• High Stability
    • Lower in cost than infrared, GC or MASS specification
    • Fast Response
    • Digital Readout
    • Long life thermal conductivity cell
    • Alarm contacts and low flow alarm optionally available
    • Built-in sample pump
    • Available in wall mount, rack mount, panel mount,
    • portable and explosion proof models
    • Sampling system available for most application
    • Optional automatic calibration
    • Cabinet purge system available for hazardous areas


Type Field / wall mounted
Detectable gases / parameters H2, O2, CO2 ( Binary gaseous mixture )
Electronics / processor Micro-controller
Power supply 110 /220 VAC 50Hz
Display Graphic LCD
Alarm Controlled alarms
Output 4 – 20 mA Standard, individual relay, potential free contacts to
control alarm
Digital Output RS 232 / 485
Technology Sensor Specific
Resolution 1 mg/m3, 1 PPM, 1% V/V, application defined
Accuracy ± 2 % FS
Response time less than 30 sec, sensor dependent
Operating temperature 0 – 55 °C
Flowrate 0.5 to 0.9 L/min
Enclosures Wall mounted NEMA 12 (122N 12), NEMA 4 (122N 4), Panel
Mount (122 PM), Explosion Proof (122 Ex), Rack Mount (122RM)


The Model GA – 251 Thermal Conductivity (TC) Analyzer has many applications in industry where the measurement of one gas in a two gas or some multi-gas mixtures is required. The HNL Thermal Conductivity cell is temperature controlled and its high stability enables it to be used even in high purity measurements. Since the Thermal Conductivity cell does not consume the sample or have any moving parts, hot wires or sealed chemicals, it will last for many years. In operation : The Thermal Conductivity cell detects the rate at which the sample gas conducts heat away from a heated thermistor with reference to a similar thermistor surrounded by air. A sample containing the gas to be measured will cause the temperature, and its resistance, to change with respect to the reference thermistor. This will cause an output from the wheatstone bridge measuring circuit which is calibrated and displayed on a digital meter. Recorder outputs and alarm are also available.

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