Connecting multiple SCXI-1127's together

[Guy04]

Hi.  I have multiple SCXI-1127 cards and I needed to know if there is a way to combine all of the cards together to form one big MUX.  I want to make sure that across all of the cards only one channel is closed at one time.  I have configured the 1127 cards as a 2-wire scanning configuration and some as a 4-wire scanning configuration.  Since these are all connected to a DMM 4070 through the backplane, is there any way for me to make sure that two channels on different 1127 cards are not connected to the backplane simultaneously?

[Guy Ferraro]

Guy04,

The relays that you close will depend on your software call. Since you are scanning it will depend on the entries in your scanlist. I recommend using the DAQmx API where the scanlist could look like this.
Device1/ch0:31->com0;Device2/ch0:31->com0; This scanlist will scan 32 channels of device 1 and then 32 channels of device2 without having channels of device 1 connected when channels of device2 are being scan and vice versa.

Guy Ferraro
Switch Product Engineer
NI - USA

[Guy04]

Thanks for your help.  Is there any other method that will prevent this besides the application program.  For example, without a sequential scan.  What if you're jumping around maybe like Device 1/ch0 and then Device 2/ch13 and Device1/ch7....Is there any other way in which multiple channels don't connect can be controlled by other than from the application program.  I know that I can use NI-Switch Executive to create channel exclusions of the "ab0" channels of each of the devices but, is there some way that I can be sure that this does not happen hardware wise?  Or maybe another, redundant software way that can validate this along with NI-Switch.

[Guy Ferraro]

If you not scanning then you are using immediate calls which means that relays will close as soon as you make the call. The relay on different device will close according to the calls you make without protection. If you call device1/ch0 and device2/ch10, then these 2 channels will be connected at the same time to their respective COM and if the 2 COMs are interconnected via the back plane both signals will be routed to the back plane. 

In NISE, as you know you can use exclusions to prevent sets of channels to not be connected at he same time \

Guy Ferraro

Switch Product Engineer

NI - USA