两线制接近开关直接接到PLC的输入端

克特接近开关按接线方制可分为三线制和两线制。       

三线制克特接近开关有两个端子接直流电源的正极和负极，另一个端子是接近开关的输出端。接近开关未动作时，输出电流近似为0。接近开关动作时，输出晶体管饱和导通，管压降近似为0，接近开关的输出晶体管相当于一个触点。

两线制接近开关的两根线兼作电源线和信号线，接近开关未动作时，需要一定的电流来维持电路的工作，所以有一定的漏电流。两线制接近开关只有两根线，接线方便，可以直接接到

PLC的输入电流小于逻辑0信号的最大电流（FX系列PLC为1.5mA）时，输入为0信号，PLC的输入电流大于逻辑1信号的最小电流（FX系列为3.5mA）时，输入为1信号。输入信号如果在二者之间，PLC读入的逻辑状态不定。FX系列连接两线制接近开关允许的最大漏电流为1.5mA。S7-200直接连接两线制接近开关允许的最大漏电流为1mA。

两线制接近开关的静态漏电流约为0.5~1.5mA，在选型时，应保证接近开关的漏电流小于PLC逻辑0信号的最大电流，并留有一定的裕量。如果不能满足这一条件，两线制接近开关可能出现误动作。使用时最好实测两线制接近开关的漏电流的大小。

KTGEE proximity switches can be divided into three wire and two wire systems according to the wiring method.

The three wire Kete proximity switch has two terminals connected to the positive and negative terminals of the DC power supply, and the other terminal is the output terminal of the proximity switch. When the proximity switch is not activated, the output current is approximately 0. When the proximity switch is activated, the output transistor saturates and conducts, and the voltage drop of the transistor is approximately 0. The output transistor of the proximity switch acts as a contact.

The two wires of the two wire proximity switch serve as both power and signal lines. When the proximity switch is not activated, a certain amount of current is required to maintain the operation of the circuit, so there is a certain leakage current. The two wire proximity switch only has two wires, making wiring convenient and allowing for direct connection

When the input current of the PLC is less than the maximum current of the logic 0 signal (1.5mA for FX series PLCs), the input is the 0 signal. When the input current of the PLC is greater than the minimum current of the logic 1 signal (3.5mA for FX series PLCs), the input is the 1 signal. If the input signal is between the two, the logic state read by the PLC is uncertain. The maximum allowable leakage current for the FX series connection two wire proximity switch is 1.5mA. The maximum allowable leakage current for S7-200 directly connected to a two wire proximity switch is 1mA.

The static leakage current of the two wire proximity switch is about 0.5-1.5mA. When selecting, it should be ensured that the leakage current of the proximity switch is less than the maximum current of the PLC logic 0 signal, and a certain margin should be left. If this condition cannot be met, the two wire proximity switch may malfunction. It is best to measure the leakage current of the two wire proximity switch during use.