National Instruments PCI-6281, User Manual

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Chapter 2 DAQ System Overview
Signal Conditioning
Many sensors and transducers require signal conditioning before a measurement system can
effectively and accurately acquire the signal. The front-end signal conditioning system can
include functions such as signal amplification, attenuation, filtering, electrical isolation,
simultaneous sampling, and multiplexing. In addition, many transducers require excitation
currents or voltages, bridge completion, linearization, or high amplification for proper and
accurate operation. Therefore, most computer-based measurement systems include some form
of signal conditioning in addition to plug-in data acquisition DAQ devices.
Sensors and Transducers
Sensors can generate electrical signals to measure physical phenomena, such as temperature,
force, sound, or light. Some commonly used sensors are strain gauges, thermocouples,
thermistors, angular encoders, linear encoders, and resistance temperature detectors (RTDs).
To measure signals from these various transducers, you must convert them into a form that a
DAQ device can accept. For example, the output voltage of most thermocouples is very small
and susceptible to noise. Therefore, you may need to amplify or filter the thermocouple output
before digitizing it. The manipulation of signals to prepare them for digitizing is called signal
conditioning.
For more information about sensors, refer to the following documents:
• For general information about sensors, visit
ni.com/sensors
.
• If you are using LabVIEW, refer to the
LabVIEW Help
by selecting
Help»Search the
LabVIEW Help
in LabVIEW and then navigate to the
Taking Measurements
book on
the
Contents
tab.
• If you are using other application software, refer to
Common Sensors
in the
NI-DAQmx
Help
or the
LabVIEW Help
.
Signal Conditioning Options
For more information about SCXI and SCC products, refer to
ni.com/
signalconditioning
.
SCXI
SCXI is a front-end signal conditioning and switching system for various measurement devices,
including M Series devices. An SCXI system consists of a rugged chassis that houses shielded
signal conditioning modules that amplify, filter, isolate, and multiplex analog signals from
thermocouples or other transducers. SCXI is designed for large measurement systems or systems
requiring high-speed acquisition.
System features include the following:
•
Modular architecture
—Choose your measurement technology
•
Expandability
—Expand your system to 3,072 channels