是否为使用不当引起的故障，如属于这类故障，则根据使用情况可初步判断出故障类型、发生部位。常见的使用不当包括供电电源故障、端子接线故障、模板安装故障、现场操作故障等。
如果不是使用故障，则可能是偶然性故障或系统运行时间较长所引发的故障。对于这类故障可按PLC的故障分布，依次检查、判断故障。首先检查与实际过程相连的传感器、检测开关、执行机构和负载是否有故障：然后检查PLC的I/O模板是否有故障：最后检查PLC的CPU是否有故障。
在检查PLC本身故障时，可参考PLC的CPU模板和电源模板上的指示灯。
采取上述步骤还检查不出故障部位和原因，则可能是系统设计错误，此时要重新检查系统设计，包括硬件设计和软件设计。
OMEGA LVCN-130 LEVEL SENSOR *USED*
Ingersol Rand (IR) Model: A, Size 202, Pneumatic Impact Gun / Tool
Exfo FOT-12AX, 780, 850, 1300, 1310, 1550 nm Wavelength, Optical Power Meter
Leuze Drill Brake Control BKL 706 SE, 10000 #52227
(9196) BEI Encoder H25D-SS-1500-AC-8830-EM16
(6248) Numatics Valve 34SAD43BK 150 Psig 120V 50/60Hz .36A
Bosch Servo Controller #47624
Precision Devices Inc Surfometer PDA-36 Scratch & Dent #60445
(8488) Pro-Log Power Board Rack Interface 105390D
Marquip Tension Control Board #11298
(10145) Robicon PC Board A1A SEALED
(U2-3) 1 RELIANCE ELECTRIC BOARD GATE DRIVER
HP / Agilent Rev: B, Step PH Det Board Assy., for 3588A, etc.
(C) GENERAL ELECTRIC FANUC IC610CHS110A RACK POWER SUPPLY WITH 3 MODULES
GE 3S7505KH501A1 RELAY
Anritsu MA9301A, 0.75 to 1.7 μm, -90 to 0 dBm, Optical Power Sensor, for ML910B
Cash Acme Pressure Reducing Valve Valve117 #75117
Weinschel 1535R-20 0.5 to 1.0 GHz, 20 dB, SMA (F-F-F) Miniature Direc. Coupler
(N2-2) INDUSTRIAL DYNAMICS MULTI COUNTER ASSY. MODULE
Parker Cm233Ae Servo Motor
Hyperlink Tecnologies HG24084 2.4 to 2.5 GHz, 8 dBi, Type N (F), Antenna
(V20) DYNAQUIP AE104 VALVE
Axiomtek Fanless Barebone eBox746-EFL1G-B #47617
Barber Colman Data Handler PC Board A #68402
PRD S 2.0 to 4.0 GHz, 20 dB, Type N (F-F-F), Coaxial Directional Coupler
(U2-2) 1 GE 12TMC11B5A OVERCURRENT RELAY
HP 2.3 to 6.1 GHz, -10 to +20 VDC, YIG Tuned Oscillator, Fpr 8566B etc
Sick Safety Interlock iE 1000 ES1 #67201
GE Speed Matcher Board 115D2221G2
Hobart Weld Control HTC880 #56856
HP C4197 110 V Color LaserJet LJ Fuser Kit (Only 4 Rollers)
Barber Colman System Control Cabinet 6NNN-CE2CB-E00-B-00 #16471
HP/Agilent 700 Watts, VXI 7000 Series, Modular Power Supply
Alnor Type 2425, 1-18" Velometer Air Velocity Probe, includes Pouch
(L26-3) 1 GE FANUC 44AG01 BOARD
Rexroth Proportional Control Valve 4WRKE10E100L-32/6EG24ETK31/A1D3M #76812
Futaba Pulscale Linear Scale SM25BB #74535
(7598) Allen Bradley EEPROM Memory Module 1745-M1
HP / Agilent OS/H: 20mm, D: 7mm, Precision Open Termination
HP 155.52 Mb/s, SMA (F-F), Bandpass Filter. For 71501D etc.
TTC Fireberd 6000A Communication Analyzer + Opt 41800 Adapter
Pulsar CS 1.0 to 4.0 GHz, 4 W Max, SMA Coaxial Directional Coupler