Initially, Plcs had only discrete I/O.
Plcs are used in many industries and machines.
Modern Plcs can be programmed in a variety of ways,
These days Plcs are used in so many different industries and machines.
Small Plcs have a fixed number of connections built in for inputs
Small Plcs have a fixed number of connections built in for inputs
and outputs.
model has insufficient I/O. Modular Plcs have a chassis(also called an I/O rack)
Plcs may include logic for single-variable feedback analog control loop,
a proportional, integral, derivative(PID) controller.
Plcs read limit switches,
analog process variables(such as temperature and pressure), and the positions of complex positioning systems.
Plcs read limit switches,
analogue process variables(such as temperature and pressure), and the positions of complex positioning systems.
The data handling, storage, processing power,
and communication capabilities of some modern Plcs are approximately equivalent to desktop computers.
PLC-like programming combined with remote I/O hardware,
allow a general-purpose desktop computer to overlap some Plcs in certain applications.
Most modern Plcs can communicate over a network to some other system,
such as a computer running a SCADA(Supervisory Control And Data Acquisition) system or web browser.
Initially most plc logic controller utilized Ladder Logic Diagram Programming, a model which emulated electromechanical control panel devices(such as the contact and
coils of relays) which Plcs replaced.
Plcs have built in communications ports usually 9-Pin RS232,
and optionally for RS485 And Ethernet, Modbus, BACnet or DF1 is usually included as one of the communications protocols.
Early Plcs, up to the mid-1990s, were programmed using proprietary programming panels
or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs.
Plcs contain input
and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations.
The main difference from most other computing devices is that Plcs are intended-for
and therefore tolerant-of more severe conditions(such as dust, moisture, heat, cold), while offering extensive input/output(I/O) to connect the PLC to sensors and actuators.
Modern Plcs can be programmed in a variety of ways, from the relay-derived ladder logic to programming languages such as specially adapted dialects of BASIC and C. Another method is state logic,
a very high-level programming language designed to program Plcs based on state transition diagrams.