通过精密时间协议(PTP)自动同步设备


All measurement technicians are familiar with the situation: today, several colleagues need devices for various measurements with a few channels, and tomorrow you have to tackle a major measuring task with several channels. This dilemma can be neatly resolved with several synchronizable data loggers. This sounds fine, but how does it work in practice?

A traditional measuring system with multiple channels is typically the established solution for recurrent identical measurements. However, a high degree of flexibility is called for when dealing with same-time measurement tasks, some of which require many, and others few channels. You could certainly resolve this situation by buying several identical data acquisitions systems. However, the high costs of this solution scarcely justify its deployment for ocassional usage. Resorting to less expensive manufacturers brings the disadvantage of potentially more inaccurate measuring results, the need for users to familiarize themselves with the different operation philosophy, not to mention installing and getting used to manufacturer-specific software. By contrast, high quality hardware and software can be used for diverse tasks, efficiency is substantially increased and procurement costs saved. The basis for this is formed by smart individual devices, which can be combined as the situation demands.

Synchronization via Precision Time Protocol (PTP) as an efficient solution. When recording measurement signals it is essential that this is performed concurrently, otherwise results may be completely misinterpreted. In principle, synchronization can be performed in two ways. The traditional solution: a separate line with a system clock is run to each device, ensuring that the respective measured values (samples) are recorded at the same time. The other option is to equip the relevant devices with a precise clock and to synchronize it periodically.

The PTP to IEEE 1588-2008 standard (corresponds to PTP V2) defines a sophisticated procedure in which the clocks of local network components can be synchronized to achieve an accuracy in the region of sub-microseconds with no additional lines at all. If measured values are then time-stamped, a higher-level computer can consolidate the data of many devices and, thanks to the time stamp, represent them precisely in a temporal context.

PTP-synchronized LabAmp types 5167A and 5165A for 6-component force measurement and 3 pressure pulse measurements of combustion instabilities in the combustion chamber.
Example: rocket engine test bay: PTP-synchronized LabAmp types 5167A and 5165A for 6-component force measurement and 3 pressure pulse measurements of combustion instabilities in the combustion chamber.

测量技术人员都熟悉这样的场景:今天有三位同事需要通过数据采集测量通道来执行不同的测量任务,而明天会面临需要测量通道来完成更大测量任务的挑战。通过多个数据采集设备同步的方法,可以解决这种困境的发生。那么具体工作原理是什么呢?

当需要完成周期性重复的相同测量时,可使用经典的多通道测量系统作为既定方案。当有时需要多通道测量,有时需要少量通道测量,且可以同时完成不同的测量任务时,就需要更高的系统灵活性。你可以通过购买几个相同的数据采集系统来实现,但成本高昂,该解决方案基本上满足不了灵活性使用的应用情况。其他制造商价格相对低廉的替代方案除了测量结果可能不准确外,其劣势在于用户必须首先熟悉操作原理,更不要说系统安装和不熟悉制造商特定的软件带来的影响。另一方面,如果高质量的设备和软件可以灵活地用于各种测量任务,那么这将显著提高效率并节省采购成本。将智能化的单个设备都组合在一起是提高效率和节省成本的基础。

通过精密时间协议(PTP)同步的高效系统解决方案
采集测量信号时,将测量信号同步非常重要,否则测试结果可能会完全出错。大体上,可通过两种方式同步。传统方案:将带有系统时钟的独立线路运行在每个设备上,并确保同步记录相应的测量值(采样)。另一种方案是为每个设备装备精密时钟并周期性同步。

PTP根据IEEE 1588-2008标准(相当于PTP V2)阐述了不借助辅助电缆调整本地网络组件时钟,使其达到亚微秒级精度的复杂方法。如果现在提供的测量值具有准确的时间标识,多种设备的数据可以在上级计算机上汇总,通过时间戳及时精确显示。

什么是精密时间协议(PTP)?

精密时间协议(PTP)的优点是用户不必再担心同步问题。设备自行通过普通网线同步。只是拓扑结构必须符合PTP要求。因此,各个PTP设备之间不得存在具有PTP功能的交换机,因为它们不能保证数据包始终以相同的速度发送。

PTP能识别两种时钟类型:主机和从机。从机分别与相应的主机同步。根据“最佳主机时钟算法”(BMC)自动确定设备组合中最精确的时钟。从选择的“最高主机”开始同步,然后同步下一个可能在下一阶段作为主机的从机。初始化成功后,定期检查同步性,并在必要时重新校准时钟。

在实践中运用精密时间协议(PTP)– 搭配奇石乐设备的应用示例

PTP实施过程中呈现出了质量差异。越靠近信号的实际数字化时间实施PTP,同步就越精确。因此,对于奇石乐的KiDAQ设备和LabAmp设备来说,数字化后的测量值可立即在模拟/数字转换器后的现场可编程门阵列(FPGA)中获取时间戳。从而可以实现亚微秒级的精度。

同步测量时,可以灵活地组合使用数个KiDAQ和LabAmp数据采集设备。以此提供一个可任意扩展的灵活测量系统,该系统不存在扩展限制。例如,压电加速度传感器的高动态信号可以通过 LabAmp 5165A获取并结合温度、电压和连接在KiDAQ数据采集系统上的压阻式压力信号 精确同步。此时连接设备的数量并不重要。由于各种KiDAQ采集模块的种类丰富,所以实际上没有不能覆盖的传感器类型。

从软件方面来说,KiStudio Lab着眼未来。在这里测试配置、测量和数据分析都十分快速、简单、直观。随着时间的推移,基于网络的测量软件也可以接管各种奇石乐现有软件工具的功能并不断扩展新功能。

结论

通过精密时间协议(PTP),奇石乐的各个KiDAQLabAmp数据采集设备可以方便且经济高效地组合成一个更大的数据采集系统,无需额外的同步线路。系统自动在后台高精度同步,并便捷地调取采集的数据。

有关所提及设备的更多信息请访问:www.kistler.com/kidaqwww.kistler.com/labamp