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ESD & Testing Methods Explained

ESD -  Overview, Testing Methods, & Common Questions

Overview

There are two main methods of testing for electrostatic discharge or ESD that are in common practice today. This post will give you the basic insight and pitfalls into both air discharge and contact discharge testing. When talking about this type of electrical event it is important to remember that these methods are attempting to duplicate a real world event.

The focus on this post is to provide the basic information on this commonly occurring electrical event. For additional information see the references/additional resources below.

This type of testing is crucial given how commonly this event occurs and impact it can have on the function of electrical systems. 

Below you will find a picture of how energy can buildup on person walking across a surface and discharge on a computer. You will notice the buildup and potential difference that exists between the person and the electrical equipment. This real world example shows the air discharge method, which will be the first method we discuss.

ESD Testing Example - Air Discharge

What is Air Discharge Testing?

This discharge method is tested to the way that it occurs naturally, moving the discharge object with a surplus of energy towards the equipment under test or EUT. With this method however, there are a variety of factors that come into place given the environment in which the discharge occurs.

Electrostatic Discharge (ESD) Air Discharge Method

 

Common Environmental Effects:

Humidity - The lower the humidity the higher probability of a electrostatic discharge event occurring.   

Temperature - The lower the temperature often leads to an increase in ESD events.

Speed of Approach - Attempting to duplicate required speed can be difficult and can also have an impact on the event.

The benefit of this testing method is that it most accurately replicates how a discharge would occur. 

When conducting air discharge testing to immunity based standards it is important to pay special consideration to the humidity and temperature requirements. Once you determine which standard you are attempting to test to it is always best practice to ensure your within the tolerances.

However, given the many factors that can have an impact on the outcome of testing many standards preferred method is contact discharge.

What is Contact Discharge Testing?

IEC 61000-4-2 states "Contact discharge is the preferred test method. Air discharges shall be used where contact discharge cannot be applied." This standard also places specific requirements on the setup required for testing. Below you will find an example of the setup required.

This method of testing is where contact between the ESD generator and the equipment under test is maintained during the entire testing. This method of testing helps eliminate many environmental factors that can often have large impacts on test results.

However, for field testing this method may need to be supplemented with air discharge given the nature and large impact that environmental factors can have.

Contact discharge would rarely occur in a normal environment. Take the example above, a person would likely rarely maintain contact with an electrical equipment while generating energy to desired levels without a discharge.

Common Questions

What does ESD Stand for?

ESD stands for Electrostatic Discharge.

Is ESD dangerous to Humans?

Electrostatic discharge in most situations would be viewed as uncomfortable rather dangerous. However, given the impact that it can have on electrical equipment it is possible to have a negative impact on medical devices. 

Why does ESD Matter?

The electrical occurrence matters in the impact it can have on electrical circuits. Given the nature of electrical based devices in our daily lives ESD has increased in importance. With the increase in devices there has also been an increase in the amount of testing required. 

References/Additional Resources

Mueller Electric - Introduction to Electrostatic Discharge

EC&M - Electrostatic Discharge: Causes, Effects, and Solutions

Desco - Electrostatic Discharge (ESD) A Person Can Feel

Desco Europe - The impact of relative humidity on ESD

InCompliance - Static Electricity and People

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