Programmable logic controller: Difference between revisions

Revision as of 16:08, 19 June 2002

Revision as of 10:53, 31 July 2002

Line 11:

PLCs generally accept contact closures (like buttons and switches) as inputs, and provides some set of switches as output.

=== PID Loops ===

PLCs usually read, calculate and respond in a hundredth of a second or so, which is too slow for some tasks and several times fast enough for others.

PLCs often also include logic for single-variable generic industrial feedback loop, a "proportional, integral, derviative" loop, or "[[PID loop]]." A PID loop is the standard solution to many industrial control processes that require proportional control. The basic idea is that the controller reads a sensor. Then it subtracts the read value from a "setpoint" to determine an "error".

Line 27 ⟶ 26:

To tune a PID loop, first set the I and D values to zero. Increase the P until the output of the loop oscillates. Then increase I until oscillation stops. FInally, adjust D until the loop is acceptably quick to reach its setpoint.

=== Links ===

Many companies manufacture PLCs including [http://www.zworld.com Zworld], GE Fanuc, Microchip (makers of [[PIC]] [[microcontroller]]s).