Miniature silicon based thermal vacuum sensor and method of measuring vacuum pressures

摘要

A miniaturized silicon based thermally controlled vacuum sensor uses thin film resistors on a membrane in a minute measuring chamber to accurately detect vacuum pressures in the range of 760 Torr to 1x10-5 Torr. The configurations of the measuring chamber and gas diffusion port of the sensor structure insure that heat transfer from the membrane is predominately conductive over the pressure detection range to provide linear output up to 0.1 Torr. A microprocessor is used to control and measure power required to maintain a predetermined temperature differential between a sensing resistive element on the membrane and an ambient temperature sensing element of the sensor base from analog voltage and current values. Pressure detection errors introduced by ambient temperature variations are minimized by measuring power dissipated into the gas. Analog and digital converters for both current and voltage signals use a SIGMA - DELTA conversion method to reject electrical noise by an averaging technique to produce stable signal detection of pressure down to 1x10-5 Torr. The sensor is thermally stable over an ambient temperature range of 0 DEG -50 DEG C. at pressures between 10-4 to 760 Torr.