How to get a DC signal to output via the DAQ assistant

[Jeremy Cohen]

I have a simulated DC signal which has either amplitude 5 or 0, based on initial input, and I need to output this signal either via the PXI-6602 (Timing I/O) or the PXI-6259 (M Series Multifunction DAQ) onto a SCB-68 device.  As of now, I am trying to use the DAQ Assistant to do this.  I'm not sure whether to use Analogue Output, Counter Output, or Digital I/O (preferred).  Which would be best to use and how do I go about connecting my simulated signal to the DAQ Assistant?  I'm eventually going to have to have this signal output either a DC signal of either 5 Volts or 0 Volts. Thanks.

~Jeremy

[Jesse_O]

Hello Jeremy,

If you are wanting to generate a 5V or 0V DC signal you could use a digital line or an analog output.  It really depends on your application.  If you ever want to change the output voltage to anything other than 0 or 5V I would use an analog output channel.  It looks like digital would prefer to use a digital line.  This should work for you depending on your current draw.   Keep in mind the current each of these channels and source.  You can find this information in the data sheets found here and here.

Regards,

Jesse O.
Applications Engineering
National Instruments

[technomage]

Ultimately I have the same question. My background includes 15 years of programming PLC's. AO's were simple. You passed the AO a value between preset ranges and it output a proportional voltage signal based on the hardware capabilities.

I foolishly thought LabView and DAQ AO's would be about the same. I built a vi to generate a DC signal which I could control the amplitude of. I also tied it to a chart to monitor how it worked. I managed to draw some very pretty ramping pictures on my chart, but when I put a DMM across the physical terminals I see no voltage.

Then I used MAX to test the channel and measured it again. Now I see voltage on my DMM. I was attempting to use the DAQ Assistant to do this. Do I need to force it to re-read the changing value I am sending it? All of the examples I find show me more primitive methods, and I could not seem to get any of them to do hat I want either.

technomage

[Jesse_O]

Hello technomage,

The examples provided with LabVIEW and the DAQ Assistant provide all the code to generate a voltage.  Please take a look at the example called "Cont Gen Voltage Wfm-Int Clk.vi" located in NI Example Finder (in LabVIEW select Tools >> Find Examples) under Hardware Input and Output >> NI-DAQmx >> Analog Generation >> Voltage.  This example shows you how to generate a continuous waveform.  If you would like to generate a single DC value you can use a simpler example called Gen Voltage Update.vi.  These examples provide the same functionality you get in MAX. 

You should also be able to do this in MAX.  You can also find more information on how to program with DAQmx here.

Regards,

Jesse O.
Applications Engineering
National Instruments

[technomage]

Hi Jesse. Thanks for your reply. I have taken a look at that link you sent me and I believe it will get me on my way quite nicely.

technomage