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WELD SENTRY 2
SECTION 5 - CALIBRATION
CALIBRATION CHECK
The Weld Sentry has a built-in Calibration Check which can be used as an easy way to check the accuracy
of the Voltage and Current measurement circuits. It is good Quality Assurance practice to establish a
regular Calibration Check. Select System Menu from the Main Menu and then select CALIBRATE
SENTRY, the following screen will be displayed:
1. Disconnect the voltage and current pick up leads from the back panel of the Sentry.
2. Check the values displayed next to Voltage Input and Current Input.
If they are less than 3, the unit is calibrated within specified tolerance.
To adjust calibration, refer to the next section on Current & Voltage adjustments.
3. Don't forget to reconnect the pick up leads after the calibration check.
Check the Current Input whenever switching from a Current Coil to a Current Shunt or back again.
The Sentry is shipped from the factory adjusted for the CURRENT COIL. It may be necessary to
adjust the Current Input if a CURRENT SHUNT is to be used.
CURRENT & VOLTAGE INPUT ADJUSTMENTS
In addition to the built-in calibration check, there are 4 precision voltage references which can be measured
on the Sentry Control Board. If the built-in calibration check shows either voltage or current inputs over 2,
the following adjustments will correct the calibration. Requires use of a DVM and should be performed by
a qualified technician.
1. Select the correct COIL/SHUNT SWITCH position.
2. Disconnect Voltage and Current Input cables from the rear of the Sentry.
3. Remove the cover and locate the control board at the right side of the unit.
4. Refer to Drawing 4-32603, Assembly PCB, Weld Monitor Module.
5. With the voltage and current leads disconnected from the UUT, verify that the COIL/SHUNT
switch is set to the SHUNT position (button out). Using TP0 as a ground reference, adjust the
following trimpots in the order listed:
Adjust
R16
R58
R33
R75
Note: The adjustments must be made in the order listed. If they are not, it may not be possible
to adjust the final stage within tolerance.
6. Set the COIL/SHUNT switch to the COIL position (button in).
7. Adjust R94 until TP3 reads 0v ± 10mv.
8. Don't forget to reconnect the pick up leads after the calibration adjustments.
Until Test Point
TP1
TP3
TP2
TP4
= Reading
0 + 10mv/-0mv
0 + 10mv/-0mv
0 ± 1mv
0 ± 1mv
Page 39
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