DIS incremental rotary encoders

DIS incremental rotary encoder is a classcial application of Hall effect discoverd by physicist Edwin Hall. It enables a contact-free measurement of an angular displacement from 0° to 360° without a mechanical stop. Unlike an absolute rotary encoder which gives an analog output linear with the angle of rotation, up to 360°, an incremental encoders gives A/B pulses indicating the rotation speed and direction.

At this moment, DIS provides QR30 series incremental encoders supporting up to 1024 ppr (ppr=pulses per revolution). New series with 4096 ppr is on our Roadmap for the coming years.

QR30 series

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Working principle

A QR30 incremental sensor works always with an external magnet. The magnet can be mounted on a rotating axle (on-axis), and it should be mounted at the back side of the sensor. The maximum distance of 3 mm between the magnet and the sensor provides sufficient space for mechanical tolerances under extreme conditions.

When you order a QR30 sensor from us, a magnet( 11,2 x 5,5 x 8 mm Neodymium/N35/nickel coated/remanention 1,2 T) is included. If you would like to replace this magnet to another, please read FAQ -> What kind of magnet works with the QR sensors?

Output explained

The QR30 incremental rotary encoder has a quadrature signal: A and B signals, which issue pulses(square waves) when the magnet is rotated, and phase delay between A and B is π /2. Together, the A and B signals indicate both the rotation speed (frequency of pulses) and direction of rotation (A leads B or B leads A). 

Many incremental encoders have an additional output signal, typically designated index or Z, which indicates the encoder is located at a particular reference position, but QR30 series dosn't have that.

Some encoders provide also a status output indicating internal fault conditions such as a bearing failure or sensor malfunction. Unfortunately QR30 series dosn't support it either.

For incremental rotary encoders, ppr (pulse per revolution) is used to describe the resolution, i.e. 1024 ppr = 1024 pulses per revolution. For example, a 1024-ppr incremental encoder that measures 360° has a quadrature output of 1024 pulses for both A and B. One pulse represent 0.35°(360°/1024=0.352°). 

You might think the resolution is 0.35° at first glance, but in fact, the sensor can provide position information with a resolution of 0.09°. That's because the sensor has a 12-bit internal chip, providing an output with a resolution of 360°/2^12=0.09°. Those two 1024-ppr pulses(A and  B) are actually generated by the 12-bit raw signals. 

When a higher resolution is demanded, a 1024-ppr quadrature signal (A and B) can be turned into a 2048-ppr signal with a logic ‘XOR’ function. The A XOR B signal doesn't contain the direction information, because you have only one signal, but the quadrature signals(A and B) are still available for direction detection.

! The XOR function is not available within the sensor and can be programmed in the application if required.

There are even circuits on the market to create a 4096-ppr signal with the XOR’ed 2048-ppr signal using both positive and negative edges (called ‘clock frequency doublers’)

Typical applications

• Speed measurement
• Motion control
• Valve control
• Robotics

Reference:

• Incremental encoders. https://en.wikipedia.org/wiki/Incremental_encoder
• Hall effect. https://en.wikipedia.org/wiki/Hall_effect
  
• Triaxis®: Unique sensing solution.https://www.melexis.com/en/insights/knowhow/triaxis-position-sensing-solution
• SIMPLE CIRCUIT DOUBLES INPUT FREQUENCY.https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3327.html