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Difference frequency

Hello everyone

 

Would you please help me with below problem: 

 

I have a velocity sensor with two tachometer sensors(measuring rotation) that I installed on a rotary disc.

velocity sensor frequency is : 8.37

Tacho frequency are : 7.88

 

These two sensors installed on the same disc, but I don't know why I have difference frequencies?

I checked velocity sensor with second tachometer but I have the same result.

I also checked frequency of these two tachometers with each other and they were ok,

I attached my Vi program to see if there is any error.

 

velocity sensor is a relative not absolute so it doesn't need calibration.

My DAQ is 6009.
What do you think?

Did you have any problem like this before?

I attached my  " Vi " and photo of result.

 

Thank you for you time 

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@Sml2010 wrote:

velocity sensor is a relative not absolute so it doesn't need calibration.


If you measure velocity on a disk, the radius where you measure the speed is greatly significant when calculating the rotational speed of the disk...

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Thank you for your reply.

Yes, but the sensor doesn't sense by changing the rotation of disk. I mean measuring the signal is freeze.

 

Please look at attached picture: 
for 600 RPM = 10 HZ
I only have 8 picks instead of 10 picks and by increasing or decreasing the RPM, The sensor shows me only 8 picks with different amplitude, so not any changing in number of picks for different frequencies.

 

Why do I have a fix detected frequency?

Why the number of picks are fixed for different frequencies?

 

I attached the vi too.

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If the tachometer and the DAQ input use the same sensor, the only thing I can think of is that you use the wrong channel.

 

At least make sure the signal disappears if you disconnect the sensor. And if it reappears when you reconnect the sensor. If this doesn't change your signal, you're sensor is not wired correctly, or you're using the wrong channel.

 

Are you sure your setup (RSE) is how you wired the sensor? (Difference Between Differential, RSE, and NRSE Terminal Configurations - NI)

 

I don't know what to expect from this kind of signal, but it looks noisy. Any change you can wire an oscilloscope?

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