Measuring Principle

SDI-12 is a communication protocol developed by the USGS so that no one sensor manufacturer would dominate the market with their own proprietary communications and has nothing to do with the way the sensors actually operate. The SDI-12 senosr available through AM&C operates on the piezo-resistive principle. Based on the conversion of the mechanical value "pressure" into an electic signal. This conversion is caused by the elastic bending of a diaphragm of monocrystalline silicon. A Wheatstone bridge diffused into the diaphragm changes its resistance caused by pressure influence. This change is measured by a microcomputer taking into account the sensor-specific data as well as the compensation of the temperature influence. The pressure-proportional signal is further processed in the transducer electronic unit and linearized. This digital signal with a high noise immunity is transmitted via the SDI-12 (Serial Data Interface / 1200 baud) to the processing unit.

Short Description

 

The pressure transducer contains a gauge-sensor which compensates the atmospheric pressure changes. The compenstation of the atmospheric pressure is performed by the vented cable. The intelligent transducer electronics also controls the communication with the processing unit and includes cyclic selftests. Besides the pressure, the temperature of the measured medium is detected and can be logged as well. Through the use of SDI-12 up to 8 sensors can be logged at the same time. The slim sensor requires little space an is therefore especialy suitable for the measurement of groundwater levels, pump sumps, river and navigation lock leves, etc. opened submersible-sensor Technical Characteristics Measuring ranges 0 ... 0.1 bar to 0 ... 200 bar (0 ... 1.45 psi to 0 ... 2900 psi) Accuracy class (linearity, histeresis, repeatability) 0.05 % FS SDI-12 0.10% FS 4-20mA Temperature influence Typ. 30 ppm/ºC Accuracy of the temperature measurement < 1.5 ºC Acid resistance pH5 ... pH9, other values on request Protection class Submersible: IP68 (submersible) Operating temperature range -20 ºC ... +70 ºC (-38 ºC ... +70 ºC, optional) Measuring speed 4 measurements/sec Weight of probe Submersible: 390 g Overvoltage protection Submersible: external

Vented Cable

Working principle The vented cable is a special construction used for baromentric pressure compenstation in connection with submersible gauge pressure transducers. Weight of 1 m cable: 72 g