Reading material 2 PC-Based Instrumentation and Control

Ask any production engineer, control or instrumentation specialist to define his objectives and his reply will probably include increasing efficiency without compromising on quality or reliability. Ask him what his most pressing problems are and lack of suitably trained personnel will almost certainly be high on the list. Happily, both of these perennial problems can be solved with the aid of a PC (or PC-compatible) acting as an intelligent controller. All that is required is sufficient peripheral hardware and the necessary software to provide an interface with the production/test environment.

As an example, consider the procedure used for testing and calibrating an item of electronic equipment. Traditional methods involve the use of a number of items of stand-alone test equipment (each with its own peculiarities and set-up requirements). A number of adjustments may then be required and each will require judgment and expertise on the part of the calibration technician or test engineer. The process is thus not only time consuming but also demands the attention of experienced personnel. Furthermore, in today's calibration laboratory and production test environment, the need is for a cluster of test equipment rather than for a number of stand-alone instruments. Such an arrangement is an ideal candidate for computer control.

The computer (an ordinary PC or PC-compatible) controls each item of external instrumentation and automates the test and calibration procedure, increasing throughput, consistency, and reliability, freeing the test engineer for higher level tasks. A PC-based arrangement thus provides a flexible and highly costeffective alternative to traditional methods. Furthermore, systems can be easily configured to cope with the changing requirements of the user.

In general, PC-based instrumentation and control systems offer the following advantages:

（1）Flexible and adaptable: the system can be easily extended or reconfigured for a different application.

（2）The technology of the PC is well known and understood, and most companies already have such equipment installed in a variety of locations.

（3）Low-cost PC-based systems can be put together at a faction of the cost associated with dedicated controllers.

（4）Rugged embedded PC controllers are available for use in more demanding applications. Such systems can be configured for a wide range of instrumentation and control applications with the added advantage that they use the same familiar operating system environment and programming software that runs on a conventional PC.

（5）Availability of an extensive range of PC-compatible expansion cards from an increasingly wide range of suppliers.

（6）Ability to interface with standard bus systems (including the immensely popular IEEE-488 General Purpose Instrument Bus).

（7）Support for a variety of popular network and asynchronous data communications standards (allowing PC-based systems to become fully integrated within larger manufacturing and process control systems).

（8）Internationally accepted standards, including ISA, PCI, PC/104, and USB bus systems.

Typical applications for PC-based instrumentation and control systems Include:

（1）Data acquisition and data logging.

（2）Automatic component and QA acceptance testing.

（3）Signal monitoring.

（4）Production monitoring and control.

（5）Environmental control.

（6）Access control.

（7）Security and alarm systems.

（8）Control of test and calibration clusters.

（9）Process control systems.

（10）Factory automation systems.

（11）Automated monitoring and performance measurement.

（12）Simple machine-vision systems.

（13）Small-scale production management systems.

（14）A “virtual” replacement for conventional laboratory test equipment.

We need get sufficient information to be able to select the necessary hardware and software to implement a wide range of practical PC-based instrumentation and control systems to design practical configurations and working circuits. Representative software is also included in a variety of languages including x86 assembly language, BASIC, Visual BASIC, C, and C++. In addition, a number of popular software packages for control, Instrumentation and data analysis have been described in some detail. Information has been included so that circuits and software routines can be readily modified and extended by readers to meet their own particular needs. Overall, the designer should gather up sufficient information so that he or she can solve a wide variety of control and instrumentation problems.