Paper VT-TuM11
Enhancement of Accuracy and Interchangeability of Multi-Sensor Gauges by Use of Individualized Calibration Parameters Stored on the Sensor Assembly Itself
Hot cathode ion gauge controllers that make use of gauge calibration information stored in memory in the gauge controller have been available for well over ten years. In recent years, high-temperature bakeout of hot-cathode ionization gauges has greatly diminished in common use, especially in commercial vacuum processing systems. For this reason, there are now many applications in which it is practical to store gauge calibration information in a memory chip attached to the transducer, rather than in a memory located in the controller. The attendant advantage in locating the memory on the transducer is that it permits maintaining a desired level of accuracy in the pressure measurement when one transducer is replaced by another or one electronics package is replaced by another. For those combination gauges containing hot cathode ionization sensors, heat-loss sensors, and piezo-resistive diaphragm sensors, calibration encompasses pressures ranging from high vacuum to atmosphere. A system for performing calibration of a multi-sensor gauge over such a wide pressure range is described, as well as the method of maintaining the reference gauges used in this system. Results are evaluated from testing of a multi-sensor gauge design in which calibration memory resides on the sensor assembly for several situations: (1) repeatability over time of pressure indication for the electronics and multi-sensor assembly as a system, (2) reproducibility of pressure indication when different sensor assemblies were used with the same electronic control unit, and (3) reproducibility of the pressure indication when different electronic control units were used with the same sensor assembly.