PLC

PLC learning series 12: Troubleshooting PLC

The PLC reads inputs, processes them, and produces outputs through a program Using a portable device, console, or personal computer, the internal operation of a PLC can be tracked and many indicator lights are provided for troubleshooting.

Here are the steps for troubleshooting a PLC:

PLC Troubleshooting:

Power supply check:

The first thing to analyze is the reliability of the power and land of the PLC. Inspect power and ground cabling visually, finding broken, corroded or otherwise dubious links.

The power supply can also be electrically tested. If there is an AC power source in the PLC processor, test the input voltage; it should be within the recommended range of the supplier.

Actually PLC processors run on DC power, so it must be tested as well. The measure can DC power supply output and test whether the voltages are within the recommended ranges

Troubleshooting inputs and outputs

The primary objective of I / O troubleshooting is to figure out why the PLC’s internal status is not in line with the external situation.

The first thing to do is to establish the relationship between the actual I / O modules and the PLC program’s I / O instructions. This is achieved by using the same PLC addressing scheme you are working on, and this scheme is unique from one manufacturer to another.

Faults in field wiring

Fault wiring can cause fire, It is therefore important to check its condition before proceeding Most modules have a “fuse blown” indicator that indicates which channel or device has a blown fuse.

Such fuses can be reached from the front of the module, or the module may need to be removed or even disassembled to reach them.

The programming machine must first be connected to the PLC and the address associated with the output must be calculated. The output can then be “forced” ON or OFF internally in the PLC and a reaction module can be observed.

Steps for PLC troubleshooting:

  • Check for the cell or sensor area and switches in the problem area. Such as a tool changer, magazine and pallet changer. Look for the potential substitutes or tools that may be defective through the electrical prints.
  • Test the PLC or the internal control diagnostics for each output LED. Build every change manually. To stop any sudden movements, put the device in ESTOP. But be careful as some ladders are not written in complete safety.
  • Test the device or PLC diagnostics inputs when you make them and break them. If all of these work properly, continue to test the outputs below. Otherwise, test the energy returns with a meter to the PLC inputs.
  • At this stage, it may be appropriate to either trigger the device with an M-code if it is a CNC or if it is a direct PLC then execute the functions you are attempting to execute.
  • Determine possible solenoids or outputs to be switched on for each condition and control when switched on. Now test the addresses of the output LED or Y to see if they are being emitted by plc or command.
  • If the inputs are switched on by looking at the diagnostics or LEDs. Check that the right voltage comes out of the PLC with a meter and check that the correct voltage is in the solenoid.
  • Most PLC outputs often go through some kind of relay to switch to 120 volts. Make sure that you test the voltage on the relay coil and the supply but on the relay to the dry array of contacts.
  • Often these relay boards will go bad with a relay or have a gadget like a solenoid that shorts to the ground allowing the relay connection to burn up.
  • These relay boards will go bad with a relay or have a machine like a solenoid that shorts out to the ground allowing the relay connection to burn up.
  • If the communication with the relay is found to be wrong. Check the power off to ground from the circuit with your meter that can be shortened. If you have less than 40 ohms or so, you will most likely have a short time to get to the surface.
  • If the communication with the relay is found to be wrong. Check the power off to ground from the circuit with your meter that can be shortened. If you have less than 40 ohms or so, you will most likely have a short time to get to the surface.
  • Many PLCs are sometimes reset to clear and large alarms within the PLC itself if they are for automation or external fixtures.
  • But you generally would have a complete shut down of PLC functions if this were the case. Use caution on mushing any buttons on PLC’s






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