Keithley 630 Instruction Manual page 11

OPERATION MODEL 630 POTENTIOMETRIC ELECTROMETER
d. Potentiometric Operating Procedures.
NOTE
Avoid large overload voltages on the null detector. No damage occurs even
with 500~volt overloads, but some open circuit offset will be caused in the
null detector. The offset will disappear after about 5 minutes.
1.
Leave the RANGE Switch at the last setting used in the voltmeter operation. If
the voltmeter reading is negative, reverse the POLARITY Switch position.
2.
Set the first two Reference Voltage Dials to the first two digits of the unknown
voltage found in the voltmeter operation.
NOTE
When switching between the 50-volt and SOO-volt ranges and when changing the
POLARITY Switch, the meter will sometimes temporarily read off-scale. This is
due to transients introduced when the circuit is interrupted and it does not
indicate a faulty instrument.
3.
Set the NULL Switch to the initial
null setting shown in Table 1. Adjust
the Voltage Reference Dials progressive-
ly for zero meter deflection while in-
creasing the null detector's sensitivity
with the NULL Switch. Deflections to the
right indicate the voltage being measured
is more positive than the Reference Vol-
I
RANGE
Initial
Most Sensitive
Switch NULL Switch NULL Switch
Setting Setting Setting
tage Dial setting.
I
TABLE 1. Recommended Model 630 Null Sen-
sitivities and Settings.
I
500 50 0.5 5v v v v 100 100 10 1.0 Mv v v v
1.0 1.0 10 1.0 Mv Mv Mv Mv
NOTE
The most accurate resistors in the Kelvin-Varley divider are in the first
two Reference Voltage Dials. Therefore,
to obtain the most accurate rea-
dings, use the first two dials as much as possible.
4.
The value of the unknown voltage is read directly from the Reference Voltage Dials.
a)
The dial reading will be within the specified limit of error if the NULL Switch
is at the most sensitive setting (Table 1) for the range used and if the meter indi-
cates as close to null as possible.
b) When the first Reference Voltage Dial is used,
only the five Dials need to be
read to be within specifications (*O.Ol% of reading or 30 microvolts).
However, the
meter may be read as an approximation of a sixth digit,
c) When the first Reference Voltage Dial is not used, read the voltage directly
from the remaining four dials.
d) Use the meter as a null indicator when balancing voltages. When the first Ref-
erence Voltage Dial is not used,
the meter approximates a fifth dial reading.
8 0166R