Why Can't I Find the Internal Counters on My NI cDAQ Chassis?

Issue Details

The specifications for the cDAQ chassis mention that there are two (9172) or four (9171/9174/9178/9181/9188/9191) on-board counters that can be used to clock and synchronize other data acquisition tasks. However, when I try to choose these counters from the counter physical channel control drop down menu, there are no counters listed for the cDAQ chassis. How do I access the counters to time other DAQ tasks such as correlated Digital I/O?

Solution

To externally access counters on the chassis, you will need a module capable of hardware-timed digital I/O plugged into your cDAQ chassis. Please see cDAQ Module Support for Accessing On-board Counters for more information on which modules can be used to access cDAQ chassis counters. On the 9172, this module must be in slot 5 or 6 to access the counters. For the newer cDAQ chassis (9171/9174/9178/9181/9188/9191), the module can be in any slot.

Even without such a module inserted in the chassis, you can still configure the internal counters and access them from other modules through the chassis backplane.

By default the DAQmx physical channel control drop down menu will not list internal channels. To view the hidden channels, modify the I/O Name Filtering as detailed below:

1. Right-click the DAQmx physical channel control.
2. Select I/O Name Filtering.

3. When the Filter Names dialog appears check the Internal Channels check box.

4. Click OK.

After configuring the DAQmx physical channel control, two or four new counters should appear in the drop down menu depending on which chassis you have. For the cDAQ-9172, the channels will be listed as _ctr0 and the other _ctr1. The other cDAQ chassis listed above will also list two more channels as _ctr2 & _ctr3. These _ctrX channels are the internal counters and can be used to generate a sample clock for another data acquisition tasks.

 

Additional Information

The Community Example CDAQ-9178 Count Digital Events Without Digital Module  shows how to count an external digital signal by accessing the internal counter without a module. The on-board counter line is internally routed to the PFI line of the chassis.