Campbell Scientific SR50A Distance Sensor - Manual (Page 13)

SR50A Sonic Ranging Sensor
3.5 RS-485 Operation
The SR50A sensor comes from the factory with the internal jumpers set to
SDI-12 mode. To use the SR50A in the RS-485 mode of operation the jumpers
will need to be set as outlined in Section 7.
The RS-485 on the SR50A supports half-duplex communications. This means
that the SR50A can receive and transmit but both cannot occur simultaneously.
Normally there is a master-slave relationship in most systems to avoid
collisions between transmissions. For this reason the Auto Measure Auto
Output is not recommended for RS-485 communications. It is much better to
have a master initiate the communications by making use of the Measure On
Poll or the Auto Measure Polled Output modes.
Campbell Scientifics’ MD485 interface can be used to connect one or More
SR50A sensors in RS-485 mode to an RS-232 device. This can be useful for
sensors that require lead lengths that exceed the limits of either RS-232 or SDI-
12 communications.
3.5.1 RS-485 Wiring
The following table/diagram illustrates the wiring for the SR50A in RS-485
mode.
Color Function Connection
Black Power Ground System Ground and/or RS-232 Receiver Ground
(Pin 5 of a computer (DTE) DB-9 connector)
Red +12VDC Power Power Source
Green RS-485 A To RS-485 A terminal
White RS-485 B To RS-485 B terminal
Clear Shield Shield/Earth Ground
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