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Лучшие 10 искателей выключателей

Klein Tools Цифровой выключатель Finder

Изображение предоставлено: Amazon

Этот искатель выключателя помогает найти соответствующий выключатель в любой стандартной розетке 120 В. Предупреждает вас с мигающим индикатором стрелки. Он имеет сильный передатчик, который может достигать до 1000 футов. Работает с 90 – 120 вольт. Это устройство с микропроцессорным управлением, которое обеспечивает более надежную идентификацию выключателя.

Содержание

Герконы различаются по контактной группе:

  • с нормально разомкнутым контактом (замыкает электрическую цепь в присутствии магнитного поля);
  • с нормально замкнутым контактом (разрывает электрическую цепь в присутствии магнитного поля);
  • с переключающимся контактом (при отсутствии магнитного поля замкнута одна пара выводов, при наличии — другая).

По конструктивным особенностям выделяют [3] :

  • «сухие» герконы (колба заполнена осушенным воздухом или специальным газом);
  • ртутные, или «смоченные» герконы (контактирующие поверхности смочены каплей ртути для уменьшения электрического сопротивления контакта и предотвращения дребезга).

Обычно колба геркона содержит азот или аналогичный инертный газ. Для увеличения допустимого коммутируемого напряжения некоторые типы герконов вакуумируются. В качестве материала для контактных пластин обычно используются сталь и никель с напылением из более стойкого металла (родий, рутений) в местах контакта. Критическим показателем качества и надёжности геркона является герметичность в месте соприкосновения стекла корпуса и металла проводников [4] .

What is a reed relay made of

The basis of any reed relay is the reed switch itself — this is the core element of the reed relay. A reed switch consists two reed contacts, typically made from nickel-iron and then plated with materials to ensure the maximum life to the device.

The reed switch contacts overlap so that when they close they make contact with each other. Normally the spacing in the open state is between 0.05 and 1 mm. The greater the spacing, the greater the voltage withstand.

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The small gaps between the contacts enable very fast switching speeds, often from around half a millisecond to a few milliseconds dependent upon the actual size, etc of the contacts.

Often the nickel-iron allow is around 52% nickel. The reed contact materials used include ruthenium, rhodium and sometimes iridium or where high voltages are involved it might be tungsten or molybdenum. Often rhodium is usually electroplated onto the reed element, whereas ruthenium is generally sputtered. There were also a very few reed switches that used gold, often for audio — but the low melting point of gold meant they used to stick and they are not seen these days.

Internal assembly of a reed switch

The assembly is surrounded by a glass envelope to give a hermetic seal to prevent the ingress of moisture and other contaminants. Most reed relays and reed switches are contained in a glass tube — the individual tubes are cut from a much longer tube. The individual tubes for each reed switch are melted at either end, to provide a hermetic seal.

Typically the glass envelope is filled with an environment to prevent wear, oxidation and better quenching of any sparks.Typically nitrogen is used and this may have a trace of helium. High voltage reeds may use a vacuum.

As the contacts do not slide across each other, there is no form of cleaning, and any pitting tends to progressively build up. To reduce this as much as possible, the cleanliness of the environment within the glass is very important. It is also necessary to maintain the inert gas within the envelope. It is important to ensure that the seal around the glass is maintained, and as a result the areas of the reed contacts that are in contact with the glass are sometimes coated with materials that provide a better seal than the nickel alloy used for the reeds. Another approach is to oxide the reed material int his area.

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The reed switch has two shaped metal blades made of a ferromagnetic material (roughly 50:50 nickel iron) and a glass envelope that serves to both hold the metal blades in place and to provide a hermetic seal that prevents any contaminants entering the critical contact areas inside the glass envelope. Most (but not all) reed switches have open contacts in their normal state.

If a magnetic field is applied along the axis of the reed blades the field is intensified in the reed blades because of their ferromagnetic nature, the open contacts of the reed blades are attracted to each other and the blades deflect to close the gap. With enough applied field the blades make contact and electrical contact is made.

what is a relay image

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What is a Reed Relay?

The only movable part in the reed switch is the deflection of the blades, there are no pivot points or materials trying to slide past each other. The reed switch is considered to have no moving parts, and that means there are no parts that mechanically wear. The contact area is enclosed in a hermetically sealed envelope with inert gasses, or in the case of high voltage switches a vacuum, so the switch area is sealed against external contamination. This gives the reed switch an exceptionally long mechanical life.

Another design variable on the reed switch is its size. Longer switches do not have to deflect the blades as far (measured by angle of deflection) as short switches to close a given gap size between the blades. Short reeds are often made of thinner materials so they deflect more easily but this clearly has an impact on their rating and contact area. Smaller reed switches allow smaller relays to be constructed – an important consideration where space is critical. The larger switches may be more mechanically robust and have greater contact area, improving their signal carrying capability.

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Generating the magnetic field:

To create a relay a magnetic field needs to be created that is capable of closing the reed switch contacts. Reed switches can be used with permanent magnets (for example to detect doors closing) but for the reed relays the field is generated by a coil which can have a current passed through in response to a control signal. The coil surrounds the reed switch and generates the axial magnetic field needed to close the reed contacts.

reed switch labeled image

Different reed switches require different levels of magnetic field to close the contact, and this is usually quoted in terms of the ampere turns (AT) – simply the product of the current flowing in the coil multiplied by the number of turns. Again this creates a great deal of variation in the reed relay characteristics. Stiffer reed switches for higher power levels or high voltage switches with larger contact gaps, usually require higher AT numbers to operate, so the coils require more power.

Use of different wire gauges for the coil and number of turns creates relays with different drive voltage requirements and different coil powers. The resistance of the wire coil controls the amount of steady state current flowing through the coil and therefore the power the coil consumes when the contacts are closed. Whenever fine wires are used in Pickering relays, the termination leads from the coils are skeined with several strands of wire twisted together to increase their physical strength.

Larger coils can be used to reduce power consumption, but that increases the size of the relay.

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Part Two will continue to explain the wonders that are reed relays, including information on changeover reed switches and two pole relays.

Looking to browse our Reed Relay range?

From high voltage reed relay options to surface mount relays, find out more about our reed relays here

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