Catalog
Introduction
A relay is a type of electrical switch that has input and output terminals for single or multiple control signals. More information regarding the precise nature of the task will need to be evaluated in order to identify which specific type of latching relay switch would be suitable for use in a given application or environment. In this article, we'll take a closer look at the many latching relay circuit switch types available, as well as how they work and in what kinds of applications they might be most useful. There are various varieties of relays available in the market depending on the requirement, such as a solid-state relay, reed relay, latching relay, automotive relay, delay relay, differential relay, timer relay, and so on. As a result, this page offers an introduction to latching relays, including how they function, different varieties, and applications.
Ⅰ What is Latching Relay?
A latching relay is a two-position electrically controlled switch. It can keep either contact position indefinitely without applying electricity to the coil. It is controlled by two momentary-acting switches or sensors, one of which sets and the other of which resets the relay. Because the latching relay remains in its position when the actuating switch is disengaged, it serves as a rudimentary memory device. These kinds of relays are also known as impulse relays or bistable relays. The latching relay symbol is depicted below.
Latching Relay Symbol
Ⅱ How does a Latching Relay Work?
When a mains voltage pulse is applied to the latching relay's coil terminals, it closes or opens its contact. Depressing one of the pushbuttons causes the pulse to be created. All of the pushbuttons are linked in series.
The zone's lighting circuit can be controlled from many locations by using latching relays. It is popular in corridors, stairwells, and large spaces.
When latching relays are used instead of contactors in lighting circuits, no coil is required, resulting in a 2W savings per relay. Each relay saves more than 5 kWh of electricity per year on average (for average use of 8 hours a day). Furthermore, the latching relays provide illumination control with an infinite number of pushbuttons. The circuit with parallel keys is quite simple to implement! This makes it particularly ideal for use in more sophisticated lighting facilities, where, for example, the sequential control of utilities is required via a single circuit of pushbuttons.
Because of their design philosophy, which consumes only a brief time of the impulse control, these devices can be employed to realize novel solutions while maintaining optimum energy savings.
Ⅲ How do You Reset a Latching Relay?
Applying a positive voltage to a latching relay allows it to be set and reset. When a positive voltage is applied to the push button, the relay is activated. Similarly, if a reverse voltage is applied via a pushbutton, the relay will reset.
The first schematic depicts a circuit in which the 'Set' switch takes precedence. This means that if both the 'Set' and 'Reset' switches are pressed simultaneously, the relay will activate.
The following design depicts a circuit in which the 'Reset' switch takes precedence. If you press the 'Set' and 'Reset' switches at the same time, the relay will turn off.
Ⅳ Latching Relay Circuit Diagram & Working
latching relay diagram
The circuit diagram for a latching relay is illustrated below. This circuit can be designed with a single push button switch, a 12V battery, two relays such as RL1 and RL2, 1N4007 diodes such as D1 and D2, and a load such as a bulb. When you connect the power to the circuit, the output load will be turned off. When the switch SW1 is pressed for 1 second, the load in this circuit-like bulb is activated. If we press the same switch for 1 second again, the load will be turned off.
Latching Relay Circuit with Single Push Button
First, if the push button switch is not turned on and the power supply is turned on across the circuit, current flows over the common pin of the RL1 relay first, followed by current flowing through the coil of the second relay, RL2. As a result, just the second relay, RL2, is triggered in this scenario, whereas the RL1 relay is not.
When the push button switch SW1 is held for one second, positive power flows through the COM & NO pins of the RL2 through RL1 relays, crossing the diode D1. Because the flow of current from RL1 is disconnected, the RL1 relay is now triggered, and the RL2 relay is deactivated. As a result, the current is supplied to the load, and the load is triggered.
The RL2 relay is now turned off, and the NO and COM pins of the RL2 relay are linked. If we press the push-button again, a short circuit will form across these pins, and the voltage at the RL1 coil will drop to zero, deactivating the RL1.
So, after deactivating the RL1 relay, the pins COM and NC are linked, and the current passes through the RL2 coil, activating the RL2. As a result, the output load is once again turned off in this circumstance.
Ⅴ Latching Relay Types
Latching relays are available in three types magnetic latching, impulse sequencing & mechanical latching.
5.1 Magnetic Latching Relays
A single pulse of current to a coil temporarily generates an electrical field that moves a reed switch in either direction in the widely used magnetic design for latching relays. When the pulse stops, the latching relay remains electromagnetically stuck in the position it was just moved to, and will not return to the opposite position until another, redirected pulse is transmitted through the coil(s) to move it back.
Magnetic latching relays are especially helpful in cases where interrupting the current flow to the coils will not result in the undesirable consequence of moving the switch to a different position between the two contacts, in addition to offering the lower power consumption common to all latching relays.
They can also conduct the switching motion very fast, are less bulky than their mechanical counterparts, and have a longer lifespan due to the very restricted range of physical movement within the switch.
Magnetic Latching Relay
5.2 Mechanical Latching Relays
A mechanical latching relay, as opposed to a magnetic latching device, employs a physical locking mechanism to keep the armature against the contact at the last position it was moved to. Electromechanical relays have several advantages and disadvantages:
Mechanical Latching Relay
- They have larger, heavier contacts than electromagnetic ones and, as a result, are less flexible in terms of space needs.
- Mechanical latching relays are superior at dealing with unexpected surge currents.
- Because of the quantity of mechanical movement required, switching speed is limited, making them inappropriate for various applications.
- In terms of the overall number of actions, mechanical latching relays typically have a little lower lifespan than their magnetic counterparts.
- However, the current size is an equally significant aspect in terms of overall longevity for any relay switch.
- The estimated lifetime of mechanical relays under greater loads is frequently substantially slower than that of magnetic reed equivalents.
- Its contacts will be less susceptible to deterioration during thermal cycling than an electromagnetic latching relay.
5.3 Impulse Latching Relays
Impulse relays are a type of magnetic latching relay in which the contact state changes with each input pulse. When power is applied, the impulse latching relay automatically recognizes which position the switch is in and energizes the opposite coil to actuate or move it each time.
The impulse latching relay often accomplishes this by the use of a solid-state steering circuit, which allows the input pulse to be unidirectional without the need to redirect or reverse the polarity. As a result, impulse switches are particularly suited to applications requiring the ability to turn a single device on or off from one or more places using a single momentary switch or push button.
Impulse Sequencing Type
5.4 Two Types of Coils for Applying the Set and Reset Pulse Voltages
A single-winding type and a double-winding type.
Basic Operation:
Item
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Basic circuit
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Operation pattern
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Outline
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Classification
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Double-winding Latching Relays
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The input pulse of the set coil allows the operational condition to be maintained magnetically or mechanically in these Relays, but the input pulse to the reset coil side causes the Relay to be reset.
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Single-winding Latching Relays
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The set input pulse maintains the operational condition magnetically in these Relays, but the reset input pulse (input with the inverse polarity of the set input) resets the Relay.
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Ⅵ Difference between Latching and Non-Latching Relays
The difference between latching and non-latching relay includes the following.
Latching Relay
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Non-Latching Relay
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A latching relay will stay in the last position when it was powered last.
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A non-latching relay goes back to its regular position.
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This relay is also known as a keep impulse, bi-stable, and lock up the relay.
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It is also known as a typical mechanical relay.
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As compared to a non-latching relay, this relay consumes less power.
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This relay consumes more power.
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These relays have noiseless switching within household applications.
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These relays have some noise while operating.
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These relays, unlike non-latching relays, are not intended to be utilized in very sensitive applications. When the latching relay is worried, it loses a lot of sensitivity.
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Non-latching relays have high sensitivity as compared to latching relays.
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The latching relays include indicating knobs that are used to control the position of the relay manually.
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This relay doesn’t have to indicate a knob feature.
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The life service of latching relay is no longer.
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The life service of the non-latching relay is longer.
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These relays are more expensive.
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Non-latching relays are not expensive as compared to latching relays.
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These relays are very efficient, so they do not have a broad range of application regions.
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Non-latching relays are used anywhere in electronics & automation.
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Ⅶ Advantages and Disadvantages of Latching Relay
Advantages
The advantages of latching relay include the following.
- It necessitates pulse excitation and can operate through a single coil if not a double coil.
- Its size is tiny, allowing it to be readily linked to a PCB.
- Load capacity is high.
- Power consumption is reduced.
- Reliable, safe, and with long service life.
- Safe and dependable.
- These relays essentially save crossbar switches, allowing lighting control to be accomplished by push buttons rather than a combination of three-way and crossbar switches.
- These relays help to save conductors.
- They offer greater convenience in handling all loads while leaving the house.
- When compared to contractors with the same nominal current, these relays simply control more bulbs.
- It takes less time to connect the devices while utilizing this relay.
- It helps to save electricity.
Disadvantages
The disadvantages of latching relay include the following.
Latching relays need two control signals for turning ON & OFF the load.
- When compared to static relays, electromagnetic relays require a large load range of transformers.
- They use more materials than electromagnetic relays.
- The relays do not have directional capability.
- It must be serviced and tested on a regular basis.
Ⅷ Applications of Latching Relay
The applications of latching relay include the following.
- These relays merely allow a consumer to control a circuit by sending a single pulse to the relay's control circuit.
- These are employed in a variety of industrial applications for a variety of objectives, including the following.
- It is utilized in industrial sorting and counting systems.
- It is utilized in power supply, as well as HVAC, anti-condensation, and refrigeration systems.
- It is used in cleaning equipment in sectors such as automated car washes.
- Commercial coffee machines, as well as automated meal preparation systems, are available.