The correct value of the series resistor to be used with a Weston Standard
Cell (1. 01859 volts) is 2,968 ohms. This figure takes into account the
internal resistance of the cell (750 ohms at 68" F. or 20' C. ).
c. For rough accuracy (1%)
Follow steps 1, 2, and 3, as above. Connect a fresh Mallory mercury
cell (such as those used in the Autograf, Mallory type #RM 12) to the
recorder input terminals with reversed polarity through a series resistor.
Proceed as in step 5 of (a).
The correct value of the series resistor to be used with a Mallory #RM 12
cell (1. 345 V) is 69,000 ohms.
d. In the event the recorder cannot be brought to "0" by use of the calibrating
control, the Mallory mercury cells should be replaced. This cell is a
Mallory type RM 12, which may be obtained from drug stores or electronic
supply houses where it is generally stocked for use as a replacement in
electronic hearing aids.
e. Replacement of Mallory Cells
1. Remove instrument case.
2. Remove old cells from clips and insert new cells in correct position
for proper polarity (plus end of battery toward red battery clip).
3. Make sure clips are clean and cells are firmly in place to insure low
contact re sistance.
2. CALIBRATION OF TIME BASE
The various sweep circuit intervals are established during manufacture and
normally will not change appreciably. If excessive deviation from the fixed
intervals is experienced proceed as follows:
a. For sweep periods of 50 seconds or over, a rough check of timing ac-
curacy may be made with a stop watch.
b. For shorter sweep periods an accurate timing function should be gen-
erated on the Y-axis for comparison to the actual X-axis pen advance.
c. Deviations from full scale accuracy may be compensated for by means
of a screw driver adjustment potentiometer on the rear function panel.
27 |
ACEC
HEWLETT-PACKARD
