Relay is one of the important control components. It is an electric control device. Its application is also more extensive, most of them are used in CNC machinery, electrical machinery, copiers and other machinery, then the choice of relays and methods of knowledge, Xiaobian to talk about:
1, the correct selection
To make good use of relays, correct selection is very important. First of all, we must have a thorough understanding of the nature, characteristics and application requirements of the controlled object, and make careful consideration. The principle, application, technical parameters, structural features, specifications and models of the selected relays should be grasped and analyzed. On this basis, according to the actual situation of the project and the specific conditions, to select the correct relay.
2, the understanding of docking point
When the relay coil is not charged, the static and dynamic contact in the disconnection state is called "normally open contact", otherwise, it is called "normally closed contact"". A moving contact is normally closed with a stationary contact, and is normally opened with another static contact. They are referred to as "changeover contacts"". In the same relay, one or more pairs of normally open contacts or normally closed contacts (both at the same time) may also have a set or array of switching contacts.
3, the method of eliminating contact sparks
The relay contact on-off current is small, but does not appear between the contact arc, there will be a "spark", this is due to the presence of inductive contact circuit, the disconnect inductance overvoltage appears, which together with the supply voltage in the contact gap, just a bit apart from the contact gap breakdown distance the discharge. Due to limited energy, will only spark discharge, alternating energy capacitance and inductance are in contact, the spark discharge disappears, and become a kind of high frequency signal, and spark discharge to contact will cause damage, and reduce service life, so we must manage to eliminate the practical antispark circuit two a.
The basic function of the principle is that the energy in the inductor is not passed through the contact point through the RC;
Two 、 when disconnecting, the diode V is consumed on the load r.L. In the application, choose one. But it should be noted that the RC parameter should be chosen appropriately, and the parameters are determined mainly by experiments. Usually, the capacitance C can be selected by the load current 1A/1 micro method. When using a diode, its positive and negative polarity should be properly connected.
4, increase the contact load method in use, if the contact load capacity can not meet the use requirements, you can take a few pairs of contact parallel method to solve. But before use, should be adjusted, so that the synchronization of contact requirements, otherwise counterproductive. The best way is to use an intermediate relay or contactor to expand the load capacity of the contact.
5, the return coefficient does not meet the requirements of the solution
The so-called return coefficient Kf is a parameter that reflects the degree of fit between suction characteristics and reaction characteristics, that is to say, the difference between the relay action value and the release value. Relays with different uses often require different return coefficients. When the return factor of the relay cannot satisfy the requirements, the circuit shown in Figure 2 can be used to improve the return factor. Figure 2a is a circuit that reduces the Kf, while figure 2b is a circuit that increases the Kf. The value of the R in Figure 2 should be appropriate. That is to say, after the R is inserted, the voltage added to the relay coil must be greater than the operating voltage (Fig. 2a) or to maintain the voltage
6, the release time does not meet the requirements of improvement
When the relay pull in and release time can not meet the use requirements, the time constant of the relay coil loop can be changed to solve it. We know that the time constant T of the relay coil is equal to the ratio of the coil inductance L to the resistance R. If a resistor Rf is inserted into the relay coil loop, then T2 (T2=L/r+Rf) is less than T1 (T1=L/r). When the utility model needs to be accelerated to pull in, the resistance Rf is connected in series in the relay coil circuit, and the power supply voltage is appropriately improved to ensure that the current of the attracting current of the coil is kept the same, and the purpose of accelerating the pull in can be achieved. If the R is connected in parallel with a capacitor C, is attracting more suicide. A diode is connected in parallel with the two ends of the relay coil to achieve the purpose of delayed pull in. The principle is that when the relay coil is switched off, a short circuit coil is added to the iron core, so that the release time is prolonged.
7. Correctly select the alarm action state of the relay
Generally with alarm and interlocking function of the instrument, DCS, frequency converter are indispensable relay, that is, mostly through the relay contact and alarm, interlocking circuit associated with alarm and interlocking. When the alarm is to make the relay coil in "live" or "lost power" state, we start from the reliability of the "live" and "lost power" status of the advantages and disadvantages.
The relay coil "charged" action of the alarm circuit design which is most easily understood, but there is a hidden danger, when the wiring is not connected and open, or relay coil power supply problems, then the accident alarm when necessary, the relay coil should be "charged" action. But because of the above reasons without operation errors, the consequence is very serious.
If it is changed to "lose power" alarm, once the instrument connection is not good or open, the relay coil power supply problems, or instrument fault, there will be no possibility of losing the newspaper. The reason is in an alarm when the relay coil is in a "live" state, but the emergence of the abnormal phenomenon, the relay coil will return to the "loss of power" status, operation and maintenance personnel will be "alarm" and find the cause of the alarm, when the signal is found