How to take in an analogue signal and discard the data which is not required from the signal

[c lees]

I am using Labview to take in two signals from a DAQmx board.  I am taking in a analogue signal from a sensor and also a quick on/off pulse from the sensor as well.  I have the DAQ express VI taking in both the signals and combining them into one. I am creating an image from the data via a reshape array, although the data which is going to the image is full of samples which i dont need and i need to be able to use the samples between the start pulse going on and off again.  So how do i take lots of data but only use part of it, can i use a basic subtract function on it or .....?

Thanks

C Lees

[devchander]

In LabVIEW

Find Examples>>Hardware input output>>DAQmx>>analog measurements>>Voltage>> yopu will find Acq&Graph Voltage-Int Clk-Dig Start.vi

This example demonstrates how to acquire a finite amount of data (Waveform) using an internal sample clock, started by a digital edge.

This should satisfy the initial part of your requirement.

To be honest, I had not come across a case where I had to stop acq based on a reference Digital pulse.

So I am not sure how to stop acq using the same digital pulse

Maybe you can monitor the same digital start pulse on a seperate DIO line and use it to stop acq loop.

And logically thinking,  you must have a check in your program wherein the initial 'off' state itself does not stop your acq loop, even before your acquisition recieves the 'on' start trigger.

Hope this helps

Regards

Dev

[Sarah_Coleman_NIUK]

Hi C Lees,

You should be able to do this but not with the DAQ Assistant. You can use a type of trigger called a pause trigger to pause the acquisition at certain points.

Could I just clarify a few things? Do you want to acquire all the data, save it but only format some of it into an image? Is it ok to only acquire the data that you need, ie the data when the digital pulse is on?

I'll put some example code together for you to demonstrate this pause trigger. This feature is only available with the lower level DAQmx functions so you won't be able to use the DAQ Assistant. If you post your code I'll try and write an example that includes the parameters you need.

Regards,

[Sarah_Coleman_NIUK]

Hi C Lees,

The attached code demonstrates a pause trigger. It's set up to acquire a single digital value on Port1/line0. This line also corresponds to PFI0 on the DAQ card which is in turn being used to gate the analog signal.

The way it's currently configured, the measurement pauses when the digital line goes high. Have a look at the code and how it is configured etc. Let me know if you have any questions.

Kind regards,

[devchander]

Sarah,

Could you plz post a pic of the block diagram too?

Dev

[Sarah_Coleman_NIUK]

Here you go Dev

Message Edited by SarahB on 08-16-2006 06:20 AM