Advantages of Motion Sensors (MSI) RF sensors are: near zero speed response, no magnetic drag, large air gaps and the ability to sense non-ferrous metals like aluminum and nonmagnetic stainless steel, as well as ferrous metals. RF sensors use a modulated carrier signal to sense rotating metals. Unlike their Variable Reluctance (VR) counterparts, RF sensors require an internal or external preamplifier/signal conditioner to operate. When a target is sensed, eddy currents are formed which decrease the signal amplitude. The preamplifier/signal conditioner demodulates the signal, detects the voltage drop-offs and produces a square pulse wave (digital) output with a frequency directly proportional to the number of turbine blades, gear teeth, etc. that have been sensed.