Posted on

How to use a Meter to Test ESD Mats

Standard ESD Mat Kit in Blue

Do you use an ESD Mat Tester? How do you check your mat's ESD grounding? In this article, I explain how to use a meter to test a mat using the methods described in ANSI/ESD S4.1 "Worksurfaces - Resistance Measurements".

1. How do I test my Anti Static / ESD Mat?

For an “ESD Resistance” test like ESD S4.1, which is used to check that the top surface of a mat is static dissipative, you would use a Surface Resistivity (ESD) Meter to perform both resistance-to-groundable point (RTG) and resistance-top-to-top (RTT) tests.

RTT Testing for ESD Resistance per ANSI / ESD S4.1
RTG Testing for ESD Resistance per ANSI / ESD S4.1

2. Surface Resistivity vs. Surface Resistance

A material is static dissipative if it is more than 1 x 106 ohms / square, which is 1 million (1,000,000) ohms per square, and less than 1 x 1012 ohms / square, which is 1 trillion (1,000,000,000,000) ohms per square.

ESD Resistance Chart for 5300 Series Anti Static Mats

However, we cannot physically measure surface resistivity per square, so we apply electricity through ESD mats to measure their surface resistance in just ohms.

Theoretically, surface resistivity is ten times greater than resistance. For example, a material that measures 108 ohms in surface resistance should measure 109 ohms / square in surface resistivity. For testing purposes, per ESD TR20.20 , the correct unit of measurement is surface resistance (just ohms).

To measure surface resistance, we use what is known as an ESD meter. Meters can measure surface resistance from electrodes (the yellow cylinders) placed on a mat we are testing.

ESD Meter with electrodes

Meters typically display surface resistance in ohm values with a mantissa and exponent (power) of the number. For example, if the #8 exponent LED illuminates and the meter displays “9.87”, the measurement is 9.87 x 108 ohms of surface resistance.

ANSI / ESD S4.1 guidelines (section 8.0) state that that point-to-point (RTT) tests should find the mat has greater than or equal to 1 x 106 ohms of surface resistance. It also states that resistance-to-groundable point (RTG) tests should find the mat has between 1 x 106 and 1 x 109 ohms of surface resistance.

3. Measure Resistance Top to Top (Point to Point) (RTT)

ESD Resistance Measurement RTT Top to Top Point to Point with Desco™ ESD Resistivity Meter

Test Procedure in accordance with ANSI/ESD S4.1 section 6.4 Periodic Worksurface Testing:
• Do not clean surface. Remove from the surface only those items that might interfere with the test.
• ESD Sensitive devices shall also be removed.
Use two 5 pound electrodes and place them on the most commonly used area of the surface. Ensure that the electrodes are about 10″ apart from each other and 2″ away from any edge and 3″ away from any grounded point.
• Push and hold the Test Button until the surface resistance reading is displayed.
• If the most used area is not obvious, use two points near the center of the surface.

4. Measure Resistance to Groundable Point (RTG)

Resistance to Ground Measurement with Desco™ ESD Resistivity Meter

Test Procedure in accordance with ANSI/ESD S4.1 section 6.4 Periodic Worksurface Testing:
• Do not clean surface. Remove from the surface only those items that might interfere with the test.
• ESD Sensitive devices shall also be removed.
Clip the black test lead to a grounded point.
• Use one 5 pound electrode on the other test lead and place the electrode on the furthest convenient point on the surface.
• Push and hold the Test Button until the surface resistance reading is displayed.