Geartooth Sensing Architecture

Geartooth Sensing Architecture

There are many ways of making Hall effect based geartooth sensors but they generally fall into a few major categories.  The categories are based  on the features of of the magnetic field being measured and how the measurement results are interpreted into an output signal.

When measuring magnetic flux density in an effort to discriminate a target, you can look for magnitude or a spatial gradient. Magnitude can be measured with a single Hall effect transducer element but a spacial gradiant can not be measured directly, it must be approximated measurements from two independent closely spaced transducer elements. Gradient detection schemes are often called differential and magnitude detection schemes are called single point.

Magnitude and gradient detect different characteristics of a target. Changes in the flux magnitude help indicate the presence of the body of a target.The greatest magnitude response is detected when a sensor is directly over the body of a target feature. In contrast, Gradient detectors respond to an abrupt change in the target, for example the edges gear teeth or edges of holes.  These characteristics are useful in different applications.

The second dividing line is the method used to interpret the transducer signal. The idea in all schemes is to compare the transducer signal to a threshold and report the absence based on the results of the comparison. The difference lies in whether there is a static threshold or a dynamic threshold. Static thresholds offer conceptual simplicity, sensors based on the use of dynamic thresholds can offer a much improved performance, ease of use and application flexibility, by allowing the sensor to adapt  itselftp the characteristics of the target being sensed.

These combinations yield a few classes of Hall effect based speed sensors such as single point/fixed threshold, single point/dynamic threshold, differential/fixed threshold and differential/dynamic threshold.

Further Reading

Geartooth Sensor

Differential Geartooth Sensor

Geartooth Sensing