Mutchus

    While connecting field devices to Programmable Logic Controllers we always get confused about sinking and sourcing operations. Also this sinking & sourcing concept is useful to answer PLC interview questions . Sinking and sourcing operations refer to electrical configurations of the circuit in the module & field input devices. When a device provides current when it is ON it is said to be sourcing current . When a device receives current when it is ON it is said to be sinking current. There are both sinking & sourcing field devices as well as sinking & sourcing input module. But it’s a common practice to use input module in sinking current mode. ·         Field devices on the positive side (+VDC) of the field power supply are sourcing field devices. ·         Field devices on the negative side (DC COM) of the field power supply are sinking field   devices. ·  ...

Ladder logic symbols are the basic building blocks for ladder diagrams. Right here you will find all the ladder diagram symbols which are described in IEC 61131-3. The symbols are available for download in all formats and in a PDF-file. It’s absolutely crucial to know about the symbols when you are working with ladder logic. Each symbol represent a certain ladder instruction. In ladder logic, these symbols are also known as bit logic instructions. The reason for this is that the programming language ladder diagram is designed for boolean signals. Standard IEC Symbols for Ladder Diagrams Ladder Logic Symbols The ladder diagram graphical programming language is standardized by the PLCopen organization, and thereby the symbols used in ladder diagrams. Since ladder logic is a graphical programming language, the PLC programs written in ladder logic are a combination of ladder logic symbols. All the symbols can be found in the standard defining ladder diagram programming: IEC 61131-3. ...

This is an introduction to PLC logic . You can use PLC logic to build PLC programs with simple electrical circuit diagrams. In this article, I will use combinatorial logic to build the functionality of a PLC program. And to get as close as possible to real a PLC programming language like ladder logic, the PLC logic in this article will be  contacts and relays in an electrical circuit . The first PLC program you will be building will be a very simple one. You will be using combinatorial logic to build your PLC program. The reason for this is that, a PLC program is really just logic . Everything in a PLC has two states, just like in digital logic. In logic the two states are called FALSE and TRUE. Sometimes these two states are referred to as “0” and “1”. Those two states are referred to as the numbers 0 and 1, so that we can use the them in binary numbers. Since the PLC works with two states only, it makes sens...

PID instruction in Allen Bradley PLC [Proportional/Integral/Derivative] Closed Loop Control For   Processor SLC 5/02SLC 5/03SLC 5/04SLC 5/05    MicroLogix 1200 and MicroLogix 1500 (A special PID file replaces the old integer file control block.) Description of PID in PLC   This output instruction is used to control physical properties such as temperature, pressure, liquid level, or flow rate of process loops. The PID instruction normally controls a closed loop using inputs from an analog input module and providing an output to an analog output module as a response to effectively hold a process variable at a desired set point. The PID equation controls the process by sending an output signal to the actuator. The greater the error between the setpoint and the process variable input, the greater the output signal, and vice versa. An additional value (feed forward or bias) can be added to the control output as an offset. The result of the PID calculation (control vari...