Appendix B - RS-485 Communication
The RS-485 Hydra Probe is also digital and uses an RS-485 communication format. The RS-485
Hydra Probe has 4 wires: a ground wire, a +12 volt power wire and 2 data wires. The RS-485
Hydra Probe communicates through two data wires and can be wired into a RS-485 port on a
logger. They can be connected to a terminal assembly like the SDI-12 version, but with four
wires instead of three. The advantage RS-485 has over the SDI-12 version is that the RS-485
version’s cable can run over 3000 feet. The disadvantage is that it draws more power.
Power Requirements
9 to 20 VDC (12VDC Ideal)
Red Wire
+Volts Power Input
Black Wire
Ground
White Wire
Data Signal A non-inverting signal
Green Wire
Data Signal B inverting signal
Baud Rate
9600 8N1
Power Consumption
<10 mA Idle 30 mA Active
Table 2.3 Digital RS-485 Hydra Probe II Information.
Stevens Hydra Probe RS-485 Command Specification
For Use with Firmware Version 2.7 and Later
Command Format
AAACC<CR><LF> Execute
AAACC=?<CR><LF>
Query current setting
AAACC=XXX…<CR><LF>
Assign new value
AAA
:
3 byte address
ASCII characters, 0-9 A-Z a-z
Wildcard
character:
“/”
Broadcast
address:
“///”
CC
:
2 byte command
XXX…
:
Command data. See command info for specific requirements.
<CR>
:
Carriage return character (ASCII 13)
<LF>
:
Linefeed character (ASCII 10)
Other Grammar
<d>
:
Digit, ASCII ‘0’ through ASCII ‘9’
<a>:
ASCII ‘A’ through ASCII ‘D’, used for custom water constant
<serial>
: Serial number, 8 digits. <d><d><d><d><d><d><d><d>
<soil>
: Soil Type, 1 character {‘1’ | ‘2’ | ‘3’ | ‘4’| ‘C’ | ‘D’}
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