Understanding and Calculating 4-20 mA Sensor Feedback

Calculating 4-20 mA from Sensor Feedback

To convert a measured value from a sensor into the corresponding 4-20 mA current, you can use the following formula:

mA = 4 + ( (Measured Value - Min Value) / (Max Value - Min Value) ) × 16

Where: - Measured Value is the actual value of the parameter being measured (e.g., pressure, temperature). - Min Value is the minimum value of the parameter that corresponds to 4 mA. - Max Value is the maximum value of the parameter that corresponds to 20 mA.

Example:

Consider a pressure sensor that measures a range of 0 to 100 psi. If the current pressure is 50 psi, the corresponding current output can be calculated as: mA = 4 + ( (50 - 0) / (100 - 0) ) × 16 = 4 + 0.5 × 16 = 4 + 8 = 12 mA So, at 50 psi, the sensor would output 12 mA.

Reverse Calculation: Converting 4-20 mA Back to Measured Value

To determine the measured value (e.g., pressure or temperature) from the 4-20 mA signal, use the reverse formula:

Measured Value = Min Value + ( (mA - 4) / 16 ) × (Max Value - Min Value)

Where: - mA is the current value in milliamps (ranging from 4 to 20 mA). - Min Value is the minimum value of the parameter that corresponds to 4 mA. - Max Value is the maximum value of the parameter that corresponds to 20 mA.

Example:

If you receive a current reading of 12 mA from the same pressure sensor (0 to 100 psi range), you can determine the corresponding pressure as follows: Measured Value = 0 + ( (12 - 4) / 16 ) × 100 = (8 / 16) × 100 = 0.5 × 100 = 50 psi This calculation shows that a 12 mA signal corresponds to a pressure of 50 psi.

Conclusion

Mastering these calculations is essential for accurate sensor data interpretation and control in process automation. Whether you're setting up a sensor or troubleshooting, being able to convert between the measured value and the 4-20 mA signal ensures that your system operates efficiently and reliably.