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3.
Depending on the exact value of the [400 ohm
load, the voltage range may be slightly higher or
lower than 1.33 to 1. 47 volts; for example, 1.34 to
1.48 volts or 1.32 to 1 . 4 6 volts.
tory provided the overall change is at least 140 mil
livolts and the maximum voltage is near 1.47 volts.
4.
Remove the 1400 ohm load and set the 3V-lMA
Switch to 3V when 'completed.
6-7.
DC BIAS ADJUST.
a.
Zero check unit, zero meter on the .001 volt
range and then set to 100 volt range.
b.
Connect DCVM across R157 (see PC - 183 layout)
and adjust DC BIAS pot for 2SMV +3MV.
must be above ground for this me a surement.
c.
Set range to .001 volts and re - zero.
across RlS7 should be 25MV � 3MV.
NOISE CHECK .
6-8.
Zero check the unit and connect the output to a
a.
Hewlett - Packard Model 3400A
1.
Set the METER Switch to CENTER ZERO and zero
the Model 610C on the 1 millivolt range.
2.
The Meter noise must be less than 25 micro
volts rms or 50 microvolts peak-to - peak.
3.
The Output noise must be less than 90 milli
volts rms.
b.
Switch the Model 6l0C to the 1 volt range.
put noise must be less than 15 millivolts rms.
c.
Excessive output noise may be due to high ripple
on ,the 120 volt or 9 volt supplies.
satisfactorily, excessive noise can generally be cor
rected by reversing the two red leads from the second
ary of the transformer.
1.
If reversing the red leads does not correct
excessive noise. the probable cause is due to high
beta for Qlll or Q112.
to 80.
2.
Reversing the two yellow leads from the sec
ondary of the transformer may also help reduce ex
cessive noise in some units.
This is satisfac
DCVM common
Voltage
Voltmeter.
RMS
If ripple checks
Select for beta range of 35
6 - 8.
OFF SET CURRENT CHECK.
whenever excessive noise or drift is suspected.
read the offset current of the Model 6l0C, set the
front panel controls to:
ZERO CRECK Button
Multiplier Switch
Range Switch
FEEDBACK Switch
METER Switch
Cap the INPUT Receptacle and unlock the ZERO CHECK
Rutton.
The offset current indicated on the meter
should be less than 5 x 10 - 15 ampere.
than 20% of full scale).
the +9 volt supply (paragraph 5-5) and the input tran
sistor, QlOl.
6-9.
DRIFT CHECK.
Set the front panel controls to:
a.
ZERO CHECK Button
Multiplier Switch
Range Switch
FEEDBACK Switch
METER Swi tch
Set the 3V-lMA Switch
b.
Connect Model 6l0C to the Model 370 Recorder.
Adjust Recorder sensitivity control completely clock
wise (maximum sensitivity) and the lMA CAL Control of·
Model 6l0C for full recorder deflection.
Model 6l0e chaSSis cover is attached with at least
two screws.
c.
Make two drift runs with the Model 6l0C to de
termine time and temperature stability individually.
For each run allow the Electrometer to warm up for 1/2
hour.
A zero drift of less than 2 millivolts after
the first half hour is indicative of a satisfactory
temperature coefficient.
the time stability should be less than 1 millivolt
per 24 hours.
less than 150 microvolts per °C.
d.
If the instrument does not meet the zero drift
Out
specification, the input transistors may be faulty.
6-10.
HIGH MEGOHM RESISTOR VERIFICATION.
a.
About every six months it is necessary to check
the value of the high - megohm resistors, RIIO to Rl12,
on the Range Switch.
its rated accuracy for two or three years from the
time it leaves the factory.
resistors may drift out of tolerance and should be
replaced.
Faulty high - megohm resistors will affect
the accuracies of measurements for the 10 - 9 to 10 -11
AMPERES and the
Switch.
Check offset current
LOCK
. 003
11
10 -
FAST
+
If this is exceeded, check
LOCK
. 03
VOLTS
NORMAL
+
the back panel to 3V.
on
After the first half hour
The offset due to temperature should be
The instrument should be within
After this, some of the
0 8 to
OHMS settings of the Range
10 12
1
To
AMPERES
(This is less
Make sure
25
23
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