and limiting resistor must be 5000 ohms if we are to obtain full-scale deflection.

Full-scale deflection indicates zero resistance, and the meter scale is marked "0"

ohms at 1 milliampere point (fig 1-10).

When a resistor (Rs) is placed between

terminals T1 and T2, the total resistance of the circuit is increased, and a

smaller current flows through the meter.

c. For mid-scale reading, the size of Rx (fig 1-17) between terminals T1 and

T2 must be of a value to limit current to 0.5 milliampere.

Thus the total

resistance of the circuit of half-scale deflection is 10,000 ohms.

d. Therefore, Rx must be 5000 ohms for mid-scale reading when Rx is placed

between T1 and T2.

This leads to an interesting conclusion.

The midscale

resistance reading of an ohmmeter is equal to the internal resistance of the meter,

and the scale may be so calibrated.

Integrated Publishing, Inc. |