(1) The ZERO pushbutton is depressed.
(2) The two dots on GA SENS key No. 1 are set perpendicular to the
line of keys.
(3) The GA SENS key No. 1 is depressed, and
using
the
GA
ZERO
control, the galvanometer reading is reduced to zero.
(4) The sensitivity of the galvanometer is increased by depressing GA
SENS keys No. 2 through 4, and the galvanometer reading is readjusted to
zero as required.
(The detector itself should be set at its medium
sensitivity by adjusting the gain of the Nanovolt Amplifier.)
(5) The GA SENS key R is depressed and any movement of the
galvanometer is noted.
The GA ZERO control is adjusted to give no
detectable change of galvanometer reading when keys No. 4 and R are
alternately depressed.
The galvanometer may not be at zero when the final balance is obtained, due
to a thermal EMF or other zero offset in the detector itself. This is not
important since input to the detector is reversed and only changes in the
balance point are of significance.
d. Standardization.
(1) The system is connected as shown in Figure 2-3.
(2) An external saturated standard cell is connected to the terminals
marked SC using solid copper wire which should preferably be twisted and
shielded.
To avoid the possibility of a reverse polarity connection or a
short circuit of the standard cell, mark the wires before twisting and
connect the potentiometer first.
Ensure that the EMF switch is in the
positive position.
(3) The Measuring Dials are set to the known voltage of the standard
cell being used as a reference.
(4) The STD pushbutton is depressed, thus connecting the external
voltage reference in series opposition to the voltage across the generating
resistor.
(5) The 9771 Thumbwheels are set to approximately 5000.
(6) The GA SENS key No. 1 is depressed and the deflection of the
galvanometer is noted. Adjust the current controls of the external current
source to zero the galvanometer.
(7) The galvanometer sensitivity is
increased by successively
depressing keys No. 2 through 4 and continuously adjust the current source to
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