Design of Relay Contact Control System

The electrical control system of the production machinery is an indispensable part of the production machinery. It plays a decisive role in whether the production machinery can work correctly and reliably. Generally, the electrical control system should meet the requirements of production machinery processing technology, safe and reliable operation and maintenance of the circuit, and low investment in equipment. For this reason, the control circuit must be designed correctly and the electrical components should be selected reasonably.

For relatively simple control lines, AC 380V ~ 220v voltage is often used directly, and this scheme is adopted without controlling the power transformer port. The overvoltage in the power supply circuit will be directly introduced into the control circuit, which is detrimental to the reliable operation of the components. In addition, due to the high voltage of the control line, which is detrimental to maintenance and safety, attention must be paid. For more complicated control circuits, when the electromagnetic coil of the machine tool electrical system exceeds 5 hours, the control circuit should use a control power transformer to reduce the control voltage to 10V or 24V. This solution is beneficial to the reliable function of maintenance and operating elements. For the control circuits of DC power drives that are operated frequently, DC power supplies are commonly used. If the control voltage is too high, a very high overvoltage (up to ten times the rated voltage) will be generated at the instant when the electrical coil is de-energized, which will affect the reliability and service life of the electrical appliance. If the control voltage is too low, the electrical contacts are not easily connected reliably, affecting the normal operation of the system. The control circuit of DC electromagnet and electromagnetic clutch is usually powered by 24V DC power supply.

In order to ensure the reliability of the operation of the control circuit, the electrical appliance should be reliable, firm, stable and meet the environmental conditions of use. The working time of the electrical component should be small (except for the delay). jobs. The electrical components must be connected to the coil of the electrical appliance correctly. The incorrect connection of the contacts will cause the control circuit to malfunction, sometimes causing serious accidents.

Coil connection Two AC contactors are connected in series to a dry AC circuit. Since the voltage on the contactor coil is distributed in proportion to the impedance of the coil, even two AC contactors of the same model cannot be connected in series after the two. On an AC power supply with twice the rated voltage, this is because when one of the contactors is working first, the impedance of the contactor is greater than the impedance of the non-sucking catcher, and the coil voltage of this contactor cannot reach the common rated voltage. Does not pull in. At the same time, the line current will increase, which may burn the coil, so the coil should be connected in parallel and then wound on the AC power supply of its rated voltage. The connection design of the contacts should be distributed in different positions. The electrical contacts should be pressed to the same group as much as possible to avoid short circuit on the electrical contacts. The AC contactor is a two-stroke control circuit. In the electrical control circuit, the joint contacts of all electrical appliances should be pressed to the left end of the coil, and the right end of the coil should be directly pressed to the power supply. In this way, the possibility of generating false loops in the line can be reduced, and the outlet and external connection of the control screen can be simplified.

When designing the control circuit, the making and breaking capacity of electrical contacts should be considered. If the capacity is not enough, an intermediate relay can be added to the line to increase the number of contacts in the line. To increase the making capacity, use multiple contacts in parallel, and to increase the breaking capacity, use multiple contacts in series. The replacement of the control circuit should be carried out in the control circuit with a small current as much as possible, which is safe and reliable.

Reduce the controlled load or the number of enzyme contacts passed by the appliance when it is connected, and the failure of the electrical contact circuit of the appliance will not work properly. This can be achieved by rational arrangement of the contact rhythm, every two relays are connected Only need to pass a pair of contacts, the work is more reliable, try to reduce the number of control electrical appliances and the number of contacts used in the control circuit. Under the condition of meeting the action requirements, the fewer electrical appliances used, the fewer contacts, the chance of failure of the control circuit The lower the reliability of the job. After merging, they can be reduced and simplified into lines, but when merging the contacts, it should be noted whether the rated current of the contacts allows the use of conversion contacts. Two pairs of contacts can merge a pair of conversion contacts to become the right line. This method is only suitable for intermediate relays with switching contacts. The unidirectional conductivity of the semiconductor diode can effectively reduce the number of contacts. The circuit shown is equivalent. The semiconductor diodes are applied by stems b and d, reducing the number of contacts. This method is economical and reliable in the control circuit of weak electric appliances. It has been applied in automatic grinders. When reducing the number of connecting wires and designing control lines, the position of each electrical contact can be reasonably arranged to reduce the number of connecting wires. In particular, it should be noted that different contacts of the same appliance should have as many common connection lines as possible in the circuit, which can simplify the wiring and reduce the number of wire segments and shorten the length of the wire. The travel switch is a multi-relay and time relay installed on the machine tool, which is installed on the control panel to go through a long distance. The circuit that prevents the parasitic circuit control circuit from being accidentally turned on during normal operation or an accident is called a parasitic circuit. If there is a parasitic circuit in the control circuit, it will destroy the working order of electrical appliances and circuits, and cause malfunction. The motor with indicator light and thermal protection is in the normal and reverse directions. When the control line is working in normal conditions, it can complete the start, reverse and stop operations. The signal light can indicate the working state of the motor. When the motor is overheated and the contacts are disconnected, a parasitic circuit will appear. Because the motor can not get the overheat protection port, if you move the contact to it in series, it can prevent the circuit from touching.

In the event of an accident, the relay press-contact control circuit should ensure the safety of the operator and the safety of electrical equipment and production machinery, and effectively prevent the expansion of the accident. When designing control lines, in order to avoid the possibility of accidents caused by main line faults, certain protective measures must be taken in the lines to ensure safety. Common protection measures include short-circuit protection, over-temperature and over-current protection, flying zero voltage protection, terminal protection, interlock protection, oil pressure protection, and some accident signals.

Electrical control equipment should be considered to operate the bureau, safe and convenient for maintenance, with isolated electrical appliances, and avoid live maintenance. The control circuit can be quickly and easily switched from one control mode to another. The electrical components should have spare contacts and spare electrical components for maintenance, adjustment and rewiring.

On the premise of meeting production requirements, control lines should be simplified and economical. Use standard links as much as possible, and reduce the number of connecting wires of components as far as possible to ensure normal operation.

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