Converting cDAQ voltage input to PSI using Y=MX B formula

[nmuleski]

Hello -

I have been tasked with writing a VI that will take in the input from 16 different Sensor-Technik Pressure Transmitters (model A08) and converting them into a readable output in the form of an on-screen gauage.

This is my first expierence with LabView so it's been an adventure!

So far I've gotten my cDAQ unit installed on a test stand server with NI 9205 module and all the drivers.  The pressure transmitters are all hooked up as well and wired into the NI 9205.  I've also got LabView 2011 installed on a development server and the cDAQ is hooked up to it via Anywhere USB.  The server finds and installs the drivers for the cDAQ unit no problem and I can take sample readings.

I've also found the formula for converting voltage to PSI for my transmitter which seems to be Y=50(10)+0

The problem is, I can't find where I would do this conversion within LabView!  I'm not even sure if I should be using LabView as opposed to MAX or SignalExpress.  Any help that could point me in the right direction would be great!

[SimonH]

nmuleski,

The DAQmx driver can actually handle this conversion for you.  Assuming you are using the DAQ Assistant you should see an option for "Custom Scaling" -- this will allow you to specify the formula for converting the acquired voltage into useful engineering units.  

If you are configuring a task in MAX you should also see this option there.

There are obviously other ways to accomplish the scaling but this is IMO the easiest.

~Simon

[SimonH]

nmuleski,

The DAQmx driver can actually handle this conversion for you.  Assuming you are using the DAQ Assistant you should see an option for "Custom Scaling" -- this will allow you to specify the formula for converting the acquired voltage into useful engineering units.  

If you are configuring a task in MAX you should also see this option there.

There are obviously other ways to accomplish the scaling but this is IMO the easiest.

~Simon

[RavensFan]

Signal Express is a different program than LabVIEW.  It provides some basic functionality for collecting data, logging, filtering, and math, but no extended programming capability.  You can set the scaling in Signal Express.

LabVIEW is the full fledged programming environment.  You can use any of the scaling VI's in there (search the palettes for "scale").   Or you can just do the math on the signal you get.

Alternatively to all of this, you can set the scale in MAX.

[nmuleski]

This is actually the first I've heard about DAQ Assistant.  It didn't install with the NI Developer Suite.  I looked it up and it seems it's installed with Measurement Studio, but the only reference I can find to Measurement Studio on my DVDs is for integration with Visual Studio.  Do I need Visual Studio in order to use Measurement Studio?

[RavensFan]

The DAQ Assistant is installed into LabVIEW when you install the DAQmx drivers from the Device Drivers DVD.  Make sure you install the device drivers after installing LabVIEW.

I don't know if the DAQ assistant has any counterpart in Measurement Studio.  There is an entirely separate forum for questions regarding Measurment Studio.

[nmuleski]

I downloaded the drivers from here:

http://joule.ni.com/nidu/cds/view/p/id/2604/lang/en

because I was having issues installing the drivers that came on the Device Drivers DVD (marked August 2011).  I ran the driver setup again and it would appear I have everything I should need installed.  I see no references to "DAQ Assistant" anywhere in the install.  The application "LabView 2011 Support" is installed, but I can't find any references to the DAQ Assistant anywhere in LabView.  I can't even find any references to my DAQ in LabView!

I'm sorry for the seemingly simple questions but I am having all sorts of trouble with this!

[nmuleski]

Ok I uninstalled and reinstalled the portion of the drivers relating to using LabView 2011 and now I can find the DAQAssistant in the Signal Express palette when using LabView.  

[RavensFan]

You should also see it under Measurement I/O >>  NI-DAQmx palette when you are in the block diagram palettes.

And if you use Quick Drop (Ctrl-Space) and type "DAQ", you should see it at the top of the list.

[nmuleski]

Yes, I see it now.  Excellent, thanks for the help on that issue!

I've got my DAQ setup inside a VI using the DAQ Assitant and I used Custom Scaling to input the equation to convert from Voltage to PSI.  

Now my question is how do I get the DAQ Assistant VI to output using the scaling?  I have the output going to a guage and a numeric indicator but when I run the VI it still shows the output in voltage.