Select Signals Express VI Does Not Show All Connected Channels

Updated Aug 28, 2018

Reported In

Software

  • LabVIEW

Driver

  • NI-DAQmx

Issue Details

I am using the DAQ Assistant Express VI along with the Select Signals Express VI to select and display between 0 and 16 analog inputs on a waveform. However, the Select Signals Express VI only gives me the option to select between channels 0 through 7. I have made sure that all my input channels have been connected correctly. Furthermore, all 16 channels can be tested in MAX with desirable results.
 

Solution

This problem occurs after the initial connection of the output of the DAQ Assistant Express VI (dynamic data type) to the Select Signals Express VI. The configure box on the Select Signals Express VI will only give you an option to select between channels 0 through 7. 
 
Figure 1: Configure Select Signals Default Dialogue Box

This issue can be resolved by simply running the program once. 

This behavior occurs because the Select Signals Express VI defaults to listing only 8 channels (channels 0 through 7).  After the program is run, the Select Signals Express VI gets the full range of channels in memory and automatically updates to give you the option to choose from all 16 channels specified in the DAQ Assistant Express VI.
 

Figure 2: Block Diagram Using Select Signals Express VI

Figure 3: Configure Select Signals After Adding Channels
 
Note: Before following the above procedure, it is important to make sure that none of the channels you are acquiring are set to differential mode since it uses a pair of channels (channel “n” and channel “n+8”) to form one differential channel. For example, if you set channels 0 through 7 as differential, you will not have access to channels 8 through 15. 

To make sure your channels are set to Reference Single Ended (RSE) or Non-Reference Single Ended (NRSE): 
1. Right-click DAQ Assistant » Properties window
2. Make sure Voltage 0 is selected
3. In the Terminal Configuration tab, choose RSE or NRSE.

Note: Alternatively, you can programmatically select the channels with a 1D array of booleans converted to dynamic data and passed into the 'Selector Input' input of the express VI.  The boolean associated with index 0 of the array would correspond to the first channel of data passed to the VI.
 

Figure 4: Array of Booleans Selecting Signals
 

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