The GT411 is a thermocouple vacuum gauge. It measures gas pressure over a limited range. The heater is run at a constant current in this case 600 mA and the close coupled thermocouple produces a voltage - 14 mV at 0.1 micron pressure. 1 Torr = 1 mm mercury = 1,000 micron.
The gas molecules carry away heat from the heater so as the gas becomes more rarefied the heater temperature, and this the thermocouple voltage, rises. The effect is small and such a device is used in precision measurements.
The label gives the operating details.
The operating range of this sensor is 1,000 microns to 1 micron of mercury. Atmospheric pressure is 760,000 microns.
The standard octal base.
The top end with protective cap.
The sensor seen from the top. There is a 6 on the cap.
The wide metal tube envelope is 32 mm in diameter and, excluding the IO base pins, is 129 mm tall.