Chapter 7, Problem 7RQ

Program Plan Intro

Programmable Logic Controller (PLC):

• Programmable Logic Controller (PLC) is a specialized computer used in industrial segments to control machines and process.
• PLC is program that consists of a set of instructions which resembles the controlling functions needed to perform specific tasks.
• The function of PLC is similar to that of a relay and hence, in an industrial segment a relay is greatly replaced by a suitable PLC.
• When compared to general Personal Computer (PC), a PLC is available in small and tiny sizes.
• The basic architecture of a PLC consists of an input-output interface module and a small Central Processing Unit (CPU) that runs by control programming language.

Timer:

• A timer refers to an instruction which waits for an amount of time before performing something.
• A timer counts fractions of seconds or seconds using the internal CPU clock.
• There are mainly three types of PLC timer delays, such as ON-delay timer, OFF-delay timer, and retentive timer ON.

Mechanical timing relays:

• The main purpose of mechanical timing relays is to delay the opening and closing of contacts for circuit control.
• Its operation is almost similar to that of a control relay.
• The only difference is that the contacts of a mechanical timing relay are used to operate at a preset time interval, that is, after the coil is energized or de-energized.
• One example for mechanical timing relay is Pneumatic timing relay.