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Open Circuit or Applied Voltage That is the Question! Dale Tucker - VPI Many of us in the ESD flooring industry believe that floor resistance should be tested with a known applied voltage. The present test methods do make this a necessary condition. The type of Ohmmeter to be used in flooring resistance test methods especially those described by the ESD Association and the ASTM is being hotly debated. This issue also applies to most other resistance tests described by the Association. However not in the case of other ASTM test methods such as D257. In the ESD Association Test Method S7.1 the Ohmmeter or measuring apparatus is described as follows: "The apparatus shall be capable of an open circuit voltage of 10 v and 100 v with 10% tolerances." In the ASTM F150 test method, the Ohmmeter is also described in regards to open circuit voltages. However, in ASTM D257 the voltages are always stated as "applied." Of course when one is measuring insulators this is more intuitive. When measuring flooring surfaces with coatings, grime, etc. etc. it should be as intuitive. Over the past year many experts in the flooring industry debated and decided that the ohmmeter should have its applied voltage specified not its open circuit voltage. The problem as described by the group was that many meters did not maintain their 100 volts or 10 volts under load. This meant that the applied voltage could be variable from meter to meter. This would not be a problem if the sample being tested had metal to metal contacts. However, in most test methods described by the ESD Association, the electrode is conductive rubber measuring a sample which is very sensitive to contact area. When the voltage is not fixed, the resistance measurement is variable. This leads to a lack of control of the test standards for the industry. When the stakes are so high as involved with installed floors, this is an unacceptable test method procedure. After much debate, the ESD Association decided to keep the meters so specified. The purpose of this article is to solicit inputs from the field. What do you think ? Email your input! Many companies specify their floors to close limits such as "greater than 1 MegOhm but less than 5 MegOhms." Some companies do not want their floors to be "over 1 MegOhm." Other do not want their floors to be "under 1 MegOhm." Manufacturing floors to such a chaotic situation is difficult at best. When the applied voltage is not fixed, this becomes impossible. Many of us in the ESD flooring business have had to "rip-up" floors over the difference of a few MegOhms. The test methods have much more variability in them than that. We in the industry believe that the use of "open circuit" Ohmmeters for specifying floors is not credible. What do you think?