National Instruments 1128 用户手册

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Figure 2-6.  4-Wire Block Diagram

When used with a DMM for 4-wire ohms measurement, the upper 
differential multiplexer provides the excitation source for the 4-wire 
channel being scanned.

The EXCITATION input to the upper multiplexer is available through the 
OUT0+ and OUT0– screw terminals on the SCXI-1331. The SENSE 
output from the lower 16-to-1 multiplexer is available through the OUT2+ 
and OUT2– screw terminals on the SCXI-1331. You can also connect the 
EXCITATION and SENSE commons of the SCXI-1127/1128 to the HVAB 
backplane. Use switches AB0 and AB2 to make this connection. You can 
do this through NI-SWITCH. This is the recommended usage with 
the DMM.

Figure 2-7 shows an example of a 4-wire channel configuration of the 
SCXI-1331 terminal block. Channel 6 consists of channel 6A+ and 6A–, 
and 6B+ and 6B–. Channel 6A of 4-wire channel 6 is the excitation channel 
and channel 6B is the voltage sense channel. Therefore, to make a 4-wire 
resistance measurement, a DMM should excite the current through 
high-voltage AB0 or OUT0 using channel 6A and sense the voltage across 
the resistor through AB2 or OUT2 using channel 6B.

HVAB

Backplane

16-to-1

Multiplexer

AB0+

AB0

Switch

AB0–

Out0–

EXCITATION Multiplexer

SENSE Multiplexer

0A+
0A–

Out0+

16-to-1

Multiplexer

AB2+

AB2

Switch

AB2–

Out2–

Out2+

15A+
15A–

0B+
0B–

15B+
15B–