Working Circuit

TM 11-6625-298-14

connect the ohmmeter terminals to the moving coil

resultant of the two opposing forces that move the

assembly. The position at which the pointer finally

coil assembly.

comes to rest on the scale is determined by the

Figure 5-5. Meter assembly,

Ohmmeter ZM-21B/U.

5-6. Working Circuit

b. An unknown resistor connected between the

line terminal and the ground terminal provide a

a. The working circuit of the insulation

another path for current flow. This path is from

resistance measuring set is designated in heavy

negative () terminal of generator G 1, through

lines in figure 5-6. The crank of the hand generator

current coil L1 of the meter, resistor R1, the line

operated at a speed of 160 rpm rotates generator

terminal, and the ground terminal to the positive

G1 at approximately 6,000 rpm. The generator

(+) side of generator G1 through the controller.

output voltage is limited to 525 volts dc by the

The magnetic field set up by current coil L1 tends

controller. With no connections made to the ohm-

to move the coil assembly and the pointer in a

meter terminals, current flows from the negative

clockwise direction. If the unknown resistance is

() terminal of generator G1, through potential

low, most of the current flows through coil L1 and

coil L2 of the meter, and through the resistors R2

and R3 (through the controller) to the positive (+)

the pointer indicates a reading close to zero. If the

value of the resistance is high, less current flows

terminal of the generator. The magnetic field set

up by potential coil L2 reacts with the field set up

through coil L1 and the pointer moves from the

zero end of the scale to indicate a point nearer

by the permanent magnet in such a way that the

coil assembly and the pointer move in a coun-

infinity.

terclockwise direction until the pointer indicates

infinity.