is approximately ten times greater (0.9962 mA compared to 0.09975 mA). What we have here is a device that steps voltage down by a factor of ten and current up by a factor of ten: (Figure below)

Turns ratio of 10:1 yields 10:1 primary:secondary voltage ratio and 1:10 primary:secondary current ratio. This is a very useful device, indeed. With it, we can easily multiply or divide voltage and current in AC circuits. Indeed, the transformer has made long-distance transmission of electric power a practical reality, as AC voltage can be ―stepped up‖ and current ―stepped down‖ for reduced wire resistance power losses along power lines connecting generating stations with loads. At either

end (both the generator and at the loads), voltage levels are reduced by transformers for safer operation and less expensive equipment. A transformer that increases voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer. Let's re-examine a photograph shown in the previous section: (Figure below)

Transformer cross-section showing primary and secondary windings is a few inches tall (approximately 10 cm). This is a step-down transformer, as evidenced by the high turn count of the primary winding and the low turn count of the secondary. As a step-down unit, this transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn't have to conduct as much current, may be made of smaller-gauge wire. In case you were wondering, it is possible to operate either of these transformer types backwards (powering the secondary winding with an AC source and letting the primary winding power a load) to perform the opposite function: a step-up can function as a step-down and visa-versa. However, as we saw in the first section of this chapter, efficient operation of a transformer requires that the individual winding inductances be engineered for specific operating ranges of voltage and current, so if a transformer is to be used ―backwards‖ like this it must be employed

within the original design parameters of voltage and current for each winding, lest it prove to be inefficient (or lest it be damaged by excessive voltage or current!). Transformers are often constructed in such a way that it is not obvious which wires lead to the primary winding and which lead to the secondary. One convention used in the electric power industry to help alleviate confusion is the use of ―H‖ designations for the higher-voltage winding (the primary winding in a step-down unit; the secondary winding in a step-up) and ―X‖ designations for the lower-voltage winding. Therefore, a simple power transformer will have wires labeled ―H1‖, ―H2‖, ―X1‖, and ―X2‖. There is usually significance to the numbering of the wires (H1 versus H2, etc.), which we'll explore a little later in this chapter. The fact that voltage and current get ―stepped‖ in opposite directions (one up, the other down) makes perfect sense when you recall that power is equal to voltage times current, and realize that transformers cannot produce power, only convert it. Any device that could output more power than it took in would violate the Law of Energy Conservation in physics, namely that energy cannot be created or destroyed, only converted. As with the first transformer example we looked at, power transfer efficiency is very good from the primary to the secondary sides of the device. The practical significance of this is made more apparent when an alternative is considered: before the advent of efficient transformers, voltage/current level conversion could only be achieved through the use of motor/generator sets. A drawing of a motor/generator set reveals the basic principle involved: (Figure below)

Motor generator illustrates the basic principle of the transformer. In such a machine, a motor is mechanically coupled to a generator, the generator designed to produce the desired levels of voltage and current at the rotating speed of the motor. While both motors and generators are fairly efficient devices, the use of both in this fashion compounds their inefficiencies so that the overall efficiency is in the range of 90% or less. Furthermore, because motor/generator sets obviously require moving parts, mechanical wear and balance are factors influencing both service life and performance. Transformers, on the other hand, are able to convert levels of AC voltage and current at very high efficiencies with no moving parts, making possible the widespread distribution and use of electric power we take for granted.

In all fairness it should be noted that motor/generator sets have not necessarily been obsoleted by transformers for all applications. While transformers are clearly superior over motor/generator sets for AC voltage and current level conversion, they cannot convert one frequency of AC power to another, or (by themselves) convert DC to AC or visa-versa. Motor/generator sets can do all these things with relative simplicity, albeit with the limitations of efficiency and mechanical factors already described. Motor/generator sets also have the unique property of kinetic energy storage: that is, if the motor's power supply is momentarily interrupted for any reason, its angular momentum (the inertia of that rotating mass) will maintain rotation of the generator for a short duration, thus isolating any loads powered by the generator from ―glitches‖ in the main power system. Looking closely at the numbers in the SPICE analysis, we should see a correspondence between the transformer's ratio and the two inductances. Notice how the primary inductor (l1) has 100 times more inductance than the secondary inductor (10000 H versus 100 H), and that the measured voltage step-down ratio was 10 to 1. The winding with more inductance will have higher voltage and less current than the other. Since the two inductors are wound around the same core material in the transformer (for the most efficient magnetic coupling between the two), the parameters affecting inductance for the two coils are equal except for the number of turns in each coil. If we take another look at our inductance formula, we see that inductance is proportional to the square of the number of coil turns:

So, it should be apparent that our two inductors in the last SPICE transformer example circuit -with inductance ratios of 100:1 -- should have coil turn ratios of 10:1, because 10 squared equals 100. This works out to be the same ratio we found between primary and secondary voltages and currents (10:1), so we can say as a rule that the voltage and current transformation ratio is equal to the ratio of winding turns between primary and secondary.

Step-down transformer: (many turns :few turns). The step-up/step-down effect of coil turn ratios in a transformer (Figure above) is analogous to gear tooth ratios in mechanical gear systems, transforming values of speed and torque in much the same way: (Figure below)

Torque reducing gear train steps torque down, while stepping speed up. Step-up and step-down transformers for power distribution purposes can be gigantic in proportion to the power transformers previously shown, some units standing as tall as a home. The following photograph shows a substation transformer standing about twelve feet tall: (Figure below)

Substation transformer.
 

REVIEW: Transformers ―step up‖ or ―step down‖ voltage according to the ratios of primary to secondary wire turns.

 



A transformer designed to increase voltage from primary to secondary is called a step-up transformer. A transformer designed to reduce voltage from primary to secondary is called a step-down transformer. The transformation ratio of a transformer will be equal to the square root of its primary to secondary inductance (L) ratio.



Liquefied petroleum gas
From Wikipedia, the free encyclopedia Jump to: navigation, search

Liquefied petroleum gas (also called LPG, GPL, LP Gas, or liquid propane gas) is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles. It is increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer. When specifically used as a vehicle fuel it is often referred to as autogas. Varieties of LPG bought and sold include mixes that are primarily propane (C3H8), primarily butane (C4H10) and, most commonly, mixes including both propane and butane, depending on the season — in winter more propane, in summer more butane[citation needed]. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. In the United States, thiophene or amyl mercaptan are also approved odorants. LPG is synthesised by refining petroleum or "wet" natural gas, and is usually derived from fossil fuel sources, being manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed, and burns cleanly with no soot and very few sulfur emissions, posing no ground or water pollution hazards. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel-oil and 43.5 MJ/kg for premium grade petrol (gasoline).[1] However, its

energy density per volume unit of 26 MJ/l is lower than either that of petrol or fuel-oil.[citation
needed]

LPG evaporates quickly at normal temperatures and pressures and is supplied in pressurised steel cylinders. They are typically filled to between 80% and 85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) (319 psi) for pure propane at 55 °C (131 °F). LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with. Large amounts of LPG can be stored in bulk cylinders and can be buried underground.

Contents
[hide]


1 Uses 1.1 Rural heating 1.2 Motor fuel 1.3 Refrigeration 1.4 Cooking 2 Security of supply 3 Comparison with natural gas 4 Environmental Effects 5 Fire risk and mitigation 6 See also 7 References 8 External links
o o o o

      

[edit] Uses
[edit] Rural heating

Cylinders with LP gas in India Predominantly in Europe and rural parts of the United States, LPG can provide an alternative to electricity and heating oil (kerosene). LPG is most often used where there is no access to piped natural gas. LPG can be used as a power source for combined heat and power technologies (CHP). CHP is the process of generating both electrical power and useful heat from a single fuel source. This technology has allowed LPG to be used not just as fuel for heating and cooking, but also for decentralised generation of electricity. LPG can be stored in a variety of ways. LPG, as with other fossil fuels, can be combined with renewable power sources to provide greater reliability while still achieving some reduction in CO2 emissions.

[edit] Motor fuel

LPG filling connector on a car Main article: Autogas

White bordered green diamond symbol used on LPG-powered vehicles in China When LPG is used to fuel internal combustion engines, it is often referred to as autogas or auto propane. In some countries, it has been used since the 1940s as a petrol alternative for spark ignition engines. Two recent studies have examined LPG-fuel-oil fuel mixes and found that smoke emissions and fuel consumption are reduced but hydrocarbon emissions are increased.[2][3] The studies were split on CO emissions, with one finding significant increases,[2] and the other finding slight increases at low engine load but a considerable decrease at high engine load.[3] Its advantage is that it is non-toxic, non-corrosive and free of tetra-ethyl lead or any additives, and has a high octane rating (102-108 RON depending on local specifications). It burns more cleanly than petrol or fuel-oil and is especially free of the particulates from the latter. LPG has a lower energy density than either petrol or fuel-oil, so the equivalent fuel consumption is higher. Many governments impose less tax on LPG than on petrol or fuel-oil, which helps offset the greater consumption of LPG than of petrol or fuel-oil. However, in many European countries this tax break is often compensated by a much higher annual road tax on cars using LPG than on cars using petrol or fuel-oil. Propane is the third most widely used motor fuel in the world. 2008 estimates are that over 13 million vehicles are fueled by propane gas worldwide. Over 20 million tonnes (over 7 billion US gallons) are used annually as a vehicle fuel. Not all automobile engines are suitable for use with LPG as a fuel. LPG provides less upper cylinder lubrication than petrol or diesel, as a consequence LPG fueled engines are more prone to wearing valves if not suitably modified. Many modern common rail diesel engines respond well to LPG use as a supplementary fuel. This is where LPG is used as fuel as well as diesel. Systems are now available that integrate with OEM engine management systems.

[edit] Refrigeration
LPG is instrumental in providing off-the-grid refrigeration, usually by means of a gas absorption refrigerator. Blended of pure, dry propane (refrigerant designator R-290 ) and isobutane (R-600a) the blend "R-290a" - has negligible ozone depletion potential and very low global warming potential and can serve as a functional replacement for R-12, R-22, R-134a,and other chlorofluorocarbon or hydrofluorocarbon refrigerants in conventional stationary refrigeration and air conditioning systems.[4]

Such substitution is widely prohibited or discouraged in motor vehicle air conditioning systems, on the grounds that using flammable hydrocarbons in systems originally designed to carry nonflammable refrigerant presents a significant risk of fire or explosion.[5][6][7][8][9][10][11][12] Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons.[13][14] One particular test was conducted by a professor at the University of New South Wales that unintentionally tested the worst case scenario of a sudden and complete refrigerant loss into the passenger compartment followed by subsequent ignition. He and several others in the car sustained minor burns to their face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window. No one was seriously injured.[15]

[edit] Cooking

Truck carrying LPG cylinders to residential consumers in Singapore According to the 2001 Census of India, 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001, which is supplied to their homes by Indian Oil which is known as Indane.[16] 76.64% of such households were from urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in rural Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the urban middle class voting pattern. LPG was once a popular cooking fuel in Hong Kong; however, the continued expansion of town gas to buildings has reduced LPG usage to less than 24% of residential units. LPG is the most common cooking fuel in Brazilian urban areas, being used in virtually all households. Poor families receive a government grant ("Vale Gás") used exclusively for the acquisition of LPG.

[edit] Security of supply

Because of the natural gas and the oil-refining industry, Europe is almost self-sufficient in LPG. Europe's security of supply is further safeguarded by:
 

a wide range of sources, both inside and outside Europe; a flexible supply chain via water, rail and road with numerous routes and entry points into Europe;

As of early 2008, world reserves of natural gas — from which most LPG is derived — stood at 6,342.411 trillion cubic feet. Added to the LPG derived from cracking crude oil, this amounts to a major energy source that is virtually untapped and has massive potential. Production continues to grow at an average annual rate of 2.2%, virtually assuring that there is no risk of demand outstripping supply for the foreseeable future.[citation needed]

[edit] Comparison with natural gas
LPG is composed primarily of propane and butane, while natural gas is composed of the lighter methane and ethane. LPG, vaporised and at atmospheric pressure, has a higher calorific value (94 MJ/m3 equivalent to 26.1kWh/m³) than natural gas (methane) (38 MJ/m3 equivalent to 10.6 kWh/m3), which means that LPG cannot simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the LPG. The method for determining the mixing ratios is by calculating the Wobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable. LPG-based SNG is used in emergency backup systems for many public, industrial and military installations, and many utilities use LPG peak shaving plants in times of high demand to make up shortages in natural gas supplied to their distributions systems. LPG-SNG installations are also used during initial gas system introductions, when the distribution infrastructure is in place before gas supplies can be connected. Developing markets in India and China (among others) use LPG-SNG systems to build up customer bases prior to expanding existing natural gas systems.

[edit] Environmental Effects
Commercially available LPG is currently derived from fossil fuels. Burning LPG releases CO2, an important greenhouse gas, contributing to global warming. LPG does, however, release less CO2 per unit of energy than that of coal or oil. It emits 81% of the CO2 per kWh produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid.[citation needed] Being a mix of propane and butane, LPG emits less carbon per joule than butane but more carbon per joule than propane. LPG can be considered to burn more 'cleanly' than heavier molecule hydrocarbons, in that it releases very few particulates when burnt.

[edit] Fire risk and mitigation

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A spherical gas container typically found in refineries Since LPG turns gaseous under ambient temperature and pressure, it must be stored in special pressure vessels. If the containers are cylindrical and horizontal, they are referred to as "cigars" or "bullets", whereas circular ones are "spheres". LPG containers that are subjected to fire of sufficient duration and intensity can undergo a boiling liquid expanding vapour explosion (BLEVE). Due to the destructive nature of LPG explosions, the substance is classified as a dangerous good.[17] This is typically a concern for large refineries and petrochemical plants that maintain very large containers. The remedy is to equip such containers with a measure to provide a fire-resistance rating. Large, spherical LPG containers may have up to a 15 cm steel wall thickness. Ordinarily, they are equipped with an approved pressure relief valve on the top, in the centre. One of the main dangers is that accidental spills of hydrocarbons may ignite and heat an LPG container, which increases its temperature and pressure, following the basic gas laws. The relief valve on the top is designed to vent off excess pressure in order to prevent the rupture of the container itself. Given a fire of sufficient duration and intensity, the pressure being generated by the boiling and expanding gas can exceed the ability of the valve to vent the excess. When that occurs, an overexposed container may rupture violently, launching pieces at high velocity, while the released products can ignite as well, potentially causing catastrophic damage to anything nearby, including other containers. In the case of "cigars", a midway rupture may send two "rockets" going off each way, with plenty of fuel in each to propel each segment at high speed until the fuel is spent. Mitigation measures include separating LPG containers from potential sources of fire. In the case of rail transport, for instance, LPG containers can be staggered, so that other goods are put in between them. This is not always done, but it does represent a low-cost remedy to the problem. LPG rail cars are easy to spot from the relief valves on top, typically with railings all around.

In the case of new LPG containers, one may simply bury them, only leaving valves and armatures exposed, for easy maintenance. Great care must be taken there though, as mechanical damage can occur to the primers, which can result in hazardous corrosion of the containers. For the buried container, only the exposed parts need to be treated with approved fireproofing materials, such as intumescent and or endothermic coatings, or even fireproofing plasters. The rest are amply protected by soil. Speciality removable covers exist for easy access to the dials and components that must be accessed for proper maintenance and operation of the equipment. LPG containers are subject to significant motion due to expansion, contraction, filling and emptying; even with very thick steel walls. This operational motion makes the burial option less attractive in the long run, because it is difficult to detect mechanical damage to the outer waterproofing of the vessel through soil. A small stone scraping back and forth across the epoxypainted hull can jeopardise the waterproofing and be the cause for corrosion. Whilst one may calculate and justify on paper the use of inorganic plasters to cover entire spheres, it can be difficult to keep plasters operable for extended periods of time. Major errors have also been made in the past in this field, as the presumption was that the steel substrate would be adequately protected from rusting through the use of alkaline plasters. The alkalinity in such plasters is due to the presence of cement stone. This alkalinity, however, does not typically have a permanent character, which means that waterproofing with high quality epoxy primers is very important. Also, exterior waterproofing of the plaster is required by some fireproofing plaster vendors, as reduced alkalinity in exposed plasters can have a deleterious effect on the cement stone, which binds the plaster in the first place. By contrast, the intumescent and endothermic coatings are usually epoxy based to begin with, meaning that corrosion of the substrate is no problem whatsoever. Fireproofing, not unlike all passive fire protection products, is subject to stringent Listing and approval use and compliance. The problem with this is though, that exterior structures of this nature are not subject to the building code or the fire code, meaning that one still sees the majority of LPG containers without any fireproofing at all, as there are often no local regulations, let alone any Authority Having Jurisdiction, apart from an insurance inspector, to force owners to use the proper mitigation methods. Insurance companies are also in a competitive quandary, where such items are concerned, as they compete not only on the basis of rates, but also on the strictness of the demands by their inspectors. LPG vessel fireproofing tests are varied. The only realistic exposure offered is done at the Braunschweig test facility of "BAM" Berlin. BAM's procedure is to expose a small LPG container to the hydrocarbon test curve and to quantify the results. North American methods are based on UL1709. While UL1709 uses the correct time/temperature curve for testing, it is limited to testing steel columns (not even beams), whereas BAM actually exposes a real LPG container that has been fireproofed. No matter the fireproofing method one uses, it is very important to pay close attention to listing and approval use and compliance and to be sure that the product one chooses has undergone product certification, whereby the original test included the environmental exposures that the product will be exposed to during operations. Particularly with organic products, such as the endothermic and intumescent ones, one must closely review the ageing criteria and be able to quantify how long the product is expected to be operable for. This is where UL1709 "shines". Anything that can withstand the full battery of environmental exposures prior to the actual fire test, is a very tough product indeed. The idea is to rule out conditions that may render the product inoperable

before it is ever exposed to a fire. By using products that have received the appropriate environmental tests FIRST, and the fire expose afterwards, using the very same test sample with all the applicable exposures, one can then demonstrate due diligence, but not otherwise. Likewise, the DIBt ageing qualifications for intumescents have proven to be very reliable. With close attention to the bounding and coverage of ageing and environmental exposures, it is absolutely possible to buy a lot of time for firefighting measures to relieve the LPG containers of the energy exposure from accidental fires and thus reduce the likelihood of a BLEVE to the maximum possible extent. In June 2009, a freight train carrying LPG derailed in the rail station of Viareggio, Italy. 29 people were killed and over 30 people were injured.

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Indian LPG Cylinders (ILC) is a leading manufacturer of LPG cylinders in India due to its uncompromising commitment to quality. ILC has earned the ISO 9002 certification from Raad Voor Accreditalie. The installed capacity of ILC is 1,000,000 cylinders per annum. We manufacture standard and custom designed steel LPG cylinders. We are fully committed to providing cylinders that offer the ultimate in quality, safety and performance globally. Our team works closely with the customers on new products and applications. Ideas, technology and expertise are exchanged. This enables us to serve our clients better and meet new challenges. Product Features Rugged all-steel manufacturing with heavy-duty collar and footing. Gas welds automatic, mig or submerged arc welding. All cylinders undergo heat treatment / stress releived / normalized. Test process includes visual, hydraulic & pneumatic. Continuous shot blasting. Cylinder exterior is of high gloss with corrosion resistant coating. Finished cylinders are packed to meet all customers demand / specifications. The Market ILC's product range focuses on intense customer satisfaction. This has enabled it to do business globally. ILC has got a list of satisfied clientele from all conceivable sectors within India and abroad.

LPG CYLINDER DESIGN SPECIFICATIONS
BRITISH SPECIFICATIONS Cylinder Model Water Capacity Tare Weight Water Capacity Specification 5 9 11 12 14 26 30 5.4 9.25 11 12.1 14.5 26.8 32.6 4.08 8 5.19 7.8 8.5 12 13.5 5.4 9.25 11 12.1 14.5 26.8 32.6 BS/5045/II/89 BS/5045/II/89 BS/5045/II/91 BS/5045/II/91 BS/5045/II/91 BS/5045/II/91 BS/5045/II/91

Capacities are appproximate and may vary slightly from the given data.
AMERICAN SPECIFICATIONS LPG Capacity Cylinder Model 4.25 11 14 20 gallons liters 1.0 3.8 2.6 9.8 3.3 12.5 4.7 Water Capacity lb. kg. 12.0 5.4 26.2 11.9 33.2 15.0 47.6 Tare Weight lb. kg. 11.9 5.4 13.8 6.3 14.6 6.6 17.0 Cylinder Volume cu. in. litres 333 5.5 726 11.9 919 15.0 1321 DOT - 4BA240 DOT - 4BA240 DOT - 4BA240 DOT - 4BA240 DOT Specification

17.9 30 40 43.5 60 7.1 26.8 9.4 35.7 10.3 38.8 14.2 53.5

21.6 71.5 32.6 95.2 43.2 103.6 47.0 142.9 64.8

7.7 25.4 11.5 33.6 15.2 34.4 15.6 48.0 21.8

21.6 1983 32.5 726 2642 2874 47.1 3962 64.9 DOT - 4BW260 DOT - 4BA240 DOT - 4BA240 DOT - 4BA240

Capacities are appproximate and may vary slightly from the given data.