PLC Question related to Memory Bits

I’m sorry if I’m wrong because I’m not an expert in PLCs, but as I understand the memory bits of a PLC simulate physical switches and push buttons. By their nature, the bits are in state (0), which is why a MAKE command coincides with a switch that changes from an open state (0) to (1) when the switch is pressed by user, but this does not happen with a BREAK command that in order to is valid, the PLC memory bit which, as we said, is in a normal state (0) should become (1), that is why the electrical continuity of the circuit does not coincide with the logic BREAK command of the PLC, which in order to be valid, the memory bit must from (0) to (1) when the user presses the switch. I hope I didn’t make the situation worse.

PLC Question related to Memory Bits

You bring up an interesting point about the relationship between the logical states in a PLC (Programmable Logic Controller) and the physical states of electrical switches. Let’s unpack it.

In PLCs, memory bits indeed simulate physical elements like switches, push buttons, and relays. However, it’s important to remember that the logic implemented within the PLC is designed to interpret these bits in a way that makes sense for the given control system. PLC programming languages use commands like MAKE (often represented as NO or “Normally Open” in ladder logic) and BREAK (represented as NC or “Normally Closed”) to interact with these bits.

In a MAKE command, a bit going from 0 to 1 represents a Normally Open (NO) switch closing, allowing electrical flow. This is straightforward and matches our physical intuition, as you noted.

The BREAK command is a bit more counterintuitive. In a physical circuit, a Normally Closed (NC) switch would allow electrical flow until manually opened, breaking the circuit. In PLC logic, the BREAK command activates when the bit goes from 0 to 1, which may seem odd because it means the switch needs to be pressed (or activated) to break the circuit, instead of being in a default ‘closed’ state.

The discrepancy between physical electrical states and PLC logic states that you pointed out arises because the PLC is abstracting away some of the complexity of the control system. The bits are not just simulating a physical state; they are often part of complex logical operations that include timers, counters, and various input/output devices. So, while a bit changing from 0 to 1 might imply a switch being pressed in some cases, in other scenarios, it could mean that a timer has elapsed, a counter has reached a certain value, or some other condition has been met.

Therefore, you are correct that the PLC logic doesn’t always perfectly mirror the physical state of the electrical circuitry. Instead, it serves as a flexible tool for creating complex control systems where the logic can be adapted to the needs of the particular application, even if that means some of the logical operations become less intuitive from a purely electrical standpoint.

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