Paper VT-ThM6
Theory and Design of a Pirani-style Thermal Conductivity Vacuum Gauge with Unique Geometries and Control Circuitry

Thursday, October 18, 2007, 9:40 am, Room 618

Characteristics of Pirani-style gauges and their causes for inaccuracy due to errors in temperature compensation will be presented. The principles of sensor thermal end losses as they contribute to pressure indication errors as well as errors due to changes in ambient temperature and non-uniformities in mounting structures will be discussed with special attention to reducing those uncertainties. The design, called Conductron (R) technology, is found to have usable pressure indication up to an atmosphere without utilization of gas convection enhancement geometry which causes orientation dependency. A geometry and method of operating the gauge, departing from the conventional Wheatstone bridge, that avoids common pitfalls of conventional Pirani gauge operation will be described. Certain operational measurements will be shown to avoid the more difficult determinations of (a) power lost to gas conductance and (b) measurement of sensor environment temperature, often used in both transducing these data to an indicated pressure and also providing temperature compensation. Also shown will be a unique method for arriving at the indicated pressure from those operational measurements. A pressure range from the low mTorr to atmosphere is encompassed by this design.