Chapter 4
Connecting and Using Accessories and Transducers
©
National Instruments Corporation
4-19
RTDs
An RTD requires excitation, thus, the SCXI-1121 module is a suitable
choice for conditioning the signal. Determine your RTD type and
configuration. The RTD in this example is a 100
Ω
, four-wire platinum
RTD, which is common. In general, the RTD uses current excitation.
However, you can use RTDs in a Wheatstone bridge configuration with
voltage excitation. Refer to your RTD specification literature to determine
the level of current or voltage excitation the RTD requires.
Follow these steps to connect the RTD to channel 1 of the SCXI-1320
terminal block:
1.
Set jumpers W22 and W23 to select current excitation, as shown in
Table 3-12.
2.
Set jumpers W24 and W25 to configure the excitation current level to
either 0.150 mA or 0.450 mA, as shown in Table 3-13.
Note
You do not need to enable the half-bridge completion network.
3.
Connect the RTD to channel 1 of the SCXI-1320 terminal block,
as shown in Figure 4-11.
Warning
Before you connect the RTD to the SCXI-1121, verify that the common-mode
voltage is within limits. Refer to Appendix A, Specifications, in the SCXI-1121 User
Manual. Common-mode voltage that is not within the specified limits can damage the
SCXI system and is potentially dangerous. National Instruments is not liable for damages
or injuries from improper configuration. If you have a common-mode voltage greater than
or equal to 42 V
rms
, ground the terminal block to safety earth ground as shown in
Figure 4-11.
