Keeping instruments trustworthy in a noisy plant

A factory floor is electromagnetically hostile: variable-speed drives, switching contactors, welding, radio transmitters. An instrument that drifts or freezes under that noise is worse than useless — it lies. IEC 61326 is the standard that makes measurement, control and laboratory equipment electromagnetically compatible: quiet enough not to disturb its neighbours, and robust enough to keep telling the truth when they disturb it.

Two sides, scaled to the environment

EMC always has two faces. Emission limits what a device radiates and conducts onto the mains, so it does not pollute the electromagnetic environment. Immunity checks that the device keeps working when hit by disturbances — electrostatic discharge, fast transients, surges, conducted and radiated RF, magnetic fields. IEC 61326 sets both, and scales the immunity test levels to the electromagnetic environment: a basic location, a harsher industrial location, or a controlled environment. The same transmitter faces tougher levels on a plant floor than in a lab.

Performance criteria — and the safety case

A device does not simply pass or fail immunity; it is judged against performance criteria. Criterion A means normal performance is maintained throughout; B allows temporary, self-recovering degradation; C allows degradation needing operator intervention. Which criterion is acceptable depends on the function. That distinction becomes critical for safety: IEC 61326-3-1 raises the bar for equipment performing safety-related functions, requiring the safety function to survive defined electromagnetic stress — the bridge between EMC and functional safety under IEC 61511.

Where it sits

IEC 61326 is the instrumentation-specific application of the generic EMC framework IEC 61000, and it travels with the safety standard for the same equipment, IEC 61010. In process automation it is mirrored by NAMUR NE 21, the recommendation EMR engineers cite when specifying field devices.