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SDI-12 sensor power supply – is 12 V needed?

Home Forums Environmental Sensors SDI-12 sensor power supply – is 12 V needed?


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    • #17745

        Usually SDI-12 sensors use 12 V power supply. In SDI-12 specification there is stated that logger should provide voltage in range 9.6 V to 16 V. I have checked sensors I commonly use (mostly Meter) and they all work with power supply 5 V or even lower. I would say using lower power supply volatage for sensors should also lead to more efficiency and longer battery life as it seems that sensors internaly use 5 V or less anyway and powering it with 12 V seems like waste of energy to me. I am wondering if there is some technical reason why power supply voltage for SDI-12 sensors is so high? Is it some historical thing for backwards compatibility? Does anyone know sensor which really needs more then 9.6 V to work properly?

      • #17747
        Shannon Hicks

          SDI-12 sensors usually use 12 volts for sensor excitation because that’s what the specification for the protocol dictates.  Fun fact:  the “12” part of “SDI-12” does not refer to the voltage, but rather the baud rate, so the name actually means “serial-digital interface at 1200 baud”).  Back in the days when the protocol was first being used, most sensor manufacturers used 12 volts for their sensor power.  Over the decades since, changes in technology resulted in sensors that can use lower excitation power, or sensors that can regulate their own power if you give them a wide input range.

          There’s lots of interesting history about the standard on the SDI-12 Support Group website:  https://www.sdi-12.org/history

          Plus there’s helpful technical details about the protocol in the full specification sheet:  https://www.sdi-12.org/specification

          I have personally used SDI-12 sensors that operate at 3.3v, 5v, 9v, 12v, so it really depends on the manufacturer’s designs and the sensors unique power requirements that dictate what excitation voltage must be supplied to the sensor.  In general, they’re supposed to all be able to be powered by 12 volts in order to meet the requirement of the SDI-12 standard.  But some manufactures have added the special feature of running from a lower voltage since nowadays many loggers operate on smaller battery supplies.

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