Pepperl+Fuchs Blog

5 Reasons to Choose a Rotary Encoder

Posted by Robert Pasho on Thu, Mar 28, 2013

Instead of laser displacement sensors

When you’re looking for a solution to a problem or application, there may be a few different ways of solving it.  How do you decide which one to use? You usually try to find reasons for why you would use one device over another. I will give you 5 reasons why I would choose a rotary encoder over laser displacement sensors.

Rotary Encoders1. The rotary encoder is not affected by dirt, grease, oil, grime, and many other contaminants

This is the biggest reason why you should use a rotary encoder over a laser displacement sensor. The laser displacement sensor needs to “see” the reflector or target. Contaminants cause problems for laser displacement users. The recommendation that you’ll be given to solve this problem is a cleaning regimen as part of your maintenance and getting a sensor with more range, so it has “burn-through power.” The translation for “burn-through power” is that your maintenance personnel only need to clean it twice a week instead of once a week.

2. The rotary encoder is not affected by moisture and liquids

Most encoders have at least an IP54 environmental protection against splashing liquid from any direction. If there is splashing liquid or water condensation, the laser displacement sensor will false trip, give an error indication, or give an incorrect distance measurement. Any of these problems will cause your maintenance personnel to visit the laser displacement sensor again.

3. Vibration affects measurement of the laser displacement sensor

Vibration for photoelectric sensors in general can be a problem, but when you are going long range or need accuracy, vibration amplifies these problems. Most encoders can handle 10 g vibration and some heavier duty types can handle even more. Most photoelectric sensors can handle only 5 g vibration and anything over 1 g has an effect on the accuracy of laser displacement output. The amount of vibration would not be a concern for encoder accuracy. Your maintenance again will take a look at the laser displacement sensor and see how they can reduce this vibration.

4. Eye safety is a concern for laser displacement sensors

Laser displacement sensors may have a Class 1 sensing laser, but they definitely have a Class 2 laser as an alignment aid. With any laser, there is a potential for unsafe power to cause damage to someone’s eye. That may be your maintenance personnel who are cleaning the laser displacement lens, reflector, or trying to reduce the vibration.

5. Achieve better resolution and longer distance with a rotary encoder

The second biggest reason to select an encoder over laser displacement is that an encoder has better resolution, accuracy, and longer distance than a laser displacement sensor. Many long-range laser displacement sensors have a maximum range of 300 m. The encoder with a 200 mm circumference gear or wheel can have over 3200 m distance (with 14 bits) and resolution of 3 μm (0.003 mm) for 16 bits.  

Environmental protection, resolution, accuracy, maximum distance, and ease of use give me enough reasons to use an encoder over a laser displacement sensor. What have your experiences been with these types of products?

Questions about Rotary Encoders?  Get the Quick Select Product Guide

Topics: Rotary Encoders, Photoelectric Sensors, Laser Sensors

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