常用的开关量输出接口按输出开关器件不同有三种类型:是继电器输出、晶体管输出和双向晶闸管输出,其基本原理电路如图4所示。继电器输出接口可驱动交流或直流负载,但其响应时间长,动作频率低;而晶体管输出和双向晶闸管输出接口的响应速度快,动作频率高,但前者只能用于驱动直流负载,后者只能用于交流负载。 PLC的I/O接口所能接受的输入信号个数和输出信号个数称为PLC输入/ 输出(I/O)点数。I/O点数是选择PLC的重要依据之一。当系统的I/O点数不够时,可通过PLC的I/O扩展接口对系统进行扩展。 ALLEN BRADLEY 1770-CD6 DATA HWY TWINAXIAL CABLE ALLEN BRADLEY 1770-CD7 DATA HWY TWINAXIAL CABLE ALLEN BRADLEY 1770-CD8 DATA HWY TWINAXIAL CABLE ALLEN BRADLEY 1770-CD9 DATA HWY TWINAXIAL CABLE ALLEN BRADLEY 1770-CF ANALOG I/O MODULE POWER CABLE ALLEN BRADLEY 1770-CG RS232C INTERFACE CABLE ALLEN BRADLEY 1770-CH RG/PERIPHERAL INTERFACE CABLE ALLEN BRADLEY 1770-CK PLC-2/RS-232C REMOTE DRIVER CABLE ALLEN BRADLEY 1770-CP RS-232C MODEM ADAPTER CABLE 16.5FT/5.03M ALLEN BRADLEY 1770-FC PLC2 KEYBOARD MOD ALLEN BRADLEY 1770-FE PLC-3 KEYBOARD FOR 1770-T4 W/1770-KDA -KDB ALLEN BRADLEY 1770-FL PLC2 KEYBOARD FOR 1770-T3 W/1770KAA -KBA -KFA ALLEN BRADLEY 1770-HT1 SMART COMM. BLOCK ALLEN BRADLEY 1770-HT16 HART 16 CHANNEL NON-ISOLATED TERMINAL BLOCK ALLEN BRADLEY 1770-HT8 HART 8 CHANNEL NON-ISOLATED TERMINAL BLOCK ALLEN BRADLEY 1770-KAA ALPHANUMERIC KEYTOP OVERLAY FOR 1770-T1 -T3