Classification, structure and selection principles of time relays

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Classification, structure and selection principles of time relays [Copy link]

Classification, structure and selection principle of time relayTime relay is an automatic control appliance that uses electromagnetic principle or mechanical action principle to realize contact delay connection or disconnection. There are many types, and the commonly used ones are electromagnetic, air damping, electric and transistor types. The graphic symbol and text symbol of time relay are shown in Figure 1. Figure 1 Graphic symbol and text symbol of time relay1. DC electromagnetic time relayAdding a damping copper sleeve to the core of DC electromagnetic voltage relay can form a time relay, and its structural diagram is shown in Figure 2. It uses the principle of electromagnetic damping to generate delay. According to the law of electromagnetic induction, during the process of relay coil on and off, the copper sleeve will induce potential and flow induced current. The magnetic flux generated by this current always opposes the change of the original magnetic flux. Figure 2 Schematic diagram of iron core with damping copper sleeve 1-iron core 2-damping copper sleeve 3-insulating layer 4-coil When the electrical appliance is powered on, the armature is in the released position, the air gap is large, the magnetic resistance is large, the magnetic flux is small, and the damping effect of the copper sleeve is relatively small, so the delay of the armature when it is attracted is not significant (generally negligible). When the relay is powered off, the magnetic flux changes greatly, and the damping effect of the copper sleeve is also large, which delays the release of the armature and plays a delay role. Therefore, this relay is only used for power-off delay. This time relay has a short delay, and the longest delay of the JT3 series does not exceed 5s, and the accuracy is low. It is generally only used in occasions with low requirements. 2. Air-type time relay The air-damped time relay uses the air damping principle to obtain delay. It consists of three parts: electromagnetic system, delay mechanism and contact. The electromagnetic mechanism is a direct-acting double E type, the contact system is borrowed from the LX5 type micro switch, and the delay mechanism uses an airbag damper. Air damped time relays have both delayed contacts driven by the pneumatic mechanism in the air chamber and instantaneous contacts driven directly by the electromagnetic mechanism. They can be made into power-on delay type or power-off delay type. The electromagnetic mechanism can be DC or AC. 3. Semiconductor time relays Electronic time relays have become the mainstream product in time relays. Electronic time relays are composed of transistors or integrated circuits and electronic components. At present, there are time relays controlled by single-chip microcomputers. Electronic time relays have the advantages of wide delay range, high precision, small size, impact and vibration resistance, convenient adjustment and long life, so they are developing rapidly and widely used. There are two output forms of semiconductor time relays: contact type and contactless type. The former is a small magnetic relay driven by a transistor, and the latter is a transistor or thyristor output. 4. Single-chip microcomputer controlled time relays In recent years, with the development of microelectronics technology, new time relays composed of electronic components such as integrated circuits, power circuits and single-chip microcomputers have been launched in large quantities. Such as DHC6 multi-standard single-chip controlled time relay, J5S17, J3320, JSZl3 series of large-scale integrated circuit digital time relays, J5145 series of electronic digital display time relays, J5G1 series of solid-state time relays, etc. DHC6 multi-standard single-chip controlled time relay is produced to meet the requirements of industrial automation control and the increasing level of requirements. Multi-standard time relays allow users to choose the most suitable standard according to their needs, and use simple methods to achieve control functions that previously required more complex wiring. This not only saves intermediate control links, but also greatly improves the reliability of electrical control. DHC6 multi-standard time relays are controlled by single-chip microcomputers and LCD displays. They have 9 working modes, forward timing, countdown can be set arbitrarily, 8 delay periods, delay range from 0.01s to 999.9h can be set arbitrarily, keyboard setting, and the keys can be locked after the setting is completed to prevent misoperation. The control mode can be selected arbitrarily as required to make the control circuit the simplest and most reliable. Its appearance is shown in Figure 3. Figure 3 DHC6 multiple standard time relays J5S17 series time relays are composed of large-scale integrated circuits, voltage-stabilized power supply, toggle switch, four-digit LED digital display, execution relay and plastic shell. It uses a 32kHz quartz crystal oscillator and has two installation methods: panel type and device type. The device type socket can be fixed on the installation board with M4 screws. It can also be installed on a standard 35mm installation rail. J5S20 series time relays are small time relays with four-digit display. It uses crystal oscillation as the time base. Using large-scale integrated circuit technology, it can not only achieve a long delay of up to 9999h, but also ensure its delay accuracy. It can be used in panel installation, 35mm standard installation guide and screw installation with different installation sockets and accessories. 5. Selection of time relays When selecting time relays, attention should be paid to: the current type and voltage level of its coil (or power supply) should be the same as the control circuit; select the delay mode and contact type according to the control requirements; check the number and capacity of contacts. If they are not enough, they can be expanded with intermediate relays. The new series of time relays, such as JS14A series, JS20 series semiconductor time relays, and JS14P series digital semiconductor relays, have the advantages of small size, high delay accuracy, long life, stable and reliable operation, convenient installation, large contact output capacity, and complete product specifications. They are widely used in electric traction, sequence control, and automatic control of various production processes.

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Basic knowledge about relays Font size 9 pt 10 pt 12 pt 14 pt 16 pt 19 pt Data description: Relay characteristics of relays When the input signal x of the relay increases continuously from zero to the action value xx when the armature begins to attract, the output signal of the relay immediately jumps from y=0 to y=ym, that is, the normally open contact changes from off to on. Once the contacts are closed, the input quantity x continues to increase, and the output signal y will no longer change. When the input quantity x drops from a value greater than xx to xf, the relay begins to release and the normally open contact is disconnected (as shown in Figure 1). We call this characteristic of the relay the relay characteristic, also known as the input-output characteristic of the relay. The ratio of the release value xf to the action value xx is called the feedback coefficient, that is, Kf= xf /xx The ratio of the control power Pc output on the contact to the minimum power P0 absorbed by the coil is called the control coefficient of the relay, that is, Kc=PC/P0