If an electronic air cleaner filter is employed, a discharge counter counts {TAIL ~ the frequency} of pops occurring across {HEAD ~ the electrodes} of that filter 
If an electronic air cleaner filter is employed , a discharge counter counts { TAIL ~ the frequency } of pops occurring across { HEAD ~ the electrodes } of that filter
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH