Keithley 610B Instruction Manual page 36

MAINTENANCE MODELS 610B, 610BR ELECTROMETERS
4.
Check the next stage by connecting the voltmeter across the collectors
of 9103 end Q104 (Figure 21), end adjusting the COARSE and MEDIUM ZERO Controls
for null.
If a null is
not
reached, check this stage and for shorts in the
base circuit of Q105 and QlO6.
5.
Connect the voltmeter across the collectors of Q105 and Ql06. Adjust
the FINE ZERO Control for null.
If null is reached,
the dc amplifier is
operating correctly and the trouble is in the output stage or the feedback stage.
6. Check the output stage cathode resistor, Rl8S (Figure 24)) end capa-
citor, Cl13 (Figure 23), for a possible short.
7.
The feedback Loop includes the multiplier resistors, RlS6 through Rl66,
the recorder output resistors, R180 on 3V position
or
R174 and R179 on 1 MA
position,
and the meter. An opening of any of these components prevents zero-
ing of the meter. An open multiplier resistor, however, prevents zeroing
for only that particular multiplier setting.
4-s.
234-VbLT OPEBATION.
The Model 610B is shipped for use with a 117-volt
power source unless otherwise ordered. To convert
it
for 234-volt sources,
use a screwdriver to change the slide switch on the beck panel to 234. Change
the fuse from l/4
ampere
to l/8 ampere. No other adjustment is necessary.
To switch from 234 to 117-volt operation, reverse the procedures.
4-6.
CALIBRATION PROCEDURES.
'a. The following procedures are recoranended for calibrating and adjusting
the mdel 610B.
Use the equipment reconrmended in Table 3. If proper facilities
are not avaflable or if difficulty is encountered, contact Keithley Instruments,
Inc., or its representatives to arrange for factory calibration.
b. Procedures
are
covered for the following: grid current check, dc ampli-
fier balance adjustment, high-megohm resistor verification, calibration of the
ohms ranges, meter zero calibration and
accuracy
check.
1. Check grid current (paragraph 4-7) et regular intervals to make sure
the electrometer tubes are functioning
correctly.
Instrument
Use
Keithley Instruments Model 241
Calibrate meter zero and verify
Regulated High Voltage Supply voltage range accuracy.
Keithley Instruments Model 261 Picoamp-
Calibrate current, resistance
gre spurce* fr#m LO-L4 to LOe4 ampere,
and charge ranges.
0 1.5/,.
Keithley Instruments Model 370 Recorder
Zero drift check.
Keithley Instruments Model 515
Verify high-megohm resistors in
Megohm Bridge
Range Switch.
KeTCh1eyRrsrrnment.s Model 662
Calibrate resisrmrre-ranges
and meter zero.
TABLE 3.
Equipment Recommended for Model 610B Calibration. Use these inetru-
ments or their equivalents.
32
0667R