What is a reed switch relay?
Latest update time：2020-10-09
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I went home on November 1 and got together with my old colleagues. I feel that everyone is making continuous progress and I have a strong sense of crisis. I will continue to work hard.
Relays are divided into mechanical relays and semiconductor relays. Today we will not expand on the concepts in detail. First, we will have a rough classification in our minds. (The picture below comes from Panasonic’s official website)
In the insulation detection circuit of BMS, we often use a device called photoMOS (PhotoMOS), which is used as a switch for the resistance bridge. It is a semiconductor relay.
For example, Panasonic's AQV258 is a model we often choose, as shown in the figure below.
PhotoMOS is a semiconductor relay with LED as input and MOSFET as output, but we are not mainly talking about PhotoMOS today. (The picture below comes from Panasonic’s official website)
In recent years, another device has appeared in the insulation detection circuit, called
reed switch relay, reed switch relay, Reed Relays,
etc. (as shown in the figure below); it is also used for the switch of the resistor bridge arm.
The reed switch relay is a type of mechanical relay, but its structure is different from the traditional electromagnetic relay. The following figure shows the structure of a traditional electromagnetic relay.
The reed switch relay is composed of
two parts:
a reed switch and a coil
. It is smaller and more energy efficient than other types of relays. Its structural composition and principle are introduced in detail below.
Reed switch
Reed Switch, also known as reed switch, let’s take a look at some reed switch products first. The pictures are from Littel’s official website.
As shown in the figure below (the picture comes from the Internet), the magnetic reed switch consists of two magnetic reeds, which are sealed inside a glass tube; the two magnetic reeds have a contact overlapping area at the middle end of the glass tube, and The default distance is a small gap; the inside of the glass tube is filled with inert gas, such as nitrogen, to prevent oxidation; in order to improve the electrical breakdown strength, the inside of the glass tube can also be evacuated into a vacuum state.
The body of the magnetic reed is made of nickel-iron alloy, and the surface of the overlapping contact area of the two magnetic reeds is plated with hard metals such as rhodium or ruthenium to provide wear resistance.
Place the reed switch in a magnetic field. When the two magnetic reeds are magnetized to opposite polarities by the magnetic field, they generate an attraction, and the contacts overcome the elastic force and close the contact; similarly, when the magnetic field disappears, the contacts are elastically Li pulled away. (The picture below comes from Baidu Encyclopedia)
Coil
In order for the reed switch to be manually controlled to close or open, a coil is wrapped around the surface of the glass tube and the coil is energized, thus forming an electromagnet, which in turn generates a magnetic field to cause the reed switch to operate.
The life of a reed switch relay is shorter than that of a semiconductor switch, but much longer than that of a general electromagnetic relay. The following figure shows the operating parameters of a certain model of reed switch relay, which can be switched up to one million times.
At present, the more common manufacturers of reed switch relays are Littelfuse and Standex Meder. Recently, a model of Standex Meder's KT series was violently disassembled, as shown in the picture below: During the actual disassembly, the glass tube in the middle was broken. The reed at one end fell out; you can clearly see the coil wrapped around the outside of the glass tube, as well as the outermost plastic layer.
Summarize:
The reason for using reed switch relays in the bridge method is that
it has higher insulation and voltage resistance regardless of the load end or input/output. I
started working today, and the next holiday I look forward to is New Year's Day. All of the above, for reference only.
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