PLC Panel troubleshooting


PLC troubleshooting is to correct the common operating problems with system components.

Check for adequate power:

An under-powered unit could result in unpredictable behavior.

  • The 400/600 DC powered terminals require 24V dc at 1.0 A.

  • The 400/600 AC powered terminals require 85 to 264V ac.

  • The 700-1500 DC powered terminals require 24V dc at 2.9 A.

  • The AC Power Supply (2711P-RSACDIN) for 700-1500 terminals meets Class 2/SELV requirements.

Check LED indicators on the terminal at startup:

The terminals have two LED indicators to isolate operating problems:

  • COMM indicator (green) for communications
  • FAULT indicator (red) for hardware faults

The red LED should be Off, except for a few brief flashes, and the green LED should be On.

  • If the LEDs remain Off on the 700-1500 terminals, the power supply or logic module has failed. Check the power cable. Replace the logic module if the power is within range; if not, replace the power supply.

  • If the LEDs remain off on the 400/600 terminals, check the power cable.

Check the voltages and temperatures:

Display Temperatures should be less than 55 °C. The CPU temperature should be less than 95 °C.

If the temperatures are higher, check for obstructed airflow through the chassis and attempt to moderate the ambient temperatures within the enclosure and surroundings.

Ethernet Cable connection:

Check for good connections and things such as quality, crimping, hub connection, and uplink ports. A bad Ethernet connection and the absence of a valid IP address are typically reported in a Communications error message box. Do not allow devices on the network with same (host) name.

Troubleshooting Input modules:

The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices.

An input filter eliminates false signals due to contact rebound or electrical interference; Optical isolation protects the circuits of the backplane by isolating the logic circuits from the input signals; The logic circuits process the signal; An input LED turns on or off to indicate the status of the corresponding input device.

Troubleshooting Output modules:

Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices.

The processor determines the output status; Logic circuits maintain the output status. An output LED indicates the status of the output signal, Optical isolation separates logic and backplane circuits from field signals; The output driver turns the corresponding output on or off.

DC outputs typically are used to drive high-current electromagnetic loads such as solenoids, relays, valves, and motor starters.

Analog outputs can be used to drive devices such as voltmeters, X-Y recorders, servomotor drives, and valves through the use of transducers.