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Troubleshoot Encoder Signal Issues
This troubleshooting guide was written to answer some common questions about our NorthStar encoder models.
Do not remove the tape from the surface of the sensor module. The tape is used to protect the glass sensor from dirt and contaminants. Do not try to put a gasket or sealant between the sensor module the housing. This will only pull the sensor away from the wheel thus degrading your feedback signal. Our
If spacing is required to improve the signal, we have .005 inches shims that can be used to space the sensor module out away from the enclosure. This is only done when the C-Face concentricity is out of tolerance and one side of the encoder housing is closer to the pulse wheel than the other side.
Our sensor modules are rated for 80° C. The signal coming from the sensor will begin to degrade at temperatures higher than 80° C. This change may become permanent if the sensor remains at a high temperature for a long period of time.
Our 8500 encoder cannot be mounted on motors with large axial end play. These motors mainly consist of the General Electric 800 frame armor duty/mill duty type motors. General Electric's specification for end play for roller bearing mill duty motors is .109 inch to .172 inch. This is more than enough movement to ensure a loss of feedback signal. If an encoder must be used in this situation, use the 6200 and connect the encoder to the shaft with a belt and pulley, or gear and chain set up as described in the 6200 manual.
Be aware that if the 8500 is mounted on a fan shroud of a motor, it may be difficult to maintain the tolerances needed to make the encoder run properly. Even if these tolerances are met, over time the fan shroud could begin to sag and the tolerances could be lost.
Phase and duty cycle are very important in the quality of the feedback signal. NorthStar recommends the use of an oscilloscope to look at the feedback signals. This scope should be a 50 MHz scope or higher. If you do not have a scope, NorthStar's M100 encoder tester is a very helpful device in determining the signal quality of our encoders. It automatically computes the duty cycle & phase angle of a given signal. Figure 1 shows what the A and /A channels should look like on the scope. This also would be true for the B and /B channels. Figure 2 shows how the A and B channels should look together. This drawing also shows 90° phase shift between the two channels and the 50% duty cycle on each channel.
Figure 3 shows what the Z and /Z channels look like on the scope. The Z channel or marker pulse only occurs once per revolution.
The following drawings are examples of an unacceptable encoder signal. These signals may look very jumpy on a scope. In order to view them better, use the hold function on the scope to clearly view the signals. press the hold key on the scope and this would allow you to clearly view the signals. Figure 4 is a drawing of a signal with a duty cycle that is out of specification. Figure 5 is a drawing of a signal with a phase angle that is out of specification. NorthStar's signal specifications are duty cycle 50% ± 15% and phase 90° ± 22°.