Best Practices for Building Mounts for Laser Measurement Sensors

How to Avoid Mounting Errors

I’d like to talk about mounting errors for a second.

Acuity sensors can be very, very accurate, and the more accurate the sensor is, the more work must be done to actually see that accuracy. But whether you have our most accurate AR700, with a ±0.95 µm linearity error, or AR2700 high-speed, long-range sensor, with an accuracy of ±60 mm, an error in mounting alignment can add significant error to your measurements.

The cause is something called a “cosine error,” and it can cause problems with any of our sensors. So much so, that everyone using our sensors should at least be testing for it. We have an article about the cosine error and the best way to correct for it–What to Do When Your Sensor is Askew–but I want to talk about the source of the error here.

No mounting solution is perfect. The position of each mounting hole has an acceptable error. The diameters of the mounting holes not only have errors, they must be bigger than the bolts mounting bolts or the bolts won’t fit through. The flatness of any mounting surface, the direction of the laser light that leaves the sensor, the bar you’re mounting your mount to, etc., etc. all have acceptable errors, and they all add up.

It isn’t worth your time or energy to try to eliminate every alignment error source. Better to get it as close as you can and correct for the rest, but there are certain mounting solutions that should be avoided if possible.

• Flexible mounts: Any mounting solution that is made to reposition an object quickly without tightening the mount into place (think of something like a snake light) will often slowly shift under the sensor’s weight or when vibrations (even footsteps) are present.
  • Choose mounting solutions where every joint is strongly fastened to each other.
• Plastic mounts: Not just plastics but any material that is likely to deform–anything with plasticity. Every material has a failure point, but materials like plastics never flex truly elastically, and the stresses of holding a sensor will cause them to deform over time.
  • Rigid metals are probably the best mounting materials, but depending on your application and accuracy needs, you can use other materials, like wood.
• Long mounts: Try not to put the sensor out on a limb. Mounting the sensor on a long mount introduces error. Not only can the long mount put stress on its own mount and cause movement, any vibrations will cause significant movement error moment-to-moment even if the mount never bends out of shape. Then there is thermal expansion. The longer the mount is, the more it will expand and contract with the temperature.
  • Sometimes longer mounts can’t be avoided, but in those cases, the mounting materials, the strength of the mount’s mounting, and vibration isolation become more important.

When it comes to precision and accuracy, an Acuity sensor is only part of the puzzle. The more precise you need your measurements to be, the more thoroughly sources of error need to be mitigated. Building good mounts and correcting for their deficiencies is one of the simplest ways to improve your measurements. In fact, for many applications, it might be enough on its own.

Regardless of your application and accuracy needs, Acuity’s sales team can help you find solutions for your company. Please email us at or call 503-210-5733 to speak with our measurement experts.