现代PLC不仅有逻辑运算、计时、计数、顺序控制等功能，还具有数字和模拟量的输入输出、功率驱动、通信、人机对话、自检、记录显示等功能。既可控制一台生产机械、一条生产线，又可控制一个生产过程。
当所有的指令执行完毕时，集中把输出状态寄存器的状态通过输出部件转换成被控设备所能接受的电压或电流信号，以驱动被控设备，这就是输出刷新阶段。PLC经过这五个阶段的工作过程，称为一个扫描周期。完成一个周期后，又重新执行上述过程，扫描周而复始地进行。扫描周期是PLC的重要指标之一，在不考虑第二个因素（与编程器等通信）时，扫描周期T为：
（读入一点时间×输入点数）+（运算速度×程序步数）＋（输出一点时间×输出点数）十故障诊断时间
显然扫描时间主要取决于程序的长短，一般每秒钟可扫描数十次以上，这对于工业设备通常没有什么影响。但对控制时间要求较严格，响应速度要求快的系统，就应该精确的计算响应时间，细心编排程序，合理安排指令的顺序，以尽可能减少扫描周期造成的响应延时等不良影响。
Siemens Simatic FDC 157-0 DP/PA Coupler Module Model # 6ES7157-0AC83-0XA0
Yaskawa SGMD-32AWA-YR12 Servo Motor 3.2 Kw 2000 RPM Encoder UTMAE-B12DA
Action Instruments Action Pak Field Configurable Isolator
GE CR304ALG6A2R Red Lens Indicating Light 120 Vac
Adept Tech I/O PC Board VME Digital DIO Module
EFC Electtromeccanica 036046 Transformer Pri V Sec 220V & 110V
Omron H5CN-XBN UP Display Timer 12-48 Vdc 0.1-999.9 Seconds
THK GL15S16 500L Linear Actuator 500mm Travel 16mm Dia. Ballscrew Omron R7M Serv
SMC MGF100-75 Compact Guide Cylinder 100 MM Bore 75 MM Stroke
Mac 82A-BB-BKA-TM-RA11 Solenoid Valve 30-120 Psi Solenoids Vac To 150 Psi
Omron E2FM-X2C1-M1 Proximity Sensor 12-24 Vdc
Siemens 6ES7 307-1KA00-0AA0 Power Supply Vac Input 24Vdc Output
Phd Inc. Set Point Module 4.5-24 Vdc Output 18-24 Vdc Input
Legris 3805 60 14 3/8" OD x 1/4" NPT Male Connector Pkg of 2
Yaskawa CIMR-J7AM40P2 AC Frequency Drive GPD 305/J7 400 Volt, 3 Phase
Bussmann LP-CC-5 Low Peak Current Limiting Fuse 600 Vac Class CC 5 Amp
SMC CDQ2A32-75DZ Compact Cylinder 75 MM Stroke, 32 MM Bore
Ferraz Shawmut TRS60R 60 Amp Dual Element Time Delay Fuse Smart Spot
Allen Bradley 193-BSB 30 Overload
Bell & Gossett P50748 Impeller
Keyence FS-V22RP Fiber Optic Photoelectric Digital Amplifier Sensor
Fanuc A16BB Emergency Brake PC Board
Mitsubishi FX-16EYT-ESS/UL Transistor Output Block
Imperial 470-FH Triple head 180 degrees tube bender w/ Roto-Lok indexing handle
Pacific Scientific BAC DC Motor 24V 1200 RPM 1/3Hp 13 Amp 56C
Spang Power Control Unit
Allen Bradley 800MR-QB24S Illuminated Push Button 24V W/O Lens
Allen Bradley 700DC-PK800Z24 DC Relay Series A 24V DC
Banner Q23SP6LPQ Photoelectric Sensor 10-30 Vdc
Baldor EM3558T Electric Motor 2Hp 1755 RPM Vac 3 Ph. 145T TEFC
Balluff BOS 18K-PS-1LOC-E5-C-S4 Photoelectric Sensor 10-30 Vdc
Smc AW40-N04E-Z Pneumatic Filter Regulator 7-125 Psi
Allen Bradley 1201-HA1 Series B Programmable Terminal
SMC CDQ2B50-25D Actuator 50 MM Bore, 25 MM Stroke
Littelfuse L70S060 Fast Acting Semiconductor Fuse Powr-Gard L70S
Marathon Motor 56B34D2028
SMC VF3130-3GSB-02 Single Pilot Body Valve Ported
Allen Bradley 800T-QT24 Illuminated Green Momentary Pushbutton 24V Ac/Dc
Allen Bradley 193-BSB 30 Overload
HONEYWELL (NICS)
Warner Electric Slo-Syn Motor M062-CE04 4.2 VDC 1.9 Amps 200 Steps/Rev
