Chapter 3
Signal Connections
SCXI-1102/B/C User Manual
3-4
©
National Instruments Corporation
input range for either positive or negative channel input is the maximum
input voltage which will result in a valid measurement. Each channel
includes input protection circuitry to withstand the accidental
application of voltages up to ±42 VAC peak or VDC.
Caution:
Exceeding the input damage level (±42 VAC peak or VDC between input
channels and chassis ground) can damage the SCXI-1102/B/C module, the
SCXIbus, and the DAQ device. National Instruments is
NOT
liable for any
injuries resulting from such signal connections.
Applying a voltage greater than
±
42 VAC peak or VDC to the
SCXI-1102/B/C is an electrical shock hazard. National Instruments is
NOT
liable for any damages or injuries resulting from such voltage application.
Note:
Exceeding the differential or common-mode input channel ranges results
in a distorted signal measurement.
Ground-Referencing Your Signals
Your input signals can be either ground-referenced, as shown in
Figure 3-2, or floating, as shown in Figure 3-3. Before you connect
your thermocouple or any other signal, determine whether it is
floating or ground-referenced. If it is a floating signal, you must
ground-reference the signal in one of two ways. You can connect the
negative channel input to chassis ground as shown in Figure 3-3 or you
can use the clamping resistors on the SCXI-1303 terminal block. The
SCXI-1303 also has a resistor pack for pulling up the positive inputs for
open-thermocouple detection. Consult the SCXI-1303 32-Channel
Isothermal Block Installation Guide for details.
Do not ground signals which are already ground-referenced; doing so
will result in a ground loop, which adversely affects your measurement
accuracy.
!
