Measurement of ionizer performance-a new approach

The ANSI/EOS/ESDS 3.1-1991 standard utilizes a charge plate monitor (CPM) to measure ionizer performance. The CPM measures positive and negative discharge times (DT+ and DT-) and offset voltage on a 200 mm/spl times/200 mm plate, not on real parts. While the CPM produces consistent measurements that are a good metric for ionizer performance, it is not necessarily the best way to measure ionizer performance on other objects. This paper analyzes an instrument and a protocol that produces measurements that correlate with CPM balance and discharge times and represent physical quantities which can project to the response of various objects in the manufacturing line. These parameters are air resistance and offset voltage. The study shows that the ionized air acts as an ohmic medium. The instrument under study, a biased plate monitor (BPM) is a biased HV plate with a nano-ammeter to measure the ion current it intercepts. The calculated discharge time from BPM as compared with the CPM measurement is excellent (<10%). The biased plate monitor (BPM) has the advantage that its readout is immediate and does not require a wait to obtain the discharge time. The biased plate also can record the offset voltage. Measurements were made over the range of 0 to 70 V of offset and compared with a CPM measurement. The results showed excellent matching.