Download Open Circuit or Applied Voltage

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?