Working Principle of Bi-metallic Instruments

Working Principle of Bi-metallic Instruments Points : Working Principle of Bi-metallic Instruments The working principle of bi-metallic instruments based upon the action of heating effect of current under measurement. The heat developed in an ohmic resistance is proportional to the square of the current through it and is independent of frequency and waveform, as long as the resistance remains constant. The steady state temperature rise above the ambient temperature is therefore a measure of the effective value of the current. These instruments have high warming up time, as 15 minutes. But the thermocouple type instruments have advantage of less warming up time i.e. mostly less than 1 second.