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Detailed introduction
Output voltage is continuously adjustable from zero to full scale by calibrating and locking the 5-turn dial. Separate output ranges of 0-5 kV and 0-500 V are available. A 10-segment bar graph indicator verifies 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 LED will indicate the selected output polarity. 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 659 has a remote shutdown feature that protects the preamplifier FETs from damage when the germanium or Si (Li) detector has not reached cooling temperature. The bias protected inputs provided are compatible with the standard temperature sensor outputs on ORTEC preamplifiers. When the preamplifier sends a rewarming signal, the Model 659 turns off the 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 high voltage switch is accidentally turned on. To further prevent operational errors in ORTEC protection mode, the bias protection input treats a disconnected or shorted cable as if the detector has not reached operating temperature and responds by turning off the bias voltage. Some detector manufacturers provide TTL logic level outputs from their detector temperature sensors. The Model 659'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. The Model 659 is factory set to 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.
