Incipient burn-out is frequently detected by using a Wheatstone bridge circuit in which two arms are provided by tappings from the heater element.nAn exact solution is presented for the sensitivity of the bridge when using an arbitrary fraction of the heater element, and an arbitrary bridge ratio. After applying simplifying approximations it is shown that the out-of-balance voltage appearing at the detector terminals is independent of the fraction of the heater element employed.nAn asymmetrical bridge has high sensitivity for a burn-out in the shorter arm but low for burn-out in the longer arm, and the centre tapped bridge has half the maximum possible sensitivity. Hence for ensuring protection of both ends of the heater the centre-tapped full length bridge is recommended.
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