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An initially charge neutral Teflon rod is used to 'scuff', wipe or impact the middle of the stretched sample area. The quantity of charge transferred to the surface is measured by lowering the rubbed end of the previously charge neutral Teflon rod into a Faraday Pail (JCI 147). Charge values are measured up to 20nC with a resolution around 10pC. Charge values are recorded manually. Fieldmeter readings are recorded either directly into a microcomputer with ¼s time steps or using a Picoscope digital storage oscilloscope (see Figure 2).

 

Fig 2. Example of signal variation during tribocharging

 

3.3 Arrangements for corona charging studies

The method for tribocharging measurements described above is simple, but only really suitable for experimental studies. Corona charging provides the basis for an easier to use, more consistent and less operator dependent way to measure the charge decay characteristics of materials [4]. The corona charging approach uses a brief pulse of high voltage corona discharge to deposit a patch of charge on to the surface to be tested and then uses a fast response electrostatic fieldmeter to measure, without contact, how quickly the surface voltage, developed by this charge, falls as the charge migrates away. The corona discharge points are mounted, as shown in Fig. 3, on a light plate that is moved quickly away (within 20ms) immediately after corona charge deposition.

Test methods based on this corona charging principle are included within a British Standard [11] and an International Standard [12].

 

Fig. 3. Arrangement for corona charge decay measurements

 

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