With this approach, there is some risk of shorting input channels and damaging hardware. Therefore, you need to ensure that only one of the channels from any module has a path to COM. In other words, it is very important that when one relay is closed on a given module, all relays on any other module tied to the same COM need to be open.In order to guarantee that only a single channel on any of the modules tied together is connected to the shared COM, you can define software exclusions in NI Switch Executive. This utility facilitates the implementation of this method for matrix expansion, and it allows you to save the custom configuration for use in your program or sequence.
This technique implements the required exclusions in hardware, inherently allowing only one channel a path to COM. This is the recommended approach for RF matrix expansion, because when working with high-frequency signals, the configuration prevents reflections between multiplexers. For a similar expansion with fewer channels, you can connect the COM channels of fewer modules to the input channels of a multiplexer and use the remaining inputs as normal channels:
The COM line of a 4x1 multiplexer is connected to an input channel of another to create a 7x1 multiplexer
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