STUDIES ON THE VARIATION WITH HUMIDITY OF CHARGE DECAY TIME AND CAPACITANCE LOADING FOR A NUMBER OF TYPES OF PAPER
John Chubb Instrumentation, Unit 30, Lansdown Industrial Estate, Gloucester Road, Cheltenham, GL51 8PL, UK. (Tel: +44 (0)1242 573347 Fax: +44 (0)1242 251388 email:email@example.com)
Measurements were made using a JCI 155v5 Charge Decay Test Unit with linked JCI 176 Charge Measuring Sample Support. These were mounted with the samples in a JCI 191 Controlled Humidity Test Chamber. Recorded observations were analysed and displayed using software JCI-Graph. Measurements were made as for recently reported studies [1,2].
In the present studies at least 3 pairs of measurements were made for each sample and each condition. The second measurement of each pair was a repeat of the first at the same location to check for reproducibility. Reproducibility was very good, and uniformity over samples fairly good ? as shown by the graphs.
80g paper, HP photocopying paper, 160g white card, a sheet of newsprint and a cotton handkerchief were used for the present studies. The samples were resident in the selected humidity conditions for 12-24 hours before each set of measurements were made.
3.1 Charge decay time
Charge decay times were measured as the time from initial peak voltage to 1/e of this.
3.2 Capacitance loading
Fairly steady values of decay times with change of humidity are observed for 80g paper, HP copy paper and 160g card. This is probably because an increase in charge mobility is roughly compensated by the increase in capacitance loading. With newsprint and the cotton handkerchief the increase in migration dominates, so decay times fall with increasing humidity. Similar earlier results on copying paper and cotton (but with poorer reproducibility) have been published .
It is not clear why capacitance loading and decay times vary as observed with the quantity of charge transferred. Maybe it is because the area charged by corona increases with the quantity of charge due to the change of local electric field as the voltage of the initial central patch of charge increases.
 J. N. Chubb "Measurement of tribo and corona charging features of materials for assessment of risks from static electricity" IEEE Trans. Ind. Appl. 36 No 6, Nov/Dec 2000 p1515-1522
 J. N. Chubb "New approaches for electrostatic testing of materials" Paper presented at ESA meeting, Brock University, Niagara Falls, May 2000 To be published in J. Electrostatics.
Webpage created 03/09/2001 John Chubb