How to Test RTT and RTG Ratings

by Andy on October 22, 2012

Voltage Meter for RTT and RTG TestingIf you use ESD-safe mats you’ve probably seen RTT (Resistance Top to Top or Resistance poinT to poinT) and RTG (Resistance Top to Ground or Resistance poinT to Ground) ratings. These are important ratings that show how mats conduct electrical charges. RTT confirms that the surface of the mat conducts electricity uniformly, while RTG shows that the mat can conduct electricity from its surface to a ground point.

While you can always look up the specifications for your mats if you need to know the RTT or RTG ratings, you may find that you want to test your mats to ensure they are meeting their expectations. To fully test an ESD-safe mat you need a surface resistivity meter. The ANSI ESD S20.20 standard recommends using a meter with 5 lb weighted electrodes. If you have the electrodes on 5 lb weights then they should give you a consistent reading.

To test RTT you simply position both of the electrodes on the surface of the mat, preferably as far apart as possible. You want to have them far away from each other so that you can test as much of the surface at once as possible. If you put the electrodes next to each other, you can only confirm that a small portion of the mat has the correct rating.

For RTG you place one of the electrodes on the surface of the mat, and connect the second one to the ground point. The ground point of a mat is typically a snap, so here you can use an electrode that can snap onto the ground. If you do use a weighted electrode then you must ensure that it is only touching the ground point and not the general surface of the mat.

That is the basic way to test RTT and RTG ratings. Do you have any more questions? Leave a comment below and we will find you the answer!

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