structure
The main composition of the intermediate relay is composed of coils and contacts. By energizing the control coil (iron core), the original normally open contact is closed and the original normally closed contact is disconnected. Similarly, if the control coil is de-energized , The normally open contact changes from closed to open, and the normally closed contact changes from open to closed;
Due to the different models of the intermediate relay, there may be one normally open and one normally closed, or two pairs of normally open and two pairs of normally closed, or four pairs of normally open and four pairs of normally closed, but there is only one control coil, and generally normally open Corresponds to the number of normally closed. This can be seen from the structure of the above figure. One normally open will accompany the one normally closed. One end is the common end, and the other corresponds to one normally open and one normally closed.
Case Analysis
As shown in the above picture, the relay generally consists of two parts, the body and the terminal. The structure shown in the structure is the body. The base is only the terminal, and the external wiring is introduced into the inside;
It can be known from the voltage description that the intermediate relay contacts can pass many medium voltage levels, from AC 6V to AC 380V, from DC 6V to DC 220V, but the current must be less than or equal to 5A.
It can be seen from the above terminal that there are 4 normally open and 4 normally closed
One thing to note is that the control coil of the intermediate relay can be DC, such as DC 24V, or AC, such as AC 220V. The specific model needs to be selected according to the designed electrical schematic diagram;
extend
There is also the relay shown in the figure above. This type of relay is only composed of multiple bodies sharing a terminal, but when used, it is actually multiple relays that are not related to each other. There is basically nothing too much about the wiring and the wiring of a single intermediate relay coil. There is a big difference. It may be that 9 DC0s need to be connected in parallel to connect 10 intermediate relays, but if you use the interconnected intermediate relays in the above picture, you only need to connect one DC0, and the wiring of the other and single intermediate relays is no different.
description
1. Used in relay protection and automatic control systems
2. Used to transmit intermediate signals in the control circuit
3. The structure and principle of the intermediate relay are basically the same as that of the AC contactor. The main difference is that the main contacts of the AC contactor can pass large currents, while the contacts of the intermediate relays can only pass small currents; and the main contacts of the intermediate relays Point and auxiliary contacts, AC contactors generally have three main contacts and one or two auxiliary contacts;
4. The definition of intermediate relay in the new national standard is K, and the old national standard is KA, so we can see signs such as KA1 or K1 on some drawings, which represent intermediate relays.
use
According to my personal use, there are generally two types, one for signal conversion and one for indirect control;
1. Signal conversion
Sometimes because of the sensor type NPN (power supply is DC24V) we purchased, that is, the signal sensor output is DC0V, but the input point of the PLC accepts the PNP type, which means that DC24V needs to be input. At this time, intermediate The relay is converted below, as shown below
The output terminal of the sensor is connected to the coil of the intermediate relay A1, and the other section of the intermediate relay coil is connected to DC24. One thing to understand is that the coil of the intermediate relay must have a positive voltage and a negative voltage. If A1 is positive, then A2 Must be negative, if A1 is negative, then A2 must be positive
Connect DC24V to the normally open end of a group of intermediate relays (this end must be the common end, if you don’t understand the common end as shown in the figure below, 1 is the common end, because if the input power supply is not connected to the common end, first it does not meet the circuit standard, and then the circuit may There will be problems, such as the normally closed point cannot be used), the other section is connected to the input of the PLC, once the sensor senses an object, it will output a DC0 signal, so that the coil is turned on, energized, and the normally open point is closed, because the upper end of the normally open point is connected The signal is DC24V, so the signal becomes 24V to the PLC
2. Indirect control one
Sometimes, when we use PLC to control the solenoid valve, because the solenoid valve coil requires a large current, and the solenoid valve is easy to be short-circuited and damaged, if you directly use the circuit as shown in the figure below, you can directly control the solenoid valve, but there will be risks, such as In the event of a short circuit, the output point of the PLC may be burned out, and serious PLCs may also have problems.
We use the intermediate relay to optimize it, as shown in the figure below
We use the output of the PLC to control the coil of the intermediate relay, and then use the normally open point of the intermediate relay to indirectly control the solenoid valve coil, so that even if the solenoid valve has a short circuit and other problems, it will not affect the PLC output point and function