Chapter 6 _______________________________________________________________ IO Terminal
VAISALA_______________________________________________________________________ 99
Connection via Active or Hot Standby Server
In duplicated systems, you can view the data without interrupting the data
flow by connecting through the hot standby CDU. For sending commands,
you need to connect through the active CDU.
Connection via Data Collector or Direct Connection
The sensors can be connected to the CDU(s) in two ways: directly or
through a data collector. If the system includes a data collector, you have
to open a line to it before you can connect to the sensor.
Auto-Send or Polled Sensors
Most sensors can be configured to operate in either auto-send or polling
mode. In polling mode the sensor sends messages only when the CDU
requests data with a specific polling string. Thus, when you make a direct
connection to the sensors, you have to send the corresponding polling
string to the sensor to display the sensor messages.
If the sensors are connected to the CDU via a data collector, the data from
the data collector to the CDU is normally in auto-send mode. In auto-send
mode, the data collector constantly sends sensor messages to the serial port
of the CDU. You can see this flow of sensor messages in the Terminal
panel when you connect to a port that is connected to an auto-send sensor
or a data collector.
CAUTION
When you connect to a field device through the data line, you interrupt
the flow of automatic weather data from sensors to the end-user
applications. If you have a duplicated system, connect through the hot
standby CDU for viewing the data.
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