Instrumentation Calculators

# 4 to 20 mA Transmitter Output Process Value Calculator

A 4 to 20 mA transmitter is widely used in industrial applications to transmit analog signals over long distances with high accuracy and minimal noise interference. The 4 to 20 mA current loop is robust against electrical noise and can transmit signals reliably over long distances, making it ideal for use in process control and instrumentation systems.

In a 4 to 20 mA current loop:

• 4 mA represents the minimum value of the measured process variable (e.g., temperature, pressure, level).
• 20 mA represents the maximum value of the measured process variable.

The below Calculator used to calculate the Process Value (PV) corresponding to a transmitter measured mA output signal.

To calculate the process variable (PV) from the measured current (I) in mA, we use the following linear interpolation formula:

Where:

• PVmin​(LRV) is the minimum process variable value.
• PVmax(URV)​ is the maximum process variable value.
• I is the measured current in mA.

This formula converts the measured current signal back into the corresponding process variable.

Consider a temperature transmitter that uses a 4 to 20 mA current loop to transmit temperature readings. The temperature range that the sensor can measure is from -50°C to 50°C. If the sensor outputs a current of 10 mA, what is the corresponding temperature?

To find the corresponding temperature for a 10 mA signal, follow these steps:

• PVmin(LRV)​: This is the lowest value the process variable can take. In this example, it is -50°C.
• PVmax(URV): This is the highest value the process variable can take. In this example, it is 50°C.
• I: This is the current measured in the loop, which is 10 mA in this scenario.

Apply the values in the formula.

So, the process temperature corresponding to a 10 mA signal is -12.5°C.

This technique allows you to find the value of the process variable for any current in the 4–20 mA range. Any kind of sensor or transmitter operating in this range can use this method, which ensures reliable signal interpretation.