SDI-12 History

SDI-12 was created in 1988 by a group of private firms and the U.S. Geological Survey's Hydrologic Instrumentation Facility (USGS/HIF).

The Hydrologic Instrumentation Facility issued procurement for a product that they called the Basic Data Recorder (BDR). The key requirement for this product was a low power standard interface between the data recorder and intelligent, micro-processor based sensors at remotes sites, called SDI-12, for serial-digital interface at 1200 baud. The SDI-12 interface was to be very simple to implement in small instruments with limited computing power, such as 8-bit control microprocessors. The goal was for all sensors using the SDI-12 standard to work with all data recorders using the standard.

To alleviate problems with older interfaces such as analog, the interface needed to be purely digital with simple wiring/connections for efficient installation and wiring at remote sites.

Before the formal procurement was issued, however, a group of companies and USGS/HIF created version 1.0 of the SDI-12. The key players included: Campbell Scientific, Environmental Systems Corporation, Handar, Hydrolab Corporation, Omnidata, Stevens Water Monitoring Systems, Sutron Corporation, Tavis Corporation; and USGS/HIF. The result of their work was version 1.0 of the SDI-12 Specification, which was released in October of 1988. Campbell Scientific was the primary author of this document.

The USGS/HIF subsequently issued a procurement for the Basic Data Recorder (BDR), with an SDI-12 interface as a requirement. This resulted in the design and manufacture of the first SDI-12 data recorders and sensors.

In 1991 the SDI-12 Support Group was formed as a non-profit corporation to maintain the SDI-12 standard.

Version 1.0 of the SDI-12 Specification was eight pages long. It was technically correct, but complaints were soon received saying it was difficult to understand. In 1992 the USGS/HIF awarded a contract to NR Systems, Inc., to rewrite the SDI-12 document, without changing the specification, to make it easier to understand. NR Systems teamed with Campbell Scientific on this task.

In September 1993, this revision, Version 1.1, was presented to the USGS/HIF and the SDI-12 Support Group at a formal meeting of the Support Group. That draft was reviewed in great detail. The companies in attendance at that review were: Design Analysis Associates, Hander, In-Situ, NR Systems, Sutron Corporation, Tavis Corporation, and USGS/HIF. Many changes were made to the draft in response to the detailed discussions at that meeting. NR Systems modified the draft of the specification in response to that meeting.

NR Systems completed its contract with USGS/HIF and submitted version 1.1 of the SDI-12 Specification in 1994. The original eight page document expanded to over 25 pages, with tables, illustrations, examples, refined logic flow charts, a glossary, and more. Version 1.1 was officially released by the USGS and the SDI-12 Support Group on July 7, 1994.

Since 1994 the SDI-12 Support Group has maintained the SDI-12 Specification. It has been upgraded numerous times since then.

SDI-12 has become an international standard. Firms that make SDI-12 products are located in Australia, Brazil, Canada, China, across Europe, India, New Zealand, Singapore, and the United States