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The 270 ionization gauge controller is a precision instrument designed to indicate vacuum pressures from I Torr to I0"8 Torr, I mbar to I0'8 mbar, or 100 Pascal to 10“® Pascal, air equivalent. The basic unit is comprised of a power supply, electrometer, emission controller, and ion gauge meter. Dual thermocouple gauge capability and process controls on the ion gauge and thermocouple gauges are included on some models. Recorder outputs provide capability for remote indication as well as continuous monitoring. In the basic controller the 270 will display pressure data in five linear decades, 10"^ to 10 '8 Torr. The range of readable data is from 0.3 x 10“® to 12 x IO“4Torr. The controller is designed to utilize a Bayard-Alpert type transducer with sensitivity ranging from 10/Torr to 25/Torr. The unit is shipped pre-adjusted for directly indicating pressure of a gauge having a sensitivity of 10/Torr, corresponding to an emission current of 2 mAdc. 2 Degas is provided by conventional resistive ( I R) heating of the grid surfaces with a nominal 80 watts of power. Ion gauge pressure measurements are not possible during degas. Ion gauge process controls, when included, provide two independent set points which operate individual SPDT relay contacts. Set point adjustment over the entire measurement range is by means of recessed front panel controls. Interlocks are provided to allow operation only during autorange operation when the filament is on and the gauge has had sufficient time to stabilize. The thermocouple section is comprised of two independent measuring circuits and, when included, extend the measurement range of the controller to I Torr or I mbar. Indication is provided by two life inch taut band ruggedized meters. Recorder outputs are also provided for each of the thermocouple circuits. The thermocouple circuitry is designed to operate with Granville-Phillips 270006 or comparable transducers. Thermocouple process controls, when included, provide an individual SPDT relay contact set point for each thermocouple gauge. Set point adjustment over the thermocouple's measurement range is adjustable by means of recessed front panel controls. The controller is wired such that the set point for thermocouple No. 2 can be used to switch the ion gauge filament on and off, thus allowing fully automatic operation. All Series 270 controllers come with an automatic ranging feature which can be defeated placing the controller in a manual ranging mode. Autoranging points are preset to occur at .95 x I0-X and I 1.7 x I0~ . While in the manual mode the controller is capable of _ x —X readings from 0.0 x 10 to 12.0 x 10 . Autoranging eliminates troublesome range changing in a variable system and prevents unnecessary shutdowns due to momentary pressure bursts. The manual/auto range function is selected via a front panel switch. The 270 ion gauge controller provides direct ion gauge pressure readout in either Torr, mbar or Pascal. The unit of measure is selectable by means of a jumper plug inside the controller and appropriate front panel labeling. The pressure signal is converted and displayed in the desired format, thus eliminating cumbersome conversion tables or calculations.