Measure RPM using NI USB-6008

[AlexCaud]

Hi

I'm having a problem connecting my DAQ Assistant to the fequency counter. The Introduction on this page http://zone.ni.com/devzone/cda/tut/p/id/7111 is very good but does not detail how to actually connect to my USB-6008 NI card channel PFI0 to the software. I have seen a few examples of block diagrams but they do not use the DAQ Assistant (Or do I not need to use it?). Please could someone explain in detail (with a block diagram) how to measure frequency. I have labView version 8.2.1.

Thanking you in advance

Alex

[Dennis_Knutson]

The 6008 counter input is only an event counter and cannot be used to measure frequency. See the manual.

Depending on what the frequency is that you want to measure, you may be able to use a analog input. Wtiht DAQ Assistant, wire the signal output to the Tone Measurements Express VI.

[oort]

Where is localed the "Tone Measurements"?

[Dennis_Knutson]

Assuming you used the search function on the functions palette and the search came up empty, then you probably have the base version of LabVIEW. the function is part of LabVIEW full or professional.

[vadajooz]

hi Dennis ,

I tried measuring frequency from an analog signal , aquired by a 6008 daq , via tone measurement  , with a desired RPM response.

switching a 0/12vdc , reaching Max 8v at the daq. And using a proximity switch picking up a signal from a bolt head on a shaft .

this worked fine when the signal was pulsing constantly . Got a nice response . The only problem was when the proxy was inactive the frequency shot up . Putting a graph on the input I found noise around 1v and the cause of the frequency to raise . I tried some filters , and a rlc circuit , no joy.

any suggestions ? Basically I need some way of only reading freq after  a rize of say 2v

thanks

[vadajooz]

OK IM sorted , I used a case structure , and a comparator ,

thanks for your tone measurement post !

[John_P1]

It sounds like you're good to go with Dennis's AI suggestion, but I wanted to mention another method just in case (or for anybody else who comes across this thread).  If the input signal is a TTL Pulse Train and you need to measure higher frequencies, there is another method that you could look into using.  See the example:

Software-Timed Frequency Measurement using Edge Counter

Essentially you count edges using the counter for a set amount of time (determined by OS clock) and use this to determine the frequency of the signal.  The longer you set the time window, the less effect that OS clock jitter is going to have on your measurement.  The method is more beneficial for higher frequency signals.

Best Regards,

[vadajooz]

I found useing the counter it never gave a accurate count , the count number jump many counts in one revolution  . i was switching threw a  n/v relay to give the counter pluses , also with a digital I/o once the RPM rose the signal kept getting lost .

I have posted this question in the signals forum

[sombudhya]

hey can u please upload jpg pic of ur block dia...am currently working on that. Your support will be appreciated.thanks

[vadajooz]

Hi , that was a long time ago ! I never actually got it towork with any satisfaction . I ended up using a high speen counter on a plc .