The lack of keyboard and other input-output devices is very noticeable on a PLC. On the front of the PLC there are normally limited status lights. Common lights indicate;
1. Power on – this will be on whenever the PLC has power.
2. Program running – this will often indicate if a program is running, or if no program is running.
3. Fault – this will indicate when the PLC has experienced a major hardware or software problem.
These lights are normally used for debugging. Limited buttons will also be provided for PLC hardware. The most common will be a run/program switch that will be switched to program when maintenance is being conducted, and back to run when in production.
This switch normally requires a key to keep unauthorized personnel from altering the PLC program or stopping execution. A PLC will almost never have an on-off switch or reset button on the front. This needs to be designed into the remainder of the system.
The status of a Programmable Logic Controller (PLC) refers to its operational state and various indicators that provide information about its functioning. The specific status indicators and their meanings can vary depending on the PLC model and manufacturer.
However, here are some common status indicators you may find on a PLC:
1. Power Status: Indicates whether the PLC is receiving power or not. This could be represented by an LED or a power indicator light.
2. Run Status: Shows whether the PLC is running or stopped. Typically, an LED or display will indicate if the PLC is in the “run” mode, meaning it is executing the programmed logic.
3. Fault/Error Status: Displays if any faults or errors have occurred within the PLC system. It could be indicated by a separate LED, an error code, or a message on the display.
4. Communication Status: Indicates the status of communication between the PLC and other devices or systems. It may show if the PLC is connected, communicating, or if there is a communication failure.
5. Input/Output Status: Provides information about the status of digital and analog inputs and outputs. This could include indicators for on/off states, voltage levels, or fault conditions on specific input/output modules.
6. Program Status: Shows the status of the loaded program or logic within the PLC. It may indicate if the program is being edited, verified, or if it’s actively running.
7. Network Status: If the PLC is part of a networked system, there may be indicators related to network connectivity and status. This can include showing if the PLC is connected to the network, data transmission activity, or network errors.
It’s important to consult the documentation or user manual specific to your PLC model to understand the exact status indicators and their meanings. PLC status indicators are designed to assist in troubleshooting, monitoring system health, and providing feedback on the operation of the PLC in real-time.