| 摘要 |
An overspeed protection system is provided which utilizes simplified construction for detecting overspeed conditions of a rotating device. In the preferred embodiment, a single up/down counter is employed in an overall sequence which includes a first time period during which the counter is counted up from a preselected value by a series of pulse representations of speed for the rotating device. After the expiration of the first time period of the sequence, the counter value is compared to an overspeed limit selected during the previous sequence. If that limit is exceeded, an overspeed condition is detected by the system. In a second time period of the overall sequence, the counter is down counted by the pulse representations of speed. After the expiration of the second predetermined time period of the sequence, the counter value is compared to the original preset value to determine the rate of change in device speed. If the rate of change exceeds some preselected value, a low overspeed limit is used for the overspeed limit of the next up count for the subsequent sequence. If the rate of change does not exceed the preselected value, a high overspeed limit is used for the overspeed limit of the next up count for the subsequent sequence. The system outputs an overspeed signal only if an overspeed is detected on consecutive up count/down count portions of a sequence.
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