Ionization gauge and method of using and calibrating same

In controller circuitry for controlling the operation of a predetermined ionization gauge having a source of electrons, an anode, and an ion collector electrode, said controller circuitry including means for biasing said electron source, anode, and collector electrode at predetermined potentials;

• means for substantially maintaining the electron emission current from said electron source at a predetermined value;
• means for measuring the heating power of the electron source to obtain a measured value of the heating power at an unknown pressure;
• means for measuring the ion current to the collector electrode to obtain a measured value of the ion current at an unknown pressure;
• the improvement comprising:
• means for storing a plurality of calibration data sets for collector electrode currents, heating powers of the electron source, and gauge sensitivities obtained with at least one reference gauge at representative values of known pressures and cathode heating powers;
• where said reference gauge has substantially the same sensitivity at any given pressure and heating power as does said predetermined gauge;
• means responsive to at least one of said data sets together with said measured values of the ion collector current and electron source heating power for calculating the gauge sensitivity corresponding to the unknown pressure so that the calculated sensitivity is compensated for variations in the electron source heating power;
• and
• means responsive to the calculated sensitivity, the measured ion collector current, and the electron emission current for calculating the unknown pressure.

An ionization gauge comprising:

• a source of electrons;
• an open anode defining an anode volume;
• a collector electrode for collecting ions formed by impact between said electrons and gas molecules within said anode volume so that the pressure of the gas can be measured;
• and
• shield means defining a shielded volume within which said electron source, said anode, and said collector electrode are disposed where the entire shield means is electrically conductive and at least partially open to permit transfer of gas molecules into the shielded volume and to permit external electrical connections to the electron source, the anode, and the collector electrode and where the shield means completely encloses the electron source, the anode and the collector electrode so that potentials external to the shield means do not disturb the electric charge distribution on the electron source, the anode, and the collector electrode to thus stabilize the sensitivity of the gauge.

A plurality of ionization gauges each providing coinciding measurement outputs under identical conditions, each said gauge comprising:

• a source of electrons;
• an open anode defining an anode volume;
• a collector electrode for collecting ions formed by impact between said electrons and gas molecules within said anode volume so that the pressure of the gas can be measured to provide said measurement output of the gauge;
• and
• shield means defining a shielded volume within which said electron source, said anode, and said collector electrode are disposed where the entire shield means is electrically conductive and at least partially open to permit transfer of gas molecules into the shielded volume and to permit external electrical connections to the electron source, the anode, and the collector electrode and where the shield means completely encloses the electron source, the anode and the collector electrode so that potentials external to the shield means do not disturb the electric charge distribution on the electron source, the anode, and the collector electrode to thus stabilize the sensitivity of the gauge;
• wherein the locations of the electron source, anode, and collector electrode with respect to each other are substantially the same for each said gauge, whereby said gauges produce said coinciding measurement outputs under identical conditions.

In a method for controlling the operation of a predetermined ionization gauge having a source of electrons, an anode, and an ion collector electrode, said method including the steps of biasing said electron source, anode, and collector electron at predetermined potentials;

• substantially maintaining the electron emission current from said electron source at a predetermined value;
• and measuring the ion current to the collector electrode to obtain a measured value of the ion collector current at an unknown pressure;
• the improvement comprising the further steps of:
• storing a plurality of calibration data sets for at least collector electrode currents and gauge sensitivities obtained with at least one reference gauge at representative values of at least known pressures where said reference gauge has substantially the same gauge sensitivity at any given pressure as does said predetermined gauge;
• and
• calculating the gauge sensitivity corresponding to the unknown pressure utilizing at least one of said data sets together with said measured value of the ion collector current;
• and
• calculating the unknown pressure utilizing the calculated sensitivity, the measured ion collector current, and the electron emission current.

In a method for controlling the operation of a predetermined ionization gauge having a source of electrons, an anode, and an ion collector electrode, said method including the steps of biasing said electron source, anode, and collector electrode at predetermined potentials;

• substantially maintaining the electron emission current from said electron source at a predetermined value;
• measuring the heating power to the collector electrode at an unknown pressure to obtain a measured value of the heating power;
• and measuring the ion current to the collector electrode to obtain a measured value of the ion current at said unknown pressure;
• the improvement comprising the steps of:
• storing a plurality of calibration data sets for collector electrode currents, heating power of the electron source and gauge sensitivities obtained with at least one reference gauge at representative values of known pressures and cathode heating powers where said reference gauge has substantially the same sensitivity at any given pressure and heating power as does said predetermined gauge;
• calculating the gauge sensitivity corresponding to the unknown pressure utilizing at least one of said data sets together with said measured values of the ion collector current and electron source heating power so that the calculated sensitivity is compensated for variations in the electron source heating power;
• and
• calculating the unknown pressure utilizing the calculated sensitivity, the measured ion collector current, and the electron emission current.