Pi-Aux Boost Unit Circuitry; Major Parts Identification And Operation - ETI PI-800 Instruction Manual

Electrical Test Instruments MAC-21
Section III – MAC-21
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The output of the adjustable Vernier assembly in the PI-800 is monitored di-
rectly by means of the Programmable Overload Monitor (POD). The overall sys-
tem status is displayed on LEDs DS10-DS12, and the peak output current is dis-
played on LEDs DS7-DS9. An interlock relay shuts down the output of the test
set if abnormal conditions are detected. More details are in the appendix. The
POD interlock may be defeated by holding switch S5 on.
The coil of interlock relay K1 is connected to overtemperature fuses in the cores
of the output transformers T4-T6, and also to thermal switches TS1-TS8
mounted on each output bus terminal. If any terminal exceeds about 150 de-
grees C, a thermal switch will open and trip the interlock, and will be displayed
on Bus Overtemperature lamp DS13.

PI-Aux Boost Unit Circuitry

The PI-Aux Boost Unit connects to the PI-800 to form the PI-1600. SCR con-
trolled voltage from the PI-800 is distributed to the four tap relays K1-K4, which
provide power to the primaries of T1-T4 when energized. Output ON indicators
DS1 and DS2 light when voltage is applied to the main input. Fans B1 and B2 are
powered from the 12VDC supply. The interlock circuit is connected through
transformer core overtemperature fuses S1-S4, and bus overtemperature
switches TS1-TS8. If any of these devices opens, the Bus Overtemperature lamp
DS3 lights.

MAJOR PARTS IDENTIFICATION AND OPERATION

PI-800 Front Panel
Input Jacks J3 and J4: These 50 ampere male jacks are to be connected to main
power of 120 or 240 VAC by means of female plugs.
Ground Terminal J2: This ¼" steel lug with wingnut is used to connect the frame
of the test set to a solid earth ground.
Input Voltage Lamp DS1: This amber neon lamp glows whenever voltage above
about 90 volts is present on the input jacks.
Input Selector Switch S1: This three-position switch is used to select the proper
input configuration for the mains voltage (120 or 240 VAC) on which the test set
is to be used. The center OFF position disconnects the test set from the input
voltage, although the Input Voltage lamp still indicates the presence of voltage.
Control Power ON switch S3: This green switch turns on 120 VAC control power
to the test set, and its green lamp lights when ON. It also resets the output in-
terlock and energizes the interlock contactor K1 if all interlocks are clear.
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