DC Inputs: The, dc inputs modules commonly available will work with 5, 12, 24 and 48 volts. The DC Inputs modules allow us to connect either PNP (sourcing) or NPN (sinking) transistor type devices to them.…

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…