ni-6211 pulse counter

[olds3800]

I am trying to use LabVIEW and an NI-6211 to measure the rpms of a small educational jet engine. The engine spins at a maximum of about 80,000 rpms.The RPM sensor is basically a 2-pole A.C. generator. For every revolution of the turbine the sensor outputs one complete sinusoidal output waveform. I am trying to use the 6211 to measure the frequency of this waveform. How am I to wire the DAQ and configure the DAQ assistant? I have read through the manual and some message boards but I am still confused about how to wire the sensor to the DAQ. 

[_Bryan]

I was recently trying to do something similar with a different card.  I was trying to use a counter but at low RPM the voltage was to low.  The sensor company makes an amplifier box that puts out a TTL signal that had to be ordered.  I am still waiting for it to show up.  You will also want to check the output to make sure the voltage does not go above 10 volts and do bad things to your 6211.

I would imagine that if your voltages are within limits you could just go into an analog in channel and use the extract single tone information.vi in signal processing > waveform measurements pallette to get the frequency.  Or see if the company sells a amplifier/converter that will put out a TTL signal that you can use with a counter.

[olds3800]

The voltage output should be about 4.5 VAC for 52000 RPM all the way to 6.89 VAC for 80,000 RPM. Thanks for your suggestions I'll give it a try.

[_Bryan]

If you are not worried about the bottom end you might be able to get away with the counter.  I just do not know what the max voltage for the counter is, but it would be much more accurate.

[Steve289]

Hello,

I'm thinking if you were to wire your generator output directly to one of your analog input channels and use MAX to monitor the voltage you would see the values you mentioned above.  You may have to use the continious mode and set the proper sampling frequency, I don't beleive the On Demand mode will be fast enough to give you accurate data.  The chart should display the sine wave output, and the number display should show the RMS value of your singal.

 If that works out, create a new Global Virtual Channel along with a Custom Scale that is based off of the linear line information that you provided (Y=11715x-719.67 / Y=RPM, X=Voltage) The voltage your channel is reading should be the RMS value of the Sine wave produced from the generator.  I'm assuming those values you mentioned are RMS values.

When you place your DAQ assistant on your block diagram, choose to aquire a voltage signal, and then choose the Global Channel you created instead of a physical channel.  The DAQ assistant should now be outputting RPM values based on your scale.

If my numbers are correct, your 80,000RPM generator should be outputting a 1.3Khz signal, a 10-20Khz DAQ rate should be more than enough to give you a decent signal.

Hope this helps, and that I am not completly off the mark.

Good-Luck.