Catalytic Pellistors

Catalytic pellistors solid-state devices used to detect gases which are either combustible or which have a significant difference in thermal conductivity to that of air. The detecting elements consists of small ‘’pellets’’ of catalyst-loaded ceramic whose resistance changes in the presence of the target gas hence the term ‘’pellistor’’ being a combination of ‘’pellet’’ and ‘’resistors’’.

To detect these gases types there are two types of pellistors; catalytic pellistors and thermal conductivity pellistors (TC), operating in different modes.

Catalytic Pellistors are gas sensors that detect combustible gases and vapours in air, in concentrations approaching the explosive range. In this case, they are operating in a catalytic mode where the target gas is burnt and the heat liberated is measured by the sensor.

Features

  • Response to a wide range of combustible gases
  • Simple circuitry
  • A wide range of sensor types and operating voltages
  • Poison and shock resistant versions available

Product range

AEP offers a wide range of pellistors. These can be supplied either as pellistor bead pairs (which are then placed in the your certified enclosure or within a certified enclosure. They can be either poison or non-poison resistant and may also be made to be sensitive to combustible gases, including or excluding methane.

Catalytic pellistors are available with a variety of working voltages and power levels. In general, the higher power devices are used in fixed systems and the lower versions in portable equipment. Low power pellistors are also available with the option of shock protection.

Part NumberDescriptionDatasheet
Catalytic Pellistors flammable gases ( No poison resistance)
VQ10BStd Pellistor Pair, 2V/175mA, Solid LegsDownload
VQ10SBStd Pellistor Pair, 2V/175mA, Solid LegsDownload
VQ1BStd Pellistor Pair, 2V/300mA, Solid LegsDownload
VQ2BStandard Pellistor Pair, 2V/175mA
VQ3BJStd Pellistor Pair 2.5V/335mA Solid LegsDownload
VQ41TSBAmmonia Pellistor Pair, 2V/100mADownload
Catalytic Pellistors flammable gases ( with poison resistance)
VQ21BPR Pellistor Pair, 2V/300mA, Solid LegsDownload
VQ21TBPR Pellistor Pr, 2V/300mA OC Solid LegsDownload
VQ21TBJPR Pellistor Pr, 2V/300mA OC Solid LegsDownload
VQ21TBKPR Pellistor Pr, 2V/300mA OC Solid LegsDownload
VQ21TSBPR Pellistor Pair 2V/300mA OC Solid LegsDownload
VQ22TBPR Pellistor Pair 2V/175mA OC Solid LegsDownload
VQ23TBPR Pellistor Pair 2.5V/335mA OC Solid LgDownload
VQ25BPR Pellistor 2V, Hydrocarbon, Solid LegsDownload
Certified Catalytic pellistor heads for flammable gases
VQ547TSVQ47 Ammonia Sensor, VQ500 head for portable applicationsDownload
VQ548ZDVQ48 Pellistor, VQ500 head for portable applicationsDownload
VQ548ZD/WVQ48 Pellistor, VQ500 Head, Mining AppsDownload
VQ548ZD-SVQ548ZDDownload
VQ549ZDVQ49 Pellistor, VQ500 head for portable applicationsDownload
VQ549ZD/WVQ49 Pellistor, VQ500 Head, Mining AppsDownload
VQ601/1VQ1 Pellistor, VQ600 Head, Metric ThreadDownload
VQ601/2VQ1 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ601/3VQ1 Pellistor, VQ600 HeadDownload
VQ603/1VQ1 Pellistor, VQ600 Head, Metric ThreadDownload
VQ603/2VQ1 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ641TS/1VQ41 Pellistor VQ600 Head, Metric ThreadDownload
VQ641TS/3VQ41 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ621T/1VQ21 Pellistor VQ600 Head, Metric ThreadDownload
VQ621T/2VQ21 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ621T/3VQ21 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ621TS/3VQ21 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ622T/1VQ22 Pellistor VQ600 Head, Metric ThreadDownload
VQ622T/2VQ22 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ622T/3VQ22 Pellistor, VQ600 Head, 0.75" 14 NPTDownload
VQ623/1VQ23 Pellistor VQ600 Head, Metric ThreadDownload
VQ625/1VQ25 Pellistor VQ600 Head, Metric ThreadDownload
VQ625/2VQ25 Pellistor, VQ600 Head, 1.5" 14 NPTDownload
VQ625/3VQ25 Pellistor, VQ600 Head, 0.75" 14 NPTDownload

Working of the Cataltic pellistors

The catalytic gas sensor consists of a coil of a small diameter platinum wire in a refractory bead. A layer of catalyst is deposited onto the bead. A current is passed through the coil heating up the catalytic material to approx. 500°C. At this temperature the catalytic material can burn the target gas producing heat. The resulting temperature rise is detected by the coil, in which the resistance rises. This active bead is known as the detector bead. In order to compensate for environmental factors such as temperature and pressure, the active bead is matched with inactive reference or compensator bead. This pair of beads is generally run in a simple wheatstone bridge circuit. The signal produced is proportional to the gas concentration up to the lower explosive limit, or LEL. The sensor will detect all combustible gases and vapours, although the response to higher hydrocarbons may not be high.

catalytic pellistor working

Applications

As these sensors measure gases in the 0 – 100% LEL range, they are routinely fitted in instruments used in applications where combustible gases could be present. The gas most often measured and encountered in the field is methane. This gas is present in coalmines, in places where organic matter is decomposing such as sewers, and as a major constituent in natural gas. There is also a sizeable market in measuring potential sources of methane in confined spaces associated with telecommunications. The majority of instrumentation is in the form of portable instruments many containing multiple gas sensors.

The main source of non-methane applications is monitoring of hydrocarbons, most commonly in the petrochemical industry both on and offshore and in monitoring for kerosene spillages. These instruments are generally calibrated for butane or pentane. In this case, as well as portable instruments, there is a significant market for fixed gas detection systems.

Applications for other gases also exist, e.g. for hydrogen in battery charging areas and ammonia in refrigeration plants.

Safety consideration

These gas sensors operate at temperatures above 400C and as such have the capability to ignite flammable gas mixtures. To prevent this, if the sensor is to be operated in an environment where combustible gases could be found, then it is necessary to enclose the pellistor beads in a certified flameproof head. This will allow the beads to be exposed to the target gas without the risk of ignition. AEP offers sensors both as beads and as beads within a certified head.