How We Achieved EN 61000-6-2 Compliance on PLC Systems
Introduction to the Electrostatic Discharge Immunity test
A commonly performed EMC immunity test, known as the Electrostatic Discharge Immunity test can significantly impact electronic equipment and this was evident during the application of the test requirements specified in the EMC generic test standard EN 61000-6-2: 2009.
At certain test locations on a PLC system (equipment under test), the static discharge events caused a disruption to a manufacturing process which meant that the performance criteria set by the standard could not be achieved.
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The Effects
It was found that the electrostatic discharges caused several adverse effects:
Data Corruption in Communications
The discharge(s) introduced instantaneous and rapid high-current spikes into the communication network, interrupting data transmission between motion controllers and process sensors. As a result, data packets whilst received were found to be corrupted in part, causing temporary process errors to the manufacturing process.
Resets observed to the main process system
The voltage spikes generated triggered an automatic system reset to one of the production lines causing it to stop unexpectedly, requiring operator intervention and the restarting of system. In the context of the standard, the Electrostatic Discharge test requirements do not allow for user intervention, and the system must continue to operate after the test is carried out.
Root Cause & Corrective Actions
The investigation identified several contributing factors:
- Insufficient grounding of several cabinet panels.
- The absence of ESD protection component devices on a communication interface.
To reduce the risk of future electromagnetic discharge events, the client implemented the following mitigation measures:
- Installed additional grounding straps to specific metal panel work.
- Added additional Transient Voltage Suppression (TVS) protection diodes between the communication interface and the process sensors.
The Results & Conclusion
Following implementation of the corrective measures led to the following:
- The EMC performance criteria set out in EN 61000-6-2 for industrial applications was met.
- The potential of production downtime and therefore a direct financial loss being reduced in the effect of an ESD phenomenon occurring in the field.
- Increased system reliability and an improvement on operational efficiency.
This case study demonstrates how an Electrostatic Discharge event can have an adverse effect on electronic and electronical equipment through the corruption of data and system interruptions. In this case, the effective grounding and ESD protection practices were essential to ensure the reliability and longevity of such equipment, and for meeting particular EMC requirements when located in an industrial based environment.
