Serial Multipoint Transmission Rs-485; Connection Of The Maintenance Terminal; Relay Controls - Vaisala PWD22 User Manual

User's Guide _______________________________________________________________________
NOTE
50____________________________________________________________________ M210543EN-B
Vaisala recommendation for the maximum length of the RS-232 cable
is 50 m. Usually, the RS-232 connection can be used with distances up
to 100 m without problems but that cannot be guaranteed.

Serial Multipoint Transmission RS-485

The RS-485 transmission standard allows several PWD22s to
communicate (half duplex) with the host computer using a single
twisted pair. For the RS-485 communication connect the PWD22
signal wires to:
- BRN RS-485 A (+)
- WHT RS-485 B (-)
In some RS232/RS-485 converters the markings may be mixed. If the
connection does not work properly, switch the position of the wires.

Connection of the Maintenance Terminal

Any computer equipped with terminal emulation software or a VT 100
compatible terminal with RS-232 serial interface can be used as a
Maintenance Terminal for PWD22.

Relay Controls

PWD22 has three open collector relay controls that are controlled by
software using the alarms limits set in the CONF command.
The three relay control of PWD22 can all be driven by the visibility
limits. The third relay control can also be driven by the hardware
status.
- ALARM LIMIT 1
- ALARM LIMIT 2
- ALARM LIMIT 3
These are visibility alarm limits of 10-minute average. Limit value 0
indicates that this limit is not used. The three visibility limits are
independent of each other, which means that ALARM LIMIT 1 sets
the limit for RELAY CONTROL 1 only. ALARM LIMIT 2 set the
limit for RELAY CONTROL 2 only and so on. For example, RELAY
CONTROL 1 is pulling whenever visibility is lower than ALARM
LIMIT 1. See Table 13 and Table 14 on page 51.