Problem with DAQ , LV7

[Multifunction DAC]

Hi,
My question is - can I read at one time from two different analog inputs and a counter (all that on one card, DAQ6023)?
When I try to do so, I only see errors ("MXDAQ device not avaliable..."). If there is such possibility, please - give me some advices...

Thanks in advance,
Radek

[JDesRosier]

Hello Radek,

Yes, you can read from two different analog inputs as well as a counter simultaneously using the 6023 card.

I am willing to bet that you are trying to make two different analog input calls using DAQ assistant twice or two DAQmx Read functions. Your 6023 DAQ card only has a single analog-to-digital (AD) converter, so it's trying to share the AD resource at the same time when making the two AI calls, hence the error.

What you will want to do to correct this behavior is place a two DAQmx Assistant Express VIs on your block diagram (one for the two analog inputs and one for the counter). You can configure the first DAQmx Assistant Express VI to take the two analog inputs by adding both channels in the properties window that appears once you place the Express VI on the block diagram. This will allow the device to multiplex the analog inputs and share the AD converter without error.

If the previous fix does not correct your problem, you will want to make sure that you are able to perform an acquisition whatsoever. To test whether your DAQmx function is working properly, place a single DAQmx Assistant Express VI on your block diagram, configure the properties for, say, a voltage capture, and run the VI. If you still see the same error, you are probably using the wrong address for the DAQ card in LabVIEW. To make sure that you are addressing your DAQ device correctly within LabVIEW, you will want to go to your desktop, click [Start]>>[Programs]>>[National Instruments]>>[Measurement & Automation Explorer(MAX)] and expand the "Devices and Interfaces" tab to see the correct address. Make sure that the device address you�re specifying in LabVIEW corresponds to the one seen in MAX.

If you are still receiving the error after trying the above solutions, please post your VI as well as a screen shot of the error.

I hope this helps! Please feel free to contact me if you need any further assistance.

Best Regards,

Joe Des Rosier
National Instruments

[Multifunction DAC]

Hello again,
Yes, You're right - I tried to call DAQ assistant twice. Your advices are very clear and helpful, but... I still have the problem.
What I wand to do, is to measure voltage (one AIO channel), current (second AIO channel) and frequency (counter input) at the same time. I tried to use one DAQ assistant to measure both voltage and current, but there is no possibility to add two different measure-types. How can I do this?

And the second thing - when I measure only one thing - eg. voltage, everything works perfectly. Same with the other measurements. But, when I try to measure voltage and frequency at the same time, I get an error - "no DMA available". I've foud at LV Help, that I should change data transfer mode from DMA to some othe
r, but - I don't know how to do this. I couldn't find such option, window, tab... Please, help me.

Thank You for Your help,
Radek

[JDesRosier]

Radek,

I apologize for my slow response time. I have been out of the office for the past several days.

I misunderstood your desired functionality. You will not be able to use the DAQ Assistant Express VI if you want to take three different types of input measurements. However, you can use the standard DAQmx functions to program your simultaneous data acquisition.

This link is to an example program that will explain the programmatic steps you will need to take in order to do this acquisition. All you will need to do is change the necessary parameters to specify AI voltage, AI current, and counte
r input.

Hope this helps!

Good Luck!

-Joe Des Rosier-
National Instruments