Abstract: The invention relates to a perturbation signal recorder. An input circuit receives a series of signals to be monitored and samples them in order to supply in respect of each sample a digital word to a pre-memory circuit which preserves the n most recent digital words. In the presence of a perturbation, a central unit excites a main memory circuit in order that it records the n most recent digital words at the time of the perturbation, as well as the following digital words during and after the perturbation. The contents of the main memory are thus transferred at a slow rate to an output circuit, which re-transforms the signals to an analogue form and applies them to a graphic recorder.

Abstract: A filter having a cut-off frequency of the order of 50Hz is included in the circuit of flame monitoring apparatus to remove signals below the cut-off frequency. In the circuit shown, a silicon p-n junction photo-electric pick-up is capacitively connected to an amplifier, the amplifier is connected to a high-pass filter, the output of the filter is connected to a further amplifier, the output of the further amplifier is applied to a detector integrator, the output of the detector integrator is connected to a Schmitt trigger, and the output of the trigger is applied to an output circuit giving a warning signal if the flame being monitored is extinguished. The use of sighting tubes for the photo-electric pick-ups is disclosed.