Understanding New Developments in Data Acquisition
Technologies in the test and measurement arena change so quickly
that you often need a scorecard to keep up—here’s one you can use.
Features and Capabilities of DAQ Tools
Measurement Specs
• Scaling
• Sampling rate
• Digital filtering
• A/D technology
Software
• Data throughput
• Computer dependence/coupling
• Measurement accuracy
• System software dependence
• Resolution/sensitivity
• Application response time
• Calibration
• Control capabilities
• Multiplexing/switching
Form Factor
Signal Conditioning
• Channel expandability
• Electrical isolation
• Multifunctionality
• Noise immunity
• Modular/customizable
• Common mode voltage
• Rack space
• Signal conditioning
• Compactness
Source: Keithley Instruments
Electronic and computer bus architectures, along with microprocessor technologies, continue to evolve and improve, as does the complexity of the systems involved and the increasing number of choices of hardware and software combinations that are available to test system developers. For those intimately involved in day-to-day test system development, it is easier to understand and keep up with these technologies. For those developers not as involved in the development of test systems, it’s more difficult.
Instrument developers at Keithley Instruments, Cleveland, Ohio, have created a handbook, Understanding New Developments in Data Acquisition, Measurement, and Control, that provides a basis for starting that development. This handbook adds to other tutorials on switching, semiconductor test, nanotechnology measurements, and ultra-low-level electronic measurements that Keithley offers.
While some of the book addresses characteristics of Keithley’s own test and measurement equipment, in general the handbook provides objective information on the technologies involved. This book is not intended to be an in-depth technical discussion of specific test products—it is an overview, with general recommendations about the options available to developers.
The book is written by test system developers for test system developers. It is not overly simplistic or generic, nor is it filled with technical jargon that would be unusable by the target audience for this book. A modicum of tabular data and appropriate graphics are interspersed with the text to provide a more readable and understandable document.
Communicating the data
Surveys indicate that about 80% of the test, measurement, and data acquisition applications in use are computer controlled. As a result, the handbook goes into some detail describing the advantages and limitations of the PC data buses that have been developed, including ISA, PCI, PCI-X, PCI Express, and PCMCIA.
This section is logically followed by a somewhat in-depth discussion of the external data communication buses and ports currently in use. This includes parallel printer ports, RS-232, RS-422 and RS-485 serial ports, IEEE-488 (GPIB), USB (Universal Serial Bus), IEEE-1394 FireWire bus, and Ethernet. Details about the ubiquitous networking of computers with Ethernet is discussed with a focus on the various network architectures that are available.
Section 3 in the handbook provides an overview of software options that are available to the test system developer. This includes discussions of text (BASIC, C++, and C#) and graphic (LabVIEW and Agilent VEE) syntax software languages, again with an objective viewpoint and advantages and limitations of each language.
A strength of this book is the depth to which basic concepts are covered. Three such topics are basic component theory and temperature and displacement measurements. Regardless of the specific configuration of the test system that is ultimately designed and developed, the basic component theories need to be well understood by the test system developer.
Roughly half of all data measurements currently made involve the measurement of temperatures. Temperature sensor technologies discussed in the book include thermocouples, resistive temperature detectors (RTDs) thermistors, and various semiconductor devices. The measurement ranges, accuracies, and ease-of-use of these sensors differ considerably, so a discussion of the specific applications and temperature ranges are covered to provide a basis for selection by the test system developer.
Another section is presented on strain measurements. A discussion of the complexities involved in using, wiring, and configuring strain gauges is made to acquaint the test system developer with potential sources of error and signal conditioning or calibration that may be needed.
The handbook is 220 pages, 32 of which are devoted to the glossary, which gives it a substantial continued “referral” use.
