4-20mA Transmitters Calculations

Given a pressure transmitter with a measurement range of 150 to 400 PSI and a signal range of 4 to 20 milliamps, calculate the applied pressure corresponding to a signal of 10.6 milliamps.

Answer : 

• Take 10.6 milliamps and subtract the LRV (4 milliamps),
• then divide by the span (16 milliamps) to arrive at 41.25% (0.4125 per unit).
• Take this number and multiply by the span of the pressure range (400 PSI − 150 PSI, or 250 PSI) and
• lastly add the LRV of the pressure range (150 PSI) to arrive at a final answer of 253.125 PSI.

Given a temperature transmitter with a measurement range of −88 degrees to +145 degrees and a signal range of 4 to 20 milliamps, calculate the proper signal output at an applied temperature of +41 degrees.

Answer : 

• Take 41 degrees and subtract the LRV (−88 degrees) which is the same as adding 88 to 41,
• then divide by the span (145 degrees − (−88) degrees, or 233 degrees) to arrive at 55.36% (0.5536 per unit).
• Take this number and multiply by the span of the current signal range (16 milliamps) and
• lastly add the LRV of the current signal range (4 milliamps) to arrive at a final answer of 12.86 milliamps.

Given a pH transmitter with a measurement range of 3 pH to 11 pH and a signal range of 4 to 20 milliamps, calculate the proper signal output at 9.32 pH.

Answer : 

• Take 9.32 pH and subtract the LRV (3 pH),
• then divide by the span (11 pH − 3 pH, or 8 pH) to arrive at 79% (0.79 per unit).
• Take this number and multiply by the span of the current signal range (16 milliamps) and
• lastly add the LRV of the current signal range (4 milliamps) to arrive at a final answer of 16.64 milliamps.

Do You know any simple 4-20mA conversions ? Share with us from the below comments section.

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