There are all kinds of variations and combinations of ESD Laminate and Continuous Monitors used by companies with ESD Programs.. There are some key factors that you need to be aware of if you intend to use ESD Laminate together with a continuous monitor that will monitor the worksurface connections.
It’s important to note that continuous monitors don’t monitor the status/condition of the outer surface of an ESD workstation. The continuous monitor monitors the connection between groundable points on the worksurface (often snaps), not the Resistance to Ground (RTG) of the surface itself. The RTG measurement must be taken separately, per ANSI/ESD TR53-01-18 – Compliance Verification of ESD Protective Equipment and Materials (Pages 6 and 7).
The basic technology is that the monitor applies a low test voltage to the scrim layer in the worksurface. Because the test voltage is so low, the resistance of the scrim layer of the mat must also be low so that the test voltage can complete a circuit of the scrim layer, worksurface connections (snaps) and ground cords. Completing that circuit indicates that the worksurface is electrically connected. The goal is to have the worksurface circuit fail because of a bad connection, not because the scrim layer resistance was too high. As mentioned earlier, testing the combination of the outer layer and the scrim layer together (RTG) is a separate test.
When choosing a continuous monitor and worksurface combination that will work together it is important to consider the following:
- Does the worksurface have a separate scrim layer? (vs. a homogenous mat material)
- Does the continuous monitor spec sheet note the resistance limit of the scrim layer required for the monitor/worksurface alarm system to pass?
- See the excerpt below from the SCS 724 Continuous Monitor Technical Bulletin – https://www.descoindustries.com/PDF/724-Workstation-Monitor-User-Guide.pdf
“Red Worksurface LED (M) This indicates that a high resistance condition (> 3.7 Megohms) exists across the conductive layer of theworksurface and/or the ground connections. Check the worksurface, ground cords and their connections for continuity. Note the audible alarm may also sound if enabled.”
- See the excerpt below from the SCS 724 Continuous Monitor Technical Bulletin – https://www.descoindustries.com/PDF/724-Workstation-Monitor-User-Guide.pdf
What this means is if the resistance of the mat scrim layer is greater than 3.7 Megohms then the continuous monitor mat alarm would alarm for a high resistance condition even if the grounding hardware connections to the worksurface were intact. There are other SCS monitors available that will monitor a scrim layer with a resistance as high as 5 x 108.
In summary, it’s critical to know both the upper limit of the “pass” condition of the continuous monitor and the construction of the worksurface material (does it have a scrim layer and if so what is the resistance of the scrim layer?)
ESD Laminate requires extra attention when being considered for use with a continuous monitor for the following reasons:
- Laminate material is rigid, which makes it more difficult for grounding hardware to make a good contact with the scrim layer.
- Consider abrading the outer, decorative surface to expose the scrim layer for better contact. Consider a flat bottom drill for this process.
- Most importantly, perform a test on the resistance between two points on the worksurface to determine if the resistance meets the requirements of the specified monitor (for the SCS 724 that requirement is less than 3.7 Megohms – 3.7 x 106 ). We recommend using an ohm meter with a test voltage similar, if not identical to the test voltage used by the continuous monitor. We recommend performing this test before the purchase/installation of any number of continuous monitor/worksurface combinations.