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Victoreen 875
Operators Manual
4-4
PreamplifierIMeter Board Power Supply (P/N 876-1-86, Schematic 876-1-3E)
A +6.2 V power supply contained on the preamplifier meter board has as its input the +15 V from the
power supply board. Integrated circuit U401, pins 12, 13, and 14 is a voltage regulator with diode U402
providing a stable reference voltage. The output is adjustable by R413.
Relay Driver Printed Circuit Board (P/N 876A-1-75A, Schematic 876A-1-3B)
The signal input to the relay driver printed circuit board which is taken from pin 13 of the preamplifier
meter may be monitored at this point through test point TP501. The signal enters pin 13 of OP AMP
U501, and the output is taken from pin 14. The gain of this amplifier stage can be adjusted by
potentiometer R503. The output of the OP AMP can be monitored at TP502; it provides inputs to:
• High Alarm circuit
• Alert Alarm circuit
• Meter buffer amplifier circuit
• Recorder/Computer drivers
High Alarm Circuit
The signal output to the high alarm circuit enter OP AMP U502 on pin 5. This is a difference amplifier,
whose other input (pin 6) is determined by the setting of potentiometer R513. The main purpose of this
stage is to control the high alarm threshold.
The output of the comparison OP AMP is connected, through diode CR504, to pin 6 of U503, which acts
mainly as a power stage for the HIGH ALARM (red) panel light. The output of this stage (pin 7) also
serves as the input to the high alarm relay driver stage U503, whose main function is to drive relay K502.
The input to the high alarm relay driver stage of U503 is on pin 9, and the output is taken from pin 8.
Relay K502 is energized in the non-alarm state, and a signal above threshold serves to de-energize it.
There is a red HIGH ALARM jumper connected to the collector (pin 8) of the relay driver U503. The
following options are available with the presence or absence of the jumper when the radiation level
exceeds the threshold and triggers the alarm:
Manual Reset - The alarm will continue to be activated even after the radiation level recedes below
threshold until the SAFE/RESET indicator push button on the panel is depressed. This option occurs
with the jumper in place.
Automatic Reset - The alarm will continue to be activated only as long as the radiation exceeds the
threshold level. This option occurs with the jumper removed.
The red warning light acts similarly to the alarms. It lights when the alarm relay is de-energized.
Each relay contains four Form C contacts, but only two of the four are accessible through the rear
connector.
The connection to the red panel warning light is from terminal 3 of the printed circuit board, which is
connected to the collector (pin 7) of U503 through resistor R521.
Alert Alarm Circuit
The signal input to the alert alarm circuit enters OP AMP U502 on pin 3. This is a difference amplifier,
whose other input (pin 2) is determined by the setting of potentiometer R509. The main purpose of this
stage is to control the alert alarm threshold. The output of the comparison OP AMP is connected, through
diode CR501, to pin 13 of U503, which acts mainly as a power stage for the Alert (yellow) panel light. The
output of this stage (pin 14) also serves as the input to the alert alarm relay driver stage U503, whose
main function is to drive relay K501. The input to the alert alarm relay driver stage of U503 is on pin 2,
and the output to the relay is taken from pin 1. Relay K501 is energized in the non-alarm state, and a
signal above threshold serves to de-energize it.