Electrostatic measurements on plastic webs

It is pointed out that, when interpreting the results of electric fieldmeter measurements on webs, one must be very careful applying the assumption that the fieldmeter head, even with a ground plane attached, and the web approximate a pair of infinite parallel planes. As the web width increases well beyond the dimensions of the fieldmeter head, the assumption that the electric field measured by the head followed E =σ/∈₀ becomes grossly in error. If this equation is used, the calculated charge density can be in error by a factor of three or four, although the error can be much greater than this for particular geometries that enable higher field concentration. Field-solver software is useful for finding a relationship between electric-field readings and the web charge density, especially in complex geometries. It gives the opportunity to separate the effects of geometry from the effects of charge transfer. This allows a better estimate of the charge density on webs and a better estimate of the electrostatic effects which might result from that charge. This leads to improved understanding of the electrostatic behavior of dielectric webs in real web paths