由模块联结成系统有三种方法：
    ①无底板，靠模块间接口直接相联，然后再固定到相应导轨上。OMRON公司的CQM1机就是这种结构，比较紧凑。
    ②有底板，所有模块都固定在底板上。OMRON公司的C200Ha机，CV2000等中、大型机就是这种结构。它比较牢固，但底板的槽数是固定的，如3、5、8、10槽等等。槽数与实际的模块数不一定相等，配置时难免有空槽。这既浪费，又多占空间，还得占空单元把多余的槽作填补。
    ③用机架代替底板，所有模块都固定在机架上。这种结构比底板式的复杂，但更牢靠。一些特大型的PLC用的多为这种结构。
    1.4.3按生产厂家分
    目前生产PLC的厂家较多。但能配套生产，大、中、小、微型均能生产的不算太多。较有影响的，在中国市场占有较大份额的公司有：
    德国西门子公司：它有SS系列的产品。有SS－95U、100U、115U、135U及155U。135U、155U为大型机，控制点数可达6000多点，模拟量可达300多路。最近还推出S7系列机，有S7-200（小型）、S7-300（中型）及S7-400机（大型）。性能比S5大有提高。
    日本OMRON公司：它有CPM1A型机，P型机，H型机，CQM1、CVM、CV型机，Ha型、F型机等，大、中、小、微均有，特别在中、小、微方面更具特长，在中国及世界市场，都占有相当的份额。
IC600PM500 CPU/DPU Power Supply Card (AC)
IC600PM502 Standard I/O Rack Supply Card (AC)
IC600PM503 High Capacity I/O Rack Supply Card
IC600PM505 CPU Power Supply, 115 Vac
IC600PM506 CPU Power Supply, 115 Vac  A-B  1746-NO4V
IC600PM507 RPU Main Power Supply (AC)
IC600PM508 RPU Auxiliary Power Supply (AC)
IC600PM509 CPU Power Supply, 115 Vac
IC600PM510 Proloop Redundant High Capacity Pow
IC600PM511 CPU Power Supply, 115 Vac
IC600PM512 Proloop Individual Power Supply (AC)
IC600PM541 CPU/DPU Power Supply (24 Vdc)
IC600PM542 High Capacity Power Supply (24 Vdc)
IC600PM543 RPU Main Power Supply (24 Vdc)
IC600PM544 RPU Auxiliary Power Supply (24 Vdc)
IC600PP510 Program Development Terminal
IC600PR500 Proloop 1 Slot Rack  A-B  1746-NO4V
IC600PR501 Proloop 2 Slot Rack
IC600PR502 Proloop 3 Slot Rack
IC600PR503 Proloop 6 Slot Rack
IC600PT601 PorableTape Loader
IC600PX500 Proloop Auto Tune Controller
IC600PX502 Proloop Single Loop Controller
IC600PX503 Proloop Multi Loop Controller 4-20
IC600PX504 Proloop Multi Loop Controller 0-10
IC600RB750 RPU I/O Switch Card
IC600RB751 RPU CPU Switch Card  A-B  1746-NO4V
IC600RB752 RPU Device Switch Card
IC600RB753 RPU Processor Card
IC600RM715 RPU CMOS Memory Card
IC600RP551 Redundant Processor Unit (AC)
IC600RR551 RPU Rack And Supply Only (AC)
IC600YB800 Local I/O Receiver Card
IC600YB801 Remote I/O Receiver Card
IC600YB802 24 -48 VAC/DC Input Card
IC600YB804 115 Vac Input Card
IC600YB805 230 VAC/DC Input Card
IC600YB806 12 VAC/DC Input Card
IC600YB808 Interrupt Input Card  A-B  1746-NO4V
IC600YB810 115 Vac Isolated Input Card
IC600YB811 5 VTTL/ 10-50 Vdc Input Card
IC600YB812 Type J Thermocouple Input Card
IC600YB813 Type K Thermocouple Input Card
IC600YB814 Type S Thermocouple Input Card
IC600YB815 Type T Thermocouple Input Card
IC600YB816 Type B Thermocouple Input Card
IC600YB817 Thermocouple Input Type B  A-B  1746-NO4V
IC600YB818 ype E Thermocouple Input Card
IC600YB819 Type R Thermocouple Input Card
IC600YB830 Advanced Local I/O Receiver Card
IC600YB831 10 - 50 Vdc Input Card w/Lights
IC600YB841 0- 10 Vdc Analog Input Card
IC600YB842 -10 Vdc To +10 Vdc Analog Input Card
IC600YB843 4 - 20 mA Analog Input Card
IC600YB900 Local I/O Transmitter Card
IC600YB901 Remote I/O Transmitter Card
IC600YB902 24 Vdc Sink Output Card
IC600YB903 48 Vdc Sink Output Card
IC600YB904 115 Vac Output Card  A-B  1746-NO4V
IC600YB905 230 Vac Output Card
IC600YB906 12 Vdc Sink Output Card
IC600YB907 12 Vdc Source Output Card
IC600YB908 24 Vdc Source Output Card
IC600YB909 48 Vdc Source Output Card
IC600YB910 115 Vac Isolated Output Card
IC600YB911 5 VTTL Output Card
IC600YB912 230 Vac Isolated Output Card
IC600YB913 10-50 Vdc Sink Output Card
IC600YB914 Reed Relay Output Card
IC600YB915 Type 1 Axis Positioning Card
IC600YB919 Type 2 Axis Positioning Card
IC600YB921 5 VTTL 32 Point Output Card w/Light
IC600YB923 10 -50 Vdc Sink Output Card w/Light
IC600YB924 120 Vdc Output Card  A-B  1746-NO4V
IC600YB929 10-50 Vdc Source Output Card
IC600YB930 115 Vac Protected Output Card
IC600YB941 0-10 Vdc Analog Output Card
IC600YB942 -10 Vdc To +10 Vdc Analog Output Card
IC600YB943 4 - 20 mA Analog Output Card
IC600YB944 12k ASCII Basic Module Card
IC600YB945 20k ASCII Basic Module Card
IC600YB947 S1 & S3 I/O Link Local Card
IC600YB948 I/O Communications Control Card
IC600YB949 28k ASCII Basic Module Card
IC600YR500 I/O Rack w/o Power Supply
IC600YR501 Standard I/O Rack
IC600YR510 Standard I/O Rack
IC600YR511 Standard I/O Rack
IC600YR514 High Cap I/O Rack  A-B  1746-NO4V
IC600YR561 Substitute IC600YR560
IC609EXP101A Series 1 Jr. Expansion Unit
IC609EXP110 Ser1 Jr Expansion 24 Vdc
IC609EXP120 Ser1 Jr Expansion 24 Vdc Sink
IC609EXP121 Ser1 Jr Expansion 24 Vdc Sink
IC609SJR100 Series 1 Jr Programmable Control
IC609SJR101 SerUr 115 VAC Input/Output
IC609SJR102 Ser1 Jr 24 Vdc Sink
IC609SJR110 Ser1Jr24VdcSinkl/0
IC609SJR114 Ser1Jr24VdcSinkl/0  A-B  1746-NO4V
IC609SJR120 Programmable Controller
IC609SJR121 Programmable Controller
IC609SJR124 Programmable Controller
IC609TCU100 Timer/Counter Setpoint Unit
IC610CCM105 Data Communications Unit