模块的外部表现就是它的工作状态的种种显示、种种接口及设定或控制开关。一般讲，模块总要有相应的状态指示灯，如电源显示、运行显示、故障显示等。箱体式PLC的主箱体也有这些显示。它的总线接口，用于接I/O模板或底板，有内存接口，用于安装内存，有外设口，用于接外部设备，有的还有通讯口，用于进行通讯。模块上还有许多设定开关，用以对PLC作设定，如设定起始工作方式、内存区等。
二、I/O模块：
PLC的对外功能，主要是通过各种I/O接口模块与外界联系的，按I/O点数确定模块规格及数量，I/O模块可多可少，但其大数受所能管理的基本配置的能力，即受大的底板或机架槽数限制。I/O模块集成了PLC的I/O电路，其输入暂存器反映输入信号状态，输出点反映输出锁存器状态。
三、电源模块：
有些PLC中的电源，是与模块合二为一的，有些是分开的，其主要用途是为PLC各模块的集成电路提供工作电源。同时，有的还为输入电路提供24V的工作电源。电源以其输入类型有：交流电源，加的为交流220VAC或110VAC，直流电源，加的为直流电压，常用的为24V。
四、底板或机架：
Square D Mod 6 Breaker MCC Bucket MCCB 60 Amp A Feeder
GE General Electric THKM826F000 800 Amp 800A A 800A
Square D I-Line HCN3263-4M 400Amp 400 Amp Interior
Cutler Hammer WH DK DK3300Z01 KT3300T DK3300 300 A Amp
ABB Breaker 600V 600 V Type LS 600A 600 Amp A LS63600L
Reliance Electric 2GU21002 2HP GP-2000 230V 2 HP GP2000
Allen Bradley AB 1336S-BRF50-AA-EN5 5 HP AC Drive NIB
Omron FND-X06H 200/240VAC Position Driver FNDX06H
Modicon AM-S985-800 Modbus Plus Network Adapter
Modicon MM-PM10-300 PanelMate Plus MMPM10300
Square D Mod 6 Breaker MCC Bucket MCCB 40 Amp A Feeder
Square D Circuit Breaker FCL FCL34090 90 A 90A Amp NEW
GE Fanuc A20B-2001-0042/03C Multiplexer Board
General Electric TFL236100WL 100Amp Amp 100 A W/ Shunt
Explosion Proof Westinghouse Size 2 starter 15A Combo
Square D Sz Size 5 8502SG01S1 2 Ph Contactor 480V 8502
Ohmart Smart-Pro Remote Electronic Control smartpro Oh
GE 12-IAC66K58A Time Overcurrent Relay 12IAC66K58A New
Eurotherm ECMA1/FA102 Process Monitor w/Base ECMA1FA102
Eurotherm ECMA1/FA108 Extrusion Combination ECMA1FA108
Eurotherm ECMA1/FA102 Control Master/Process Monitor
Eurotherm ECMA1/FA108 Control Master/Extrusion Combo
ITE Gould 5600 Breaker Size 3 A203E MCC Bucket 100A
Viking H-2 958A Alarm Valve 175PSI H2 958-A 175-PSI 6in
Foxboro 40PR-A412-SE2B Circular Chart Recorder 40PR
Yaskawa CIMR-3.7B.E04 230V Series AC Drive CIMR3.7B.E0
Endress+Hauser FTL366QGN2A14G Liquiphant II 2 EH Switch
Square D I-Line LA36400 LA-36400 400 Amp 400A A
Westinghouse WH Sz Size 4 A200M4CAC Motor Starter 120V
GE Spectra Series ADS32100HD Bus Plug 100 Amp Fusible
ITE Gould 5600 5640 Fused Size 3 14HSt32A* MCC Bucket
Furnas 40JB32A* Size 4 135A Motor Starter 120V Coil
Furnas System 89 Size 3 Breaker Type Combo MCC Bucket
Westinghouse HMCP Breaker HM2P400X5C 400Amp A 400A 400
TI/Siemens 505-6860 RS485/RF I/O Channel Converter
GE 7700 Size Sz 3 Breaker MCC Bucket MCCB 100 A Amp
GE 7700 Size Sz 3 Breaker MCC Bucket MCCB 100 A Amp
Kollmorgen BDS4A-206J-W/O Servo Drive/Amplifier
Vaisala HMP234 D2B1A1AA23A2A3A Humidy and Temp Transmit
Vaisala HMP233 D2C0A2AA23A1A3B Humidy and Temp Transmit
Square D Transformer 25 kVA 480/240 240/120 1 Ph 25kVA
GE Fanuc IC600RB751K CPU Switch IC600RB751-K
DuPont 571001 5700 Moisture Analyzer Du-Pont
General Electric 7098 6″ 150 A Amp MCC Feeder Bucket
Mitsubishi Melsec A1SD75M2 Cnet Positioning Module NIB
Acme Transformer 11 kVA 575/230Y/133 11kVA 230 Y 3R 3PH
Viking H-2 958A Alarm Valve 175PSI H2 958-A 175-PSI 6in
Rosemount 3051 Transmitter 3051S2TG3A2E11A1AK5M5C4
GE General Electric TFL236125WL 125Amp A 125A W/ SHUNT
GE General Electric Breaker TFL236080WL 80Amp 80 A 80A
Westinghouse Molded Case Switch LA3600FS 600 Amp A 600A
Ashe Transformer 29 kVA 480/415Y V 29kVA 415 Y 3 PH
Maxon Shut-off Valve 4″ F 808CP 1 Natural Gas
Gould Shawmut A4BY5000 Fuse Amptrap L A4BY 5000 A 600V
Modicon MM-16MP-001 Interface Panel AS-040A-003
Challenger CJH 65k CJH3250 225 Amps CJT3225T Trip NICE
Fanuc A06B-6076-H101 6 Axis Servo Amplifier
GE A Series Panelboard W/Main Breaker 225 Amp A 208Y
General Electric GE Disconnect Switch 400 Amp A TH3365
Powerformer Transformer 30 kVA 480/208Y/120 3PH 208 Y
Fanuc A06B-6076-H001 6 Axis Servo Amplifier
GE General Electric Tri-Break TB 43F TB43400 400Amp A
Norgren VM106517AQ6616 EtherNet Valve Manifold
Powerformer 30 kVA 480 / 208Y / 120 3PH Y 30kVA 208 Y
Cutler Hammer WH HJD HJD3250F JT3150T HJD3150 150 Amp A
Square D I-Line KC34175 KC-34175 175 Amp 175A A breaker
MagneTek GPD 505 VS Drive 2 HP GPD505V-B003 GPD505
Westinghouse Circuit Breaker LB3400FS LB 400 Amp A 400A
Westinghouse Breaker FB3015PL 15Amp 15 Amp A Tri-Pac
GE A Series Panelboard W/Main Breaker 225 Amp A 208Y 49
GE A Series Panelboard W/Main Breaker 225 Amp A 208Y 55
Square D D325N Disconnect Safety Switch 400 Amp D 325 N
Siemens ITE Breaker FXD63B150 150A A 150Amp Amp 150 New
Westinghouse Transformer 30kVA 480 Delta / 208Y / 120
ABB ACS-601 AC Drive ACS601-0009-6 3PH 525-600 VAC 63Hz
Square D I-Line I-Limiter IK36225 225 Amp IK-36225
Cutler Hammer WH KDB KDB2350 KT2350T KDB2350 350 A Amp
Square D I-Line KH36125 KH-36125 125 Amp 125A A breaker
