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