Automatic device synchronization with Precision Time Protocol (PTP)

Winterthur, June 2018 – 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.

What is Precision Time Protocol (PTP)?

What is neat about Precision Time Protocol (PTP) is that users don't have to worry about synchronization. The devices are automatically synchronized via the usual network lines. Only the topology has to comply with PTP standards. So, for instance, you cannot use switches that are not PTP-enabled between the individual PTP devices since they cannot guarantee that data packets are always transferred at an identical speed.

PTP recognizes two clock types: master and slaves. Slaves are synchronized to their respective master. The highest-precision clock in a group is defined in the automatic 'Best Master Clock Algorithm' (BMC). The slave is then synchronized with this chosen 'grand master' and may possibly in turn act as master for the next level. Once successfully initialized, synchronicity is checked regularly and the clocks adjusted as required.

Precision Time Protocol (PTP) in practice – Application example with Kistler devices

Quality varies in the implementation of the Time Protocol (PTP). The nearer PTP is performed to actual signal digitization, the more precise the synchronization. On Kistler's KiDAQ and LabAmp devices the digitized measured values are immediately time-stamped after analog/digital conversion in a field programmable gate array (FPGA). Precision in the sub-microsecond region is thus possible.

Several KiDAQ and LabAmp data loggers can be flexibly grouped together to perform synchronized measurements. Users are thus offered a variable system that can be extended almost infinitely as desired. For instance, highly dynamic signals from a piezoelectric accelerometer can be captured with a LabAmp 5165A in combination with temperatures, voltages and piezoresistive pressure signals, which are connected to a KiDAQ data acquisition system – and precisely synchronized. How many devices are connected is of no consequence. Thanks to the many different KiDAQ modules there are practically no sensor types that are not covered.

In terms of software KiStudio Lab already belongs to the future. Configuration, measurement and analysis, all are performed quickly, simply and intuitively. Over time, the functions of different current Kistler software tools and new capabilities will be added to the web-based measuring software.

Conclusion

Precision Time Protocol (PTP) is a user friendly, cost-saving way of grouping together individual Kistler KiDAQ and LabAmp data loggers into one larger data acquisition system with no need for any additional synchronization lines. Synchronization is run automatically with high precision in the background. Easy central access to the captured data is available.