Spindle DRO not reading correct RPM.

[Zadig]

I’ve been using UCCNC for a few years now on my mill and very successfully, I like it a lot and can’t fault it. A couple of years ago I put a Hall effect sensor on the spindle and coupled it up to the software. Whilst I can see the correct RPM in the ACT DRO I’ve never been able to get a programmed S# to match the ACT, it has always been out by a couple of hundred RPM here and there. When going from say S1000 to S5000 the difference between the inputted S# figure and the ACT is not always the same difference. I’ve lived with this as for what I do the software is excellent but I have spent hours trying to put this right and it would be nice to have it functioning pretty much as it should. If anyone can point me in the direction of where I might look I would be most grateful, cheers.

[Zadig]

Not even a “read the manual”?

[dezsoe]

You didn't mention how you control your spindle. Usually, the read speed is correct if the speed signal is in the range that the sensor and the inputs can handle.

[Zadig]

I’m using 1 - 10v to control an inverter. I’d be happy just to get in the ball park of the true reading from the sensor whereas at the moment I’m about 200rpm adrift, sometimes more, sometimes less dependant on s# figure programmed. If I knew where to look at what the issue might be it would be a great help. I’ve come back to the problem over the years to try and sort it but never got any further. I’ve kinda disappeared up my own backside looking for the answer, not a lot makes any sense any more and much has been forgotten. Again any clues on where to look would be helpful and thanks for your input.

Mike

[MikeM]

Measure the actual spindle rpm with a non-contact tachometer, that will tell you whether you have a sensor calibration or an inverter setup issue

[dezsoe]

Also, check the voltage on the analog input of the VFD when setting different speeds. It should be proportional.

[Zadig]

Thanks Guys, I’ve just broken my machine down from a job, I’ll take a look.

[Zadig]

Ok, first of all I’ve checked the Hall effect sensor output from the spindle with a known good tachometer and it reads the same. It was a good point and needed checking, cheers.

Here are some samples of programmed speeds and the ACT DRO read outs.


S#. ACT DRO. Difference
500. 712. 212
1000. 1180. 180
1500. 1691. 191
2000. 2214. 214
2500. 2748. 248
3000. 3272. 272
3500. 3800. 300
4000. 4328. 328
4500. 4856. 356
5000. 5270. 270

Question? Am I likely to see much from reading the analogue input voltage? The difference is relatively consistent within 100 rpm or so and I would think that would be difficult to detect with a meter looking for linearity. I’ll go now am measure just to see what readings I get but I thought I’d post these in case someone can see something glaringly obvious. Thanks for looking, Mike

[Zadig]

I’ve checked the 0 -10v going into the inverter and it’s as linear as I can make out. It’s a few years ago since I put this machine together and because it gives me no problems I’ve forgotten a lot of what I have done so I’m having to re-acquaint myself with how it went together and the config. It is a Santerno vfd of the sinus range.
One thing that is obvious to me is that I have a reduction between my 7hp spindle motor and the spindle itself. I have tried to use the “pulleys” setup in setup but it has never seemed to work. No matter whether I tick the pulleys check box or not the result is the same. The same thing happens when I alter the pulley ratio, nothing happens. It makes perfect sense that this will have an impact on the output speed. Can anyone tell me if I’m correct in this approach and if so what am I doing wrong. Cheers, Mike.

[dezsoe]

Hi Mike,

Please, upload your profile for checking.