Relay Driver

The relay driver consists of a transistor that controls the relay (K1) coil

voltage.

Bar Graph Display

This ten-segment indicator graphically displays the level of ripple and is

used during EDM-200 calibration and for monitoring EDM-200 operation.

AVR Ripple Amplifier

Since the AVR output consists of pulses, a strong ripple component

consisting of these pulses is present in the field current and makes the

detection of an open diode difficult. To eliminate the AVR ripple, the

AVR voltage at terminal F+ is passed through a filter, a null adjustment,

and the AVR ripple amplifier. The amplifier output is then used by the

input amplifier to cancel out the AVR ripple component in the field current.

Power Supply

EDM-200 circuitry operates from a regulated +14 Vdc source that is provided

by the transformer-rectifier type power supply. The relay output will be

inhibited and the bar graph display may indicate incorrect information until

the input voltage is at least 50% of nominal.