Read tach signal using DIO to measure RPM

[dacad]

I have a brushless motor with a pulsed tach-out signal (2 pulses per revolution).  I will be running 5 of these on test and desire to read the speed at regular intervals during the test.  I only have one counter available but in conversation with a consultant, was told I may be able to read the tach signal with a DIO channel.

I am operating with a PCI-6221 card with an SCC-68 right now. (The other counter I am using to control the digital PWM input on the motors as I can use one counter for all 5 motors)

If anyone is aware of a method to accomplish this, I would very much appreciate some assistance. This type of programming is a couple levels above my current capabilties.

Thanks....    Doug

[MattBradley]

I would recommend trying to do the measurements you want in MAX first -- then you know more about how you want to do it.

In LabVIEW, it would be a matter of either using a loop to get a set  of data (say 1 seconds worth -- set up with the DAQmx functions), counting the number of pulses, and then figuring out the speed.  So, which part(s) do you need help with:

1) DAQmx setup

2) The loop

3) Retrieving DAQmx data

4) Counting pulses

5) Figuring out speed

[dacad]

[I would recommend trying to do the measurements you want in MAX first -- then you know more about how you want to do it.]

I am actually doing that.  I have one task using /port0/line4 on dev6221 and configured with continuous signals. I don't know if this will work or not but the problem is figuring out what type of clock settings to use.

A second task I am working with uses /ctr1 set to "rising edge" and "1 counter" method.  I obtain a measured value with this method but it doesn't equate to the actual speed of the motor.  I am using an LED strobe to verify true motor speed.  I am also not sure how to verify what counter timebase rate is being used.

Thanks...   Doug

[ziasaga]

Hi Doug,

Did you able to solve your problem? I have the similar kind of problem of measuring RPM data from encoder. I only get single RPM value not continuously. We can also discuss about it if you want.

Thanks, Zia

[dacad]

Hi Zia,

While I am able now to obtain a tach reading using one of the counters on the DAQ device, I still have not been successful using just the DIO. 

This is the code using the counter.  The Task uses a Counter channel for Frquency.   I set it for 1 sample on demand, Rising edge and 1 Counter measurement method.  It took a little trial and error for the multiplier to get the actual speed as it wasn't obvious what daqmx was using for internal timebase.  If needed, I can post a screen capture of that set-up as well.  This vi needs to run continuous.  I used a meter on the front panel with the additional numerical readout to give it a little jazz.

I have not been successful using a DIO yet and am still working that off and on.  I would like to be able to have five independent tach inputs for running multiple units on a life test. I will be trying some more next week and if/when I am succesful, I will certainly post.  If you have any ideas, I am open to try different things.

Thanks....    Doug

[ziasaga]

Hi Doug,

I am using laser tacho with 60 pulse disk and inputting it into PXI 4472B analog channel. I will try your NI for my purpose. Can you send LabVIEW NI of it?

I tried analog Tacho processing sub-pallette, but getting wrong speed profile. How did you set tacho into your motor? What type of tacho are you using? Waiting for your reply. Thanks.

Regards, Zia

yahoo

[tektronix]

Hey Kudos

Do You know how to make a counter with Labview, I am struggling. I know the post is from 2009 but I hope you have a solution for it.