[Relay usage knowledge]: 1. It is very important to select relay correctly. First of all, we must have a thorough understanding of the nature, characteristics and usage requirements of the controlled object and give careful consideration to them. The principle, use, technical parameters, structural characteristics, specifications and models of the selected relays should be mastered and analyzed. On this basis, we should ___________.

1. Choosing the right type

In order to make good use of relays, it is very important to choose the right type. First, we must have a thorough understanding of the nature, characteristics and requirements of the controlled object, and give careful consideration to them. The principle, use, technical parameters, structural characteristics, specifications and models of the selected relays should be mastered and analyzed. On this basis, relays should be selected correctly according to the actual situation and specific conditions of the project.

2. Understanding of Contact Points

When the relay coil is not live, the dynamic and static contacts in the open state are called "normal open contacts" and vice versa, they are called "normal closed contacts". A moving contact is often closed with one static contact and open with another static contact at the same time. They are called "conversion contacts". In the same relay, there may be a pair or a number of pairs of normally open or closed contacts (both can also have), or a group or array conversion contacts.

3. Method of eliminating ignition spark

Because the current of relay contacts is small, there will be no arc between contacts, but there will be "spark discharge". This is because there is inductance in the contact circuit, and there will be over-voltage on the inductance when the relay contacts are disconnected. It is added to the contact gap together with the power supply voltage, so that the gap just separated a little distance breaks down and discharges. Due to energy limitation, spark discharge will only occur. There are alternating transformations of capacitance and energy in inductance between contacts, which make spark discharge appear and disappear, and become a high frequency signal. Moreover, spark discharge docking point will cause damage and reduce service life. Therefore, we must try to eliminate them. There are two practical spark circuits, as shown in Figure 1. The basic principle is that the energy in the inductor passes through RC without passing through the contacts. Secondly, it is consumed on the load R.L by the diode v when the inductor is disconnected. Choose one in the application. However, it should be noted that the parameters of RC should be selected appropriately. The parameters are mainly determined by experiments. Usually, the capacitance C can be selected by 1a/1 micro-method of load current. The positive and negative polarities of the diode should be connected correctly when using it.

4. Ways to Increase Contact Load

In use, if the load capacity of the contacts can not meet the requirements of use, several pairs of contacts can be adopted to solve the problem in parallel. But before use, it should be adjusted to make the synchronization of the contacts meet the requirements, otherwise it would be counterproductive. The best way is to use intermediate relays or contactors to expand the load capacity of the contacts.

5. Solutions when the coefficient of return does not meet the requirements

The so-called return coefficient KF is a parameter reflecting the degree of coordination between suction characteristics and reaction characteristics, that is, the difference between action value and release value of relay. Relays for different purposes often require different return coefficients. When the return coefficients of relays can not meet the requirements of use, the circuit shown in Figure 2 can be used to improve the return coefficients. Fig. 2a is a circuit to reduce kf, while Fig. 2b is a circuit to increase kf. The value of R in Figure 2 should be appropriate, that is to say, the voltage added to the relay coil must still be greater than its action voltage (Fig. 2a) or holding voltage (Fig. 2b) after series R.

6. Improvement of inconsistent absorption and release time

When the time of absorption and release of relay can not meet the requirements of use, the time constant of relay coil circuit can be changed to solve it. We know that the time constant T of the relay coil is equal to the ratio of inductance L to resistance R. If a resistance RF is connected in series in the relay coil circuit, then T2 (t2 = L / R + rf) is less than T1 (t1 = L / r).

When accelerated suction is needed, a resistance RF is connected in series in the relay coil circuit, and the power supply voltage is increased appropriately to ensure that the coil suction current remains unchanged, so as to achieve the purpose of accelerated suction. If a capacitor C is connected in parallel at both ends of r, the suction time is shorter as shown in Fig. 3a.

When a diode is connected in reverse parallel at both ends of the relay coil, the purpose of delayed suction can be achieved. See Fig. 3b. Its principle is that when the relay coil is cut off, it adds a short circuit coil to the core, which prolongs the release time.

7. Correct selection of alarm action state of relay

Generally, instruments, DCS and frequency converters with alarm and interlocking functions all use relays, that is, they are mostly connected with alarm and interlocking circuits through relay contacts to carry out alarm and interlocking. When alarming, is it better to make the relay coil "live" or "lose power"? We analyze the advantages and disadvantages of "live" and "lose power" from the point of reliability.

It is the most understandable design that the relay coil acts to make the circuit alarm when it is "live", but there is a hidden danger, that is, when the relevant wiring is not connected properly and the circuit is open, or when the power supply of the relay coil is out of order, the relay coil acts when the accident needs to be alarmed, but because of the above reasons, it fails to act, and the consequence is very serious. .

If we change [knowledge of relay use]: 1. It is very important to select relay correctly. First of all, we must have a thorough understanding of the nature, characteristics and requirements of the controlled object, and give careful consideration to them. The principle, use, technical parameters, structural characteristics, specifications and models of the selected relays should be mastered and analyzed. On this basis, we should ___________.

Alarm for "power loss".