National Instruments 1128 用户手册

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The SCXI-1127/1128 contains a safety interlocking mechanism that 
prevents high voltages from appearing on the input connector when a 
terminal block is not present. However, when a SCXI-1331 or SCXI-1332 
is plugged into the front of the SCXI-1127/1128, the module detects its 
presence and allows the module to close relays.

If you are using a custom terminal block, you must provide this interlocking 
feature on your terminal block so that it is possible for the SCXI-1127/1128 
to detect that a terminal block is present. Please refer to Appendix D, 

, for information on how to do this.

You can use the SCXI-1127/1128 as a 32-channel, 2-wire (differential) 
multiplexer. Figure 2-2 shows the block diagram of the input switching 
structure in 2-wire mode. You can connect up to 32 channels to the 
SCXI-1127/1128 using the SCXI-1331 terminal block. The input signals 
are switched using a 32 to 1 multiplexer. The output of the multiplexer is 
available at the OUT0+ and OUT0- screw terminals on the SCXI-1331.

OUT0± is also referred to as the multiplexer common or COM0±.

Figure 2-2.  2-Wire Block Diagram

You can also connect the output of the SCXI-1127/1128 to the high-voltage 
backplane using switch AB0 to make the connection. On power up, switch 
AB0 is open, disconnecting the SCXI-1127/1128 from the high-voltage 
bus. If you are using the module with a high-voltage backplane, you need 
to close the AB0 switch to connect the multiplexer output to the 
high-voltage analog backplane. You can do this through NI-SWITCH.

HVAB

Backplane

32-to-1

Multiplexer

AB0+

AB0

Switch

AB0–

COM0+

COM0–

Out0+

Out0–

CH0+

CH0–

CH31+

CH31–