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Process Calculator
(4 to 20) mA
The analog (4 to 20) mA communication standard is used to communicate process transmitters with a PLC, computer, indicator, recorder, etc., located in a control room or remote location.
How to enter the values:
-Maximum and Minimum Range: This is the range in which the equipment operates (for example, 0 to 100) °C). Enter the lowest operating range and then the highest.
- Unit: the unit in engineering units; example " °C "
-Current: Enter the measured value in mA with a minimum range of 3 mA and a maximum of 22 mA.
The range (4-20) mA can also be calculated if two points are known, and for each point the value in units and the value in mA are known, example:
Knowing that 19.634 °C is equivalent to 5.789 mA and that 128.265 °C is equivalent to 15.687 mA, the range can be calculated as 4 mA = 0.20 mA = 175.6
Why is the 4 to 20 mA range used?
1. Diagnostics: Using 4 mA as the starting point, rather than 0 mA, allows for the differentiation of a device's idle state from a fault due to a power failure, a short in the wiring, a turned-off device, or a damaged device.
2. Robustness: Current signals are much less susceptible to electromagnetic interference than voltage signals, ensuring more accurate transmission in industrial environments and allowing the signal to be transmitted over long distances. The current maintains its value with almost no loss along the circuit, regardless of the wiring resistance, allowing for reliable transmissions even over considerable distances.
3. Reliability and installed equipment: Most industrial sensors are designed to operate with 4-20 mA signals. Although this technology began to be used in the 1950s, it remains in use today due to its reliability. It has also evolved with integrations such as the HART digital communication protocol, which offers advanced diagnostics and the ability to integrate the equipment into a distributed control system, allowing it to visualize and control different variables at the same time.
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