Somat eDAQlite, Руководство пользователя

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Somat eDAQ
lite
212 I2773-4.
4
en
14.4.1 Bus-Oriented Channel Synchronization
The vehicle bus, serial bus, and GPS messages are time stamped as they are
received by the eDAQ
lite
. The time stamps are synchronized to the same eDAQ
lite
MSR clock used for all other inputs. As such, the inherent skew (always a lag) for
vehicle bus inputs is dependent on how much time elapses between the actual data
sampling on the vehicle computer(s) and the time it takes for the vehicle bus message
to be posted by the source processor and read and time stamped by the eDAQ
lite
.
14.4.2 Thermocouple Channel Synchronization
The ELNTB channels source from a clock on these layers that is not synchronized to
the eDAQ
lite MSR clock. There is a latency of about 70 milliseconds between the
actual time the data is sampled and the time the data is made available to the
eDAQ
lite (for reading and time stamping).
14.5 Networked eDAQ
lite
/eDAQ System Synchronization
14.5.1 Hardwired Network Synchronization
Master Mode
For a set of hardwired networked eDAQ lite /eDAQ systems, the data acquired on all
of the slave nodes lead the data acquired on the master node by approximately one to
two microseconds. The reason for this is that there is a one to two microsecond delay
in the propagation of the sample clock signal from the master to the slaves.
GPS Master Mode
When using the GPS master network mode, the slave data channels lead the master
by the following:
•
ELDIO GPS clock, 100-kHz MSR - 90-microsecond lead time
•
ELDIO GPS clock, 98.304-kHz MSR - 112-microsecond lead time
Because of these limitations on GPS master data synchronization, it is recommended
to use the GPS master mode with ELDIO GPS clock generation only at low sample
rates on the order of 100 Hz.
14.5.2 Wireless Network Synchronization
For wireless eDAQ
lite
/eDAQ networking using a GPS timing signal, test results for the
accuracy of the synchronization show that data can be synchronized to 0.1
milliseconds or better assuming all systems maintain consistent GPS lock. If an
eDAQ
lite /eDAQ loses GPS lock for only a short period of time (i.e., 10 minutes or
less), then the synchronization is still maintained to within 1.0 milliseconds or better as
long as there are no sudden or significant temperature changes in the
eDAQ
lite
/eDAQ GPS hardware.
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