Radiation Detector and Meter DT-590A/PDR-56F Scintillation Probe

This pdf file shows the schematic diagram of my home-built circuit to drive the PDR-56 probe. A JKL BXA-12579 inverter commonly used to drive cold-cathode fluorescent lamps is used as the high-voltage power supply. The BXA-12579 produces 1, 500 VACRMS for a 12 VDC input. The AC output is tapped straight from the transformer`s secondary and rectifie
Radiation Detector and Meter DT-590A/PDR-56F Scintillation Probe - schematic

d by D1, a high-voltage diode rated at 20 kV and 0. 5 A. The rectified signal is filtered by C1, R1 and C2. -950 VDC for operation of the photomultiplier tube inside the PFR-56 probe are regulated by a series of Zener diodes (D2 D9). -9 V are generated by an isolated DKE 10A-05 DC/DC converter, and +3. 8 V are derived from the 12VDC input by a 3-pin 5 V linear regulator (U1) with its output voltage dropped by 2 series diodes (D11 and D12). The signal input circuit is based directly on the military DT-590A/PDR-56 radiac meter as described in US Army Technical Manual TM 11-6665-245-34. In this part of the circuit, Q1, Q2 and Q3 form a discriminator and buffer-inverter circuit that determines the level of incoming pulses which are measured and provides a positive going pulse for use by U2. Prior to any signal (positive pulse from the buffer inverter circuit Q3), the inputs to NOR gate U2A are both low, the output is high and transistor Q4 is conducting. A positive going pulse from Q3 starts the circuit into operation. When pin 1, U2A, goes high, its output goes low. The voltage change is coupled directly to the base of Q4 through timing capacitor C10. Q4 is then cut off and its collector goes high holding the output of U2A low. This condition holds until timing capacitor C10 discharges through resistor R10 enough to allow Q4 to turn on, causing pin 2 of U2A to revert to a low condition. This action results in pin 3, U2A, first...

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