Thermal Conductivity Sensor for Binary Gas Analysis

Thermal Conductivity Sensor All gases conduct heat to differing degrees, and the amount of heat transferred by a gas is determined by its 'Thermal Conductivity' (TC) value. This property can be exploited in sensing because each gas has a different TC value. Michell’s Thermal Conductivity Sensor uses this property to accurately measure one of the two gases present in a sample of a binary or pseudo-binary mix.

The sensor uses matched thermistors forming one half of a Wheatstone bridge. One thermistor is in the sample cell, the other is housed in a reference chamber (sealed and flowing reference versions are available). The whole assembly is heated to +50°C to ensure an iso-thermal environment, where the condition of the sample is consistent, providing an accurate and stable platform for measuring the target gas concentration.

When gas is flowing through the sample chamber, heat is drawn from the thermistor and this changes one element of the bridge. A current is required to keep the bridge balanced and from this, the TC value of the gas can be determined.

This technology is suitable for measuring 0 – 100% of a target gas in a background gas by using the former for the span and the latter for the zero. Other ranges are available to offer better accuracy for specific concentrations.

The two gases in the binary mix may either be pure gases – such as nitrogen and hydrogen – or a pseudo-binary mix. Air is an example of a pseudo-binary mix: it has a fixed proportion of oxygen and nitrogen, both having very similar thermal conductivities and so behaves much like a single gas.

XTC601 Binary Gas Analyzer XTC601 Binary Gas Analyzer
A robust, linear and stable thermal conductivity analyzer for measurement of binary gas mixes such as air in hydrogen, nitrogen, argon, helium or carbon-dioxide.