Some flame detectors, for example, a UV tube, may have a nonfailsafe failure mode, meaning their operation needs to be verifiedperiodically. Continuous operation can be achieved by using a device containinga mechanical shutter that allows the detector to self check by simulation of ano flame condition.More modern flame detectors use more sophisticated methods forself checking. A characteristic of nearly all flames is that they flicker. Thisis a product of the fuel type, combustion process and mechanical design of theburner. Flicker frequency tends to increase with firing rate as a result ofhigher air velocity and fuel mixing at the burner head or nozzle. Flickerfrequency varies along the flame path dropping off significantly towards theend of the flame. This characteristic can be used to tune a flame detector todiscriminate one flame from another in multi-burner systems or to discriminatethe flame from other background radiation. These more intelligent flamedetectors monitor the flicker and the self check using software rather thanmechanical operation.
Siemens UV Flame detectors Models