Questions And Answers

2) Humidity Read our paper on Humidity and ESD Control, specifically looking at Table I Tribocharging and Relative Humidity (RH)

3) Speed Read our paper on “ESD DISCHARGE TIMES: Controlling your Discharges”, specifically the tables and graph

4) Pressure of contact This has a direct effect on the resulting contact resistance, which will have a large correlation to the measured surface resistance. The standard ANSI/EOS/ESD-S4.1-1990 ESD Protective Worksurfaces, Resistive Characterization, specifies a specific meter and probe system where the weight of the probes is held constant as well as the material construction (5 pound gravitation force) having a certain durometer (durometer hardness of 50 ±10): 6.1.1 Resistance Measuring Apparatus Self-contained resistance meter or meters or power supplies and current meters in the appropriate configuration for resistance measurement with ±10% accuracy. For safety, all power supplies should be current limited, usually below 5.0 milliamperes. 6.1.1.1 For the material evaluation tests of 6.2, this apparatus shall be capable of open circuit voltages of of 10 ±1 volts and 100 ±10 volts, and capable of reading resistance values from 1.0 X 10⁵ ohms to 1.0 X 10¹¹ ohms. 6.1.1.2 For the installed worksurface tests of 6.3 and 6.4, this apparatus shall be capable of an open circuit voltage of 100 ±10 volts, and capable of reading resistance values at least a factor of ten higher and a factor of ten lower than the expected resistance values of the worksurface. In addition, both test leads should be isolated from ground. 6.1.2 Electrodes Two cylindrical 2.27 kg (5 pound) electrodes with a diameter of 63.5 mm (2.5 inches) each having contacts of electrically conductive material with a thickness of 0.25" and Shore-A (IRHD) durometer hardness of 50 ±10. The resistance between the two electrodes should be less than 100 kilohms when measured at 10 volts on a metallic surface. Standard electrodes constructed in accordance with ASTM F-150 can easily be modified to achieve these characteristics.