* Question
What is the basic structure of the magnetic holding relay?
* Answer
A magnetic holding relay, also known as a latching relay, is a type of relay that maintains its contact position after the control power has been removed, making it energy efficient for applications where the relay needs to stay in a set position for extended periods. Here’s a look at the basic structure of a magnetic holding relay:
1. Coils
– Set Coil: Energizing this coil changes the state of the relay contacts from their resting position to the active position.
– Reset Coil: Energizing this coil returns the contacts to their original resting position.
– In some designs, a single coil may be used for both setting and resetting, depending on the direction of the current or the sequence of pulses.
2. Contacts
– Normally Open (NO): This contact closes when the relay is activated.
– Normally Closed (NC): This contact opens when the relay is activated.
– Common (COM): The common terminal that switches connection between NO and NC contacts.
3. Magnetic Core
– A magnetic core is used to focus and enhance the magnetic field generated by the coils, improving the efficiency and response of the relay.
4. Armature
– This is a movable arm that pivots when the magnetic force is applied. It mechanically links to the contacts and moves them between their open and closed positions.
5. Holding Mechanism
– Permanent Magnet: This magnet holds the armature (and therefore the contacts) in the last position they were moved to by the coils, even after the coil’s power is turned off.
– Mechanical Latch: Some designs use a mechanical latch to hold the armature in position instead of a magnet.
6. Return Spring
– In some designs, especially those using a single coil, a return spring may be used to move the contacts back to their original position when the coil is de-energized.
Operation:
When the set coil of a magnetic holding relay is energized, it creates a magnetic field that attracts the armature, changing the position of the contacts. A permanent magnet or a mechanical latch then holds the contacts in this new position even after the coil is de-energized. To reset the contacts, the reset coil is energized, or the current direction/pulse sequence in a single coil system is changed, which releases the armature from the hold of the permanent magnet or latch and allows the contacts to return to their original state.
Magnetic holding relays are used in various applications where it is necessary to reduce power consumption and maintain the state of the relay without continuous power supply.
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