15. Calibration Measurement,
Content
TWI
CSWIP 3.2
WIS 10
SENIOR WELDING
INSPECTION
CALIBRATION
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration/Validation
BS 7570: 1992 Covers the calibration
and validation of welding equipment.
Grade 1 (general purpose equipment)
all parameters should be +/- 10%.
Grade 2 (Automatic or automated
equipment) parameters should be +/2.5% for current and +/- 5% for all
other parameters.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration/Validation
Calibration can only be done on equipment
with meters or gauges as theses can be
adjusted.
Validation can be done on equipment with
and *without meters or gauges.
Oil fill transformers etc.
All equipment can be Validated but not all
equipment can be Calibrated.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Measuring in welding
The
purposes of
measuring
Demonstration of
Welding
conformance to
process
specified
control
requirements
Parameters to be measured:
• welding current
• preheat/interpa
• arc voltage
ss temperature
• travel speed
• force/pressure
• shielding gas flow rate
• humidity
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding current
measurement
Definition: the current delivered by a
welding power source during welding
•
•
•
measured with an ammeter
measured in A
the ammeter may be connected at any point
in the circuit
• in case of AC, either the root mean square
value (=0,707 peak value) or the mean value
of the rectified waveform is measured
• due to its sensitivity, a shunt is needed
• indirect measurement: tachogenerator and
tongue tester
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
The
tachogenerator
•directly coupled to the
feed motor spindle
•the output is an analogue
DC voltage which is a
precise function of rotation
speed
•this voltage is used to
provide a speed feedback
signal for the DC Power
Drive powering the main
motor
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
The tongue tester
•used for AC current
•special types can be used
also for DC (Hall-effect device)
•no need to insert the meter
into the circuit
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Arc voltage measurement
Definition: the potential difference
across the welding arc
•
•
•
•
varies with the arc length
measured with a voltmeter
measured in V
the voltmeter may be connected only across
the circuit (to the workpiece and as close as
possible to the electrode!)
• if the voltmeter is connected at the welding
power source, a higher voltage will be
recorded (due to potential drops across
cables)
• usually not required for MMA and TIG
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Travel speed
measurement
Definition: the rate of weld progression
• measured in case of mechanised and
automatic welding processes
• in case of MMA can be determined
using ROL and arc time
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Gas flow rate
measurement
Definition: the rate at which gas is
caused to flow
• set with a gas
regulator
• can be checked
with a flowmeter
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesdefinitions
• is the temperature of the workpiece in the
Preheat
temperature weld zone immediately before any welding
operation (including tack welding!)
• normally expressed as a minimum
• is the temperature in a multirun weld
Interpass
and adjacent parent metal immediately
temperature
prior to the application of the next run
• normally expressed as a maximum
Minimum interpass temperature = Preheat
temperature
• is the minimum temperature in the
Preheat
maintenance weld zone which shall be maintained if
welding is interrupted
temperature
• shall be monitored during interruption
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesWHERE?
Point of measurement see BS EN ISO 13916
• if t 50 mm A = 4 x t
but max. 50 mm
• the temperature shall be
measured on the surface
of the workpiece facing
the welder
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesWHERE?
Point of measurement see BS EN ISO 13916
• if t > 50 mm A = min. 75
mm
• where practicable, the
temperature shall be
measured on the face
opposite to that being
heated
• allow 2 min per every 25
mm of parent metal
thickness for temperature
equalisation
• interpass temperature
shall be measured on the
weld metal or immediately
adjacent parent metal
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesHOW?
Test equipment
Thermocoupl
e (TE)
Temperatur
e sensitive
materials
(TS)
Contact
thermomet
er (CT)
Copyright © 2005, TWI Ltd
Thermistor
(CT)
Optical/electric
al devices for
contactless
measurement
(TB)
World Centre for Materials Joining
Temperature test
equipment
Temperature
sensitive materials:
•crayons, paints and
pills
•cheap
•
easy the
to
•convenient,
doesn’t measure
use
actual temperature!
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Contact thermometer
•use bimetallic strips steel + INVAR (36% Ni 64% Fe alloy)
•accurate
•easy to use
•gives the actual
temperature
•need calibration
•suitable for moderate
temperatures
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Thermocouple
•based on measuring the thermoelectric
potential difference between a hot junction
(on weld) and a cold junction
•accurate method
•measures over a wide range of
temperatures
•gives the actual temperature
•need calibration
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Thermistors
•are temperaturesensitive resistors whose
resistance varies
inversely with
temperature
•used when high
sensitivity is required
•gives the actual
temperature
•need calibration
•can be used up to 320°C
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Devices for
contactless
measurement
•IR radiation and
optical pyrometer
•measure the
radiant energy
emitted by the hot
body
•contactless
method can be
used for remote
measurements
•very complex
•for measuring
high
World
Centre for Materials Joining
Copyright © 2005, TWI Ltd
PAMS (Portable Arc Monitor
System)
For
measuring
and
recording
the welding
parameters
Copyright © 2005, TWI Ltd
The
purposes of
a PAMS
For
calibrating
and
validating
the welding
equipment
World Centre for Materials Joining
PAMS (Portable Arc Monitor
System)
What does a PAMS
measure?
Welding
current
(Hall
effect
device)
Gas flow
rate
(heating
element
sensor)
Arc
voltage
(connectio
n leads)
Wire feed
speed
(tachomete
r)
Copyright © 2005, TWI Ltd
Temperature
(thermocoupl
World Centre
e) for Materials Joining
Use of PMAS
•Welding current monitoring - the Hall
effect
Magnetic field
(produced by
welding current)
Electron
deviation due to
magnetic field
eElectric
current
Copyright © 2005, TWI Ltd
Voltmeter
World Centre for Materials Joining
Use of PMAS
•Wire feed
speed
monitoring
Incorporated pair
of rolls connected
to a
tachogenerator
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Use of PMAS
•Shielding gas
flow rate
monitoring
Heatin
g
elemen
t
sensor
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Use of PMAS
Shielding gas flow rate
sensor
Metallic
tube
Increased gas flow
rate
Increased
cooling
Heating
resistance
Drop in
temperature
Thermocoupl
e
Thermocouple
Copyright © 2005, TWI Ltd
Potential
difference
World Centre for Materials Joining
Calibration, validation and
monitoring
Definitions:
• Measurement = set of operations for determining a value
of a quantity
• Repeatability = closeness between successive measuring
results of the same instrument carried out under the
same conditions
• Accuracy class = class of measuring instruments that are
intended to keep the errors within specified limits
• Calibration = checking the errors in a meter or measuring
device
• Validation = checking the control knobs and switches
provide the same level of accuracy when returned to a
pre-determined point
• Monitoring = checking the welding parameters (and other
items) are in accordance with the procedure or
specification
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is required?
• once a year unless otherwise specified
• whenever there are indications that the
instrument does not register properly
• whenever the equipment has been damaged,
misused or subject to severe stress
• whenever the equipment has been rebuild or
repaired
See BS EN ISO 17662 for details!
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is NOT required?
• when verification of the process is not required
• in case of small series and single piece
production when all the following conditions
are fulfilled:
- procedures are approved by procedure
testing
- production is carried out by the same
welding machine used during procedure
testing
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is NOT required?
• in case of mass production when all the
following conditions are fulfilled:
- production is controlled by pre-production
testing, followed by testing of samples
from production at regular intervals
- a statistical quality control system is used
- the process is stable between testing of
samples
- pre-production testing and sampling are
performed separately for each production
line (robotic cells)
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding parameter
calibration/validation
Which parameters need calibration/validation?
• depends on the welding process
• see BS EN ISO 17662 and BS 7570 for details
How accurate?
•
•
•
•
•
depends on the application
welding current - ±2,5%
arc voltage - ±5%
wire feed speed - ±2,5%
gas flow rate - ±20% (±25% for backing
gas flow rate)
• temperature (thermocouple) - ±5%
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 1 - MMA elementary
monitoring
IN THEORY any M.M.A. operation could
require monitoring of:
• welding current
• arc voltage
• R.O.L.
• preheat/interpass temperature
• electrode treatment and storage
IN PRACTICE (depending on the application)
only the welding current could require
monitoring with a tongue test ammeter
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 2 - High integrity MMA
operation
• IN THEORY, this might require monitoring of all the
activities previously mentioned.
• the equipment thus required would be:
•
•
•
•
•
•
ammeter
voltmeter
stop watch
tape measure
thermometer
calculator
OR
• a PAMS
• all of the above equipment would require
calibration; any meters fitted to the
power source or electrode ovens would
also require calibration.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 3 - MIG/MAG welding with a
robot
IN THEORY, the following would require monitoring:
• wire feed speed
• amperage
• voltage
• travel speed
• gas flow rate
• repeatability of the controls
IN PRACTICE, a data logger would be preferred
to monitor all the parameters; also a PAMS
would be required to check the repeatability
of the control knobs.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Summary
• a welding power source can only be
calibrated if it has meters fitted
• the inspector should check for calibration
stickers, dates etc.
• a welding power source without meters
can only be validated that the control
knobs provide repeatability
• the main role is to carryout “in process
monitoring” to ensure that the welding
requirements are met during production
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Typical examination
question 1
• “The measurement of welding parameters is common
in arc welding practice. Comment on the parameters
that can be measured and recorded,including the
different types of equipment that maybe used.”
This question by definition is related to monitoring
• Introduction: would include monitoring is
dependent on the integrity of the product.
• Welding parameters: need to be identified. (with
comments!)
• Equipment details: can be established from the
welding parameters identified.
• Conclusion: should incorporate
calibration/validation and the need for checking
temperatures (interpass/preheat).
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Typical examination
question 2
• “Describe how you would ensure that the welding
parameters listed in a WPS are being adhered to
during production welding. Give the advantages
and limitations of the methods used.”
This question is related more to the whole
fabrication process: e.g.
• QA/QC requirements
• Training, experience and qualification of welders
and inspectors
• Inspection procedures (during welding)
• Auditing to ensure that the above is taking place
• Calibration/validation and in process monitoring
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
CSWIP 3.2
WIS 10
SENIOR WELDING
INSPECTION
CALIBRATION
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration/Validation
BS 7570: 1992 Covers the calibration
and validation of welding equipment.
Grade 1 (general purpose equipment)
all parameters should be +/- 10%.
Grade 2 (Automatic or automated
equipment) parameters should be +/2.5% for current and +/- 5% for all
other parameters.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration/Validation
Calibration can only be done on equipment
with meters or gauges as theses can be
adjusted.
Validation can be done on equipment with
and *without meters or gauges.
Oil fill transformers etc.
All equipment can be Validated but not all
equipment can be Calibrated.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Measuring in welding
The
purposes of
measuring
Demonstration of
Welding
conformance to
process
specified
control
requirements
Parameters to be measured:
• welding current
• preheat/interpa
• arc voltage
ss temperature
• travel speed
• force/pressure
• shielding gas flow rate
• humidity
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding current
measurement
Definition: the current delivered by a
welding power source during welding
•
•
•
measured with an ammeter
measured in A
the ammeter may be connected at any point
in the circuit
• in case of AC, either the root mean square
value (=0,707 peak value) or the mean value
of the rectified waveform is measured
• due to its sensitivity, a shunt is needed
• indirect measurement: tachogenerator and
tongue tester
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
The
tachogenerator
•directly coupled to the
feed motor spindle
•the output is an analogue
DC voltage which is a
precise function of rotation
speed
•this voltage is used to
provide a speed feedback
signal for the DC Power
Drive powering the main
motor
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
The tongue tester
•used for AC current
•special types can be used
also for DC (Hall-effect device)
•no need to insert the meter
into the circuit
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Arc voltage measurement
Definition: the potential difference
across the welding arc
•
•
•
•
varies with the arc length
measured with a voltmeter
measured in V
the voltmeter may be connected only across
the circuit (to the workpiece and as close as
possible to the electrode!)
• if the voltmeter is connected at the welding
power source, a higher voltage will be
recorded (due to potential drops across
cables)
• usually not required for MMA and TIG
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Travel speed
measurement
Definition: the rate of weld progression
• measured in case of mechanised and
automatic welding processes
• in case of MMA can be determined
using ROL and arc time
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Gas flow rate
measurement
Definition: the rate at which gas is
caused to flow
• set with a gas
regulator
• can be checked
with a flowmeter
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesdefinitions
• is the temperature of the workpiece in the
Preheat
temperature weld zone immediately before any welding
operation (including tack welding!)
• normally expressed as a minimum
• is the temperature in a multirun weld
Interpass
and adjacent parent metal immediately
temperature
prior to the application of the next run
• normally expressed as a maximum
Minimum interpass temperature = Preheat
temperature
• is the minimum temperature in the
Preheat
maintenance weld zone which shall be maintained if
welding is interrupted
temperature
• shall be monitored during interruption
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesWHERE?
Point of measurement see BS EN ISO 13916
• if t 50 mm A = 4 x t
but max. 50 mm
• the temperature shall be
measured on the surface
of the workpiece facing
the welder
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesWHERE?
Point of measurement see BS EN ISO 13916
• if t > 50 mm A = min. 75
mm
• where practicable, the
temperature shall be
measured on the face
opposite to that being
heated
• allow 2 min per every 25
mm of parent metal
thickness for temperature
equalisation
• interpass temperature
shall be measured on the
weld metal or immediately
adjacent parent metal
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding temperaturesHOW?
Test equipment
Thermocoupl
e (TE)
Temperatur
e sensitive
materials
(TS)
Contact
thermomet
er (CT)
Copyright © 2005, TWI Ltd
Thermistor
(CT)
Optical/electric
al devices for
contactless
measurement
(TB)
World Centre for Materials Joining
Temperature test
equipment
Temperature
sensitive materials:
•crayons, paints and
pills
•cheap
•
easy the
to
•convenient,
doesn’t measure
use
actual temperature!
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Contact thermometer
•use bimetallic strips steel + INVAR (36% Ni 64% Fe alloy)
•accurate
•easy to use
•gives the actual
temperature
•need calibration
•suitable for moderate
temperatures
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Thermocouple
•based on measuring the thermoelectric
potential difference between a hot junction
(on weld) and a cold junction
•accurate method
•measures over a wide range of
temperatures
•gives the actual temperature
•need calibration
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Thermistors
•are temperaturesensitive resistors whose
resistance varies
inversely with
temperature
•used when high
sensitivity is required
•gives the actual
temperature
•need calibration
•can be used up to 320°C
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Temperature test
equipment
Devices for
contactless
measurement
•IR radiation and
optical pyrometer
•measure the
radiant energy
emitted by the hot
body
•contactless
method can be
used for remote
measurements
•very complex
•for measuring
high
World
Centre for Materials Joining
Copyright © 2005, TWI Ltd
PAMS (Portable Arc Monitor
System)
For
measuring
and
recording
the welding
parameters
Copyright © 2005, TWI Ltd
The
purposes of
a PAMS
For
calibrating
and
validating
the welding
equipment
World Centre for Materials Joining
PAMS (Portable Arc Monitor
System)
What does a PAMS
measure?
Welding
current
(Hall
effect
device)
Gas flow
rate
(heating
element
sensor)
Arc
voltage
(connectio
n leads)
Wire feed
speed
(tachomete
r)
Copyright © 2005, TWI Ltd
Temperature
(thermocoupl
World Centre
e) for Materials Joining
Use of PMAS
•Welding current monitoring - the Hall
effect
Magnetic field
(produced by
welding current)
Electron
deviation due to
magnetic field
eElectric
current
Copyright © 2005, TWI Ltd
Voltmeter
World Centre for Materials Joining
Use of PMAS
•Wire feed
speed
monitoring
Incorporated pair
of rolls connected
to a
tachogenerator
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Use of PMAS
•Shielding gas
flow rate
monitoring
Heatin
g
elemen
t
sensor
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Use of PMAS
Shielding gas flow rate
sensor
Metallic
tube
Increased gas flow
rate
Increased
cooling
Heating
resistance
Drop in
temperature
Thermocoupl
e
Thermocouple
Copyright © 2005, TWI Ltd
Potential
difference
World Centre for Materials Joining
Calibration, validation and
monitoring
Definitions:
• Measurement = set of operations for determining a value
of a quantity
• Repeatability = closeness between successive measuring
results of the same instrument carried out under the
same conditions
• Accuracy class = class of measuring instruments that are
intended to keep the errors within specified limits
• Calibration = checking the errors in a meter or measuring
device
• Validation = checking the control knobs and switches
provide the same level of accuracy when returned to a
pre-determined point
• Monitoring = checking the welding parameters (and other
items) are in accordance with the procedure or
specification
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is required?
• once a year unless otherwise specified
• whenever there are indications that the
instrument does not register properly
• whenever the equipment has been damaged,
misused or subject to severe stress
• whenever the equipment has been rebuild or
repaired
See BS EN ISO 17662 for details!
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is NOT required?
• when verification of the process is not required
• in case of small series and single piece
production when all the following conditions
are fulfilled:
- procedures are approved by procedure
testing
- production is carried out by the same
welding machine used during procedure
testing
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Calibration and validation
When it is NOT required?
• in case of mass production when all the
following conditions are fulfilled:
- production is controlled by pre-production
testing, followed by testing of samples
from production at regular intervals
- a statistical quality control system is used
- the process is stable between testing of
samples
- pre-production testing and sampling are
performed separately for each production
line (robotic cells)
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Welding parameter
calibration/validation
Which parameters need calibration/validation?
• depends on the welding process
• see BS EN ISO 17662 and BS 7570 for details
How accurate?
•
•
•
•
•
depends on the application
welding current - ±2,5%
arc voltage - ±5%
wire feed speed - ±2,5%
gas flow rate - ±20% (±25% for backing
gas flow rate)
• temperature (thermocouple) - ±5%
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 1 - MMA elementary
monitoring
IN THEORY any M.M.A. operation could
require monitoring of:
• welding current
• arc voltage
• R.O.L.
• preheat/interpass temperature
• electrode treatment and storage
IN PRACTICE (depending on the application)
only the welding current could require
monitoring with a tongue test ammeter
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 2 - High integrity MMA
operation
• IN THEORY, this might require monitoring of all the
activities previously mentioned.
• the equipment thus required would be:
•
•
•
•
•
•
ammeter
voltmeter
stop watch
tape measure
thermometer
calculator
OR
• a PAMS
• all of the above equipment would require
calibration; any meters fitted to the
power source or electrode ovens would
also require calibration.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Example 3 - MIG/MAG welding with a
robot
IN THEORY, the following would require monitoring:
• wire feed speed
• amperage
• voltage
• travel speed
• gas flow rate
• repeatability of the controls
IN PRACTICE, a data logger would be preferred
to monitor all the parameters; also a PAMS
would be required to check the repeatability
of the control knobs.
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Summary
• a welding power source can only be
calibrated if it has meters fitted
• the inspector should check for calibration
stickers, dates etc.
• a welding power source without meters
can only be validated that the control
knobs provide repeatability
• the main role is to carryout “in process
monitoring” to ensure that the welding
requirements are met during production
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Typical examination
question 1
• “The measurement of welding parameters is common
in arc welding practice. Comment on the parameters
that can be measured and recorded,including the
different types of equipment that maybe used.”
This question by definition is related to monitoring
• Introduction: would include monitoring is
dependent on the integrity of the product.
• Welding parameters: need to be identified. (with
comments!)
• Equipment details: can be established from the
welding parameters identified.
• Conclusion: should incorporate
calibration/validation and the need for checking
temperatures (interpass/preheat).
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
Typical examination
question 2
• “Describe how you would ensure that the welding
parameters listed in a WPS are being adhered to
during production welding. Give the advantages
and limitations of the methods used.”
This question is related more to the whole
fabrication process: e.g.
• QA/QC requirements
• Training, experience and qualification of welders
and inspectors
• Inspection procedures (during welding)
• Auditing to ensure that the above is taking place
• Calibration/validation and in process monitoring
Copyright © 2005, TWI Ltd
World Centre for Materials Joining
