Nortek Vectrino, Руководство пользователя

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26
Chapter 8
Synchronizing Multiple Instruments
Synchronizing From a TTL Source
TTL signal levels can be mixed with the RS485 levels of the Vectrino:
Connect your sync pulse to
Sync+ and connect Sync– to a constant voltage,
1.5 volts for instance. This provides a defined transition when the TTL signal
changes, which is not the case if you ground
Sync– .
RS485 levels: These levels
define the signal the Vectrino
reads for Input Sync:
High level: Sync+ > Sync– by
200 mV
Low level: Sync+ < Sync– by
200 mV
Noise problems:
If you
encounter noise problems, try
terminating the
Sync+ line at the
TTL input by connecting a 120
ohm resistor in series with a 1nF
capacitor between the
Sync+
line and ground. The best
solution for external sync is
using RS485 as the input/output
device.
Note: This implies that a
Vectrino can operate as a
master for a Vector, but the
opposite is not possible.
When Vectrino functions as master, the Sync+ line can be connected to the
TTL input and the two systems must be connected so they share common
ground.
How Synchronization Works
Output Sync (operating as the master) transmits a pulse on RS485 with a
duration of 40 μ s. SyncOut for Vectrino transmits the pulse by the end of
the sampling interval and a single pulse at the beginning of the first
sampling interval to start off everything. For other sensors, SyncOut
transmits a pulse at the middle of the sampling interval.
Input Sync triggers on any edge, rising or falling, on RS485. After each trig
the input is discarded for the next 64 μ s.