Bird Technologies 4314B - Manual (Page 40)

28
Calibrating the Wattmeter
Zero adjustment of the meter is the only calibration required for the 4314B. This
should be done any time the meter pointer is not exactly aligned with the zero
mark on the meter scale when no power is being applied. Zero adjustment must
also be performed after the meter or instrumentation module has been
replaced.
1. To assure that the meter reads correctly for both average and peak opera-
tion,
2. Apply direct current from a battery source to the input of the amplifier cir-
cuit (figures 5 and 6, pages 20-21).
The steady direct-current peak level should be the same as the average current
level because no peaks exist in this current.
Apply a direct current and adjust as necessary so that the same reading is
attained in both average and peak modes.
Install a voltage-dropping variable voltage dividing potentiometer and a battery
in series with the input of the amplifier.
Make sure the resistor is set for zero output. Connect the positive (+) side of the
circuit to input and the negative (-) side to ground.
Install a voltmeter across the circuit. Slowly operate the potentiometer to adjust
output to apply approximately 21 millivolts. Use a suitable resistive network.
Check the reading of the meter.
The pointer should deviate or travel about half of full scale. Set the CW/PEAK
switch to PEAK mode while watching the meter pointer. There should be no
deviation of the pointer from average to peak reading.
If the pointer reads a different value for peak reading than for average reading,
adjust potentiometer R8 until the two readings coincide.
Figure 12 Calibration Potentiometer
Calibration
Potentiometer
Access Hole
X