Topic:
embedded systems
Topic:
ladder diagram
Topic:
process control systems
Topic:
state machine
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Summary
Programmable controllers are currently the largest use of microprocessors in process control. Programmable controllers control processes involving on-off decision logic, specified sequences, interlocks, alarm conditions, and status inputs. They are computerized replacements for relay based control systems, and can similarly be programmed by boolean algebra or ladder diagrams. Programmable controllers are widely used because simple control requirements abound; even complicated processes contain many simple sub-systems. (cbb 5/80)
Subtopic: programmable controller 
| Quote: a programmable controller accepts binary inputs from limit switches etc. and uses preprogrammed logic to generate output signals for indicators, pumps, etc. [»instrumentcontrol]
| | Quote: with programmable controllers, can change reactors dynamically [»instrumentcontrol]
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Subtopic: examples
| Quote: example of sequencing a quenching bath; very simple logic [»controleng]
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Subtopic: programming programmable controllers
| QuoteRef: controleng ;;12/76 28 Ledgerwood BK: "In general there are two types of aids for programming PC's: so-called black boxes with coded keyboards and in-line alphanumeric displays, and crt-based units
| | QuoteRef: controleng ;;4/77 insideCover: Square D Class 8881 Programmable Controller: ladder diagrams, boolean logic, full management data reports and diagnostic monitoring. Gives formatted reports of production tallies, alarm annunciation logs, maintenance scheduling, and keyboard logs.
| | QuoteRef: instrumentcontrol ;;7/78 57 "Rockwell's STC Universal Controller stands out in the world of microcomputers as one of the few designed expressly for control. What's more it can be programmed with 13 English commands, so it's easy to use. [Interpreter in ROM for commands like 'at Time', 'Turn on A', 'add F2 to F1', 'repeat', 'wait'. Controllers 50 input and 50 output lines for interfacing to A/D etc. Has 32 4-decimal-digit counters.
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Subtopic: operations
| Quote: CORDIC algorithms compute one-bit-at-a-time using small lookup tables, right shifts, and additions; represents numbers by alternating series; good for microcontrollers [»pashM9_2000]
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Subtopic: interlocks
| Quote: each interlock in a process requires a separate control line; e.g., keeping a valve closed, or sequencing a process [»instrumentcontrol]
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Subtopic: as relay controllers
QuoteRef: cbb_1980 ;;2/24/80 note that most programmable controllers are modeled off of relay controllers. These will become obsolete as more complicated control functions are developed.
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Related Topics
Topic: embedded systems (26 items)
Topic: ladder diagram (5 items)
Topic: process control systems (3 items)
Topic: state machine
(67 items)
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