38
Rev. C • 10.2004
CHAPTER 6
Use with Other Instruments
The SyncIn signal permits external control of the sampling.
Two options are available:
•
Initiation of the Vectrino sampling upon receipt of an input pulse
• Full external control of the data collection rate.
Typically, the other instrument will provide TTL pulses required to trigger the
data collection or the signal can be used as a remote switch that allows the opera-
tor to start data collection at the push of a button.
The SyncOut signal is always generated by the Vectrino. The SyncIn signal is
treated differently depending on the settings in the
Advanced tab in the Deploy-
ment Planning
menu.
There are three possible modes of operation that can be set for Input Sync:
• No Sync.
In this mode, the Vectrino ignores the SyncIn signal and data collec-
tion starts under software control only.
• Start on Sync. In this mode, the Vectrino starts data collection on the rising
edge of the SyncIn signal. Sampling of velocities then proceeds at the set
sampling rate. After data collection is started the SyncIn is ignored. The fi rst
velocity sample is completed one sample interval (which equals
1
/
SAMPLING RATE
)
after SyncIn becomes “high”.
• Sample on Sync. In this mode, the Vectrino outputs a sample after every rising
edge of SyncIn. To use this mode, the Start on Sync mode must be used as well.
Therefore, the fi rst rising edge starts the averaging pro cess for the fi rst sample
only. The fi rst data sample is output on the sec ond rising edge of SyncIn. The
output data at each rising edge of SyncIn will correspond to an average since
the previouis rising edge of the SyncIn. The Vectrino must be confi gured with
the setup software for a sampling rate that is equal to or higher than the sam-
pling rate that will be used. For example, if the signal on the SyncIn input to the
Vectrino is generated to correspond to a sampling rate of 25 Hz, the Vectrino
should be confi gured in software for a sampling rate of 32 Hz.
In most cases it will be suffi cient to synchronize different Vectrinos using Start
on Sync
. All Nortek instruments shipped after November 2000 are fi tted with
a real time clock with an accuracy of ±1 min/year over a temperature range of
0–40 °C. Over a burst period of for example 1 hour, the maximum clock drift
between two Vectrinos will then be 13.7 ms. Since they will operate at the same
temperature the clock drift is likely to be even smaller. At 8 Hz sampling rate this
will be
1
/
10
of a sampling interval over one hour of measurements.
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