Quadrature Output Dual Channel Speed Sensors – HD Series

The HD series quadrature output sensors are based on Hall Effect sensor technology, which can sense a change in target motion from true zero to 15 KHz. The HD series offers dual channel output and, where required, directional logic. The output frequency of HD sensors has a square pulse waveform (digital) that directly relates to the number of turbine blades, gear teeth, etc. that have been sensed. These pulses, in turn, can be correlated to determine flow rate, RPM, or velocity.

HD sensors are based on the H series which incorporate a magnet within the sensor, enabling them to sense ferrous metal as well as magnet targets. Maximum air gap sensing distances are typically 0.100″ and these sensors can be optimized to detect fine as well as large pitch targets.

General Operation

The HD series sensors consist of two hall-effect elements biased with a magnet to detect the change in magnetic field strength caused by the rotation of a ferrous target gear. When the target gear passes by sensor element A, the output switches from a logic 0 to a logic 1 at half the pitch (P/2) of the target gear. As the target gear continues, the output switches from a logic 1 to a logic 0 at the gear pitch (P).

Sensor element B is placed at a distance of one fourth of the pitch of the target gear (P/4) from element A. The output of element B is shifted by one forth (P/4) from the output of element A. In electrical terms, this creates a phase shift of 90°. When the gear turns in the counterclockwise direction, output A leads output B. When the gear turns in the clockwise direction, output A lags output B.

The descriptions above are only a theoretical ideal model to explain the fundamental operation of the HD series sensors. The realities of the physical world such as mechanical tolerances, magnetic field variations, and other physical phenomenon cause deviations from the ideal model. Visit our Practical Application Guide to learn more.