LD (Ladder diagram), ladder diagram programming language, the program is represented by one or more program segments. The program segment contains a power rail to the left of the ladder source position
Ladder diagram, which gives a graphical table of relay logic. On the left and right sides of the ladder diagram program, there are vertical power rails on the right. The power rail on the left nominally provides energy for the power flow from left to right along the horizontal steps through various contacts, functions, function block coils, etc. The end of the power flow is the power rail on the right. Each contact represents the state of a Boolean variable, and each coil represents the state of an actual device
Power flow: In a ladder diagram, the energy flow is symbolically similar to a power flow and is used to indicate the progress of the ladder logic solving algorithm. The sequence of logical operations is consistent with the execution of the user program. Using the concept of energy flow can help us better understand how to analyze ladder diagrams
Power rails: The left side of the LD ladder diagram is bounded by a vertical line called the left power rail, and the right side is bounded by a vertical line called the right power rail. The power rails can be either explicit or recessive. Power rails are also referred to as “busbars”, and left and right power rails are also referred to as left and right busbars or primary and secondary busbars
Electromagnetic relay: generally composed of iron core, coil, armature contact reed, etc. As long as a certain current flows through the coil, an electromagnetic effect is generated to drive the pairs of moving contacts and static contacts of the armature to close. When the coil is powered off, the paired movable contacts and static contacts are released. When the relay coil is not energized, the pair of contacts in the disconnected state are called "normally open contacts". On the contrary, the pair of contacts in the connected state are called normally closed contacts
Contacts: It follows the terminology of electrical electromagnetic relay, but in ladder diagram, it is a language element used to represent the 0, 1 state of a Boolean quantity. A touchpoint will only reference but not modify the value of its associated Boolean
Coils: He follows the coil terminology of electrical electromagnetic relays, but in the ladder diagram, it is a language element, and the coil must be associated with a Boolean quantity. Store the associated function output value of the state or transition of the left horizontal line into the Boolean variable associated with the coil
Rundle (Ladder rung): In ladder diagram, it refers to a path composed of parallel and series connections of contacts, coils and connections connected between the left and right power rails. A rung is the smallest unit of the ladder diagram network structure. No connections are allowed between steps
Label: In ladder diagram, also known as jump label, it is an optional identifier of the rung. When defining a jump, the label must be specified to determine the target rung of the jump