Beckhoff EL3702, Документация

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Commissioning
EL37x2 147 Version: 3.5
Fig. 189: Process Data tab, activation of index 0x1b10, entry “StartTimeNextLatch”
The StartTimeNextlatch process data is 32 bits wide. During each process data cycle the time is specified at
which the
next SYNC1 pulse and therefore the next block of sample values begins. StartTimeNextLatch thus
changes in each cycle by the amount of that task cycle time with which this terminal is operated. This time
specification is based on the terminal’s local Distributed Clocks time. The EL37x2 only maps the lower 32
bits of the generally 64-bit distributed clock time.
In this way all samples can be synchronized with other time data within the EtherCAT bus based on the
known oversampling factor.
Sample:
With a cycle time of 1 ms (= 1,000,000 ns) and an oversampling factor of 20 in the regarded cycle, the
EL37x2 supplies a StartTimeNextLatch = 7,777,216
dec
and 2 x 20 measured values at 16 bits each as
process data. The time of measurement of the 5
th
supplied sample is now to be determined, i.e. the
Distributed Clocks time at which the 5
th
sample was determined.
The currently supplied set of 20 samples was started at the time
7,777,216 – 1,000,000 (cycle time) = 6,777,216 ns.
The time interval between the samples is 1,000,000/20 = 50,000 ns.
Hence, the 5
th
sample was determined at the time 6,777,216 + ((5 - 1) * 50,000) = 6,977,216 ns.