GTC-390 Thermocouple Dual Bar Graph

GTC-390 Thermocouple Dual Bar Graph

GTC-390 Product Manual – click to download (Note: Requires the Adobe Acrobat Reader)


The GTC-390 thermocouple vacuum gauge is a dual station thermal conductivity type gauge and controller housed in a DIN-style case. The unit uses the rugged and proven GTC-036 sensor and covers a pressure range of 1 mtorr to 5000 mtorr. Pressures are displayed simultaneously for both stations on two 40-segment bar graph displays. Each station includes a relay set point that can be set within the range of the gauge. The relay set point for each station may be viewed by pressing the “View” buttons on the front panel. Adjusting the set points is accomplished by turning the front panel potentiometers marked “Set”. An LED indicator displays the output status of each relay control output.


  • Dual pressure display
  • Measures from of 1 m torr to 5000 m torr
  • Each station has a relay output adjustable from the front panel
  • Front panel LED for relay output status
  • Panel mountable or beach top use
  • Uses the rugged and proven GTC-036 sensor

Principal of Operation

The GTC-390 thermocouple gauge consists of two identical pressure measurement and control circuits that function as follows: A constant current source is supplied to the heating element of the GTC-036 sensor. The thermocouple junction in the sensor generates a voltage signal that varies with the temperature of this heating element. A decrease in pressure reduces the number of gas molecules available to transfer heat away from the heating element, resulting in a temperature rise and an increased output from the sensor. This small voltage signal is filtered, amplified, and inverted resulting in a signal with a span of several volts that is proportional to pressure. This pressure signal is then passed through a signal selection circuit to the display drivers where it is compared to a high and a low reference and the proper display segments are illuminated. A voltage comparator is used to activate the set point relay as well as the front panel set point indicator. There is a small amount of hysteresis built into this circuit. The “View” button causes the signal selection circuit to send the pressure set point level to the display drivers rather than the pressure.


Power Input: 100-120 VAC 50/60 Hz 40 watts or 9 VDC 9 watts

Pressure Scales: 1 mtorr to 5000 mtorr on a 40-segment bar-graph

Number of Sensing Stations: 1 or 2

Pressure Sensing Tube: Type GTC-036 with 1/8” pipe thread or 0.406” diameter O-Ring sealing surface.

Tube Cable: 10 ft length standard with both 9-pin gauge and octal sensor connector

Cabinet Dimensions: 5.67” wide 5.10” deep , 2.84” high

Mounting Hole Dimensions: 5.45” wide x 2.68” high (allow 8” for mounting depth)

Relay Connections: One removable three position terminal block for each station with common, normally closed, normally open connections

Relay Trip Point Adjustment: 1 mtorr to 5000 mtorr

Relay Types: SPDT 5 Amp 250 VAC Max

GTC-036 Tube Specifications: click here

Ordering Information

GTC-390 Thermocouple din panel mount, dual 40 segment bar graph display, with single set point, pressure scale of 0-5 torr with cables, less sensors – Part Number 500623-0210

GTC-390 As above, complete with two GTC036 sensors – Part Number  500623-0212

GTC 036 Sensor Tube (No Calibration required) – Part Number 5504358

Both Sensors attach to vacuum chamber with 1/8” pipe thread or 3/8” tubulation seal

Adapters available

  • KF-16 to 1/8″ FPT KF – Part Number 500230-16
  • KF-25 to 1/8″ FPT – Part Number 500230-25
  • KF-40 to 1/8″ FPT – Part Number 500230-40
  • KF-50 to 1/8″ FPT – Part Number 500230-50
  • CF-16 to 1/8″ FPT – Part Number 500231-1
  • CF-35 to 1/8″ FPT – Part Number 500231-2
  • 1″ hole mount to 1/8″ FPT – Part Number 500236
  • EXP Housing – Explosion Proof Housing Part Number 501065

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