The GTC-395 thermocouple vacuum gauge is a microprocessor controlled single station thermocouple type gauge controller housed in a 1/8th DIN case. The unit uses the rugged and proven GTC-036 sensor over a pressure range of 1 mTorr to 3000 mTorr with an at atmosphere indication. The gauge features two independent relays that can be set within the range of the gauge, each set point includes a separate high and low pressure value. Three front panel buttons allow the user to toggle through and adjust the values. LED’s indicate which value is being displayed with separate LED’s to indicate the status of the set points. The unit features an RS-232 serial interface that allows a remote system to request information and a separate linear analog voltage output that is proportional to pressure. 
 
The GTC-395 gauge supplies a constant current source to the heating element of the GTC-036 sensor. The thermocouple junction in the sensor generates a voltage signal that varies with the temperature of this heating element. A decrease in pressure reduces the number of gas molecules available to transfer heat away from the heating element, resulting in a temperature rise and an increased output from the sensor. This signal is filtered and amplified, and then sent to an analog to digital converter. The microprocessor reads this signal, does further filtering and uses the result as an index into a lookup table for pressure. This value is written to the display and to a digital to analog converter that generates the analog voltage output. The set points are implemented in software and their values are stored in nonvolatile memory on the microprocessor.