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：
Pacific Scientific Control Driver SC422-460-T2 for BBH
Omron E5BS-QHKJ Temperature Controller
Omron E2K-C25ME1 Adjustable Capacitive Switch (8)
Numatics R2 Series 2 & 3-Position 4-Way Valves
Novellus CMP 676 Polisher Ind. Computer SpeedFam MP2
Motorola NTN5196A 6-Unit Battery Charger Radius P100
Motorola MVME 946C Mainframe Chassis PLC Module Rack
Motorola MVME 2600-1 VME Mainframe Processor Board
Mizar MZ VME8400 Floppy Disk Controller Board VME MVME
Mizar MZ VME8210 512K Ram Board VME MVME
Mizar MZ VME8115 CPU Board VME MVME
Lightwave Comm Lantronix SAR6105 Shared-Access Router
Linear Instruments 156 Strip Chart Recorder
Lightwave Comm Lantronix Network Interface
ISCO Model 900 Delay Timer
Cisco PSA18U-480C AC Power Adapter BRAND NEW!!
Dickson THTrace THP7F Temp Humidity Chart Recorder
Hewlett Packard HP C7670A ScanJet Auto Document Feeder
Georg Fischer +GF+ 199.021.947 Diaphragm Valve 1/2″
Georg Fischer +GF+ 199.027.973 Diaphragm Valve 1″
Georg Fischer +GF+ 168.315.534 A Type 315 Valve 1″
Omron 3G8B2-Z8040 MA010 CS001 NI021 NO020 PS000 PLC Rac
Ohaus 6010 Moisture Determination Laboratory Balance
Motorola NLN766B 6-Unit Battery Charger
Mizar MZ VME8315 Real-Time Clock & SRAM Board VME MVME
Mizar MZ VME8305 PIO Board VME MVME
LKB 2089 Bromma Uvicord III Control & Detector Units
Linear Instruments 212 Single-Pen 10″ Chart Recorder
Linear Instruments 885 Versagraph Chart Recorder 2-CH
ISCO Power Supply Model 453
Human Designed Systems HDS ViewStation BA-G2500G2-101
HP J2552A/B JetDirect Print Server Ethernet & LocalTalk
Gilford Inst. Lab Inc. 2520F InVitro Diagnostic Column
Georg Fischer +GF+ 199.021.427 Diaphragm Valve 32mm
Georg Fischer +GF+ 175.315.534 Type 315 Valve 1″
Gordos PB-24SM 24-Pos Mounting Board w/ IDC5 ODC5 OAC5
Gordos PB-24SM 24-Pos Mounting Board w/ Crydom Relays
GLI AccuChlor Residual Chlorine System AC1000P1
Dell TrueMobile 2300 Wireless Broadband Router
InFocus Systems PanelBook 550 LCD Projection Panel
Black Box MX881A Async Sync Local Mux Multiplexer
Fujitsu FC9607AWA1 Alarm & Orderwire Unit FLM 2400 ADM
Fuji Film Fujica Single-8 Z1 Camera w/ Fujinon Lens
Fujitsu EA1550S EA1000 Telecom ATM Switch Mainframe
FPM Analytics 8200-110-030 Analytical Information Sys
Fluoroware Dymak 8PC-16F-01 Pneumatic Pinch Valve
Fisher Scientific Accumet15 Accumet 15 pH Meter
