When voltage changes occur in rapid succession, with magnitudes large enough to cause lighting level variations. The human eye-brain response is most sensitive to periodic r.m.s. voltage changes that occur at around 8 - 10 cycles per second.
A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system and by using messages from the master supervisory. This is accomplished by transmitting telemetry data to the system and/or changing the physical state of connected objects based on control messages received from the automation system. It is used to interface field devices with SCADA. RTUs can support multiple communication protocols at the same time. A limited number of input and output devices can be added to it.
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