1.0 Introduction

SDI-12 (Serial Data Interface at 1200 Baud) is a communications protocol designed to allow the interfacing of a number of low power analog sensors with a common SDI-12 recorder or datalogger.

This User Guide focuses on the Solinst Model 301 Water Level Temperature Sensor (WLTS) for use as a device in a SDI-12 set up. Configuration, communication, installation and description of the SDI-12 protocol are included.


1.1 WLTS SDI-12 Interface Overview

To connect the WLTS to the SDI-12 customer equipment, you must ensure correct wire-to-wire connection of the cables, including a continuous external power supply to the WLTS (12V). The sensor connects to a Communication Cable (vented or non).

The communication settings for the WLTS comply with the SDI-12 standard at 1200 baud, 1 start bit, 7 data bits, 1 parity bit (even parity), and 1 stop bit. A simple PC Software Utility is used to specify the device address.

The SDI-12 interface circuitry requires the +12V connection to be powered by customer equipment. The current draw from the 12 volt source normally peaks at several 10's of mA, but idles around 2 mA.


Wire Colour SDI-12 Function Connection
Red 12 Volt Line +12V DC at SDI-12 Recorder
Black Ground Line Ground at SDI-12 Recorder
White Serial Data Line SDI-12 Data at SDI-12 Recorder


Table 1-1 SDI-12 Interface Cable Wire Definitions