Calculate RPM from analog inductive sensor

[maurlind]

Hi!

I have an analog inductive sensor hooked up to a rotating shaft that as a screw in it. I'm trying to get the RPM value from the shaft but I'm stuck. I have already implemented someone ells code here on the forum to calculate the total number of revolutions, but not the rpm. 

I know there is several ways of getting the values, I have tried to convert my analog signal (0-5V) to a digital square wave (0, 1) so I could then use pulse measurement or tone measurement to get the frequency (w=2*pi/T), with the frequency I can get the rpm. But I didn’t succeed with converting my analog signal to a digital one. 

I have also tried to use pulse management and tone measurement directly on the analog signal but I don’t get the right values, reason why is because there is some nose around 0V that the pulse measurement calculate as a frequency, I have tried filtering it away without success. 

And I have also tried to use FFT on my analog signal to get the frequency, but nor did I get this to work either. 

What I'm I doing wrong? Is there an easier way? I’m I on the right track at least?

Best regards Maurlind

[billko]

I'm not sure I understand your problem.  It seems to me you were successful at reading the RPM.  Is there another question?

Oops, I think you were explaining how you should be able to calcuate it and couln't actually do it.

[billko]

Unfortunately I only have LV 2013 so I can't see your VI.

[Hooovahh]

Here is a quick example that I posted on a similar question.

[Stuart.Parkinson]

Hi Maurlind. Well, at least some of what you tried should have worked somehow and it should be easier than this. What is your captured signal like? - a nice even waveform or full of noise? If Hoovahh's example doesn't help you, can you capture some of the raw waveform into a tdms file and post it so we can see what the signal that you are trying to analyse looks like. It would make it much easier to suggest a solution which can actually filter out and count the taco pulses.

Stu.

[maurlind]

Hi Stuart!

I will post som tdm files of the waveform that i get from my signal. Unfortunately I only have acces to my equipment on monday, so I will post it then!

Thanks!

Best regards Maurlind!

[maurlind]

HI !

Here is the  two tdm files and a screenshot of them. The one to the left in the screenshot is the filtered  signal with a lowpassfilter, and the one to the right is the raw signal.

Best regards Maurlind!

[crossrulz]

Why not just use a counter to measure the frequecy on the pulses?  That would be, by far, the simplest approach to this problem.

[maurlind]

Hi!

To use a counter, dosen't I need to have that kind of module? 

Since I only have a analog input module for my signal, I don't think I could use a counter.

Best regards Maurlind!

[crossrulz]

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@maurlind wrote:

Hi!

To use a counter, dosen't I need to have that kind of module? 

Since I only have a analog input module for my signal, I don't think I could use a counter.

Best regards Maurlind!

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What DAQ hardware do you have?  Many of the PCI/PXI DAQ modules have counters on them that you could use.