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Precautions for finder relay selection

文章出处:芬德电子科技 / 作者:芬德电子科技 / 发表时间:2023-07-05

In order to use the finder relay correctly, please understand the characteristics of the selected finder relay and confirm whether it meets the service conditions and environmental conditions of the finder relay. At the same time, you must master the coil use method, contact mode and environmental conditions of finder relay in actual use. The following summarizes the factors and precautions to be considered in the selection of finder relay.


1. Correct model selection

To use the finder relay well, it is very important to select the correct type. You must first have a thorough understanding and careful consideration of the nature, characteristics and use requirements of the controlled object. Master and analyze the principle, purpose, technical parameters, structural characteristics, specifications and models of the selected finder relay. On this basis, the finder relay should be correctly selected according to the actual situation and specific conditions of the project.


2. Understanding of contacts

The dynamic and static contacts in the disconnected state when the coil of finder relay is not energized are called "normally open contacts", otherwise they are called "normally closed contacts". When a moving contact is usually closed by a static contact and normally open by another static contact, they are called "transfer contacts". In the same finder relay, there can be one or more pairs of normally open contacts or normally closed contacts (or both) or one or more groups of transfer contacts.

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3. Method of removing contact spark

Because the current of the finder relay contact is small, no arc will be generated between the contacts, but "spark discharge" will be generated. This is because there is an inductance in the contact circuit, and the inductance will have overvoltage when it is disconnected. This overvoltage will be added to the contact gap together with the power supply voltage, so that the contact gap just separated a little distance can be broken down and discharged. Due to the limitation of energy, only spark discharge will occur. The alternating conversion of energy in the capacitance and inductance between the contacts makes the spark discharge appear and disappear, becoming a high-frequency signal. In addition, spark discharge will damage the contacts, thus reducing the service life. Therefore, we must try to eliminate, and there are two practical spark elimination circuits. First, its basic function principle is to make the energy in the inductance not pass through RC rather than contact; Second, when it is disconnected, it is consumed on the load R.L through diode V, and only one application needs to be selected. However, it should be noted that the RC parameters should be properly selected. The parameters are mainly determined by experiments. Generally, the capacitance C can be selected according to the load current 1a/1 micro method. When using a diode, its positive and negative polarity should be connected correctly.


4. Method of increasing contact load

In use, if the load capacity of the contacts cannot meet the requirements, several pairs of contacts can be connected in parallel to solve the problem. However, it is necessary to adjust before use to make the synchronization of contacts meet the requirements, otherwise it will backfire. The best way is to use intermediate relays or contactors to expand the load capacity of contacts.


5. Solution when the return coefficient does not meet the requirements

The so-called return coefficient KF is a parameter that reflects the matching degree of suction characteristics and reaction characteristics, that is, it represents the difference between the action value and release value of finder relay. Finder relays for different purposes usually need different return coefficients. When the return coefficient of finder relays cannot meet the use requirements, circuits can be used to improve the return coefficient.


6. Improvement of closing and releasing time that does not meet the requirements

When the pull in and release time of the finder relay cannot meet the use requirements, it can be solved by changing the time constant of the coil circuit of the finder relay.

When it is necessary to accelerate the pull in, a resistor RF is connected in series in the coil circuit of the finder relay, and the purpose of accelerating the pull in can be achieved by appropriately increasing the power supply voltage and ensuring that the pull in current of the coil remains unchanged.