3.0OPERATION OF VACUUM GAUGE
3.1Powering ofVacuum Gauge
Plug the 8 ft. power cable into a single phase 115 VAC
Plug the gauge tube cable onto the gauge tube. When the tube is exposed to a pressure greater than1000 mTorr, the analog output will be over 2 volts, and the display will read “1”.
The relay will energize when the pressure is below the trip points. “Normal” relay position is de- energized (ATM pressure side of set point.)
3.2 Switch Position
“OPR” Normal operating position. Display reads pressure. Output on back panel reads
“SET A; SET B” Displays the trip point of the appropriate relay. If the pressure is below the trip point the relay is energized and the LED will be lit. The trip points can be set from
“CAL” Used when zeroing the vacuum gauge tube at hard vacuum. Adjust the Cal pot on the rear panel for 000 on the display.
“Test” A voltage is injected into the 2nd stage AMP so that the GAIN of the gauge can be set on the average curve. Adjust ‘GAIN’ pot on rear panel for “400” on the display. NOTE: The signal output will change when the switch is put in this position and the set points may trip. See section 4.2.1 Reference Check.
4.0CALIBRATION AND TROUBLESHOOTING GUIDE
All Hastings vacuum gauges and tubes have been carefully checked and calibrated at the factory before shipment. If a calibration check is desired the methods in the following sections may prove helpful.
4.1 Check of Tube Accuracy
The simplest and quickest method of checking the operation and calibration of power supply/ display and gauge tube is to keep a new, clean gauge tube on hand as a “standard”. To check operation, install both of the gauge tubes together in the same clean, dry vacuum system, and pump until a steady pressure is obtained. Plug the gauge onto both tubes alternately and check reading. Be sure to allow time for readings to settle. If the tube reads a considerably higher pressure than the tube being used as a standard, a calibration shift in the old tube has occured. This is most likely resulting from tube contamination. The tube calibration can possibley be restored by gently rinsing the interior of the tube with a solvent such as trichlorethylene. After cleaning, thoroughly dry the tube and degas it before reinstallation into a vacuum system. This is done to avoid system contamination by the solvent. If calibration cannot be restored by this precedure, replace the old tube with a new gauge tube.
CAUTION: Do not attempt to measure the resistance of the gauge tube element while it is under vacuum. Some ohmmeters apply measuring voltages sufficient to burn out the thermo- pile while under vacuum. The resistance of the gauge tube can be measured safely at atmo- spheric pressure. This measurement is made between pins 3, 5 and 7 counting clockwise from the key looking at the base of the gauge tube. A measuring device such as the Triple Model 630 Test Set with ohms switch on the “X10” range, is suitable for this purpose.
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