Paper VT-TuP11
Thermistor Vacuum Gauge; High Sensitivity Shows Direction and Acceleration Which Enables Vacuum Leak Detection

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Thermistor gauge sensors are rugged sensors that have been used to measure vacuum indirectly for many decades. The single resistor element is employed in a bridge-type detector. A constant source to the heating element of the sensor is maintained to a fixed resistance. The amount of drive needed to maintain this value is measured. A decrease in pressure reduces the number of gas molecules available to transfer heat away from the heating element. This results in a temperature and resistance output change 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. High sensitivity over most of its range allows for direction indication as well as how fast pressure is accelerating in which direction. Due to its quick response, a solvent can be used to trigger the response near a chamber vacuum leak.