Wrap It Up


Wrap It Up!

Whew! This chapter has been a heavy oneif you read it end-to-end, you deserve to take a break.

We've covered basic signal and data acquisition theory. Different types of signal can be classified for measurement purposes into analog AC, analog DC, digital on/off, digital counter/pulse, and frequency. Signal sources can be grounded or floating. Grounded signals usually come from devices that are plugged in or somehow connected to the building ground. Floating source examples include many types of sensors, such as thermocouples or accelerometers. Depending on the signal source type, signal characteristics, and number of signals, three measurement systems can be used: differential, referenced single-ended (RSE), and nonreferenced single-ended (NRSE). The big no-no is a grounded source using a referenced single-ended system. The sampling rate of a data acquisition system (for AC signals) is very important. According to the Nyquist Theorem, the sampling rate must be more than twice the maximum frequency component of the signal being measured.

Selecting a DAQ device or system that will do the right job is the next step. Many kinds of DAQ devices exist for different platforms, applications, and budgets. National Instruments' SCXI and PXI systems provide ways to work with a very high number of channels, as well as performing elaborate signal conditioning. Installing a DAQ device is getting easier than before, but still requires a little knowledge of how to set parameters in the configuration utility NI-MAX. The collection of software drivers for National Instruments' devices is called NI-DAQmx, which NI-MAX relies upon to function properly.

Don't feel bad if much of the material in this chapter eluded you. DAQ is a complex subject and often requires the expertise of an instrumentation engineer. However, for relatively simple DAQ systems, if you are willing to experiment and have a sense of adventure, you can assemble your own DAQ system at your PC. Remember to consult the manuals that come with your device and hardware for more details.




LabVIEW for Everyone. Graphical Programming Made Easy and Fun
LabVIEW for Everyone: Graphical Programming Made Easy and Fun (3rd Edition)
ISBN: 0131856723
EAN: 2147483647
Year: 2006
Pages: 294

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