DEFINITIONS

Quadrature Output
When discussing gear tooth sensors a quadrature output consists of two pulsing square wave outputs that are offset (ideally by 90 degrees). These two offset outputs can then be used to resolve speed and direction or count with direction by comparing the states of the two outputs.

Duty Cycle
When looking at the digital square wave output, the duty cycle is the percentage of time that the output is in the high state over the period of the square wave. The image below shows the formula for calculating the duty cycle as well as examples of 50% and 25% duty cycle pulse trains.

Phase Angle
When looking at Quadrature Sensor Outputs, the phase angle is a measure of the offset between the two pulse trains. When the duty cycles are not both 50% the entire period needs to be considered in calculating the phase angle. The image below shows an examples of 90 degree phase angles with 50% duty cycles compared to 25% duty cycles.

 

To calculate Phase Angle the delay between the two pulses is measured relative to the period of the pulse. Sensor Solutions measures the delay from the center of the high pulse from channel A to Channel B. The formula for calculating phase angle is shown below.

 

For more in depth explanation of Phase Angle and Duty Cycle refer to the following Application Note Why Duty Cycle and Phase Angle Matter in Quadrature Speed and Counting Applications

WHY DOES THE PITCH OF THE GEAR MATTER?

For accurate determination of direction of motion, the two internal sensing elements need to be located relative to each other so that one output will see a passing gear tooth before the other in one direction of rotation. When the direction of rotation changes, the other output needs to see that tooth passing first. For this to happen the outputs need to be both properly offset and produce pulses where the square wave has a similar length of time in the high state as it does in the low state.

Knowing the pitch of the target gear allows Sensor Solutions to properly space the sensing elements for the best possible phase angle and to calibrate the internal back-biasing magnetic field to provide the best possible duty cycle so that the meter or controller can properly resolve direction. Although it is possible to produce a quadrature sensor that will accurately track direction with multiple gear pitches, there will always be exceptions where meters and controllers will not be able to properly resolve the direction.

Here at Sensor Solutions we want to ensure that the sensors we provide are always the best sensor for the application. This is why we build and calibrate all of our Quadrature Gear Tooth Sensors specific to the pitch of the gear being targeted.

If you need additional information related to selecting sensors and targets that best fit your application, we have multiple other Application notes in the index linked below. Or, you can contact Sensor Solutions Application Engineers by phone at 970-879-9900 or use the Contact Us form to send an email.

 

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