TABLE OF CONTENTS A wide variety of batch control systems is available, but only half as many as there were ten years ago. This section discusses a few of the differences among systems that may matter to you.
Data may be owned by a big database in redundant servers. Independent sales reps that sell services benefit from this because they can configure in the database without requiring hardware to be present. The disadvantage is the inability to respond rapidly to the need for change. A new instrument that measures new properties may be unusable while the vendor takes more than a year to design, recompile, and test the big database and all the applications that use it.
Data can be owned by field devices or by distributed controllers. Some advantages are on-line configuration, no extra work required to maintain the database, and no possible difference between what's in the device or controller and what's in the database. The new instrument goes on-line immediately. The disadvantage is the need for hardware or simulators for initial configuration. It is possible to have an initial configuration database that is loaded into the equipment, when that is possible, and then discarded. Backup copies of the distributed data allow spares to be loaded with a copy of their part of the current control configuration.
Writing code for a PLC is like writing assembly language code. There are lots of cryptic symbols and numbers. You can simulate PLC coding by...
