Chapter 3
Signal Connections
© National Instruments Corporation
3-9
SCXI-1122 User Manual
Table 3-1. Maximum Load per Excitation Channel
Excitation Level
Maximum Load
3.333 V
225 mA
1 mA
5 k
Ω
Using the Internal Half-Bridge Completion
Your SCXI-1122 includes half-bridge completion for half-bridge and quarter-bridge setups. The
completion network consists of two 2.5 k
Ω
±
0.02% ratio tolerance resistors with a temperature
coefficient of
2 ppm/
°
C. These resistors are connected in series. To use the network, connect
the VEX/2 screw terminal on the terminal block to the negative input of the channel of interest.
CH+0
CH-0
VEX/2
VEX-
SCXI-1322 Terminal Block
120
Ω
Strain
Gauge
VEX+
120
Ω
Dummy
Resistor
Figure 3-7. Connecting a Quarter-Bridge Strain Gauge to Channel 0
Note: When using the half-bridge completion network with a quarter-bridge setup, you must
use an extra resistor to complete the bridge. Place this resistor on the terminal block
between the positive input channel and the negative excitation output.
Temperature Sensor Connection
Pins A1 and A3 are for connecting the isolated temperature sensor located on the SCXI-1322
terminal block for cold-junction compensation (CJC) of thermocouples connected to the
SCXI-1122. The connection is overvoltage-protected to 250 Vrms with power on and off.
Warning:
Exceeding the overvoltage protection on the temperature connections can damage
the SCXI-1122, the SCXIbus, and the DAQ board. National Instruments is
NOT
liable for any damages resulting from such signal connections.
