The NAMUR NE43 Loop Simulator is an interactive tool for understanding how a 4–20 mA instrumentation signal behaves during normal operation, over-range and under-range conditions, and simulated wiring faults.

Adjust the process variable, observe the loop current in milliamps (mA), and see how the signal status changes. You can also cut and restore the simulated wire to understand how an open-circuit condition affects the signal.

This simulator is useful for instrumentation engineers, DCS and PLC engineers, maintenance technicians, engineering students, and anyone learning about industrial analog signal troubleshooting.

What Is NAMUR NE43?

NAMUR NE43 is a recommendation that defines signal levels used by field transmitters to distinguish valid measurement signals from certain fault conditions in 4–20 mA instrumentation loops.

In a typical 4–20 mA loop:

• 4 mA represents 0% of the configured measurement range.
• 12 mA represents 50% of the configured measurement range.
• 20 mA represents 100% of the configured measurement range.

The 4 mA lower limit is known as the live zero. It allows a control system to distinguish a valid zero-percent measurement from a signal that has dropped significantly below the normal operating range.

How to Use the NAMUR NE43 Simulator

1. Adjust the process variable: Move the slider to change the simulated process value from below 0% to above 100%.
2. Monitor the loop current: Observe how the mA reading changes as you adjust the slider.
3. Check the signal status: Identify whether the simulator indicates normal operation, over-range, under-range, or a fault.
4. Simulate a wire break: Click the “Cut the wire” button to simulate an open circuit. The simulated current drops to 0 mA.
5. Restore the connection: Click “Repair the wire” to restore the simulated loop.

Understanding 4–20 mA Signal Conditions

Normal operation: The current remains between 4 mA and 20 mA, representing the configured measurement range.

Under-range condition: The current falls below 4 mA. This can represent a measurement below the configured range, depending on the transmitter’s behavior and configuration.

Over-range condition: The current rises above 20 mA. This can indicate a process measurement above the configured range.

Low fault signal: Under commonly used NAMUR NE43 conventions, a current at or below 3.6 mA can indicate a transmitter fault.

High fault signal: A current at or above 21.0 mA can indicate a transmitter fault.

Open-circuit condition: A broken wire or loss of loop power may cause the current to fall toward 0 mA. The exact response depends on the loop design.

The region between the normal measurement range and the fault thresholds must be interpreted according to the transmitter configuration and the receiving DCS or PLC logic.

Why Is NAMUR NE43 Important?

NAMUR NE43 helps instrumentation and control engineers distinguish ordinary process measurements from signals that may indicate an instrument problem.

It is useful when troubleshooting:

• Pressure transmitters
• Temperature transmitters
• Flow transmitters
• Level transmitters
• DCS and PLC analog input signals
• Open-loop and wiring faults

Correct interpretation of the current signal can help engineers narrow down possible causes of abnormal readings. However, a low or high current does not always identify the exact fault. Transmitter diagnostics, loop power, wiring, and analog input configuration should also be checked.

Frequently Asked Questions

What does 12 mA represent in a 4–20 mA loop?

For a linearly scaled 4–20 mA signal, 12 mA represents 50% of the configured measurement span.

What happens when a 4–20 mA wire breaks?

An open circuit generally causes the loop current to drop significantly, often toward 0 mA. The DCS or PLC may detect this as a signal fault, depending on its configuration.

Can NAMUR NE43 detect transmitter failure?

NE43 defines signal thresholds that help receiving systems recognize certain transmitter fault indications. It does not identify every possible instrument, power-supply, or wiring problem.

Is this simulator suitable for actual plant testing?

No. This is an educational software simulation. It does not generate a physical 4–20 mA signal and cannot replace calibrated loop-testing equipment or approved plant testing procedures.

Conclusion

The NAMUR NE43 4–20 mA Loop Simulator offers a practical way to explore analog signal scaling, over-range and under-range conditions, and simulated wiring faults. Use it to strengthen your understanding of industrial instrumentation and DCS/PLC signal interpretation.

For actual plant troubleshooting, always verify the transmitter’s configured fault behavior, analog input settings, and applicable site standards.