# Spindle Speed Read Out In Mach3



## Transformer (Feb 13, 2016)

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


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## jbolt (Feb 13, 2016)

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


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## ch2co (Feb 13, 2016)

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


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## Transformer (Feb 13, 2016)

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?


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## Transformer (Feb 13, 2016)

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.


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## derf (Feb 14, 2016)

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.


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## JimDawson (Feb 14, 2016)

What are the specs on your sensor?  Is it fast enough to use as a tach sensor?


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## Transformer (Feb 14, 2016)

Jim:
I cannot seem to do a link to the specific page with the specs but they are on page 28 of this catalogue

http://www.automationdirect.com/static/catalog/images/product-pdf/PX-Proximity-Sensors.pdf

Switching frequency is 300HZ.  Model number is AK1-AN-3H. Not sure which of the spec items would give you the info on how fast the sensor is.


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## JimDawson (Feb 14, 2016)

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.


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## Transformer (Feb 14, 2016)

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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## JimDawson (Feb 14, 2016)

I think this is the one I would go with in your application http://www.automationdirect.com/adc...ion/Standard_Sensing_Distance_(8mm)/AE1-AN-1F

Note:  The above requires a 8mm Q/D cable, yours is a 12MM Q/D

This is the same specs as above with a attached 2M cable.
http://www.automationdirect.com/adc...ion/Standard_Sensing_Distance_(8mm)/AE1-AN-1A


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## Transformer (Feb 14, 2016)

Thanks, I will try it.  Dennis


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## JimDawson (Feb 14, 2016)

I should ask, what exactly are you connecting this to.  The question is because of the output.  Your original is NPN (sinking) output, as are to ones I suggested, but PNP (sourcing) is available also.


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## Transformer (Feb 14, 2016)

I am connecting into a Camtronics control unit which is based on a Gecko G540 drive.  My objective is to get spindle RPM readout, readout only not control, in Mach3 so I can do CNC threading, G76 command.


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## JimDawson (Feb 14, 2016)

Take a look at this thread on CNC Zone http://www.cnczone.com/forums/gecko-drives/112349-cnc.html

It looks like what you are doing now should work.  I'm not quite sure why yours is not working.


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## Jim_Hbar (Feb 15, 2016)

TR:

Inductive Prox's like your original choice can be a a real biotch to get working correctly - Been there, done that - got the tee-shirt. 
One challenge is that they can have significant hysteresis.. 

Please refer to page 96 to 99 in the catalog you linked to...  
It says that the target should be a square, with sides 3 times the sensing distance for the sensor, and there should be no other metal within a similar distance.  
Optimally, the target should swing 1/2 of the sensing distance from the face.

Your original prox. is a 8mm shielded, with a 8mm sensing distance. So it would take a big lump to make it work reliably, and you will have created a significant imbalance on your machine.  

The sensor Mr.Dawson linked to has a 1.5mm sensing distance, so will work much better - but be aware that you need to get it dang close to the target!!
Also, a flat-head or hex-head screw would be a better target than the pan-head that you have, and it should stick 5mm beyond the edge of the pulley.
Make sure your mount is rigid, and can hold the required clearance!!


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## Transformer (Feb 15, 2016)

Jim_Hbar said:


> TR:
> 
> Inductive Prox's like your original choice can be a a real biotch to get working correctly - Been there, done that - got the tee-shirt.
> One challenge is that they can have significant hysteresis..
> ...


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## Transformer (Feb 15, 2016)

Thanks.  Good stuff.


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