A sensor drive signal is controllably perturbed and sensor sensitivity monitored by monitoring {TAIL ~ the sensor response} to {HEAD ~ the perturbation} 
A sensor drive signal is controllably perturbed and sensor sensitivity monitored by monitoring { TAIL ~ the sensor response } to { HEAD ~ the perturbation }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD