Prostat Corporation | ESD Blog

Is it possible to add one (1) order of magnitude on the resistance reading if I want to get an estimate of ASTM D-257 Surface Resistivity in ohms/square? If not, how can you get the surface resistivity when using the Prostat PRF-922B Two-Point Probe?

In fact, surface resistivity is a calculation, and the probe used for the PRF-922B is specifically measuring point to point resistance.

Specifically, resistivity calculations are only possible if a concentric ring is available (sometimes referred to as an 11 point probe). The  922B would not be able to make this measurement, and the 10x rule therefore cannot be applied.

By definition, surface resistivity is the resistance between two opposite sides of a square and is independent of the size of the square/dimension space. Two points would not be enough to define a dimension, hence why resistivity is expressed in ohms/square.

Basically, you need an area to define resistivity. The 10x rule is simply used due to statistical testing where the average results of the calculations and diference between resistance & resistivity of a defined area of homogenous material were found to be roughly a decade higher for resistivity.

The two probes capable of concentric ring measurements are the Prostat PRF-912B and the PRF-911.