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3.
Overcurrent
This calibration should not need adjustment (factory adjusted). If the Overcurrent Circuit is out of
calibration, perform the following steps.
a.
a.
With unit off, short the output terminal to ground through an appropriate currentmeter. (A
High Voltage Load will give better resolution and make calibration easier and more accurate.
Minimum recommended resistance: 100K ohm, 100 watt.).
Set the Current Trip potentiometer on the front panel to "1" and the current range switch to 5mA.
b.
c.
Turn on HV On and adjust the output current slowly until 10% of rated current (1mA) is displayed
on the currentmeter.
d.
Adjust potentiometer R69 until the Reset lamp illuminates and high voltage is shut off.
e.
Set the Current Trip potentiometer on front panel to "11."
f.
Turn on HV On and adjust the output current slowly until 110% of rated current (11mA) is displayed
on meter.
g.
Adjust potentiometer R72 until the Overload lamp illuminates and high voltage is shut off.
h.
Repeat steps "b" through "g" as necessary until both settings are calibrated.
4.
Range Overcurrent. R87 sets an overcurrent for the ranges and should be set to trip at approximately
112% of full range current on medium range setting (2mA) with current trip potentiometer set at "11.".
5.
Voltage offset adjustment (R113):
The voltage offset should be done with the voltage output lead connected to board ground. This typically
can be done by connecting the output to the guard terminal. Once connected the offset should be
adjusted till the output meter reads nearest to zero. This offset adjustment should be done before
adjustments to the voltage ranges are made. Test point T10 may also be used to make this adjustment.
6.
Current offset adjustment (R77):
The current offset should be done with the current input connected to board ground. This typically can be
done by placing a jumper from the guard to the return terminal. Once jumped the offset should be
adjusted till the output meter reads nearest to zero. This offset adjustment should be done before
adjustments to the current ranges are made. Test point T37 may also be used to make this adjustment.
DCD 4120-10
CALIBRATION
6-2
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