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There is a great variety of relays available in our country, and consumers generally choose based on their actual usage needs. The digital core of a microcomputer-based protection device generally consists of a CPU, memory, timers/counters, a watchdog, etc. Currently, the mainstream of digital cores are embedded microcontrollers, namely what are commonly referred to as single-chip microcomputers. The input/output channels include analog input channels (analog input conversion circuits that convert the values measured by CTs and PTs into voltages suitable for internal A/D conversion, such as ±2.5V, ±5V, or ±10V, along with low-pass filters and sampling/A/D conversion functions), as well as digital input/output channels (for human-machine interaction, as well as various alarm signals, trip signals, and power meter pulses). Microcomputer-based protection is a type of relay protection that makes use of microcomputers; it represents the future direction for the development of relay protection in power systems. It features high reliability, high selectivity, and high sensitivity. The hardware of such protection devices consists of a microprocessor (microcontroller) as the core, along with input/output channels, a human-machine interface, and communication interfaces. This system is widely used in the power, petrochemical, mining and smelting, railway, and civil construction industries. The production of relays is labor-intensive; developed countries transferred the manufacturing of general-purpose relays to countries with lower labor costs such as China at an early stage. The first batch of enterprises in China in this field were mostly foreign-funded companies or their OEM manufacturers (large-scale factories), which is why the internationalization level of the relay industry has remained high. For a relay with two coils having the same parameters, its coils can be used in various ways. In series, in parallel, used separately. Regardless of the method of use, it is necessary to meet the operating ampere-turns and releasing ampere-turns of the relay. What are the general principles for selecting a relay? Next, the editor will introduce to you: 1. The types of relays and their coil resistances must meet the basic requirements of various circuits. 2. When relays are used in series in a circuit, the number of series-connected relays must meet the voltage requirements. Relays are now widely used in computer peripheral interface devices, temperature control systems, temperature regulation, electric furnace heating control, motor control, CNC machinery, remote control systems, and industrial automation devices ； Signal lights, dimming, flashers, lighting stage light control systems ； Instrumentation, medical devices, copiers, automatic washing machines ； Automatic fire suppression systems, security systems, as well as switchgear for power capacitors used to compensate for the power factor of electrical grids, etc. They are also widely used in industries such as chemicals and coal mining where explosion prevention, moisture resistance, and corrosion protection are necessary. 3. The current passing through the relay contacts should not be less than the operating current of the circuit; parallel connection should be used if necessary. Digital display instruments feature high precision, good stability, reliable quality, small size, ease of installation and use, and low cost. They are suitable for scientific research, precise measurements, and new product development. They can be widely used as display components in various instruments and meters, automation control equipment, power electronics, medical devices, digital devices, as well as AC/DC voltage stabilizers, serving to upgrade existing products and representing the preferred replacement for various analog gauge panels. 4. When the number of relay contacts is insufficient (and the circuit requirements cannot be met), a duplicate relay is used to indicate the operating status of the main relay. Relays are now widely used in computer peripheral interface devices, temperature control systems, temperature regulation, electric furnace heating control, motor control, CNC machinery, remote control systems, and industrial automation devices ； Signal lights, dimming, flashers, lighting stage light control systems ； Instrumentation, medical devices, copiers, automatic washing machines ； Automatic fire suppression systems, security systems, as well as switchgear for power capacitors used to compensate for the power factor of electrical grids, etc. They are also widely used in industries such as chemicals and coal mining where explosion prevention, moisture resistance, and corrosion protection are necessary. 5. When relay contacts are connected in series in a circuit, the contact resistance meets the requirements of the circuit (without affecting its normal operation)