Choosing the resolution of a rotary incremental encoder

grandma.

“What resolution of rotary encoder do I need?” is a question designers often ask themselves.  A common mistake is that a higher resolution is always better.  This may or may not be the case.  Ultimately it is the nature of the application that decides.

Here are some things to take into consideration.

Cost
Higher line count encoders typically cost more.  Higher line counts require tighter disk to sensor alignment and air gapping, as well as, improvements in the light source and the associated electronics.  All of these factor in to an increase in cost as resolution increases.

Frequency Limit & RPM
It is important to note that interface electronics have a maximum input frequency that will cap the speed of the encoder.  You would like to use a 5000 line count encoder in a 6000 RPM application, but if the encoder or the interface electronics is limited to 200 kHz, you can’t as this combination of RPM and resolution is putting out 500kHz.
Quantum Devices has a standard frequency response of 500kHz over most of their rotary encoder line.

How does the math work out?
Sometimes it is more important for a programmer to be able to make their math work cleanly than possibly introducing rounding errors that could compound over time.  A 360 line count works nicely as one pulse equals one degree. A 3600 line count rotary encoder is popular for this same reason.

Does the performance of my application actually benefit from a higher line count?
Higher line count rotary encoders allow a drive or controller to make faster and more accurate decisions with regard to speed regulation, but much of that is application dependent. For applications that are running with a large inertial load, the added information from a higher line count may not improve the systems performance as there is only so much any motor can do to overcome the mass of the load.  Higher resolution may add information that can aid in the electronic decision making, but the system may not be able to respond any better than with a lower line count device.

A crude analogy and the reason for the photo at the top:

A race car driver can certainly out-drive my elderly grandmother when it comes to auto racing, but I bet they are both on even ground with a lawn tractor.  The race car driver has a much faster reaction time than my grandmother, but the lawn tractor cannot benefit from this, so the race car driver would be overkill for this application.

You can also see how my grandmother behind the wheel of a race car would limit the performance of the vehicle, much in the way that too low of resolution on a rotary encoder can limit speed regulation, acceleration/deceleration profiles and the precision to which a system can position.

Choosing the resolution that best suits your application is a careful balance between Cost, Frequency limitations, Math, and application limitations.

Quantum Devices Inc. is a leading manufacturer of Rotary incremental encoders. They can assist in encoder slection and can be reached at (608) 924-3000 or via E-mail

Advertisements

About Quantum Devices Inc.
Quantum Devices, Inc. (QDI) Barneveld, WI, was established as a Wisconsin corporation in October 1989, as an outgrowth of activities in the general area of optoelectronics. The main goal of QDI is to provide customers with a complete source for all stages of product design and development, starting from concept to a marketable commodity. These products include application specific Silicon Photodiodes, Optical Encoders and Light Emitting Diodes (LED) for commercial, industrial and medical applications. QDI's photodiodes and LED's are used in instrumentation for photosynthesis and photobiological research, biomedical and medical instrumentation for measuring blood sugar levels (glucometer), oxyhemoglobin and pulse rate (pulse oxymeter). One of the most dramatic products developed at QDI was the application of LED lighting systems for use as the light source for Photodynamic Therapy (PDT). Sales of QDI products include both domestic and international markets. Quality and reliability are very important concepts in maintaining our company wide commitment to overall product performance. Quality simply means continuous process improvement. We are committed to continually increasing our product excellence through increased quality and reliability. Quantum Devices, Inc. is ISO 9001 certified and the ISO Standard will provide the guidance for the vital function of maintaining our commitment to constantly improve our product quality. Quantum Devices is now proud to introduce it's new line of rotary encoders. Incorporating QDI's patented sensor technology, our QPhase™ Family of Encoders feature high resolution, increased frequency response and superior reliability over temperature (0 to 120 degrees C). QDI incremental and absolute encoders set a new standard and are backed by a 2 year factory warranty. We invite you to request an evaluation unit, additional information or price quotations. Mission Statement Quantum Devices is dedicated to the principle that light provides the power for all life on earth. We believe the quality, delivery and control of light is essential to the wellness of man and his advancement into the future.

One Response to Choosing the resolution of a rotary incremental encoder

  1. Sam Sharp says:

    Thanks for the article – I recently tried to make a case for using a higher resolution encoder in one of our products to which the response was “Well will it actually be any better?” – I inherently understood the benefits in terms of having more data to play with but was struggling to say it in a coherent/easy to understand manner.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: