Acquiring Data from Multiple CompactDAQ Modules in SignalExpress

Updated Dec 13, 2017

Reported In

Hardware

  • NI-9211
  • NI-9201

Software

  • SignalExpress

Driver

  • NI-DAQmx

Other

  • Measurement & Automation Explorer (MAX)
  • CompactDAQ

Issue Details

I want to acquire data from multiple modules in my CompactDAQ chassis using SignalExpress. How do I accomplish this?

Solution

Data acquisition from multiple C Series modules in SignalExpress can be done in two ways, depending on your application needs:

  • Adding another DAQmx Acquire Step to the project
  • Adding all channels to the same DAQmx Acquire Step
Adding another DAQmx Acquire Step to the project - Use in the tasks, where you have different settings for each acquisition. If you have a thermocouple module and an analog input module in the same acquisition, the sampling rate of both modules will be the same - lower of the two devices. In this case it is better to use two separate DAQmx Acquire steps. However, each step has to run in its own while loop and you cannot combine analysis sections. Each set of data must be processed individually.

Adding all channels to the same DAQmx Acquire Step - simplifies the acquisition by combining all task settings into one step. This includes settings like timing and triggering. An example of adding multiple channels to one DAQmx Acquire step is shown below:
  1. Select Add Step » Acquire Signals » DAQmx Acquire » Analog Input » Temperature » Thermocouple.
  2. Select cDAQ"x"Mod"y" (NI 9211) and then the channels from which you want to acquire. Here "x" denotes the cDAQ device identifier and "y" the module slot number as it is displayed in Measurement & Automation Explorer (MAX). You can hold the Ctrl key and select as many channels as you need. This will create a step that only acquires data from channels in the NI 9211 module.
  3. To add channels from another module, click the Add Virtual Channels button. This button looks like a blue plus sign located above the channels list box. Now you can select the type of data you want to acquire, in the case of the NI 9201, strain. Then select the channels from the NI 9201 module.

After completing this, you should have a single step containing channels from both modules, as shown below. If you need to acquire from more modules, simply repeat the steps above for every module.
 

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