Servo Motor Encoder Testing

We recently received a request for encoder testing help. The following is what transpired:


“Bill from Warwood gave me your information and thought you may be able to help us with testing encoders. We have a customer who claims that his encoders aren’t working correctly. I was not able to see the motors during dismantle but after looking up the information on the encoder I saw the air gap between the encoder and the magnetic wheel is very strict. I’m almost sure that was the problem with both of the ones that came in but I want to be able to test the encoders by using an oscilloscope and dc power supply as soon as possible so I can order new encoders if needed. I would like to know the best way to test them so I can make sure they are giving the correct output signals. Also, I would like to know if there is a controller that we can connect up to the encoder while the motor is running so I can make sure it is sensing the correct speed. The type of encoder we have is a Leonard Bauer GEL2444T-1G5K250E. I have attached the pdf if it is any help at all. We are all new to testing these kinds of things so any input would greatly be appreciated”.



“The instructions on page 29 of the manual are fairly straight forward for testing the output. Simply apply 5 volts DC to the red and black wires and check the output voltage of both phases. They should be very close to 5 volts and a clean square wave. If your signal is in any way distorted or voltage is low, you probably have an issue with the air gap. The manual is very specific about the gap required at either .15mm or .2mm depending on the model that you have. I don’t know of any controller that will test the pulse, although the Mitchell system may work for this. I will leave that to Jason to answer for you on Monday.

I hope this helps. Have a great weekend”.



“Kevin explained the testing pretty well, I don’t think I can add much more to it. The air gap is very critical and can cause issues if not set correctly as explained in the manual. It did give an air gap spec depending on your model but I didn’t see where it gave a target output amplitude after setup. As an example GE Fanuc gives an amplitude spec of .66-.93 volts for the A-B signal and 1.08 volts from the Z (or index) signal. I like to adjust the air gap until it meets this spec which can be anywhere from .006-.10.
As far as a controller to test the pulse to guarantee it will work when installed, I do not know of one better than running the motor on the controller/amplifier. It will run when getting to your customer. They can be tested on the Mitchell system as long as they have a Z (or index) pulse but that wont guarantee proper function for the end user as the controller may look at the signal a little differently.

Let me know if this helps”.

Senior Servo Technician


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Servo Motor Repair at RepairZone


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