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What is the difference between optical relays and ordinary relays
Sep 05,2025
The main differences between optical relays (photoelectric relays) and ordinary relays are reflected in their working principle, electrical isolation, response speed, and service life. The former achieves contactless control through photoelectric conversion, while the latter relies on mechanical contact operation of electromagnetic coils.
Differences in working principles
Optical relay:
Using light-emitting diodes (LEDs) to convert electrical signals into optical signals, photosensitive components (such as phototransistors) receive the optical signals and trigger the output circuit.
Realize the signal conversion of "electricity → light → electricity", with complete electrical isolation between input and output.
Ordinary relay:
Based on the principle of electromagnetic induction, the coil is energized to generate a magnetic field that drives the mechanical contacts to close/open.
The input-output circuit is directly physically connected through metal contacts.
Core performance comparison
Electrical isolation:
Optical relay: The isolation voltage between input and output can reach over 2500V, effectively blocking electromagnetic interference.
Ordinary relay: without electrical isolation, there is a risk of contact arc interference.
Response speed:
Optical relay: The action time is about 1-10ms, suitable for high-speed control scenarios.
Ordinary relay: Mechanical contact action takes 10-50ms.
service life:
Optical relay: without mechanical components, the switch life can reach more than 10 ^ 8 times.
Ordinary relay: The mechanical contact life is about 10 ^ 5 times.
Application scenario differentiation
Applicable fields of optical relays:
High frequency switch control system (such as PLC, semiconductor testing equipment).
High voltage environment (industrial equipment with AC voltage above 380V).
Precision instrument anti-interference circuit (medical equipment, communication base station).
Common relay application scenarios:
Conventional power control (contactor control, motor start stop).
Household appliances (air conditioning, refrigerator temperature control system).
Low frequency switch requirements (lighting systems, security equipment).
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