4-20 mA Current Scaling
Convert a 4-to-20 mA current signal into the corresponding process variable, PV = LRV + (I − 4)/16 · (URV − LRV), the universal standard of industrial instrumentation. The 4 mA represents 0% of the range and 20 mA, 100%; the 'live zero' at 4 mA distinguishes a null reading from a broken cable (0 mA). Enter the measured current and the lower and upper range values.
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4-20 mA current scaling
The 4 to 20 mA signal has been the lingua franca of industrial instrumentation for decades. A transmitter turns the process variable (temperature, pressure, level) into a proportional current: 4 mA = 0% of the calibrated span, 20 mA = 100%. Converting back to engineering units is PV = LRV + (I − 4)/16·(URV − LRV), where LRV is the lower range value and URV the upper range value of the span. Why current instead of voltage? Because a current signal does not degrade over long cable runs — the same current flows through every point of the loop — so it shrugs off wiring voltage drops and picked-up noise. And why start at 4 mA rather than 0? That is the 'live zero': if the reading drops to 0 mA, the operator knows the cable has broken or the instrument has failed, which separates a genuine 'zero measurement' from 'no signal at all'. Enter the measured current and the range limits.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.