NI SCXI-1127, Руководство пользователя

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Chapter 2 U s i n g the SCXI-1127
CHO+ -
CHO- -
• •
. . 32-to-1
COMO+
ABO+
HVAB
COMO-
ABO-
• •
• •
Multiplexer
Backplane
mode configurations. For more information on scanning and triggering,
consult the Hardware and Software Scanning section.
The SCXI-1127 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, 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 to
detect that a terminal block is present. Please refer to Appendix D for
information on how to do this.
Two-Wire Channel Scanning Configuration
You can use the SCXI-1127 as a 32-channel, two-wire (differential)
multiplexer. Figure 2-2 shows the block diagram of the input switching
structure in two-wire mode. You can connect up to 32 channels to the
SCXI-1127 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 OUTO+ and OUTO- screw terminals on the SCXI-1331.
I; N o t e O U T O ± is also referred to as the multiplexer common or COMO±.
OutO+ .411
OutO-
CH31+ -
C H 3 1 -
ABO
Switch
Figure 2-2. Two-Wire Block Diagram
You can also connect the output of the SCXI-1127 to the high-voltage
backplane using switch ABO to make the connection. On power up, switch
ABO is open, disconnecting the SCXI-1127 from the high-voltage bus. If
you are using the module with a high-voltage backplane, you need to close
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