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Pulse Counting on an Anemometer


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3 replies to this topic

#1 HgInNY

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Posted 25 June 2013 - 01:21 PM

I recently purchased a U3 and a Young anemometer model #05305. Using DAQfactory and the U3 I have been able to get wind direction working well. My problem is with the pulse counting from wind speed. The anemometer outputs an AC sine wave that has a frequency and voltage proportional to wind speed. I can get the counter to work in DAQfactory but it doesn't seem to respond to small inputs. I sample every ten seconds and unless the prop is really going I seem unable to get an increase in my number of counts. The spec sheet for the anemometer shows a threshold of 0.4 m/s which converts to about 3.9Hz. Over my sampling period then the smallest increase in counts I should get is ~40. Is it possible the voltage output is too small to register with the counter? It should be in the range of 60mV at 4Hz. If I interpret the input as analog with a fast sampling rate I seem to be able to get some good looking peaks. So my question really is, why isn't the counter registering the inputs?

#2 LabJack Support

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Posted 25 June 2013 - 01:40 PM

You mentioned the problem that you are having, "Is it possible the voltage output is too small to register with the counter?"

Counters are digital I/O lines and require that the voltage level oscillate from below a specific logic voltage level and then back above it. When this is happening repeatedly the LabJack counts the number of times it has crossed. You need a signal that gets below 0.8V (reading as logic low) and above 2V (reading as logic high). This specification is menioned in the U3's users guide under the Digital I/O, Timers, Counters section:
http://labjack.com/s...uide/appendix-a

#3 LabJack Support

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Posted 25 June 2013 - 01:59 PM

Here is a related topic also with an anemometer:

https://forums.labja...?showtopic=4420

For a bunch of other related topics, search labjack.com using the term "comparator":

http://labjack.com/search

#4 HgInNY

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Posted 27 June 2013 - 12:18 PM

I added an old op amp as a comparator on a circuit board and it appears to work right. Thanks!


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