Frequency measurements off USB 6009 digital in

[Adrian_S.]

I am fairly new to using lab view, but there has to be an extremely obvious answer to this I haven't found it.

I have a digital reference signal from an optical chopper that controls some other functions of my setup, but I want to know the frequency of the digital signal with some degree of error would be nice as well. I am using lab view 8.5.

[johnsold]

I think that the digital I/O on the USB-6009 is software timed with a maximum rate of about 150 readings per second.

This means that it is almost unusable for frequency measurements unless you can measure the frequency with a calendar.

You might be able to use an analog input (which can sample up to 48 kS/s, I think). You could then analyze the data collected to get a frequency.

Lynn

[Adrian_S.]

My frequency range is 10Hz-80Hz so that should not be an issue.

[johnsold]

You could use the analog input for that range.  The digital input would not work at the higher end of the range because of the Nyquist limit and because the timing jitter would make it rather difficult to actually determine frequency.

Lynn

[Adrian_S.]

I don't terribly care about the higher range of frequencies. I constructed a program that will count and then divide by time, but that will not tell me if there is any variation between pulses or error in the frequency. I would like to keep the digital becasue other wise I will be rewriting the section of my program that opperates off of the digital reference signal coming in.

Adrian

[Greg_S-Video]

Hello Adrian

Thank you very much for choosing National Instruments!  Lynn has provided some excellent advice on this matter.  If you are interested in more accurate readings, perhaps you may consider a more accurate device such as the USB-6210.  NI USB-6210  This device has digital inputs.

You can see more of our devices here:

USB Multifunction Data Acquisition (DAQ)

The USB-6008/USB-6009 may not be as robust as you need for your accurate measurements.

[wolfp]

Hello Greg,

I have USB 6210 DAQ and going to measure pulses frequency around 10 kHz and 50% duty sycle using analog inputs. The reason why I'm not using counter inputs is because I need multiple inputs (up to 8), but DAQ has only 2 counters inputs. I can't find any example for this application. Please advise.

Thank you

Wolf 

[SnowMule]

I would definitely recommend using an analog input for this, not only for the accuracy but also for code simplicity.

Take a few (thousand) samples over half a second or so and read in that analog waveform.  Use the Waveform:Analog Waveform:Waveform Measurements VI's to extract frequency information from the acquired signal.  The tricky stuff to code has already been done for you 🙂

[Greg_S-Video]

Hello wolfp

Thank you for posting to our forums!  Have you considered any of the examples included in the National Instruments Example Finder?  This can be accessed by clicking "Find Examples..." under "Help" at the LabVIEW splash screen or by accessing the "Help" drop-down menu in a VI and clicking "Find Examples" in the third division.  Which version of LabVIEW are you running and what is your operating system?  Has any of the other information provided by our esteemed forum users been of assistance?  Please update me on the status of your issue so that I may proceed.  Any other information you can provide me on your issue would be much appreciated.

All the best!

[wolfp]

Hi Greg,

Thank you for your response.

I have LabView 2010 and XP operation system. Currently I have USB 6009 DAQ and got notofication that it's not supported frequency measurement for analog input configuration. So I ordered USB 6210 DAQ from NI and expect it delivery next week. Can you please tell me wich example I've to use for this application?

Thank you

Wolf