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03-24-2014 09:25 AM - edited 03-24-2014 09:26 AM
Dear All
I have an anemometer that sends digital signal. I try to analyse the signal to determine the wind speed.
I have a NI cRio 9024 and NI 9205. When I connect the anemometer, it gives me back voltage square pluses (see attachment). I wonder if I could transform this to readings of frequency because it is linear to the wind speed.
I tried to follow the link below, but my module does not have the Specialty Digital Configuration option
http://digital.ni.com/public.nsf/allkb/C9088DFDF803CD8B862575F3007C40FD
or I should have another NI module that could measure the frequency of the signal directly?
I would appreciate any ideas or suggestions. Thank you so much!
Labview Newbie
Solved! Go to Solution.
03-25-2014 04:17 AM - edited 03-25-2014 04:18 AM
Hi zhuleijia,
when you use an AI module you have to deal with voltage signals. But using a simple comparison will transform them into booleans…
- The pulse is only very small in amplitude. Is this intended?
- The pulse has an offset. Usually I would expect positive voltages from an anemometer… Did you check wiring and aquisition settings?
- To calc the frequency you need to count rising edges of your signal(s) per time unit.
- A DI module would be better suited for that task. Please call your local NI support for suggestions!
Du benutzt eine deutsche LabVIEW-Version. Kennst du das deutschsprachige LabVIEW-Forum?
03-25-2014 05:03 AM
Thank you so much for your answer, it turns out I connected it wrong. In fact all ports were sending the same wave, even the ones that were not connected. I will check the wiring and hope I can get some meaningful outputs. Thank you again!
03-25-2014 05:11 AM - edited 03-25-2014 05:11 AM
03-25-2014 05:45 AM
Dear GerdW,
thank you for the clearification. I have trouble with the wiring. I am not sure where I should connect the voltage supply and GND on 9205
I always connected the Erde(earth) to COM, tried many ways to connect the supply and GND (AI0/AI8, V1/C on the controller, AI0/AI1...) but none of them worked. I am sorry if this questions is too stupid.
Best Regards,
LV newbie
03-25-2014 05:53 AM
Hi newbie,
I don't know what kind of "supply" you want to connect to your 9205 module. It doesn't need any supply!
You have to connect the output signal of your sensor to any of the AI pins as wll as GND (or COM as it is named in the 9205 manual)! You surely want to measure RSE as shown on page 14…
03-25-2014 06:52 AM
The anemometer needs a power supply DC 4-18V. Thank you for the help throughout today. I really appreciate it.
03-25-2014 07:39 AM
03-26-2014 08:24 AM
Thank you for your answer, I found my mistake with the wiring and now I am able to see the square wave with different frequency at different wind speed.
However I failed to measure the frequency with Tone Measurements function or Extract Single Tone.VI. They only gave me 0, what did I do wrong?
or it is better to count rising edges like the link below
https://decibel.ni.com/content/docs/DOC-10885
Thank you so much
03-27-2014 10:15 AM
Hello iamnewhere
I am not sure what you are doing wrong but you could implement this calculation in the FPGA with different methods or in the RT implementing Math and Analysis VIs. You can find below a list with names of LabVIEW examples implementing different methods for those calculations.
You need to go to help>>find examples. You are going to see the "NI example finder" window, if you go to the second tab "search", you can type the names below.
You could use the "Analog Period Measurement.lvproj".
You could use the "FFT.lvproj".
You could use the "Period and Phase Measurement.lvproj".
All the examples above implement different techniques.
Please review this as well. Accuracy of the FPGA Math & Analysis VIs
Regards
Frank R.