The current is then measured between the electrodes at {TAIL ~ the plurality} of voltages and {HEAD ~ a contamination level} is determined using the measured currents 
The current is then measured between the electrodes at { TAIL ~ the plurality } of voltages and { HEAD ~ a contamination level } is determined using the measured currents
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH