Chapter 3 ________________________________________________________________ Installation
VAISALA ________________________________________________________________________ 63
To connect DXL421 wires to the screw terminals, do the following:
1. Disconnect the red and blue wires from the screw terminals
1 and 2.
2. Replace the screw terminals with the ones included in the DXL421
delivery.
3. Reconnect the red and blue wires to the lower row of the screw
terminals 1 and 2.
4. Connect the red and black wires to the DXL421 modem.
Multipoint Modem Connection
If a multipoint modem connection (several pieces of equipment on the
same line) is used, the only available connection standard is 300 bps
V.21. In this configuration the data collection computer or the weather
station acts a master that polls all the FS11P sensors and the other
possible sensors.
The master modem must be in the Originate mode. All other modems on
the line must be in the Answer mode and the Carrier signal must be
disconnected by default. In the FS11P sensor, this can be set with the
jumper/dip switch settings on the DXL421 modem, as described on page
61. In this mode the sensor turns the Carrier signal on only when it gets
the appropriate poll signal and turns it off when the message has been
sent. If there are several FS11P sensors on the line, they must have
different identifiers.
Due to the limited transfer capability of the 300 bps V.21 mode, there can
be a maximum of four FS11P sensors on the line provided that message
number 7 and a polling interval of 15 seconds are used. If some other
message type or interval is used, calculate the maximum number of
sensors (N) with the following formula:
N*message_chars/30(char) + N*1 second < interval
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