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电磁转差离合器调速又称滑差调速(简称电磁调速),调速系统是由普通笼型异步电动机、电磁转差离合器与控制器组成。请回答下列与电磁转差离合器调速系统有关的问题。关于电磁转差离合器调速系统的特性以下描述错误的是()。

A. 如负载恒定,励磁电流增大,磁场与电枢只有较小的转差率,可产生足够大的转矩带动负载,使转速升高
B. 如励磁电流恒定,负载增加则转速降低
C. 电磁调速电动机的自然机械特性是软特性
D. 采用转速负反馈的闭环控制系统可以获得较硬的入为机械特性,转速负反馈的作用是使负载引起的转速降低由增加定子一次电流来补偿

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Estimating schedule activity costs involves developing an (1) of the cost of theresources needed to complete each schedule activity. Cost estimating includes identifying and considering various costing alternatives. for example, in most application areas, additionalwork during a design phase is widely held to have the potential for reducing the cost of the execution phase and product operations. the cost estimating process considers whether the expected savings can offset the cost of the additional design work. cost estimates are generally expressed in units of (2) to facilitate comparisons both within and across projects.the (3) describes important information about project requirement that is considered during cost estimating.空白(2)处填()

A. activity
B. work
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