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特别值得一提的是，针对当前各种新型应用，罗克韦尔自动化推出了全新的Allen-Bradley PowerFlex 4M交流变频器。它采用馈通配线、安装方便并且易于对各种频率电机进行编程，为用户带来可观的经济效益。PowerFlex 4M交流变频器的工程应用也十分简单，可以帮助用户减小机械应力的影响，提高应用的灵活度。PowerFlex 4M是Allen-Bradley PowerFlex变频器中尺寸最小和成本的变频器，功率范围从0.2 到 11kW。PowerFlex 400P是罗克韦尔自动化款支持中文显示的低压矢量型变频器，实现低速高转矩输出的性能。这两款Allen-Bradley PowerFlex新产品将提高机械设备的性能和生产效率，有效地服务中国用户。下午，与会者们饶有兴致地参加了罗克韦尔自动化产品演示及动手试验，对罗克韦尔自动化的Allen-Bradley PowerFlex变频器有了更直接的认识与了解。 该研讨会为罗克韦尔自动化与客户及业内人士之间搭建了一个交流、沟通与学习的平台平台。一方面，罗克韦尔自动化从专家、客户对变频技术发展、青岛当地应用情况获益匪浅，听取了中肯意见；同时，他们也获取了罗克韦尔自动化的Allen-Bradley PowerFlex变频器的技术发展和应用的重要信息，更加充满信心与罗克韦尔自动化合作。

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This time information can be used by both hardware and software resources within the system. In hardware, one or more physical clock signals (clock outputs) are derived from the oscillator’s clock and can be used to drive or trigger other parts of the system. The time maintained in software is typically referred to as system time. The system time can be represented in the form of numbers of clock pulses or in second/nanosecond notation. The system software derives the time from the number of oscillator clock pulses and its frequency information, and provides application-programming-interface (API) functions that other parts of the software use to retrieve and set the time. If an absolute time is desired, the provided time is associated with a predefined epoch, which identifies a reference point in time.

Synchronize Your Watches

Many applications require two independent devices to operate in a synchronized fashion. If each device were to rely solely on its own oscillator, differences between the specific characteristics and operating conditions of the individual oscillators would limit the ability of the clocks to operate synchronously. Some possible simplistic solutions to address these limitations include:

All the devices could use a single physical oscillator. This is only feasible for distributed systems in close proximity; a high-frequency clock signal cannot be reliably delivered over a long distance.

All the devices could utilize oscillators with nearly identical characteristics. This approach is impractical due to the difficulty of acquiring nearly identical oscillators and keeping them from drifting apart over time. More importantly, each oscillator will be subjected to different operating conditions.

If all the devices are interconnected via a communications network such as Ethernet, they can dynamically adjust their individual clocks to a single “master” clock by exchanging time messages over the network. With network time protocol (NTP), the traditional time synchronization protocol, every device in the system adjusts its clock according to the time information it retrieves from an NTP time server. However, this protocol can only achieve synchronization accuracy on the order of milliseconds.

IEEE 1588 defines a newer protocol capable of nanosecond synchronization accuracy. How it can achieve this level of clock synchronization is discussed in the following sections.