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The relay has several strengths that make it very useful in certain industrial logic control applications. For instance, relays are fairly easy to troubleshoot to determine if the contacts are open or closed and if they are passing voltage signals. Some relays have an indicator lamp mounted where the technician can look quickly at the cabinet and determine if the relay coil is energized. Also relays have been used in industrial applications for purposes other than logic and their operation is similar to contactors and motor starters, so the technicians are very familiar with them. Some relays used in critical logic circuits are available with plug-in sockets that make them easy to remove and replace for testing and repair. ill. 1 (below) shows examples of relays with indicator lamps and plug-in sockets. AMAZON multi-meters discounts AMAZON oscilloscope discounts |
Above: ill. 1: Examples of relays with indicator lamps and plug-in sockets that make them easy to troubleshoot and replace. (Omron Electronics.).
Other strengths of relays are that they are durable and can withstand stray induced voltages without changing state. Relays also hold up well in extremely warm temperatures. Even though relays do require more power than solid-state devices, the power issue becomes clouded if an air-conditioning unit must be added to the electrical panel where solid-state devices are used because the air-conditioning unit will use large amounts of electrical power. Relays are also available in encapsulated packages if they are used in an explosive atmosphere, or conditions such as electroplating processes where the air is corrosive and acid vapors tend to corrode the contacts.
A large variety of miniature relays is available. These smaller relays require less power and take up little space in cabinets. If the circuit is strictly for logic, the smaller relays are very reliable for the job.
Some of the weaknesses of relays include the requirement for larger amounts of power in circuits that use large numbers of relays. Other problems occur when the relay contacts wear prematurely due to excessive arcing. The relay is also a mechanical device that uses springs and other moving components that tend to wear out over time. The life expectancy of a relay may only be 2-3 million operations, which means they could wear out over a period of a few years.
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