Ladder Diagram ( eng. LD , eng. LAD , eng. RKS ) - the language of relay (ladder) logic.
The names also apply:
- contact logic
- ladder charts
- relay contact schemes (RKS)
- programming language ladder logic standard IEC 61131-3 .
Designed for programming programmable logic controllers (PLCs) . The syntax of the language is convenient for replacing logic circuits based on relay technology. Focused on automation engineers working in industrial enterprises. It provides an intuitive interface of the logic of the controller, facilitating not only the actual programming and commissioning tasks, but also the quick troubleshooting of equipment connected to the controller.
The program in the language of relay logic has a graphical interface that is visual and intuitively clear to electrical engineers, representing logical operations, like an electrical circuit with closed and open contacts. The flow or absence of current in this circuit corresponds to the result of a logical operation ( true - if current flows; false - if current does not flow).
The main elements of the language are contacts, which can be figuratively likened to a pair of relay contacts or buttons. A pair of contacts is identified with a logical variable, and the state of this pair is identified with the value of the variable.
There are normally closed and normally open contact elements that can be compared with normally closed and normally open buttons in electrical circuits.
- ─┤ ├─ Normally open contact is open when the value is false , the variable assigned to it and closes when the value is true .
- ─┤ / ├─ A normally closed contact, on the other hand, is closed if the variable is false and open if the variable is true .
- ─ () ─ The result of the logical chain is copied to the target variable, which is called the coil ( English coil ). This word has a generalized image of the actuator, therefore, in the Russian-language documentation they usually talk about the output of the chain, although one can also find particular meanings of the term, for example, a relay coil .
Specific versions of the language are usually implemented as part of software products for working with certain types of PLCs. Often, such implementations contain commands that expand many of the standard language commands, which is caused by the manufacturer’s desire to more fully take into account the wishes of the customer, but in the end lead to incompatibility of programs created for various types of controllers.
The AvB disjunction corresponds to a circuit composed of two parallel-connected contacts A and B.
Conjunction A & B corresponds to a circuit composed of two series-connected contact A and B.
The negation of the statement A corresponds to the opening contact A, controlled by the same device as the contact A
In 1910, physicist Ehrenfest P.S. He pointed out the possibility of using algebra of logic when creating relay-contact circuits. In 1938, Claude Shannon wrote a book, Symbolic Analysis of Relay-Contact Circuits.
See also
The programming languages of IEC 61131-3 :
- FBD - Function Block Diagrams
- IL - list of instructions
- SFC - Sequential Function Charts
- ST - structured text
Literature
- Shannon K. - Symbolic analysis of relay-contact circuits, 1938
- Michelle J. Programmable Controllers: Architecture and Application. - M.: Mechanical Engineering, 1986
- E. Parr. Programmable Controllers: An Engineer's Guide. - M .: BINOM. Laboratory of Knowledge, 2007. - 516 p. ISBN 978-5-94774-340-1
- Petrov I.V. Programmable controllers. Standard Languages and Applied Design Techniques / Ed. prof. V.P.Dyakonova. - M .: SOLON-Press, 2004. - 256 p. ISBN 5-98003-079-4
- Minaev I.G. Programmable logic controllers. A practical guide for a novice engineer. /AND. G. Minaev, V.V. Samoilenko - Stavropol: AGRUS, 2009 .-- 100 p. ISBN 978-5-9596-0609-1
- Minaev I. G. Programmable logic controllers in automated control systems / I. G. Minaev, V. M. Sharapov, V. V. Samoilenko, D. G. Ushkur. 2nd ed., Revised. and add. - Stavropol: AGRUS, 2010 .-- 128 p. ISBN 978-5-9596-0670-1