ESD Systems - Questions And Answers

Wrist ground straps are the primary method of ESD protection in our facility. There are several associates who work in areas requiring ESD precautions, who consistantly fail wrist strap testing. They have tried numerous wrist straps on all of our testers with the same result...failure. Are there methods of correcting this problem? –Dave, Hebron, OH

Yes, there are some methods to troubleshoot your wrist straps. First, let’s make sure your tester is properly adjusted and calibrated to the ESDA standard on wrist straps ESD-S1.1, where the wrist strap system continuity test passes at less than or equal to 1x10⁷ ohms (or 10 megohms). The wrist strap itself is recommended to have a 1 megohm resistance +/- 20% for electrical safety to the user, which is the lower limit for the tester. An ideal tester for this is our Combo Testers. Things to test/look for when troubleshooting wrist straps:If the operator and wrist strap system fails low - ? make sure that the person is not directly connected to ground via another path, i.e., touching a grounded metal structure.? The most common cause of a fail low is a shorted resistor in the wrist strap coil cord. Try replacing the coil cord with a new one and repeat the test. If the operator and wrist strap system fails hi - ? make sure the coil cord is firmly attached at both ends (to the banana jack to tester and stud snap to wrist strap buckle)? make sure there is continuity in the coil cord (you can test with an ohmmeter ~ 1 megohm), if not about 1 megohm, replace with new cord? make sure the wrist strap is firmly connected to the users wrist. The band should be snug, but not uncomfortable. If the unit still fails hi, then proceed to the following checks -? remove the wrist strap and hold the bottom part of the band tightly between the testers thumb and index finger and test. If the test fails high, the band may be soiled and need cleaning or the buckle to band connection may be suspect. Either clean and retry or replace band.? If the above test is okay, then the wrist may be to dry. Apply ESD lotion to the wrist to re-moisturize the skin thereby increasing its conductivity. Retry test. Another consideration, for operators with systematic dry skin should wear metal banded wrist straps to minimize the contact resistance. If their skin is very dry, application of an ESD lotion may be required as part of their donning process.

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