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4-20 mA Current Loop Equation:
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The 4-20 mA current loop is a standard for transmitting sensor information in industrial instrumentation systems. The 4 mA represents the lowest value of the measurement range, while 20 mA represents the highest.
The calculator uses the standard 4-20 mA scaling equation:
Where:
Explanation: The equation linearly scales any process value between its minimum and maximum range to a corresponding current between 4 and 20 mA.
Details: 4-20 mA signals are widely used in industrial applications because they are less susceptible to noise than voltage signals, can power the transmitter, and provide a "live zero" (4 mA indicates both the low end of the scale and a functioning circuit).
Tips: Enter the process value you want to convert, along with the minimum and maximum values of your measurement range. The calculator will output the corresponding 4-20 mA value.
Q1: Why is 4 mA used instead of 0 mA?
A: 4 mA provides a "live zero" which allows the system to distinguish between a zero signal and a broken wire (which would show 0 mA).
Q2: What if my calculated mA is below 4 or above 20?
A: This indicates the input value is outside your specified range. The transmitter will typically saturate at either 4 mA (below range) or 20 mA (above range).
Q3: Can this be used for reverse-acting signals?
A: Yes, simply swap your Min and Max values to create a reverse-acting signal where 4 mA corresponds to the high end of the scale.
Q4: How accurate is this calculation?
A: The calculation is mathematically precise, but actual system accuracy depends on transmitter calibration and measurement precision.
Q5: What about 3-wire vs 2-wire transmitters?
A: This calculation applies to both, though wiring differs. 2-wire transmitters are powered by the loop current itself.