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RS-232 to SDI-12 Interface

The H-4191 converter allows a PLC, RTU or other host device with a RS- 232 port to access SDI-12 sensors.

With the WATERLOG® Model H-4191 interface you can use your laptop computer to configure and test SDI-12 sensors and monitor the communication between a data logger and its sensors.

• Provides both the electrical and protocol functions for interfacing a RS-232 host device to one or more SDI-12 sensors.
• Works with any sensor command & response message including vendor specific extended commands.
• Buffers the command so no special timing is required, even hand-typed commands will work.
• Generates proper parity for the SDI-12 bus.
• Automatically sends SDI-12 breaks & retries.
• Passes the sensor service request to the host.
• Supports optional CTS/RTS hardware flow control for a slow host device.
• Low power mode facilitates use with a RS-232 data radio.
• LED shows when the H-4191 is awake.
• Built in “sensor” can measure the SDI-12 bus battery voltage.


RS-232 Port
Type: Asynchronous, 9600 baud (fixed), 8-bit, no parity
Flow Conrol: RTS/CTS (optional)
Command Buffer: 60 characters

SDI-12 Port
Baud Rate: 1200
Protocol: SDI-12, 7-bit even parity, 1 stop bit
Output Voltage Levels:
Minimum high level: 3.5 volts
Maximum low level: 0.8 volts
Internal Voltage Monitor (Address “Z”)
Range: 6-18V
Resolution: 8-bit (.08V)
Accuracy: ±1%

Power Requirements
Voltage Input: 9 to 16.0 Volts DC
Supply Current:
Sleep Mode 100μA typ
Active 20mA typ
Surge Protection: Built in, 1.5 KVA

Operating Temperature: -40/ C to +50/ C
Storage Temperature: -50/ C to +70/ C

Material: ABS plastic
Size 3.75" Long x 2.65" Wide x 1.25" Deep

RS-232: 9-Pin, female, D-sub, DCE (modem)connections
SDI-12 4-position terminal strip, pluggable, Phoenix Combicon™

Ordering Information:
H-4191 RS-232 to SDI-12 Interface (Includes Cable Set)