PLC logic and drive coil command (LD, LDI, OUT) usage and usage precautions - Database & Sql Blog Articles

1) Usage Example

Figure 1 illustrates the use of logic coil drive instructions. This example shows how a photocoupler can be used in a control circuit to isolate different voltage levels while transferring signals.

2) Important Notes for Use

1) The LD instruction is used to represent a normally open contact at the beginning of a circuit, connected to the left busbar. It is typically used for starting a rung in ladder logic.

2) The LDI instruction represents a normally closed contact at the start of a circuit and is also connected to the left busbar. It is useful for creating logical NOT conditions.

3) The OUT instruction is used to output a coil or signal, but it cannot be applied to input relays like X. This ensures that only output devices are controlled by this command.

4) When using ANB (AND Block) and ORB (OR Block) instructions, LD and LDI can be used as the starting contacts for series or parallel circuits. This allows more complex logic structures to be built efficiently.

5) For timers and counters, after using the OUT instruction, the coil must be set with a constant value. This ensures accurate timing or counting behavior and prevents unexpected results.

By following these guidelines, you can effectively implement logic circuits using PLC programming techniques, ensuring safe and reliable operation of your system.