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Adapted from the SDI-12 Support Group Page. Access their webpage here

What is SDI-12?

SDI-12 stands for serial data interface at 1200 baud. It is a standard communications protocol, which means that it allows a micro-processor based sensor designed for environmental data acquisition (EDA) to transfer measurement data to a battery-powered data logger. The sensor typically takes a measurement, makes computations based on the raw sensor reading, and outputs the measured data in units we can understand. For example, an SDI-12 pressure sensor would take a series of pressure measurements, average them, and then output pressure in psi, inches of mercury, bars, millibars, or torrs. The sensor’s micro-processor makes the computations, converts sensor readings into the appropriate units, and uses the SDI-12 protocol to transfer the measurements to the data logger.

What features make SDI-12 particularly useful?

The following features could make SDI-12 useful for you in your research applications. SDI-12 offers:

  • Battery powered operation with minimal current drain
  • Deployment of many more sensors with a single data logger, as multiple sensors can be wired into the same port. Useful for extremely large scale studies.
  • Used with microprocessor-based sensors that perform complex calibration algorithms or make internal computations

Can more than one sensor be connected to a single data logger port?

Yes. SDI-12 is a multi-drop interface that can communicate with multi-parameter sensors. Multi-drop means that more than one SDI-12 sensor can be connected to a data recorder. The maximum number of sensors that can be connected to a single data logger port is 62, although connecting that many sensors to a single port is not advisable for reasons that are explained here.

Can a sensor take more than one measurement?

Multi-parameter means that a single sensor may return more than one measurement. For example, the Decagon GS3 sensor reports soil volumetric water content, electrical conductivity, and temperature.