5.
Voltage measurement.
a. Between 0 and 2.1 volts.
(1) With the potentiometer standardized as outlined in the previous
section, raise the GA SENS and the function keys ZERO, STD, and MEAS by
turning keys 1 and ZERO until the dots lie in the vertical position. The
+EMF switch should be in the positive position.
(2) The voltage to be measured is connected to the EMF terminals
using untinned solid copper wire, preferably twisted and shielded. Set the
Measuring Dials to the approximate value of the unknown voltage if possible.
(3) The range switch is set to the X1 position.
(4) To connect the EMF terminals to the generating resistor the ZERO
key is rotated and the MEAS key depressed.
(5) The GA SENS key No. 1 is turned through 90, depressed, and using
the Measuring Dials, the galvanometer is zeroed.
(6) The sensitivity of the galvanometer is increased by depressing GA
SENS keys No. 2 through 4 and readjusting the Measuring Dials to maintain
the null on the galvanometer. Final null should be obtained by alternately
depressing keys No. 4 and R and adjusting the dials to minimize any change
in the galvanometer reading.
The measured voltage may now be read from the dials.
b. Between 0 and 0.21 volts.
(1) The procedure is exactly the same as that described in Subsection
3-5(a) above, except that the range switch is moved to the X0.1 position,
and the zero adjustment procedure should be repeated if greater zero
accuracy is required.
For the greatest measurement accuracy on the X0.1
range, the potentiometer would be zeroed as outlined below.
(a) Connect the measuring
leads
to
the
Model
9931
and
short-
circuit them at their other end.
(b) Set all the EMF dials to read zero.
(c) Depress the MEAS function button.
(d) Adjust the GA ZERO control until there is no change in
galvanometer deflection when the GA SENS keys 4 and R are successively
depressed.
(2) This procedure eliminates
the
effect
of
thermal
EMFs
in
the
measuring leads to the known EMF.
21
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