Small perturbations in {TAIL ~ the drive voltage} are applied at a level to cause a measurable variation in {HEAD ~ the sensor output current} 
Small perturbations in { TAIL ~ the drive voltage } are applied at a level to cause a measurable variation in { HEAD ~ the sensor output current }
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD