Our traditional relays can also implement many logic circuits, and the simple problems we commonly use in PLC practice can be implemented using traditional relay circuits. Our ladder diagram programming is also a process of planning logic circuits, with a simple lineage termination circuit.

This is how we use relays to connect the termination circuit.

S1 is the stop button connected to NC, S2 is the start button connected to the normally open contact, and KM2 is the upper inlet point of the contactor. When we pressed the start button, the coil power supply KM2 also turned on. When we release the start button S2, KM2 short circuits the S2 start button, so it can continue to supply power to the coil. Therefore, after pressing the start button, pressing the coil will continue to supply power. This type of circuit is also known as a self-locking circuit.

When we connect the button coil on the PLC relay to complete the start stop function, we usually use this program. In fact, this ladder diagram is the same as the actual wiring diagram in the above figure. Also use the NC with the abort button. In fact, there is not much difference between programming with ladder diagrams and planning circuits with relays. Of course, after learning PLC, we have more alternative instructions, but there is almost no difference in logical analysis.

When upgrading the forward rotation circuit of the next electric motor, press the stop button first before switching to the forward logic circuit.

Relay planning for a forward rotation circuit

This is the forward existing circuit that we connect with the existing contactor. When moving in the forward direction, we cannot move the contactor in the reverse direction. This is a logic circuit planning that helps prevent misoperation and contributes to electrical safety. This is because when the S2 forward start button is pressed, the NC point of the reverse contactor coil will be attached in front of the forward contactor coil. Due to the lack of action of the reverse contactor coil, the circuit here is interconnected. The forward contactor coil can still operate normally as a power contactor, but the NC of the forward contactor coil in front of the reverse contactor coil is disconnected due to the movement of the forward coil and the power contactor. At this time, pressing the S3 reverse button will prevent the contactor from supplying power normally. Mistakes can be avoided here. To press in reverse, first press abort. This is what our logic needs to do with the circuit.

When we connect the button contactor to the PLC, the internal program of our PLC is manufactured in the same way as the circuit we connect with relays.

In fact, even the most chaotic devices and large programs can be programmed based on this logical thinking to create ladder charts. Although we can program without using ladder shapes, our logical thinking is the same, only the game rules are different. The instructions we use have very simple functions. Similar to contactors and switches, they are very simple things. The opening and closing quantities only need to pass through and cut off, and the imitation quantity only needs real-time data sets. Each instruction can only perform very simple actions, imitating the famous saying. In fact, we can use PLC to perform chaotic sequential actions, including many functions. In fact, there are no shortcuts in programming. More often than not, it is done with basic instructions and is something with strong logic.

Article source: Zhongshan Relay Manufacturer www.jxzhongxuan.com