ReadADC.flx output

[CaterMatt]

What is the meaning of the analog value output from ReadADC.flx?  The help box indicates that it is the signed 12-bit signal (NI7330,UMI7764) but we are getting much lower values than we expect based on our input voltage from a signal generator.  When we apply a +/-2 volt signal the output from the ReadADC.flx is +/-8 on a +/-5 volt range.  We were expecting output values around +/-800 from this based on the +/-2048 range of the analog output.  The oscillatory behavior of the input signal is indeed read correctly, but the magnitude seems small.

[Paul_M.]

Hi CaterMatt,

This is Paul, the applications engineer here at National Instruments who will be helping with your issue. Could you provide me a little bit more information about your hardware and software set up. In particular, what version of NI-Motion are you using? I have a Read ADC.vi here on my end but not ReadADC.flx which indicates that we might be using two different versions of NI-Motion. A screenshot of your block diagram and the results that you're getting would also be really helpful. Also, can you replicate this issue on multiple computers or just on this single machine? I appreciate your patience and cooperation, we'll figure this one out!

Paul M

[CaterMatt]

Hey Paul,

Thanks for your response.  We are using NI-Motion 8.1, help file shows Read ADC.vi though other posts have referred to Read ADC.flx.  We have a PCI-7332 Motion Controller connected to the UMI-7764.  We are trying to read an analog input for later use with a pressure transducer and in order to test it we supply an oscillating voltage between -1 and +1.  According to the range settings (say +-5) we should be getting readings between +-800 since it is a 12 bit ADC.  As seen in the attached front panel shot, the value oscillates between -3 and 4ish.  The behavior is exactly as the input, namely the .2 Hz frequency.  Also attached is the block diagram.  We have not tried the hardware on a different machine yet but will if necessary.  Currently there are no drivers or motors assigned to the axis (that will come later).  

Thanks for your help. 

[Paul_M.]

Hey CaterMatt,

So I noticed a couple things with your block diagram image that you posted. First off, I noticed that there coercion dots from the Bd ID out to the Board ID input of the subsequent VIs. Also I noticed that you weren't utilizing the motion error handler. Go ahead and modify your block diagram to look like the one below and we'll see if that has any impact on your results. Let me know what happens.

Paul M

[CaterMatt]

Happy New Year!

I set up the block diagram exactly as shown and supplied +-4 V.  The analog value alternates between -10 and 15 at the same frequency.  The UMI-7764 has a 5 V power source connected.  The only other connection is the analog in and ground from the function generator.

[Paul_M.]

Hi CaterMatt,

Happy New Year to you too! Sorry that we weren't able to solve your problem before the ball dropped but we'll get it figured out soon. Anyway, I just wanted to make sure that you had correct pins connected on the UMI 7764. Could you tell me which pins you have connected to what?

Also, have you disabled the Axis prior to accessing it within your code? You can do this by navigating to Measurement & Automation Explorer and selecting the PCI-7330 and under Axis Configuration select the disabled option.

Paul M

[CaterMatt]

Sorry for the delay (Conference in town last week).  I tried disabling the axis in MAX, saving and initializing the axis settings, but had the same results.  I only have the signal and ground from the function generator to the Analog in 1 and Analog ground respectively, in the UMI-7764.  I have also tried on other analog ins even on the second axis but with the same results.  I can't imagine why it shows the same behavior as the function just through such a small range.

Thanks for your help and patience.

Matt

[Paul_M.]

Hi CaterMatt,

So I discussed your issue with R&D and they provided me with a loop back test you can run. All you have to do is connect the following on your UMI:

connect aout 1 to ain 1
AI ground to AO1 ground
make sure 5v is connected to the UMI

Then run the program and let me know what happens.

Paul M

[CaterMatt]

Is it possible to send another which is compatible with LabVIEW 8.2?  We are unable to open it.

Thanks

[Paul_M.]

Hi CaterMatt,

The example is fairly easy to recreate. It wasn't letting me save in a previous version due to toolkit incompatibilities so I think it would be better if you tried to recreate it from the below image. Let me know if you have any issues.

Paul M