It is used for the detection and measurement of combustible gases and vapour. It depends for its operation on the heat developed by the actual combustion of the flammable portion of the sample.
The sample is drawn over a heated filament which forms one arm of a balanced Wheatstone‘s bridge circuit.
The current for the circuit is provided by six standard dry cells. Combustible gas in the sample is burnt on the filament.
Thus its temperature is raised and its resistance increases in proportion to the amount of combustible gas burnt i.e. in proportion to the amount of combustible gas in the sample.
The circuit is now unbalanced which causes a deflection of the meter. The scale is graduated in percentage of the lower explosive limit. The scale is graduated in percentage of the lower explosive limit. The initial balance of the circuit is achieved in fresh air with the meter at zero by adjustment of a rheostat R.
The Limitations of the Explosimeter are:-
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