If you work in a factory that uses programmable logic controllers to run the machinery, you may have come across a problem not being reported by the computer's display. If this is the case, there could be a problem with system's wiring. Use the two-step guide below to help you find and solve the problem.

Step 1:  Inspect The AC And DC Inputs And Cables

The first thing you need to do is inspect the AC and DC inputs. Because one works differently from the other, it is important to make sure they are wired correctly and using the right type of switch. Since the currents react differently, wiring these two types of inputs incorrectly could fry the system or shock you.

Locate the AC and DC input ports on the back of your PLC console. They should be clearly marked. After you find the ports, inspect the wires carefully to make sure they have not been switched. If the AC has been plugged into the DC port, or the other way around, unplug them and replace them in their proper ports.

Once you have made sure the cables are in their right ports, look at the cables themselves. There should be no fraying or other signs of visible damage to them. If there are, replace the damaged cable. 

After doing the above, look at the readout on the PLC computer console. If the relays do not light up or you do not have any readout on the screen, go on to the second step.

Step 2:  Check The Relay Outputs

Once you have repaired or ruled out any problems with the AC and DC inputs, the next step is to check the relay outputs. The relay outputs are what run the machinery it is hooked up to, also referred to as a load. This step also involves checking for problems with the relays as well as for shorts in the wiring or motor of your factory equipment.

Find the wires connecting the computer console to each piece of equipment its program is responsible for. Check the schematics located near the console to make sure each machine is connected to its proper relay output port. If not, switch them around until they are in their right positions.

Once this is done, check the cables running from the ports to the machines to make sure there are no gouges, fraying, or cracks in the outer rubber casing. If you do see one that shows signs of damage, replace it. Not only could a damaged cable present an electrocution hazard, but it could create a power surge that could harm the machine or the console.

After making sure the wires are intact, check the console's screen to see if you start getting a readout about the problem. If the screen is still dark or the relays keep toggling off, look at the wires and motor of the machine. 

If the wires are broken or the motor is running too hot, it could create an inductive load. This type of load is caused by a surge of power whenever a motor or fan kicks on. The surge creates a back current that could switch off the power source or relays. This happens as an attempt to save the main circuits in the computer.

If you feel the machine's motor or wiring is causing excessive inductive loads, they will need to be repaired or replaced. Once you have replaced all of the wires and repaired any machinery, look again at your console's readout screen to see if you receive an error code. If you do, follow your company's protocol for that particular code to complete your repairs.

Once you have completed the steps above, you may discover the system is still not working properly. If so, you may want to contact the eaton PLC manufacturer to discuss additional steps for determining whether the trouble lies in the system's hardware or the computer's software.