Symbol Counter: Symbol Counter – A counter is a simple device used for counting. There are different types of counters. There are up-counters (that only count up 1, 2, 3 …). These are called CTU (Count up), ‘CM’, C or CTR. There are down counters (that only :count downwards, that is, reversed 9, 8, 7). These are […]
Timer: Timer is an instruction that waits a set amount of time before doing something. The different kinds of timers are available with different manufacturers. Most of the timers are: ON-delay Timer: This type of timer simply “delays turning on”. In other words after our sensor (input) turns on, the timer waits for some seconds
PLC Register: PLC Register – Let us consider a simple example and compare the ladder diagram with its real world external physically connected relay circuit. In Fig. 21.32 (a), the coil circuit will be energized when there is a closed loop between the ‘+’ and ‘—’ terminals of the battery. The same circuit can be drawn
Relays Definition: The main purpose of a PLC is to replace real world relays. A Relays Definition is basically an electro-magnetic switch. When a voltage is applied to the coil, a magnetic field is generated. This magnetic field attracts the contact of the relay in, causing them to make a connection. These contacts act like a
PLC Applications: The PLC Applications takes a certain amount of time to react to changes. The total response time of the PLC is a fact that has to be considered while selecting a PLC for some application where speed is a concern. For example, if you take a moment off to look away from this text
PLC System Operation: A PLC System Operation works by continually scanning a program. This scan cycle can be considered as made up of three important states as shown in Fig. 21.23. In addition there are also more than three states and these are used for checking the system and updating the internal counter and timer
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PLC Structure: The PLC Structure mainly consists of a CPU, memory areas, and appropriate circuits to receive input/output data as shown in Fig. 21.22. A PLC can be considered as a box full of hundreds of thousands of separate relays, counters, timers and data storage locations. (These counters, timers, etc. really do not exists physically but
PLC Definition(Programmable Logic Controller or Programmable Controller): PLC Definition – Programmable Logic Controller (PLC) or commonly simply called a Programmable Controller, is a solid state, digital, industrial computer. It is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC basically operates by looking at its inputs and
Cascade Control with Digital Controllers: A simplified system to control the temperature of a process employing a gas burner using two Cascade Control digital controllers is shown in Fig. 21.21. Each controller has a number of digital inputs and outputs, and also a number of and outputs, the actual inputs and outputs are limited to
Digital Process Control: A digital process control functionally needs to operate in much the same way as a conventional analog controller. That is, it must provide facilities to raise or lower the set point and to provide proportional, 2-term or 3-term control. It must be capable of operating in one of many modes including, manual,
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