Centrifugal compressor tachometer
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What is the function of a centrifugal compressor tachometer (other than measuring speed)? Why are 5.6 tachometers installed?
This is used to measure the speed of the turbine, right? Generally, three devices are used for measuring speed, while the other three are used for triggering an emergency shutdown.
Why 3? Can’t it be 2?
Two-out-of-three, three-out-of-four mechanisms prevent shutdowns caused by errors in the table itself
These are the six speed probes on the turbine. Three are used for the two-out-of-three electronic overspeed protection, two for the governor, and one for local indication!
Depending on the application, there are those connected to TPS, SI, SIC, as well as KI which can provide a certain speed indication
Generally speaking: two are used for speed control after high selection, three are used for two-out-of-three over-speed protection, and one is used for local display
Can’t the speeds of the two governors and the on-site indicated speeds be monitored using electronic over-speed sensors? That way, three sensors would be saved
To prevent misjudgment by operators or interlocked shutdowns due to a failure of a single tachometer