Keithley 610C, Instruction Manual

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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 1.46 volts. This is satisfac­
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. DCVM common
must be above ground for this measurement.
c. Set range to .001 volts and re-zero. Voltage
across RlS7 should be 25MV �3MV.
6-8. NOISE CHECK.
a. Zero check the unit and connect the output to a
Hewlett-Packard Model 3400A
RMS
Voltmeter.
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. Out­
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. If ripple checks
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.
Select for beta range of 35
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.
6-8. OFFSET CURRENT CHECK. Check offset current
whenever excessive noise or drift is suspected. To
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
LOCK
. 003
10-11 AMPERES
FAST
+
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. (This is less
than 20% of full scale). If this is exceeded, check
the +9 volt supply (paragraph 5-5) and the input tran­
sistor, QlOl.
6-9. DRIFT CHECK.
a. Set the front panel controls to:
ZERO CHECK Button
Multiplier Switch
Range Switch
FEEDBACK Switch
METER Swi tch
LOCK
. 03
VOLTS
NORMAL
+
Set the 3V-lMA Switch
on
the back panel to 3V.
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.
Make sure
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. After the first half hour
the time stability should be less than 1 millivolt
per 24 hours.
The offset due to temperature should be
less than 150 microvolts per °C.
d. If the instrument does not meet the zero drift
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.
The instrument should be within
its rated accuracy for two or three years from the
time it leaves the factory.
After this, some of the
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
1
08 to
1012
OHMS settings of the Range
Switch.
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