Thermal Conductivity

Because pellistors measure the flammability of a gas, they cannot be used to measure levels of gas above the Lower Explosive Limit (LEL), since the reducing level of oxygen will result in a fall-off of signal. However, a similar device can be used to monitor these high levels of gas, the themal conductivity pellistor.

We have a range of thermal conductivity sensors, which are designed to complement the pellistor range in terms of electrical characteristics, so that they can be used in the same Wheatstone Bridge circuits. They are supplied with a compensator bead which is in a sealed enclosure of air. This enclosure acts as the thermal conductivity reference in exactly the same way as it acts as the reference for a pellistor.

Because thermal conductivity measurements do not rely on the flammability of the gas, the technique can be used to analyse a whole range of gas mixtures, provided that there are only two gases present and that the two gases have significantly different thermal conductivities. Examples include:

0 – 100% Hydrogen in Air

0 – 100% Methane in Air

0 – 100% Carbon Dioxide in Air

0 – 100% Carbon Dioxide in Methane

0 – 100% Helium in Air

Thermal conductivity cannot be used for gas mixtures where the thermal conductivities of the two gases are similar. The best example of this is oxygen levels in air, as the thermal conductivities of oxygen and nitrogen are too close to give a meaningful signal.

Part Number DescriptionDatasheet
Thermal Conductivity pellistors for 100% volume gases with and without air
VQ5MBPellistor Pair 2V/175mA, TC Closed Can CompensatorDownload
VQ6MBPellistor 2V, TC, Closed Can Compensator, Solid LegsDownload
VQ35MBPellistor Pr 4.2V/55mA TC Closed Can compensator, Solid LegsDownload
VQ31MBPellistor Pr 3.5V/90mA TC C Can Solid Lg, closed can compensatorDownload
Certified thermal conductivity heads for 100% volume gases with and without air
VQ546MVQ46 Pellistor, VQ500 HeadDownload
VQ546MRVQ46 Pellistor, VQ500 Head, +ve OutputDownload
VQ605M/1VQ5 Pellistor, VQ600 Head, Metric ThreadDownload
VQ606M/1VQ6 Pellistor, VQ600 Head, Metric ThreadDownload
VQ606M/3VQ6 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ631M/1VQ31 Pellistor VQ600 Head, Metric ThreadDownload
VQ631M/2VQ31 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ631M/3VQ31 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ635M/1VQ35 Pellistor VQ600 Head, Metric ThreadDownload
VQ635M/2VQ35 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ635M/3VQ35 Pellistor, VQ600 Head, 0.75" 14 NPTDownload