Detection switch is a kind of switch connected with other circuit elements to detect the parameters (such as current, voltage, etc.) of elements or circuits. The detection switch has induction function. The main body is usually various induction switches or proximity switches, which need external power supply to work.



1. Contact output type

Taking the contact of micro switch, limit switch and relay as the output switching element, and connecting with electromagnetic switch, small motor and electromagnetic device as the main purpose, it can carry out switching control of several amperes of current. When connecting with electronic control equipment, pay attention to vibration time and minimum load current.

2. Photoelectric coupling output type

The electrical insulation of the detection circuit is the same as that of the contact output type. Switch capable of controlling 10 ~ 50mA current.

3. DC 3-wire type

a. Voltage output type

The output circuit outputs a voltage signal to the load during detection. The voltage output type is mainly manufactured for the purpose of connecting electronic control equipment composed of transistors or ICs such as electronic counters, contactless relays, etc.

b. Current output type

It can also be called open collector output type. When the output transistor acts, there are NPN type (current absorption) of suction current and PNP type (current source) of discharge current. Using a small capacity power transistor in the output transistor, it can switch the current of 50 ~ 200mA, and directly drive the loads such as electromagnetic relay, electromagnetic valve, DC solenoid and display lamp.

4. DC 2-wire type

The proximity switch of this mode has two wires. Therefore, if you pay attention to the polarity during use, not only the use method can be the same as that of the mechanical limit switch, but also the wiring is simple, but you should pay attention to the following conditions.

(1) Even if the switch is closed, it is necessary to supply current to the detection circuit of the proximity switch. For this reason, a small amount of current flows in the load. This current is called leakage current. In case of leakage current, the "leakage current" is generated at both ends of the load × Load resistance value ", at this time, using high impedance load will produce poor recovery.

(2) When the switch is turned on, it is necessary to supply voltage to the detection circuit. At this time, if the switch is not in the fully open state, a few volts voltage drop will occur. This voltage is called residual voltage. Therefore, the power supply voltage needs to be the voltage value of "residual voltage + load action voltage". For recent products, the leakage current is generally below 1mA, and the residual voltage is 3 ~ 5V.

PC, relay, electromagnet, lamp, etc. can be used as load, and the input of TTL and other logic circuits should pay attention to the above matters.

5. AC 2-wire type

Ac200v municipal power supply can be used to switch 50mA ~ 1A AC load power supply. The switch components use thyristor, and the action principle is the same as that of DC 2-wire type. Therefore, it is necessary to supply current to the load even when the switch is closed.

When the switch is turned on, it supplies current to the internal circuit. Therefore, it is necessary to make the thyristor a non on angle, or insert a zener diode in series with the thyristor, so as to generate residual voltage. Therefore, attention should be paid to load selection. The leakage current of AC 2-wire type is 1.5 ~ 2mA, and the residual voltage is about 10V. In case of poor action and recovery, it should be connected in parallel with the load and installed with shunt resistance in advance