Figure 6. Identical measurements of Figure 5. But with the ion path blocked.
To further confirm the conclusion, the period of the ionizer was increased 5 times to 500 msec ON times and the ion path was again blocked. See Figure 7. Note that the swing is reduced when the ions are blocked and the reduced swing matches that of the tests in Figures 5 and 6. The remaining swing is again caused by displacement current.
Figure 7. Effect of blocking ions for a longer ON time.
The Effects of Displacement Current vs. Ion Current
The displacement current and the ion current cannot be simply separated from each other electronically, but their effects are quite different. For the purposes of discussion, these currents can be thought of independently in the case where the voltage on the product or CPM plate is predominantly due to one current or the other.
The voltage on a product caused by the displacement current often is not an ESD hazard. In contrast, the voltage on a product caused by the ion current is a source of charge that can remain in place after the product leaves the environment of the ionizer. If the voltage on a product, due to ion current, becomes high enough and a path to ground is provided, an ESD event will occur.
When a product made of dielectric material experiences a displacement current, it is totally unaffected as the field passes through unabated. The charging caused by the waves of positive and negative ion current will charge the dielectric. If the product is withdrawn when the charge on it is near its maximum, there is potential for an ESD event. MORE