A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a hard real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.

PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands or millions of units.

The Simatic 505 programmable controller provides a special combination of open-loop control tasks, closed-loop control tasks and complex mathematical functions for a large variety of applications in process engineering.
Heavy- Duty Math is No Problem for SIMATIC® 505®:
•  Math/Trig expressions can be entered as a line in a Special Function program or subroutine just like you
   would write them.
•  SFPGMs and SFSUBs can be called from RLL or PID Loops
•  SFPGMs can operate on Loop PV or Output
•  Supports IEEE floating point & Double Word Math.

Our model is the Siemens Simatic 505 - reference number 505-6660 and was very kindly donated by Mike Briggs of Knight Warner Limited.

Manufacturer: Siemens
Date: 1998

This exhibit has a reference ID of CH14328. Please quote this reference ID in any communication with the Centre for Computing History.

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