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Detailed introduction
Output voltage is continuously adjustable from zero to full scale via a calibrated, locking, 5-turn dial. Each power supply provides two outputs controlled by the same dial: 0 to 5 kV output and 0 to 500 V output. Two 10-segment bar graph indicators verify that the selected voltage is available at the output.
Two features are used to prevent accidental changes of output polarity to the wrong state. When the NIM chassis is powered on, the front panel LEDs will indicate the selected output polarity for each power supply. Therefore, correct polarity can be verified before using a high-voltage switch to apply bias voltage to the detector. Additionally, the side panel must be removed to change the output polarity. This prevents unexpected changes from occurring.
The Model 660 features high voltage protection to protect the preamplifier FETs from damage while the germanium or Si(Li) detector is still cool. Each power supply contains a bias-off input that is compatible with the standard temperature sensor output on the ORTEC preamplifier. When the preamplifier signals a high temperature, the Model 660 turns off the detector's bias voltage and turns on the off indicator light. Regardless of changes in the signal from the preamplifier temperature sensor, the bias voltage remains off, and off mode can only be canceled manually by pressing the reset button. This protects the preamplifier FETs if the detector is cooled due to an accidental opening of the high voltage switch. To further prevent operating errors in ORTEC's shutdown mode, the bias shutdown input treats a disconnected or shorted cable as a detector rewarming condition and responds by turning off the bias voltage. Some detector manufacturers provide TTL logic level outputs from their detector temperature sensors. The Model 660's onboard jumpers can be moved to the TTL position, making the bias protection input compatible with detectors providing TTL outputs. The bias protection feature can also be disabled by moving the onboard jumper to the BYPASS position. Both power supplies on the Model 660 are factory set in ORTEC mode.
Both high-voltage outputs are protected against overload. When the bias supply detects excessive output current demand, it turns on the overload indicator and reduces the output voltage before the output current drops to the allowable range. Recovery from overload occurs automatically when the excessive current demand is eliminated.
