A catalytic sensor consists of two matched, heated Coristor elements arranged in a Wheatstone bridge - one catalytically active and one inert. The active element is sensitive to all flammable gases, while the inert one compensates for ambient temperature and pressure changes and physical properties of the sample gas.

When a flammable gas sample comes in contact with the active Coristor element, this heated element catalytically oxidizes the gas. The resulting thermal reaction is displayed in terms of 0-100% Lower flammable Limit (LFL) on the control monitor meter.