-
The device cannot start or stop normally
Start failure:
When the PLC output wiring has a circuit break, such as the output wiring connecting the motor start contactor coil is disconnected, even if the PLC program logic has issued a start command, the motor cannot receive the start signal and cannot start normally. This situation will cause the entire production process to stagnate in the automated production line, affecting production efficiency.
If it is a short circuit fault, it may trigger the protection mechanism of the PLC output module, causing the corresponding output point to be disabled. For example, in a PLC system that controls multiple devices, a short circuit at an output point will cause the point and other output points that may be related to it (depending on the protection circuit design) to fail to output signals, making the corresponding device unable to start.
Stop failure:
For equipment that requires emergency stop, if the PLC output wiring fault causes the stop signal to fail to be transmitted normally, the equipment may continue to run, causing a safety accident. For example, in woodworking machinery, if the stop signal of the saw blade cannot be delivered, the saw blade will continue to run, posing a threat to the safety of the operator.
-
Unstable equipment operation status
Intermittent failure:
Loose output wiring is one of the common causes of failure. When the wiring is loose, the equipment may work intermittently. For example, the heating equipment controlled by PLC, due to the loose output wiring, the heating element sometimes receives the heating signal and sometimes loses the signal, making the equipment temperature unable to be stably controlled, affecting the product quality.
Poor wiring contact may also cause unstable equipment speed. Taking the conveyor belt motor controlled by PLC as an example, if the output wiring contact is poor, the power supply voltage of the motor will fluctuate, and the motor speed will fluctuate accordingly, which may cause the material on the conveyor belt to pile up or fall.
-
Increased risk of equipment damage
Overcurrent or overvoltage damage:
When the PLC output wiring is short-circuited, it may cause overcurrent to pass through the external device. For example, for the PLC output wiring connected to the solenoid valve, if a short circuit occurs, the current flowing through the solenoid valve coil will be too large, which may burn the solenoid valve coil.
Similarly, in some cases, output wiring failure may cause overvoltage. For example, when the contacts of the output relay are stuck, the power is still applied to the device when the device should stop running, which may cause the device to be in a high voltage state for a long time, damaging the electronic components of the device.
Damage to mechanical parts:
Due to the fault of PLC output wiring, the equipment operation status is unstable, such as frequent motor start and stop or abnormal speed, which will increase the wear of mechanical parts such as motor and reducer. If it is in this state for a long time, the mechanical parts may be damaged prematurely, increasing the equipment maintenance cost.
