7
10. Calibration
The measuring circuits in the PSC are very stable and should not require any adjustment for
several years. As with any test equipment, it is recommended that the displayed values be
compared to known accurate instruments to verify calibration is within acceptable limits.
Acceptable limits should be defined by the user. In typical battery applications, acceptable
tolerances are:
V
cell
=
±
0.01 volt I
charge
=
±
0.25 amps T =
±
1%
The voltage and current readings are calibrated using a potentiometer adjustment to set the upper
level of the input range. The circuit uses an auto zero feature, so there is no adjustment for that
end of the range. Because the time is software generated using a crystal oscillator as the
reference, there are no calibration adjustments for time. The time is either correct or there is a
problem with the PSC.
WARNING
: Remove power before opening the unit. Opening the equipment may expose you to
dangerous voltages. Do not let unauthorized persons service this equipment.
To access the voltage and current calibration adjustments, remove the top cover of the charger.
Refer to Figure 9 for the locations of potentiometers P1 and P2. After the top is removed, proceed
with calibration as follows.
10.1. Cell Voltage Calibration
Power up the charger, and connect it to a nominal 2 volt battery of at least 25 ampere hours
rating, using a calibrated 10 amp shunt in series with the positive test lead. Select the Cell
Voltage display mode on the PSC.
Read the actual cell voltage with a known calibrated 3½-digit voltmeter, and adjust
P1
until
the value displayed by the PSC matches that of the digital voltmeter.
RV1
RV2
Figure 9. PSC-10A Control Board
10.2. Charge Current Calibration
Set the PSC to the Power Supply mode, and increase the charger voltage until the charge
current reaches a stable level at or close to 10 amps.
Read the actual charge current flowing through the calibration shunt, and adjust
P2
until the
value displayed by the PSC matches this current reading.
