Synchronization of Measurement Systems
A measurement campaign consisting of more than one data acquisition system in parallel always requires synchronization.
Sounds reasonable, but why is synchronization so important?
There is a simple example for it:
When you use several standalone systems for the same test, each one has an individual timing error in the ppm range.
Assuming the use of two systems in parallel, system A has a timing error of 39 ppm and system B a timing error of 15 ppm. When both systems would start a long time recording for 30 days, without synchronization, there will be a time drift of about 62 seconds at the end of the recording.
Those 62 seconds are calculated as follows:
30 days * 24 hours * 3600 sec * (0.000039 ppm – 0.000015 ppm) = 62.2 sec
Synchronization is an easy way of avoiding this problem. The device that is the sync master forwards its time base to the other system. Both systems will run with the same error and will still record data time-synchronously even after one month of recording.
The following figure shows the comparison. The left figure shows the time drift without synchronization. The right figure the time base without timing error (right).
The system time base does not only affect the timing error, but also everything that measures time or is derived from a timing measurement like the sample rate, sample time stamping or frequency measurement.
DEWETRONs world of synchronization
All DEWETRON DEWE2 and DEWE3 chassis have the same internal clock structure. The core of this structure is the TRION-SYNC-BUS that is connected to every slot of the chassis. Additionally, every DEWE2 and DEWE3 system has an internal chassis time base. This is the default synchronization source that creates a signal for clocking the ADCs of the input channels. Every DEWE2 or DEWE3 system also forwards this signal via the SYNC OUT connector to the SYNC IN or SYNC I/O connector of another DEWE2 or DEWE3 system. This is an easy way to synchronize several DEWE2 and DEWE3 chassis.
Different timing signals
You can use a timing module and PTP (IEEE 1588), GPS, IRIG or PPS signals to clock DEWE2 and DEWE3 systems. When using modules, the clock engine will transform the external sync signal into a signal that can be transferred via the TRION-SYNC-BUS and interpreted by the ADC clock dividers.