Reed Relay : Construction, Circuit, Working & Its Applications

The reed switch concept was first proposed by a professor at the Leningrad Electrotechnical University in 1922. He proposed the idea of what was named a contact that is controlled magnetically and switched in a magnetic field influence. Reed switch was invented by Walter B. Ellwood in 1936 at Bell Telephone laboratories. These relays are used in automatic telephone exchanges. After that, the telephone exchange technology moved from the reed switch but the technology still endures in sensors and relays. So this article provides brief information on reed relay – working with applications.

What is Reed Relay?

A type of relay that operates one or equal to eight reed switches by using an electromagnetic coil is called a reed relay. This switch is normally in the coil of the relay. These relays are applicable in different areas wherever faster, smaller relays are required in an electrical or electronic circuit. The performance of this relay is very fast and available in small size which needs very less power to activate as compared to other kinds of the relay. Thus, they are used in different types of electronic circuits. The reed relay diagram is shown below.

Construction

The construction of the reed relay is very simple which is shown below. This relay is constructed with a reed switch, blades, electromagnetic coil, etc.

The reed relay switch is a sealed glass envelope that includes two reed blades which are made with magnetically sensitive based material like ferromagnetic material. This glass envelope of the relay is filled with dry inert gas to avoid contact oxidation.

The electromagnetic coil is wounded around the switch wherever the switch performs like the armature. So the reed switches both the ends are simply connected to the circuit’s input & output.
The reed blades are arranged at the two ends of the relay. Once an axial magnetic field is applied to these blades then they come in contact with each other and form a repeatable electrical contact. In this type of relay, the magnetic field is generated by a coil that covers the envelope of glass.

Reed Relay Working Principle

This relay works through a few simple steps. Primarily, the electromagnetic coil of this relay produces current once voltage is applied. After that, the current of the coil generates a magnetic field that shuts the contacts of the reed switch. Lastly, detaching the voltage supply from the coil will open the contact of the relay. In addition, these relays work with advanced methods.

For instance, an RF reed relay is mainly designed for switching high-frequency signals. Arranging a coaxial shield in the region of the reed switch simply allows the relay to switch signals equal to 7 GHz. The reed relay operating speed ranges from 200 µs – 500 µs.

Reed Relay Circuit Diagram

The circuit diagram of the reed relay is shown below. This relay includes a switch with magnetic contacts that move in an external magnetic influence otherwise the induced field from its solenoid. These relays have quick switching speed as compared to the electromechanical ones however their switching voltage & current is lower due to the thickness of their contacts.

In the above first circuit diagram when no voltage is provided to the coil, the reed switch will be opened & the LED is not activated. In the second circuit, if we provide a DC voltage to the coil then a magnetic field is generated & the contacts will be closed by allowing the flow of current from the battery so that the LED will be turned ON.

Thus, we should know that there is a main dissimilarity between the reed relay & a reed switch. A reed relay is one kind of relay that utilizes an electromagnet to operate directly on a reed switch contact enclosed in a glass envelope, normally bringing the reeds jointly to make contact once the electromagnet is strengthened.

Types of Reed Relay

There are different types of reed relays available which include the following.

5V Reed Relay

A 5V reed relay is a standard relay that is used like an electronically controlled switch. This relay utilizes magnetic force to move the contact and it can switch up to 200VAC or 200VDC voltages at 500mA. The coil within the relay needs 10mA and is rated at 5VDC.

In this type of relay, a small electromagnet is used beside the contacts. Once the power supply is applied, the contacts in the relay are closed. These relays are activated very quickly because these relays do not contain a mechanical armature.

High Power Reed Relay

These relays are available in 1,000 VDC switching packages then these relays are called high-power relays. These particular series of relays work very well in high voltage applications like solar, automotive, medical, EV battery management systems, automated test equipment, test, and measurement & ATE. In addition, the H, HM & HE series relays switch up to 10,000 VDC.

DIL Reed Relay

Dual-In-Line (DIL) Relays are available with 7.5 mm standard housing height with a 19 x 10 mm base area. These types of relays are potted by a stable flexible plastic material. The main benefit of these Relays is a broad difference in special pin configurations and contact arrangements. Because of the small housing, these types of relays can replace typical housing relays.

Fast Switching Reed Relays

The relay which can switch faster by a factor of about 5 to 10 is known as fast switching reed relay. As compared to EMRs, these types of relays have simpler & lighter moving parts that can switch very faster. This relay’s operating speed ranges from 200 to 500 µs.

Micro Reed Relay

These miniature relays are available in small sizes & much faster as compared to the EMRs or electromechanical relays. In addition, these types of relays provide lower insertion loss & also superior hot-switching performance. These relays are applicable in compact module designs.

These micro relays are appropriate for up to 10W, 0.5A switching. In addition, these types of relays are mainly developed for RF systems with high-frequency up to 3GHz which are used in digital switching systems & automatic test equipment that demand low insertion & low RF losses.

Reed Relay Vs Electromechanical Relay

The difference between the reed relay Vs electromechanical relay includes the following.

What is the Purpose of Reed Relay?

These relays are used for switching applications that require stable & low contact resistance, high insulation resistance, low capacitance, small size & long life. This relay is used to control single or more reed switches by using an electromagnet.

What is Hs Code of Reed Relay?

The Harmonized System code or HS code is an identical numerical technique used for classifying traded products through customs authorities around the globe. In industry classification systems, HS Codes are mainly used during the export procedure of goods. The HS code of the reed relay is – 85364900.

• Throughout the export process of any product, you need both the Schedule B number of the USA as well as the HS code version of the foreign country. This code is used for several purposes like the following.
• These codes are useful in physical goods classification for delivery to a foreign country;
• Report shipments within the AES (Automated Export System), once the value is above $2,500, or the product, need a license.
• It needs complete shipping documentation like instructions letter of shippers, origin certificate, or commercial invoice
• It is used to determine import tariff rates & discover if a product meets the criteria for a preferential tariff in a free trade agreement;
• It is used to perform market research & attain trade statistics;

Advantages

The advantages of reed relay include the following.

• These are simple, not expensive, and have a reliable operation which allows significant design flexibility.
• These relays have reliable, simple sensing & actuation capacities.
• Fewer price points for each unit.
• Durability & performance over the extended service life.
• Less-profile designs for ease of integration in space-constrained environments.
• Less component weight will avoid mass loading of responsive electronics.
• They have high performance.
• Its customization is easy.
• They have a fast switching speed.
• These are easily fitted into DIL or SIL packages.
• They provide complete isolation between the switching current as well as the switched circuit.
• Additional components are not needed except a magnet for its operation.
• These relays can switch both AC & DC.
• It can switch up to 200 V voltages in particular cases.
• Some variants are capable of switching 500 mA current.
• This relay is used with a magnet within open or closed conditions indefinitely without any consumption of power.
• The performance of this relay is not affected because of dirt or dust not like an optical switch.
• This relay can be turned on through nonmagnetic materials like paper or plastic.

The disadvantages of reed relay include the following.

• This relay operates by using a separate magnet. In addition, it does not function satisfactorily once the magnet is a few millimeters away from the switch part.
• This relay cannot be miniaturized like any other surface mount-based chips.
• Glass covers can be damaged easily.
• Arcing may take place in between contacts.
• This relay can be accidentally activated through other magnetic fields.
• It should be denounced when connected with a logic chip or controller.

Applications

The applications of reed relay include the following.

• These relays are used in microwave & RF switching applications.
• These are also utilized in applications that use very low leakage current like photomultiplier detectors & other very low current handling circuits.
• The application of this relay utilizes an electromagnet for controlling single or above reed switches used for low current & voltage switching requirements.
• These relays are preferably used in switching applications that need stable & low contact resistance, high insulation resistance, low capacitance, etc.
• These types of relays are designed carefully to provide the least RF signal loss & less contact resistance.
• These relays simply provide a quick switching cost-competitive method to give maximum voltage isolation equal to 15kVDC.
• These relays switch as well as route power signals at RF equal to 30MHz.
• These relays are used in antenna tuners for selecting fixed capacitor or inductor values to tune the output of the RF amplifier to the antenna.
• These relays are used in several parts of the measurement & test market to route high voltage signals, charge or discharge & separate various test circuits & system parts.

Thus, this is all about an overview of a reed relay – working with applications. These relays are used where smaller and very fast-acting relays are required in different electrical or electronic circuits. As compared to traditional type relays, these relays need less power to activate them. Here is a question for you, a reed relay is made of?