Using the NI 9411 Inputs as Differential or Single-Ended

Issue Details

The NI 9411 documentation claims the device can operate in differential or single-ended mode. How do I set the module's inputs for each mode?

Solution

The NI 9411 does not need to be configured in software to perform differential or single-ended measurements. The only change will be the connections between the signal or transducer and the module.

In differential mode, the NI 9411 makes a differential measurement between the DIa (positive) and DIb (negative) terminals. The hardware takes the difference between the two inputs and will determine if it's High (between 300 mV and 24 V) or Low (between -300 mV to -24 V). 

For single-ended mode, only the positive input terminal is wired while the negative terminal is floating. The NI 9411 can then pull the negative line to a set voltage. This allows users to set new input limits for single-ended measurements either high (2-24V) or low (0-0.8V)

In single-ended mode, only the positive input terminal is wired for each input and the negative terminal is left floating. The NI 9411 will internally connect the floating negative input line to a reference for single-ended with a High between 2 to 24V and a Low between 0 to 0.8V.

Finally, a user cannot request the software to report the mode the NI 9411 is using. Therefore, it is impossible to detect the connections the device has from a software command.

Additional Information

Refer to the NI 9411 Datasheet for more information about logic levels and other specifications and to the NI 9411 Getting Started Guide for instructions and diagrams about how to connect differential or single-ended devices or encoders to its input.