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TEMPERATURE CONTROL OF COOLED PHOTOMULTIPLIER HOUSINGS Temperature stability and control is important in photo-multiplier applications for reasons which include: Dark current drift as a function of temperature change. Gain change as a function of temperature change (approximately -1/2% per °C .) Loss of red sensitivity as a result of over cooling. Degradation of performance of bialkali photocathodes as a result of over cooling.

Temperature control can be affected electromechanically or electronically. Electronic temperature control is best achieved using digital PID (proportion, integral and derivative) technology. Products for Research DIGITAL PID TEMPERATURE CONTROL provides setability with digital accuracy, as opposed to potentiometer knob estimation, and is available in the S600 power supply series . The microprocessor based controller utilizes an "auto-tune" algorithm to automatically adjust PID parameters. The controller simulates process upsets, repeated three times, in order to build history on the process. The parameters are then automatically set, based on this history. This "auto-tune" function enables the controller to easily and effectively accommodate a wide range of operating conditions.

In the case of thermoelectric cooling , Products for Research DIGITAL PID TEMPERATURE CONTROLLERS provide extremely stable temperature control, since they are not susceptible to regulation coefficients (changes in tube temperature with changes in coolant temperature). These changes are a function of the semi-conductor nature of thermoelectric devices when controlled by a potentiometer balanced bridge circuit, and are typically in the order of ± 0.1°C change in PMT temperature for a 5°C change in coolant temperature. The Digital PID controller with "auto-tune" eliminates this problem, and provides control regulation of ± 0.1°C regardless of changes in coolant temperature. Precise temperature control of ± 0.1°C with minimal overshoot or undershoot is also achieved with liquid nitrogen cooling  and  compressor cooling , due to the "auto-tune" function of the Products for Research DIGITAL PID TEMPERATURE CONTROLLERS.

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