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Multi channel data acquisition and save


I have an measurement plan which I am trying to implement step by step. Till now using the forum and tutorials I am able to get single channel data and save it to a file. I am stuck at multichannel and related save options.

I am trying to achive is

The module with current input 4-20 mA is connected to humidity , temperature, wattmeter, and a flow rate meter all with current output. The daq assistant allow me to select multiple channel but after this step how to achive:-

1 have different frequency of data logging as flow rate is pulse output and rest is not. I plan to record every reading after 10 sec and being pulse i need to record flow cummulatively.

2. save  multichannel output to a single file with custom header and timestamp with dates.

3. I want this to run unattended and also alert for any error on the data sensor.



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Message 1 of 8

Hi rajcerc,


To clarify point 1, everything but your flow meter will be an analog input?



Joel I.
Applications Engineer
National Instruments
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Message 2 of 8

Yes, I have multiple sensors connected to my module all with analog current Input to the logger. I can get single channel input into waveform of eben write a file, however, I am struggling with multi channel. Also to add to to this I will have a pulse output flow meter to be configured to this.

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Message 3 of 8
I don't understand the struggle. When you start the assistant, there are instructions on how to select multiple channels. After the assistant is created with a single channel, you just have to click the Add button.
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Message 4 of 8

Thanks, I can get the multiple channel into the DAQ, The requirement being that I have to hook up a pulse sensor for flow measurement which need continuous recording and rest of the measurement are at constant intervals. I don't know how can I get the two data point simultaneously as DAQassistant has only one option of data capture for all channels. I read somewhere that we should not use multiple DAQass as they will fight for common resource. Keeping that as one need.

2) to save data continuously with appending to file like lmv format.

I am a starter so relying of examples but did not find anything very useful on these lines.


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Message 5 of 8
If you want to sample at a higher rate for one channel, you sample all channels at that higher rate and discard the extraneous ones. There is a decimate function that is handy for that.
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Message 6 of 8

What about the Pulse counter with module that have 8 current and 8 voltage inputs. If I pulses get 4 per ft3 of gas consumption and the consumption is dynamic with the load hence the frequency keep changing. What detecter block will be required to capture the pulse with time stamp. I believe I will have to save the two data separately as their time stamps will not coincide. I am working on the VI as suggested above and post it if required.

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Message 7 of 8

I worked this far getting multiple input and saving to one file following few examples. I still dont see any data being saved on the lvm file. Am I missing something.


See code attached

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Message 8 of 8