All That You Wanted To Know About Electronic Discharge Immunity Test

electronic discharge immunity test esd gun emc testing

Electronic and electrical products must go through EMC testing to ensure that it is fully compatible electromagnetically. Various testers are available for rent from companies like TRS-RenTelco. The product should be capable of withstanding electromagnetic disturbances that it encounters, and at the same time, its own electromagnetic emissions must be within the specified limits so that it does not interfere with the operations of other equipment and devices. Having an EMC certification is mandatory, and manufacturers just cannot afford to take it lightly. 

What Is IEC 61000-4-2? 

IEC 61000-4-2 is a set of guidelines and standards for electronic equipment's ability to withstand ESD or electrostatic discharge generated from metal objects or a human body with a built-up static charge. The standard is based on the assumption that the source is an electrified human body discharge, and the testing creates the same pattern of the current waveform that those conditions would create. Transient Specialists is a renowned company that manufactures and provides EMC test equipment on hire, and the name has become so much synonymous with EMC testing that often many people refer to the IEC standards as Transient Specialists - 61000-42. 

ESD Guns 

ESD gun or an ESD simulator is the device widely used for EMC testing to determine the equipment's ability to withstand electromagnetic waves, noise, and other disturbances. The handheld device helps to ascertain how much immune it is to electrostatic discharge. ESD guns must comply with the following specifications. 

• Energy accumulation capacity – 150pF 
• Charging resistance – 50MΩ to 100 MΩ 
• Discharge resistance = 330Ω 
• Output voltage - For contact discharge 8kV and discharge 15kV 
• Polarity – Positive (+) and Negative (-) 
• Tolerance - ±5% 
• Hold time - ≥ 5 seconds 

ESD Gun Testing 

Before testing by electricians or EMC experts, you must get the ESD gun calibrated that involves testing and verifying its output due to the peak bandwidth, slew rate, unintended capacitive and inductive coupling in addition to proper grounding and peak energy. The process of testing begins by measuring the resulting current across a high frequency resistive and low impedance shunt connected to the ground. The target is mounted at the center of a 1.2m 2 ground plane having less than 1.22 VSWR and insertion loss less than 0.3dB and up to 4GHz. 

According to the guidelines of IEC 61000-4-2, placing the measurement oscilloscope within a Faraday cage will protect it from radiated ESD pulse. You must use a low-loss cable of good quality to connect the target with the oscilloscope and attenuator. In conformity to IEC specifications, the cable length should never exceed 1 meter. Moreover, use a double shielded cable only that prevents signal leakage, which can affect the measurement considerably. 

ESD & EMC Summary

Electric discharge immunity test is just one part of EMC testing with the other part being the emission testing that measures how much electromagnetic noise generates during the use of a device. 

EMC testing is very stringent, and with a low passing rate of 50% it makes sense to keep testing emissions at various stages of manufacturing the product, so that saves the time needed to launch the product.

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