How Well Is Your ESD Flooring and Footwear System Working? – Guest Blog

Figure 1: System Resistance Test

by Craig Zander, Transforming Technologies

Craig’s latest Q Source Resource Guest Blog looks at how a Walking Voltage Test reveals how well your ESD flooring & footwear system is working.

The ESD flooring and footwear system is an effective way to ground people that need to be on the move in a factory. ESD footwear, when worn properly, is designed to drain the voltage from a person to the floor and then to ground. Periodic testing of both the floor and the footwear is required to verify proper functioning.

Until recently, a System Resistance Test (ANSI/ESD STM97.1) was all that was needed to qualify an ESD control flooring and footwear system. If the resistance was less than 35 megohms, it was assumed that the person’s voltage would not exceed 100 volts (the upper limit for ANSI/ESD S20.20). However, this testing is done with the person stationary and having both feet flat on the ground. What happens when the person starts moving and the entire foot is not making contact with the floor?

Figure 2: The Walking Test Pattern

The most recent version of ANSI/ESD S20.20 now requires a Walking Voltage Test (ANSI/ESD STM97.2) be performed when qualifying flooring and footwear systems. The test consists of measuring body voltage generated during a six-step pattern used to simulate moving throughout a facility. This test will determine the actual voltage on the person while moving. Research has shown that when tested separately, ESD floors and footwear systems may pass the resistance test, but when used together, can greatly exceed the 100-volt threshold.


Determining the maximum voltage generated by people moving on the factory floor is very valuable information. By knowing the maximum voltage generated you will know that your flooring and footwear investment is performing as designed. You may also be pleasantly surprised to find out that the system is working quite well and you are able to handle devices with much lower Human-Body Model (HBM) damage thresholds.

WT5000

Equipment is available to accurately measure and record the walking voltage. One such instrument is the WT5000. The WT5000 Walking Test Kit (Warmbier WT5000 Electrometer Walking Test Kit) measures and records the walking voltage while providing a graphical readout. The instrument connects to a PC using any Windows version for easy data collection. The WT5000 identifies the peak voltages per the requirements in the standards.

The two-in-one EFM51WT (Transforming Technologies 7100.EFM51.WT Warmbier EFM51WT Field Meter Walking Test Kit) meter holds the PEAK value of the measured body voltage, as well as the LIVE static voltage measured on the operator’s body. The kit includes the EFM51 static field meter, walking test adapter plate, hand probe and conductive carrying case. The EFM51 is a fully functional field meter that, in addition to the Walking Test, measures and detects electrostatic fields, surface potentials, and discharge times (with optional charge plate accessory (part number 7100.EFM51.CPS.SET).

EFM51

You have made the investment in an ESD flooring and footwear system so that people can be mobile while still protecting your products from ESD events. Determining your actual walking voltage generated is critical to knowing that your products are being protected.

CLOSING: Thanks, Craig! We appreciate you filling us in about the necessity of Walking Voltage Tests to ensure proper ESD protection for flooring and footwear systems. Your expertise is invaluable to our Q Source community.

For information about Transforming Technologies and their ESD control/monitoring products (including walking test kits), please visit QSource.com. you.

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The Importance of Testing & Monitoring Your ESD Grounding Devices – Guest Blog

by Craig Zander, Transforming Technologies

In Craig’s debut Guest Blog for Q Source, he explains the importance of testing and monitoring of ESD grounding devices.

Transforming Technologies PDT 800K Test Station

The first line of defense for protecting electronic devices and assemblies from damage due to Electrostatic Discharge (ESD) is to properly ground all personnel that come in contact with the product. When a person is effectively grounded, all of the voltage that accumulates on their body when moving rapidly travels to ground before it can affect the product.

The most common and reliable method for grounding operators is the wrist strap and coil cord combination. The conductive materials inside the wrist band contact the skin and transfer the voltage from the operator through the cord and to ground. When worn correctly, and tested or monitored, wrist straps are the preferred method for grounding people.

When grounding a person through a wrist strap, ANSI/ESD S20.20 requires the resistance of the person to equipment ground to be less than 3.5 x 107 ohm (35 meg ohm). Typically, the resistance to ground of a person properly connected with a wrist strap is just over 1 meg ohm (the value of the resistor in the cord assembly).

Wrist strap and coil cord assemblies need to be tested or monitored regularly. Some companies chose to test the wrist strap system one or more times per day at central testing stations (for example, the PDT 800K Test Station). Other companies opt to continuously monitor (using a device such as the CM1602 Constant Monitor) the wrist strap connection so that product is not handled if the grounding system fails.
 

Transforming Technologies CM1602 Constant Monitor

There are situations, however, when being connected to a ground jack via a cord is not conducive to efficient or even safe operation. Operations that involve frequent transportation of product within the facility, as well as operations that involve machinery, present a challenge to the wrist strap and coil cord grounding method. In these cases, factories may use a combination of conductive flooring and foot grounders to effectively ground the operator.

The requirements for grounding a person through flooring and footwear have changed in the ANSI/ESD S20.20 2014 Standard. Previous versions of ANSI/ESD S20.20 provided you with two options. If the resistance from the person through the footwear, through the floor and to ground was less than 35 megohm, no further testing was necessary. If the resistance was greater than 35 megohm, you could still meet the requirements of the standard if the resistance was less than 1.0 x 109 ohms and you can demonstrate that the operators generate less than 100 volts. The latest version of S20.20 (ANSI/ESD S20.20-2014) requires the resistance test and the walking voltage test for qualifying flooring and footwear materials together. While many flooring and footwear options may pass the resistance test, it has been discovered that some combinations of floor materials and foot grounding materials do not work well together.

To test the walking voltage generation of flooring and footwear systems you use ANSI/ESD STM 97.2 Floor Materials and Footwear - Voltage Measurement in Combination with a Person. This test involves recording the voltage of a person while they perform a repetitive walking pattern. To record the voltage you can use a charge plate monitor with data recording capability, or a similar instrument with the same specifications listed in the test method.

Body voltage measurement test set-up.
The new software “Digilloscope”
can mark the five highest
peaks automatically and calculate
the average value.

Transforming Technologies developed the Warmbier WT5000 Walking Test Kit to meet the needs of the ANSI/ESD STM 97.2 test. The WT5000 is a battery-operated instrument that is easily transported to various areas of the factory floor. The system includes the trademarked data acquisition and analysis software “Digilloscope for Windows™.”

The WT5000 records the voltage on the operator while they are performing the walking steps called out in the standard. Once several repetitions of the pattern are complete, the software will provide the peak voltage and average value. The data is used to confirm compliance to standards and to determine the lowest possible voltage device (Human Body Model Discharge Threshold) that can be handled in the facility.

Thanks for that very important information about ESD control and testing, Craig. We look forward to future Guest Blogs to learn from your expertise.

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