Myers Vacuum

GT-340A & GT-345B
Thermistor Gauges

GT-340A Product Manual
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  • Measures from atm to 1x10-3 torr
  • Rugged thermisitor sensor - excellent for high vapor applications
  • Interchangeable pre-calibrated tubes
  • High reliability provided through rugged circuitry
  • Two scales for accurate pressure reading
  • External circuit control feature available
  • Leak detect capability on STA.1
  • Second station can be added on-site
  • Analog meter indicates direction of pressure change
  • 115/230V, 50/60 Hz operation

The 340 is an electrically powered gauge for use in harsh environments. The rugged electronics are designed for longevity and occasional accidental misuse. Two analog scales allow the user to take vacuum measurements from atmosphere to 1x10-3 torr. A separate meter scale for the 1 to 100 millitorr range provides increased readability in this critical area. Meter scales are calibrated in dry air pressure units; calibration curves for other gases are supplied.

Principle of Operation
A single element is employed in a bridge-type detector driven from a constant regulated voltage source. The inverse resistive characteristics of the sensor unbalances the bridge as pressure changes occur, thereby causing a current change. A microammeter scaled in pressure units measures this current.

Leak Detection
Gauge has Leak Detect Mode. Front panel switch allows adjustment of the gauge sensitivity to aid vacuum leak detection.

Recorder Connection
Connections on the rear panel of the gauge cabinet provide a pressure-responsive output independent of the selector switch. A 10-, 50-, or 100-millivolt high-impedance recorder with suitable attenuating network can be connected here to cover the entire pressure range of the gauge at either sensing station.

Modular Construction
The Type GT-340A thermistor gauge and the GT-005A controller are each mounted in quarter-rack modular cabinets. The GT-345B controlling gauge combines these two modules in a single half-rack cabinet. Two GT-340A two-station gauges can be mounted side-by-side for applications requiring four-station operation, with the added advantages of two read-out meters and redundant circuitry.

Automatic Control of External Circuits (GT-345B)
Relay control unit available. This can either be built with the original gauge, or as an accessory (GT-005A). The trip points of the control are independent of the setting of the selector switch. Normally open or normally closed relay contacts rated at 3-amps, 115/230 volts are available for connecting external loads such as safety circuits for tuning off pressure-sensitive components or automatic circuitry for operating vacuum valves at preset pressures. By utilizing the separate adjustment provided, the pull-in and drop-out point of the relay contacts can be set so control is established at any two pressures within the operating range of the gauge. Indication lights on the front panel show position of relay contacts.

GT-340A GT-345B
Width 4" 8"
Depth 6 1/2" 6 1/2"
Height 6" 6"
Net Weight 6 lbs. 11 lbs.
Number of stations 1 or 2
Type of Mounting Bench or panel
Normal Operating Temperature Range 15 to 35ºC
AC Power Input 115/230 volts, 50/60 Hertz
Meter Scale Ranges 0 to 100 milliTorr
0 to atmosphere
Recorder Output 0 - 2.5 Volts
Operating Range Entire range of gauge
Relay Differential Adjustable
Relay Contact Capacity SPDT, 3 amp, line voltage energized
Envelope w/ baffle housing length including base 2-9/16"
Envelope O.D. 1-1/4"
Tubulation Material Nickel-plated steel
Tubulation Length 1-3/8"
Tubulation O.D. 0.405" diameter sealing surface and 1/8" pipe thread
Thermistor Element Operating Temperature 90ºC
Maximum Bakeout Temperature of Sensor Envelope 100ºC
Pressure Range High Vacuum to 60 psig

Ordering information for the components mentioned on this page is listed below.

GT-340A-1 Thermistor gauge, single-station 5506330-1
GT-340A-2 Thermistor gauge, two-station 5506330-2
GT-345B-1 Thermistor gauge, single-station w/ relay 5506789-1
GT-345B-2 Thermistor gauge, two-station w/ relay 5506789-2
GT-005A Relay control unit 5506611
CGB port connector
Fittings for installing sensing tubes in a vacuum system (all have quick-disconnect seal for 3/8" tubulation). To fit 1/2" FPT hole 061083
Bushing for above P/N 061083 CGB Type 3/8" nom. I.D. 061081-2
Cable 10' standard - Station 1 5505863-1
Cable 10' standard - Station 2 5505889-1
Cable 15' standard - Station 1 5505863-2
Cable 15' standard - Station 2 5505889-2
Cable 25' standard - Station 1 5505863-3
Cable 25' standard - Station 2 5505889-3
Cable 50' standard - Station 1 5505863-4
Cable 50' standard - Station 2 5505889-4


Myers Vacuum Repair Services, Inc * 1155 Myers Lane , Kittanning PA 16201 * Phone 724-545-8331 or 888-780-8331 * Fax 724-545-8332 *