Electrical Test Instruments PI-6000
Section II - Detailed Description
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Page II-9
Output current is detected by means of an air core CT around both main busses.
When the series bar is attached to the output, a switch is actuated, which
divides the signal by a factor of 2. Calibration of series and parallel modes is
accomplished with potentiometers on the S/P calibration/switch assembly
under the output face plate.
The output section is energized when a signal is applied to the trigger board of
the SCR controller. The initial phase angle is determined by a zero-crossing
detector in the trigger PCB, and a delay which is normally preset to 70 degrees.
The rheostat autotransformer may be adjusted manually by means of a
handwheel, or by activating the motor drive. Increasing output is clockwise for
all taps.
When T1 is energized, 120 VAC is applied to the primary of T5. This provides a
voltage of about 12 VAC which is used for output ON detection in the indicator
control panel.
Thermistor TH1 senses the temperature of the output bus, and TH2 reads the
temperature of the first primary of T2. These normally have a resistance of 10 K
ohms at room temperature, and lower values as the temperature increases.
Relays K1 through K6 are energized through the indicator control panel. Relays
K1, K2, and K3 are equipped with an electrical interlocks to avoid damage if all
three are simultaneously energized. Catastrophic protection is provided by
fuses F7 through F16.
The adjustable rheostat assembly in the PI-6000 consists of a stack of four 120
VAC decks, with each series connected pair connected to a 240 VAC primary on
T2A. Minor voltage imbalance up to about 2 VAC is corrected by means of
paralleling transformer T7, and actual current in each primary circuit is
monitored by means of 50:5 current transformers T10 and T11. Resistors R1
through R4 ensure voltage balance on the series connected pairs, and also
provide a resistive load to stabilize the SCR controller at low output settings.
The secondary currents from T10 and T11 are monitored by the Programmable
Overload Monitor (POD), which also measures actual temperature in the
primary winding of T2A. The overall system status is displayed on the bar graph
of the indicator control panel, and an interlock relay shuts down the output of
the test set if abnormal conditions are detected.
The voltage on the coil of interlock relays K13 and K14 is monitored by interlock
detector relay K7. If the voltage drops to a point where the relays would drop
out, this module turns off the signal to the SCR trigger board, so as to turn off
main output current before the interlock relays actually open.
The PI-6000 features a very efficient low impedance output transformer with
enhanced reliability and cooler operation due to output plates brazed directly
to the secondary bus conductors. The high strength and corrosion resistant
