Only while there is an input to the contacts is there an output. When the switch is closed, i.e., there is an input, the output of the motor is activated. There are no other input devices and the line terminates with the output, denoted by the symbol ( ). Starting with the input, we have the normally open symbol jj for the input contacts. The input is thus the switch and the output the motor. To illustrate the drawing of the rung of a ladder diagram, consider a situation where the energizing of an output device, such as a motor, depends on a normally open start switch being activated by being closed. Output coils are represented by just one form of symbol. The action of the input is equivalent to opening or closing a switch.
![study the ladder logic program in figure 6-77, and answer the questions that follow: study the ladder logic program in figure 6-77, and answer the questions that follow:](https://media.cheggcdn.com/study/05b/05ba287c-ac57-4c6e-ae3a-08ec83e44c2e/image.png)
Note that inputs are represented by different symbols representing normally open or normally closed contacts.
#STUDY THE LADDER LOGIC PROGRAM IN FIGURE 6 77, AND ANSWER THE QUESTIONS THAT FOLLOW: FULL#
Some slight variations occur between the symbols when used in semi-graphic form and when in full graphic. This is the address of the input or output in the memory of the PLC.įigure 1.4 shows standard IEC 1131-3 symbols that are used for input and output devices. The inputs and outputs are all identified by their addresses, the notation used depending on the PLC manufacturer.The same letters and/or numbers are used to label the device in each situation. For example, we might have a relay that switches on one or more devices.
![study the ladder logic program in figure 6-77, and answer the questions that follow: study the ladder logic program in figure 6-77, and answer the questions that follow:](https://www.coursehero.com/thumb/17/c1/17c153bf96b232937229a6f9f74ee0144a5af577_180.jpg)
![study the ladder logic program in figure 6-77, and answer the questions that follow: study the ladder logic program in figure 6-77, and answer the questions that follow:](https://www.coursehero.com/thumb/34/c8/34c85b70f5eafcc5eb67edaed223fbcca94ff0dd_180.jpg)
![study the ladder logic program in figure 6-77, and answer the questions that follow: study the ladder logic program in figure 6-77, and answer the questions that follow:](https://d2vlcm61l7u1fs.cloudfront.net/media%2F57e%2F57ea6e5d-ef78-4615-a8a9-205922db8a7f%2Fphp8eizrh.png)
Thus we have a motor which is started by pressing button I and stopped by pressing button 2. Thus when push button 2 is released, there is still no power to the motor. This disconnects the power to the motor and the holding contacts open. Thus when the push button 1 is released, the holding contacts maintain the circuit and hence the power to the motor. When button 1 is pressed, the motor circuit is completed and the motor starts.Īlso, the holding contacts wired in parallel with the motor close and remain closed as long as the motor is running. In the normal state, push button 1 is open and push button 2 closed. Figure 1.2 shows an example of a ladder diagram for a circuit that is used to start and stop a motor using push buttons.