Exactly why do magnetic encoders have higher inherent reliability, and what do the reliability numbers really look like?  Let me explain why they are reliable, and it’s not just because they can handle dirt and debris in the air gap.

There are some other inherent factors:

• Magnetic encoders are a system on a chip. The one sensor chip takes in the magnetic field and does all processing right to the output signals. Other technologies often require multiple chips (optical) and/or extra wires (resolvers) or even separate sensor and processing chips. One chip means less component and interconnects to cause problems.
• One tough magnet. The magnet is robust compared with a delicate optical disk. Timken sensor magnets are being used in the harshest environments, where an optical disk would never perform.
• Works in high temperatures. Both the chip and the magnet are inherently shock and vibration resistant and easily handle temperatures up to 125 C or more. Designed for high temperatures, which means lower temperature operation is no challenge at all.
• Allows larger tolerances without failure. Reliability is determined not just when things go right, but when things go wrong as they often do in the field. This means when tolerances aren’t met:  axial, radial or other. Timken sensor-to-magnet tolerances are much larger than those of both other magnetic technologies and optical sensors. The sensor-to-magnet tolerances are forgiving and handle the job much better when things go wrong. This means higher reliability for the entire system.
• Outstanding track record. There are over 12 million Timken sensor chips in the field, most of which are automotive. Timken’s MPS160 sensor has undergone the rigorous automotive AECQ100 qualification. The qualification is severe and thorough, pushing components beyond their specified limits. The actual accepted die failure rates are in the low single-digit PPM range, an impressive track record.

So what are some of the applications that really test the reliability?  Here is a sample of some of the harsh applications it is being used in:

• Mining trucks
• Tractors
• Farm equipment
• Off-road transmissions
• Robots – civilian and military
• Box-making machines

When you look at all the factors that make Timken’s magnetic sensor technology reliable, why take a chance?  Go with Timken magnetic encoder technology.

Questions?  Call me at 603.358.4737 or send me at email at [email protected].  Please join our LinkedIn Group to continue the discussion.

A. John Santos, Chief Engineer for Sensors

Let’s say your motor needs a rotary encoder to provide feedback to a controller. Which would you choose: a magnetic or an optical encoder?

In the past, an optical encoder might have been your only choice. Today, you have a second option. Magnetic encoders – once reserved for high-end process-industry applications – are now cost effective for virtually all encoder applications.

Magnetic encoders have benefited from overall advancements in integrated circuit technology. There is a wide range of Hall effect-based high-resolution encoder chips, modular encoders and kit encoders on the market.

Magnetic Encoder Advancements Outpace Optical Technology

The decision to use optical or magnetic technology for your next sensor will likely depend on the environmental and mechanical characteristics of your application. Magnetic encoder technology advancement has been outpacing optical technology for years. This has led to significant improvements in performance and pricing. While optics used to be the only choice for resolutions greater than 1,000 PPR, there are now 1.5 in. modular magnetic encoders and encoder kits available with up to 8,192 PPR.

Optical Encoders: How They Work

Traditional optical encoders have a light source, two or three light sensors, and a glass, metal or plastic code wheel placed between the light source and the sensors. These are the only functional components of an optical encoder. The other components you might find are used to keep contamination like dirt, dust and condensation out of the optical path or used to precisely position the optical disk in the working range between the light source and light sensors. A typical recommended tolerance range for an optical disk is +/- .003 in.

Traditional optical encoders have the optical components packaged in a sealed can with the code wheel precisely positioned using two ball bearings.  The packaged encoder is mounted using a shaft coupling or, in the case of a hollow shaft encoder, using a flexible tether. The housing, bearings and couplings are often the largest and most expensive parts of the assembly.

Magnetic Encoders: How They Work

Modular magnetic encoders can offer the same standard resolutions as optical encoders with greatly improved resistance to environmental conditions such as dirt, dust and humidity. Magnetic encoders consist of a system-on-a-chip encoder chip on a PCB and magnetic target wheel that is set to run with an air gap of between .020 in. and .060 in. above the PCB.

Magnetic encoders typically have much more lax assembly and shaft end play requirements. The ability of magnetic encoders to perform well over a wide range of assembly tolerances have eliminated the need for bearings in most magnetic encoders. This in turn has resulted in eliminating failure modes, lowering component cost and reduced overall axial length may applications.

Maybe the benefits of using magnetic encoders over optical encoders have captured your attention. They have greater durability and reliability, an ability to withstand harsh environments, higher vibration and shock tolerance, withstand higher temperatures, come with much larger gap tolerances and come in compact packaging.

But motors and many industrial environments have high magnetic fields. What happens to a magnetic encoder when it is used in a high magnetic field?  Are any of the advantages or its performance compromised?

Most magnetic sensing technology is differential. The sensor detects the difference between the magnetic north and south poles. Stray (common mode) magnetic fields are cancelled. At Timken, we’ve tested the quadrature signals to more than 800 gauss common mode field.

Some magnetic encoders do appear to handle stray fields better. Look at the chart below for a comparison of some of the leading magnetic sensors/encoders on the market that we have tested. Only two of them show no effect from the stray magnetic fields – see the green and blue lines. (The Timken encoder is the blue line at the bottom). In fact, Timken sensing technology is successfully buried inside motors on a regular basis where there are large magnetic fields.

Magnetic encoders have a number of advantages and stray magnetic fields won’t compromise the performance if you’ve chosen the right one.

Magnetic encoders from Timken offer the highest accuracy and are resilient in the most challenging environments, including those with high magnetic fields. Questions? Reach me at 603.358.4760 or send me at email at [email protected].