NorthStar Encoders Troubleshooting Tips
This troubleshooting guide was written to answer some common questions about our NorthStar encoder models.
RIM Tach® 6200 Tips
RIM Tach® 8500 Tips
Sensor Module Tips
Installation Tips
Signal Interpretation
Common Start-Up Problems
RIM Tach 6200 Tips
What type of coupling is best to use on the 6200?
The 6200 needs a coupling that allows for axial movement with little to no backlash. A stiff coupling with little to no axial movement is not recommended. This type of coupling will transfer the axial force on the 6200 bearings thus causing them to wear quicker.
Also, make sure that the shaft or stub shaft does not have any run-out. This also transfers a lot of wear on the bearings. If you are in doubt of the tolerances, connect the 6200 to your motor shaft or any other shaft that you plan to measure the speed of with a chain and gear, or pulley and belt setup as described in the 6200 manual.
Do not drop the 6200. If the unit lands with the shaft hitting the ground first, it will push the pulse wheel out of alignment causing the encoder not to function properly thus voiding the warranty.
RIM Tach 8500 Tips
A common failure mode for the 8500 is when the pulse wheel is not properly aligned with the sensor module. The first thing one should check is the depth of the pulse wheel with reference to the 8500 housing. The pulse wheel should be within .792 inch ± .010 inch from the surface of the 8500 housing. This can be checked with a depth gauge in reference to the depth holes in the 8500 housing as referred to in the instruction manual. To check for wobble, set a dial indicator on the outer surface of the pulse wheel. There should be no more than .007 inches of wobble on the pulse wheel. To check for run-out set the dial indicator on the surface of the shaft. There should be no more than .003 inches of run-out on the shaft.
To properly align the thru-shaft 8500 pulse wheel, simply align the pulse wheel alignment surface with the 8500 housing alignment surface. The set screw portion of the wheel should be just outside the 8500 housing area. The wheel surface and the housing surface should be flush as referred to in the instruction manual. If you have an end- of-shaft pulse wheel you may need to add or remove a shim sent the unit to get the pulse wheel within the .792 inch tolerance required for optimum performance. If the wheel has a wobble of .007 inch or more, make sure that the shaft is machined properly and that the wheel shim is perfectly flat. If the run-out on the shaft is greater than .003 inch, the bearings on the motor should be checked or the shaft should be machined to have zero run-out.
It is very important for brake applications when a thru-shaft encoder is being used to dimple or drill the shaft where the set screw engages the shaft. This is done to prevent the wheel from spinning on the shaft when the brake is applied. NorthStar also has special pulse wheels designed for high slew rate applications.
Do not drop the sensor modules or the pulse wheels. Impacts on either of those devices will most likely damage them thus making the warranty on the units void.
Sensor Module Tips
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 magneto resistive technology is impervious to water, oil, and other contaminants. Sealing the encoder to the outside world is not necessary.
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.
Installation Tips
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.
Signal Interpretation
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°.
