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…

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…

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…

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…

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…

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…

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…

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…

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…