illustrated in Figure 5-12. Here the reference voltage is represented as a
battery. A calibrated voltage divider, R1, provides an adjustable output.
The unknown input voltage is connected to input terminals A and B. When the
voltage divider is adjusted so that the two voltages are equal, there will
be no current flow in the meter.
This condition is termed a null.
magnitude of the unknown voltage is equal to the product of the reference
the voltage-divider controls are calibrated in terms of the input voltage.
Typical accuracies of this type of dc voltage measurement are of the order
The principal elements of the Model 887A Voltmeter are depicted in the
In this diagram, the Reference
Supply battery of Figure 5-12 has been replaced by the Reference Power
Supply; the voltage divider has been replaced by the Kelvin-Varley Divider;
and the Meter has been replaced by the Null Detector.
input circuit has been modified to include an AC to DC Converter and a DC