Simpson 311 Operator's Manual page 18

MAINTENANCE
CALIBRATION
The Simpson Vacuum Tube Voltmeter Model 311 has been
calibrated carefully at the factory, and changes should not
be necessary. After a long period of use, or when any in-
ternal parts have been replaced, recalibration may be re-
placed, recalibration may be required. Use the following
procedure:
1:
16
Allow the instrument to warm up for a period of at least
one hour. Set the function switch at — DC and the range
switch at 1.5V.
Turn the ZERO ADJUST knob to the extreme left and
note the position of the meter pointer. Return meter
pointer to zero. Turn the function switch at + DC and
turn the ZERO ADJUST knob to the extreme right. Note
the meter pointer position again. The pointer position
should be the same for both polarities. If there is any
difference between them, adjust potentiometer R29
until the readings are the same. See figure 2, sche-
matic diagram, to help locate potentiometer R29 inside
the instrument. |
With the function switch at — DC, the switch on the
probe handle at DC, and the probes shorted together,
set the ZERO ADJUST control for a zero pointer indi-
cation.
Turn the function switch to AC and set the switch on
the probe handle at AC. If the pointer does not rest at
zero, adjust potentiometer R22 to correct it. See figure
3, schematic diagram, to help locate potentiometer R32
inside the instrument.