Suitable system for reading and writing analog voltages

[Aily]

The system I am using is the SCXI 1001 chassi with modules 1102, 1124, 1600 and terminal blocks 1303 and 1325. I am attempting to initially generate a 0-10V increaing ramp voltage  using the 1102  which is successful by observing my output file and a multi -meter. However when I try to measure this signal using the 1102 module I get significant fluctuations in my signal towards the end as is evident from my attached screen shots. I dont know whether this problem is a symptom of my labview program or the acquisition module. I also tryed to read the voltage from a 9V battery and the voltage I read is 8.7 V and fluctuates + and - 0.2V around this. However when viewed on the multimeter the measured voltage is a steady 9.013V with occasional variation to  9.014V. I have attached a screen print of situations I have described here and also the vi in question. Any suggestions would be much appreciated.

[Steve_B]

Hi Aily,

It would be helpful to know how your hardware behaves running a similar test with an example program. There are shipped examples that can be found in the Example Finder (Help>>Find Examples). You can locate a synchronized AI and AO example by the following folder structure: Hardware Input and Output>>DAQmx>>Synchronization>>Multi-Function>>Multi-Function-Synch AI-AO.vi. This example is set up to perform a generation and acquisition at the same time. You will have to adjust the devices, rates, and samples accordingly but testing an example would help narrow down the issue. I noticed that you are starting and stopping your DAQmx task each iteration of the loop and manipulating the data within the loop which can cause some issues in the time it takes for the loop to iterate.

[Aily]

Hi Steve,

Thanks for your suggestion. I've attached screen shots of what results when I try to use and example program. I get an error relating to the clock. Previously I used to use DAQmx Express vi's but I used to get similar problems with the clock so I used to select one sample on demand which was the only option I was allowed to choose and this was the reason that I then began to introduce loops. However with this sample program you suggested I dont know wher to select on demand. Can you suggest how I should deal with this clock issue.

Thanks,

Ailish 

[Steve_B]

Hi Ailish,

It looks like a did not choose a very good example for you to look at. It is possible to make the changes you are looking for, but I set up a test with your code and I did not observe this behavior. At this point I think we can focus more on your code. I was using an M Series DAQ device and looping the output back to the input. Can you explain how you have made your connections? Is it possible for you to test out your code only using your DAQ device? If you are able to run this test let me know how it goes and the model of your DAQ device.

[Aily]

Hi Steve,

Thanks for your reply. I again implemented the example program you last suggested and I still get the error about choosing sample clock and being allowed to use sample on demand and the program does not run. When I look at the list of devices which can run this program a whole list of comes up of different PCI,PXI and USB devices which can run that program but not my system. I have a SCXI 1124 as my generate voltage module and SCXI 1102 my acquire signal module. My output wires from 1124 plug into my input wires of the 1102 directly . I also tried a simple program using express DAQ Assistant but again I have the same sample clock problem and can only use sample on demand which requires a loop. Basically I have SCXI 1001 chassis, SCXI 1600 USB module, SCXI 1102, and SCXI 1124 and their corresponding terminal blocks 1303 and 1325. Can you suggest a simple program with these modules to generate a voltage, and acquire a voltage or current. I am interested in ramping a voltage from 0-10V. Any suggestions would be much appreciated.

Thanks

[S_Hong]

Hi Aily,

Perhaps, a very simple way of testing your 1102 is to generate a voltage on your SCXI-1124 using Test Panels in Measurement and Automation Explorer (MAX). To do this, simply open up MAX under Start » All Programs » National Instruments and open the Test Panels for your SCXI-1124 module. The SCXI module can be found in the Configuration pane under My System » Devices and Interfaces » NI-DAQmx Devices. Once you have updated the voltage value on the SCXI-1124 module, try measuring the voltage on your SCXI-1102 by running the Cont Acq&Graph Voltage - Int Clk.vi, which should be found under Hardware Input and Output » DAQmx » Analog Measurement » Voltage.

Another thing to note is to make sure that you ground one of the terminals to ensure that no nodes are floating.since you will be measuring a differential voltage with your SCXI-1102.

I hope this helps.