SignalExpress

cancel
Showing results for 
Search instead for 
Did you mean: 

Measuring Frequency with NI 9402

Solved!
Go to solution

Has anyone successfully been able to measure frequency in SignalExpress with the NI 9402 module? I have the 9402 connected to a tachometer (on a centrifuge) that puts out a TTL signal. Right now I can get the line input light to work. (Right click Project, Acquire Signals: DAQmx Acquire: Digital Input: Line Input.) When the tach completes the first round, the light or "blip" comes on indicating the sensor then goes back off during the remainder of the round. I would like to read the frequency of this "blip" instead. I cant seem to figure out the settings required in Signal Express. I have tried (Right Click Project, Acquire Signals: DAQmx Acquire: Counter Input: Frequency) but maybe I do not have the correct settings. This centrifuge usually runs between 0 and 3 hz. I attached a picture of what I have. Am I doing this correctly, with incorrect settings? Or is there a better way to accomplish this? I need to read Hertz over time. Thanks!

0 Kudos
Message 1 of 9
(8,266 Views)

Hi Choover,

 

If you would only like to measure frequency, you do not need to configure a digital input task along with your counter frequency task.  I have been able to get a counter frequency task to Run Continuously in 1 Sample (On Demand) mode and record the data for as long as I need.  To do this you can select the Record checkbox under Signal Selection in the Recording Options Tab.  Just make sure you connect your signal to the 9402 as shown in the connections diagram.

 

 

Brian

Brian G.
0 Kudos
Message 2 of 9
(8,258 Views)

I get an error, Logging Stopped because an error something - I attached photo. Also, I get a timeout error. Are my settings correct?

 

Edit: Fixed that error by doing what they had said. Now im just getting the Specified operation did not complete because the specified timeout expired. Im thinking my settings or sample rate may be wrong.

Download All
0 Kudos
Message 3 of 9
(8,255 Views)

I just noticed under starting edge (rising) it says: Connect your Signal to (Input Terminal) PFI1. I currently have channel 0 selected and the data is plugged into channel 0. I decided to unplug and plug it into channel 1 (even though my programming is still at channel 0), and data started flowing. I have no idea why, but that seemed to fix the problem.

0 Kudos
Message 4 of 9
(8,244 Views)
Solution
Accepted by topic author Choover

Hi Choover,

 

Although you are using counter 0 to measure frequency, your singal acts to gate the onboard clock source to measure the period (and hence frequency).  This is why you need to use PF1 to connect to the counter gate.  You can find out more about how DAQmx performs counter measurements in any cDAQ chassis user manual:  http://digital.ni.com/manuals.nsf/websearch/2C061605E17C7D04862578D200677B90

 

9402 Counter Terminal Defaults.PNG

 

 

Brian

Brian G.
0 Kudos
Message 5 of 9
(8,241 Views)

Interesting. That explains it for me. I appreciate your help Brian. Lastly, any quick way to convert this signal to G's? I am currently reading Hertz, and I know I would need to insert a variable (which would be a length). Just curious if this is possible in Signal Express. Thanks.

0 Kudos
Message 6 of 9
(8,239 Views)

Centripetal acceleration is (ω^2)*R. Depending on how you are measuring frequency, you can use a Processing>>Analog Signal>>Formula to do this calculation.

 

Brian

Brian G.
0 Kudos
Message 7 of 9
(8,236 Views)

Dear All

 

I have plotted waveform graph frequency vs amplitude of real time signal. I am using measurement computing USB1208FS. I used fft.vi to plot the graph and get the waveform which is attached. On X-axis frequency is form 0 to 0.49HZ. But I want to increase that from 50 to 500 hz. When X-axis scale is in auto select mode then it automatically adjust to 0 to 0.499 hz. When I deselect autoselect mode and edit x-axis from 50hz to 500hz then no waveform comes on display. I have set the sapling rate of 1024 and count of 500. Please guide me how can i get the desired waveform graph.

 

The waveform which i plot is shown in attch1 and my desired waveform is shown in attach2.

 

 

 

 

waiting for response

 

Kind Regards

Urfee

Download All
0 Kudos
Message 8 of 9
(8,168 Views)

Again.  Wrong forum.

 

Create a new thread in the LabVIEW forum.

 

Asking the same question scattershot in all the wrong places is going to do nothing but irritate the people who you are hoping will help you.Smiley Mad

0 Kudos
Message 9 of 9
(8,160 Views)