【振动监测专栏】小知识——什么是报警倍乘

之前有一篇文章里提到过水泵在低于最佳工作流量时会振动变大，所以要设置报警倍乘。同样在大机组启停机时为了避免因共振造成意外报警也需要设置报警倍乘。

报警倍乘，意思是说在一定限制区域内，将所有的报警阈值临时放大N倍，通常设置为3倍。过了这个限值区域后，或者手动取消报警倍乘的功能，报警阈值便恢复到正常值。该功能通常用于启停机分析，来躲避共振点。

如图，以某个振动监测设备的组态为例。在这个Advanced Alarm Configuration窗口中来配置报警倍乘。其功能如下：

启动阶段 (Start-up Period)：为阈值应用 “ 阈值倍乘 ”(Threshold Multiplier) 的时长。重新断开设定值倍乘开 关 ( 按钮已松开或拨动开关已按动至关闭 ) 后启动阶段开始。

Enter the length of time (0 to 1092 minutes, adjustable in increments of 0.1 minutes) that the Threshold multiplier is applied to the thresholds. The startup period begins when the setpoint multiplier switch is reopened (push button disengaged or toggle switch flipped to on). Refer to the module’s XM Module User's Guide for more on the setpoint multiplier switch.

阈值倍乘 (Threshold Multiplier)：闭合设定值倍乘开关 ( 按钮已按下或拨动开 关已按动至打开 ) 后再在启动阶段重新打开 时，将要采取的操作。模块在此期间将该倍 乘应用于报警阈值的目的是，避免在共振频 率处出现假报警。 

重要说明：在某些情况下应用倍乘可能会产 生相反的效果。例如，当 “ 条件 ”(Condition) 设置为 “ 小于 ”(Less Than) 且阈 值是正数时，对阈值进行倍乘将增大测量值 达到报警范围的可能性。因此，可以将 “ 阈 值倍乘 ”(Threshold Multiplier) 设置为 0，以 在启动阶段禁用报警。

Enter the value for the alarm threshold multiplier. The module applies the multiplier to the alarm threshold during this time to avoid false alarms at resonance frequencies. The multiplier is applied when the setpoint multiplier switch is closed (push button engaged or toggle switch flipped to off) and during the startup period once the switch is reopened.

The multiplication may have the opposite effect under certain circumstances. For example, if the Condition is set to “Less Than” and the threshold values are positive, then multiplication of the threshold values increases the likelihood of the measure value being within the alarm range. Therefore, you may want to set the Threshold multiplier to 0 (zero) to disable the alarm during the startup period.

需要注意的还有一点就是，如果带有转速通道的话，可以选择设置报警的转速有效范围，这样便可以避免在启停机中产生不必要的报警。

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