This week’s ESD Q&A question::
Question: When measuring ESD Product such as ESD Mat resistance, I have noticed that the resistance measures higher on some of my older ESD rubber mats when using 10V and will sometimes be greater than 10^9 ohms. Switching to 100V will lower the resistance into the green, passable range(less than 10^9 ohms). If the mat passes at 100V, is that sufficient to give the mat a pass? When should I use 10 volts vs. 100 volts?
Answer:
Industry standards specify the test voltage required when testing or verifying ESD control items (i.e. mats).   For verification of mats, or work surfaces, you can reference the ESD Association TR53 Compliance Verification document.  This is a free download at www.esda.org (select the Standards tab and scroll down to TR53).
The following rule applies for resistance testing of ESD control items:
Perform the test at 10 volts.  If the resistance is < 1.0 x 10^6 ohms record the reading.
If the measurement at 10 volts is ≥1.0 x 10^6 ohms, switch to 100 volts, make your measurement and record the result.
Most ESD mat materials are designed to have a resistance greater than 1.0 x 10^6 ohms, so you can start your testing at 100 volts.  In the example that you stated, the mat that you tested meets the requirements.  If you are seeing the values creep higher it would be wise to test the older mats more frequently to verify that they are still under 1.0 x 10^9 ohms.
Periodically, Transforming Technologies will answer questions concerning all things ESD: static causes, threats,  ESD prevention, best practices and all things static in a feature we call ESD Q&A.  If you have ESD questions that you would like to be answered, email info@transforming-technologies.com  with Q&A in the subject line.