Voltage influence of a channel on other channels

[Abo_Rashid]

Hi Everyone,

I am using an Omega data acquisition device that measures mV signals, OMB-DAQ-2408. It is a USB based device. I am facing two problems:

1. After calibrating my two pressure transducers together, when I increase the pressure in one transducer the voltage increases but it also increases the voltage of the other transducer that is kept under atmospheric condition. Any change in the voltage in one of the transducers affect the other one. How can I eliminate this communication between the voltages?
2. How can I extend the sampling time without changing the sampling rate? It looks like there is a certain capacity that I cannot exceed. Something like 25 kb, which is really small. Any suggestions please?

My code is attached below.

Thanks for your time

[PackersFan]

1 - It seems like you are experiencing cross-talk.  Depending on why it is happening, there may be something that you can do about it.  Take a look at this article: http://digital.ni.com/public.nsf/allkb/B9BCDFD960C06B9186256A37007490CDc

2 - You cannot increase the sampling rate of a piece of hardware beyond its capabilities.  Sorry, just doesn't work that way.

[Abo_Rashid]

Hi PackersFan,

Thank you for your reply. The link you provided for the first problem doesn't seem to work. Regarding the second problem, it is not about the sampling rate really. As you said, I cannot increase the sampling rate above a certain value but my problem lies in not being able to continue logging data at an acceptable sampling rate once it reaches a certain file size. I hope this clarifies the problem more.

Thanks again 

[PackersFan]

Sorry about the link.  Try this one: http://digital.ni.com/public.nsf/allkb/B9BCDFD960C06B9186256A37007490CD

Okay, so the question is, how are you logging the data?

[Abo_Rashid]

Hi Packers Fan,

Thanks for the link. I will try the solutions there. About the data logging, I connected the analog input to an index array function that returns the two voltages from each channel. The returned voltages are connected to a calibration tool,  a wave chart and write to measurement file vi. All these vi's are inside a while loop. So I am counting on the write to measurement vi to do the logging. I also set the sampling clock for continuous sampling.

I hope this is clear and thanks again for your help.

[PackersFan]

What type of file do you have the Write to Measurement File.vi set to create?  TDM or TDMS is going to be the fastest.

Depending on your loop rates, you may need to implement the file I/O with the basic functions (i.e. not with an express VI) or you may even need to move to a producer consumer architecture (check out the templates in LabVIEW).

[Abo_Rashid]

Hi Packers Fan,

I am saving the data in LVM file type. About the producer consumer architecture, I will check it out and see how can I use it.

Thanks