Spindle Speed Read Out In Mach3

T

Transformer

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With a lot of help from this forum I finally got my proximity sensor to give a read out of spindle RPM which appears in Mach3. However the reading is not stable. Running the spindle at 100 RPM I get readouts in mach3 of 1/5, 1/4, 1/2 of actual spindle speed, and occasionaly an accurate read out. I have a small bolt epoxied to the pulley and the proximity sensor does seem to flash on every revolution, that is the flash seems regular but the read out in Mach3 is not stable. I have moved the sensor in and out, up and down but I can never get the read out in Mach3 to be stable for more than about 4 seconds. I also put a small magnet on the end of the bolt head to see if that would give me a better reading, but as far as I can tell it made no difference. I am open to all suggestions as to how I might go about tracking down the source of this problem. Thanks.

Transformer

DSC01304.jpg
 
My experience with proximity sensors on my mill for the homing switches is to use a large flat head and set the sensor gap per the manufacturers recommendations. I think the slotted button head screw is most of your problem and the gap looks too large. Also it looks like the sensor may be overlapping the pulley.

Jay
 
Transformer:
Are you by any chance running a VFD. The high frequency produced by many VFD's can make many of the after market tachs inaccurate and sporadic.
I don't know if this would be the case with the Mach3 implementation or not. I had to add a filter to the power line to the tach assembly.


CHuck the grumpy old guy
 
Chuck: Yes I am running a VFD. The sensor I am using gets its power from the controller, so I assume power to the sensor is 12-24 volts DC. Do you think the VFD would still interfere with the signal?
 
The only other thing I would mention is that the only way I can get any readout of spindle RPM is to set the debounce levels in General Configuration to zero. Any thing other than zero and the RPM counter in Mach3 just sits unmoving at zero. Also I did try moving the cable from the controller to the proximity sensor as far away from the VFD as possible but that did not seem to make any difference.
 
It could be a vibration problem. I had the same thing happen on mine when it got past about 4000 rpm. The problem went away after I mounted the sensor bracket in rubber.
 
What are the specs on your sensor? Is it fast enough to use as a tach sensor?
 
300 Hz is the number I was looking for. It's slow, but should be fast enough. Try using a longer tab. In other words, attach a piece steel sheet metal, maybe an inch or long to the screw to get a longer pulse. Make it as wide as you can fit into that area. Maybe even a fender washer on the screw would work. Looks like it needs more mass. That's a pretty big sensor for that application.
 
Jim: Thanks for the suggestion. I replaced the bolt with a 30mm strip of sheet metal bent to the contour of the pulley and glued on. A slight improvement as the correct spindle speed would hold for up to 10 seconds and then resume its 1/10th, 1/4 and so on of true speed. Then I reread your post, "mass" so I stuck on a large nut to the pulley. Again a slight improvement as this would also hold correct RPM for about 10 seconds.

At this point I think I will try a different sensor. Any recommendations?

Thanks
 
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