Qualified grounding is the most important ESD control measure for a plant. However, we cannot take it for granted that grounding is good. The ground wires may not change in appearance, but they may be broken, they may be connected to different grounds, and so on. The best way to verify the ground connection is according to the standard ANSI / ESD6.1. In all cases, when measuring, we must know a reliable ground reference. Considerations for checking grounding are:
The grounding of metal tools should be measured with AC impedance as specified in the standard ANSI / ESD6.1. In some cases, the conventional multimeter can be used to measure with the DC resistance method, but in other cases, especially when there are many noise signals on the ground wire, the measurement results of the multimeter will be very inaccurate. When measuring small impedances, such as the range of 1 ohm, the resistance of the measuring instrument itself must be considered.
Dissipative (soft) ground
Due to high resistance, there are some challenges in detecting grounding of static dissipative mats. In this case, we apply a special test instrument with a high resistance range. Due to the signal integration of such instruments, the effect of the constant 50/60 Hz noise is reduced. Because the applied test voltage is quite low, the resistivity of the static dissipative material and the applied voltage may be non-linear, so we must be careful not to use high voltage (typically megohmmeter) to measure the dissipative surface resistance rate.