The first model of an automatic current switch, which later received the name "relay", was presented by the American scientist Joseph Henry back in 1835, that is, almost two centuries ago, and was a kind of electromagnet, the magnetic pole of which attracted a ferrimagnetic body, closing or, on the contrary, opening electrical contacts. These types of electromagnetic relays found their application on the telegraph in devices of the Morse system, when, under the influence of an incoming electrical impulse, the local power supply batteries were connected with a contact with the windings of power writing electromagnets.
In addition to the classic electromagnetic switch equipped with a fixed control winding, other types of electrical switches were developed in the nineteenth and twentieth centuries:
- Contact, created on the basis of electromagnetism.
- Contact electrostatic, electrostrictive and thermal.
- Contactless based on magnetic, gas-discharge, semiconductor and vacuum amplifiers.
USA vs USSR
In the 50s of the last century, the United States of America had on its territory about fifty companies engaged in the production of more than 1000 types of electromagnetic switches, including time relay and other devices common today. At that time, the USSR had only three dozen enterprises that produced about 350 types of devices. Based on the power that their switched circuits possessed and electronic components , they could be divided into:
- Low and high voltage (> 1000) relays.
- Medium power devices.
- High and low current relays.
According to the scope of their application, the following classification took place:
- Electrical relay.
- Automotive, aviation, railway relay.
- General industrial predominantly low power hardware relay.
- Relays for general industrial automation.
Present
Nowadays, relays can be distinguished by slightly different parameters. At the moment, 7 types of relays are relevant:
- voltage;
- time;
- reed;
- phase control;
- pressure;
- temperatures;
- current.
By the way, it is with the operation of the time relay that we most often have to deal with in everyday life when using any household appliances, be it a TV, coffee grinder, washing machine, etc.
Today, all types of relays are ubiquitous devices, and you can literally buy them in any store of electronic and household appliances, and sometimes even household goods.
