The self diagnosis and fault diagnosis functions of PLC.
1、 Fault characteristics
After the PLC is powered on, the internal self diagnostic program of the system is first executed to check whether the various components of the PLC are operating normally, and the results of the inspection are displayed to the operator. The content of self diagnosis includes I/O part, memory, CPU, etc.
RUN LED, PROG LED, ERR LED, and ALARM LED indicator lights are installed on the front panel of the FPl series PLC control unit. During the execution of the system's user program, if there is a malfunction or special situation, it can be displayed to the operator through the above indicator lights, making it easy for the operator to detect and troubleshoot the problem in a timely manner.
|
Control unit indicator light status |
Explanation |
state |
||
|
RUN |
PROG |
ERR/ALARM |
|
|
|
bright |
extinguish |
extinguish |
Normal operation in operating mode |
operate |
|
extinguish |
bright |
extinguish |
Normal operation in programming mode |
stop |
|
flicker |
extinguish |
extinguish |
Use forced I/O function in operating mode |
operate |
|
bright |
extinguish |
flicker |
When a self diagnostic error occurs |
operate |
|
extinguish |
bright |
flicker |
When other malfunctions occur |
stop |
|
extinguish |
extinguish |
bright |
When the system watchdog timer encounters an error |
stop |
2、 Common faults and their diagnostic methods
Once a malfunction occurs during the system's operation, the first step is to fully familiarize oneself with the fault, such as the symptoms at the time of occurrence, the location of the fault, etc. Then, analyze the cause of the fault and try to eliminate it.
Common faults and their diagnostic methods
|
Serial Number |
Fault phenomenon |
Speculation on the reason |
diagnostic method |
|
1 |
Multiple insurance circuit breakers |
Short circuit or burnout of the circuit |
Replace power components |
|
2 |
The indicator lights of the control unit are all off |
① Sharing the power supply of the control unit with other devices |
① Disconnect other devices from the power supply |
|
② Poor power supply circuit or low voltage |
② Replace power components |
||
|
3 |
All inputs are not connected |
① No external input power supply added |
① Connect the power supply |
|
② Low external input voltage |
② Replace the rated voltage power supply |
||
|
③ Loose terminal screws |
③ Tighten the screws |
||
|
④ Poor contact at the terminal board connection |
④ Fully insert the terminal board into the lock or replace the terminal board |
||
|
4 |
The input of a certain number is not connected |
① Input wiring disconnected |
① Check input wiring |
|
② Loose terminal screws |
② Tighten the screws |
||
|
③ Poor contact at the terminal board connection |
③ Fully insert the terminal board into the lock or replace the terminal board |
||
|
④ Program error |
④ Modify the program |
||
|
5 |
The input of a certain number is not turned off |
program error |
Modify the program |
|
6 |
Irregular ON/OFF input |
① Low power supply voltage |
① Replace the rated voltage power supply |
|
② Noise causes misoperation |
② Install peak suppressors (or insulated transformers) or wire with shielded wires |
||
|
③ Loose terminal screws |
③ Tighten the screws |
||
|
④ Poor contact at the terminal board connection |
④ Fully insert the terminal board into the lock or replace the terminal board |
||
|
7 |
All outputs are not connected |
① No external output power supply added |
① Connect the power supply |
|
② Low external output voltage |
② Replace the rated voltage power supply |
||
|
③ Loose terminal screws |
③ Tighten the screws |
||
|
④ Poor contact at the terminal board connection |
④ Fully insert the terminal board into the lock or replace the terminal board |
||
|
⑤ Insurance circuit breaker |
⑤ Replace insurance |
||
|
8 |
The output of a certain number is not connected (the indicator light is off) |
program error |
Modify the program |
|
9 |
The output of a certain number does not turn off (the indicator light is off) |
① Output wiring disconnected |
① Check the output wiring |
|
② Loose terminal screws |
② Tighten the screws |
||
|
Poor contact at the terminal board connection |
③ Fully insert the terminal board into the lock or replace the terminal board |
||
|
10 |
The output of a certain number does not turn off (the indicator light is off) |
Cannot turn off due to leakage current or residual voltage |
Replace the load or add a fake load resistor |
|
11 |
The output of a certain number does not turn off (indicator light is on) |
program error |
Modify the program |
|
12 |
Output irregularly ON/OFF |
① Low power supply voltage |
① Replace the rated voltage power supply |
|
② Noise causes misoperation |
② Install peak suppressors (or insulated transformers) or wire with shielded wires |
||
|
③ Loose terminal screws |
③ Tighten the screws |
||
|
④ Poor contact at the terminal board connection |
④ Fully insert the terminal board into the lock or replace the terminal board |
||
|
⑤ Program error |
⑤ Modify the program |
||
|
13 |
ERR/ALARM flashing |
Error codes 1-9: There is a syntax error in the program |
Modify the program |
|
Error code 20 or above: Self diagnostic error |
Clear errors or take actions indicated in the error code table in PROG mode |
||
|
14 |
ERR/ALARM is on |
System watchdog timer error occurred |
Turn the mode switch of the control unit from "RUN" to "PROG", and turn off the power before turning it on again |
|
Control unit indicator light status |
Explanation |
state |
||
|
RUN |
PROG |
ERR/ALARM |
||
|
bright |
extinguish |
extinguish |
Normal operation in operating mode |
operate |
|
extinguish |
bright |
extinguish |
Normal operation in programming mode |
stop |
|
flicker |
extinguish |
extinguish |
Use forced I/O function in operating mode |
operate |
|
bright |
extinguish |
bright |
When a self diagnostic error occurs |
operate |
|
extinguish |
bright |
bright |
When other malfunctions occur |
stop |
|
extinguish |
extinguish |
bright |
When the system watchdog timer encounters an error |
stop |
