This week’s ESD Q&A question stems from StaticCare reader Paul, he asks:
Query: What measurement or measurements do I want to make when auditing an ESD worksurface?
Thanks for taking the time to file your question to Transforming Technologies.
There are three primary measurements for evaluating a function surface; Resistance Point to Point (RTT — also called Resistance Top to Top), Resistance to Groundable Stage (RTGP) and Resistance to Ground (RTG).
Figure 1 — Resistance To Ground (RTG)
Resistance to Ground Measurement
For overall auditing functions, the principal measurement is RTG. This measurement is made using a 5 pound electrode connected to the positive terminal of the resistance lever. The electrode is put on the surface at the most heavily used area. The negative consequence is connected to electrical ground. This measurement guarantees that the mat is joined to AC Gear Earth. ESD standard process says to test in 10 volts, and if the measurement exceeds 1.0 x 106 ohms, change to 100 volts. If you’re certain that your worksurface material has a resistance greater than 1.0 x 106 ohms, you might choose to begin in 100 volts to conserve time.
A very simple and safe way to connect to AC Ground is using a grounding plug, like the Transforming Technologies AD22. The AD22 guarantees a good link to the third wire ground of an AC outlet, while insulating the plug from the neutral and hot wires. Constantly check electrical outlets for good wiring prior to utilizing grounding plugs.
In case the consequent RTG measurement is within your necessary limitations, no further work surface testing is needed and you are able to proceed to the next job surface. If the RTG measurement exceed your limitations, wash out the work surface with an approved cleaning merchandise and check all wiring connections to ensure that they are protected and re-test. If the measurements still exceed your limitations you will then need to conduct a Resistance to Groundable Point (RTGP) measurement.
Figure 2 — Resistance Degree To Groundable Point (RTGP)
Resistance to Groundable Point Measurement
This measurement is similar to the RTG measurement except that the negative outcome is connected to the grounding point (snap) of the surface. The testing is performed using 100 volts when the anticipated resistance is higher than 1.0 x 106 ohms.
If this measurement provide a reading that is within your requirements the issue is somewhere between the snap and AC Ground. Typically, either the earth cable became compacted or it is faulty. Check and confirm all wiring between the surface and the AC equipment ground.
Whether this measurement also provides a value that exceeds your requirements, then there might be a issue with the surface. A point-to-point resistance measurement can be done to verify the functioning of the surface material.
Figure 3 — Resistance Point To Point (RTT)
RTT — Resistance Point-to-Point
This measurement is made using two 5 pounds electrodes. The electrodes are put 10″ apart on the surface in a variety of locations. Figure 3 is an illustration of a point-to-point test.
The testing is performed using 100 volts when the anticipated resistance is higher than 1.0 x 106 ohms.
In case the reading fulfills your requirements, there’s maybe a link issue with the groundable point. If the scanning transcend your limits the work surface is most likely faulty and must be replaced.
It is necessary that RTG measurements be made regularly. The frequency of testing depends upon on internal demands and testing background. RTG testing has to be performed even if constant observation is in place, as continuous monitors affirm ground link of the worksurface, but not the functioning of the worksuface.