可编程序控制器一直在发展中，所以至今尚未对其下最后的定义。国际电工学会（IEC）曾先后于1982.11；1985.1和1987.2发布了可编程序控制器标准草案的第一，二，三稿。
在第三稿中，对PLC作了如下定义：可编程序控制器是一种数字运算操作电子系统，专为在工业环境下应用而设计。它采用了可编程序的存储器，用来在其内部存储执行逻辑运算、顺序控制、定时、计数和算术运算等操作的指令，并通过数字的，模拟的输入和输出，控制各种类型的机械或生产过程。可编程序控制器及其有关的外围设备，都应按易于与工业控制系统形成一个整体、易于扩充其功能的原则设计。
7易于扩充
Nash 904R2 904R1 vacuum pump
Nash CL9001 CL9002 vacuum pump
Zyra Research ZRI-XP-1x1 Abatement System Used
Zyra Research ZRI-XP-1x1 Abatement System Used
Head/Lobe for Nash HP liquid ring compressor, 316 SS
Three Zones Tube Furnace with Vacuum Pump for CVD
Edwards Booster Pump
Nash CL3001 CL3002 stainless vacuum pump
Seiko Edwards STPA2203 Turbo Pump Refurbished Unused
Nelmor 60 Hp Granulator, Bin, Vacuum Pump, Conveyor
1989 Vac Con V290TR Vacuum Jet Rodder Truck, Good cond.
SIHI LPH 85353 Liquid Ring Vacuum Pump 1600 CFM 28" Hg
Patterson Kelley Stainless Steel Vacuum Dryer
Patterson Kelley Stainless Steel Vacuum Dryer
Patterson Kelley Stainless Steel Vacuum Dryer
GODWIN DRI PRIME 8" ELECTRIC VACUUM PUMP **75 HP
Osaka Turbo Molecular Pump TG2003M Vacuum
Stokes 1721 Vacuum System, 615 blower w/ 212H-11 pump
ATMI Ecosys CDO 862 Abatement System Used
Edwards iGX600N Dry Vacuum Pump Refurbished Unused
Edwards iGX600 Dry Vacuum Pump Refurbished Unused
ATMI Ecosys Vector Ultra 3000 Abatement System Used
AM&D Vacumizer 100, Ametek 7.5HP, 480V Vacuum Pump Good
MKS Portable Vacuum Calibration System PVS-6 Baratron
NASH CL9002 VACCUM PUMP TEST #85S0182 CAST IRON POS 1
PreVac GDF-950 50hp Liquid Ring Rotary Vacuum Pump NICE
Vactronic PECVD Plasmatherm Etch Tool Oxford Novellus
Stokes Microvac 612-30 Vacuum Pump, 612 CFM, 20HP Mint!
Pfeiffer Balzers, Gas and Vacuum Station, Working
NASH CL9002 VACCUM PUMP TEST # 7041 CAST IRON NASH
Busch 1600 , RC1600 RC-1600 vacuum pump
Busch RA0630 Vacuum Pump, Reconditioned to OEM Specs
Nash CL9001 CL9002 vacuum pump
