Submersible level transmitters are typically used for hydrostatic level measurement where the only access point is from the top of a tank, river, borehole or vessel. The sensors can be lowered into the media to the lowest point of where the measurement is required. The head of liquid above the sensor generates a pressure which we can measure and convert to a readable level measurement.

Impress Sensors & System Ltd have been manufacturing submersibles level sensors for many years and have recently included the increasingly popular SDI-12 serial interface to accompany the standard analogue 4-20mA and voltage signals. With 1200 baud rate this serial interface is idea for battery powered applications such as those incorporating data logging and acquisition systems particularly in environmental monitoring. Multiple sensors, typically up to 10 devices, can be attached to a single data logger and simply addressed using the SDI-12 protocol, this therefore helps in cutting the costs of interfacing, wiring and channels per data logger.

Advantages of using SDI-12 submersible level transmitters:

• Low power consumption
• Measurement in understandable engineering units
• Level AND temperature output as standard
• Multiple sensors connected to a single bus
• Sensor output is internally compensated and calibrated
• High levels of accuracy, <+/-0.1% / FS TOTAL error band!
• User adjustable parameters
• Very good cost vs. performance ratio

By integrating the microprocessor based SDI-12 Interface into the submersible level transmitter we can calibrate and characterise the raw millivolt sensor output into user selectable engineering units and eliminate static and thermal errors by a series of algorithms. The microprocessor takes several pressure readings from the sensing element, averages them and then outputs the specified engineering unit using the SDI-12 protocol to communicate with the data logger.

The other interesting features of this technology means we can also utilise the internal temperature sensor used for the compensation of the pressure sensor and also output this temperature reading in Celsius or Fahrenheit to the data logger. This means level and temperature is available from a single submersible transmitter eliminating the need for a separate device!

The ‘SDI-12L’ transmitter is offered with two types of technology integrated for the sensor, a ceramic piezo-resistive sensor and a media isolated stainless steel piezo-resistive sensor.  The ceramic is particularly suited to applications where compatibility may be an issue when used with aggressive media asuch as seawater, brakish and saline solutions, chemicals where stainless steel will be destroyed.  For these applications we also have the option of using marine bronze, plastics and delrin to ensure complete compatibility.

The stainless steel sensor produces slightly better resolution and can achive pressure ranges as low as 0.5mWG up to 200mWG whereas the ceramic sensor has a minimum range  of 5mWG and up to 200mWG.  Both sensors achieve the 0.1% total accuracy by means of the microprocessor cmpensation and calibration.

Some typical applications that use the SDI-12 output are:

• River and reservoir level
• Tank level and vessel level
• Seawater and estuary level
• Borehole and Aquifer level
• Tsunami monoring systems
• Tidal and wave height monitoring
• Environmental monitoring

The increasing availability of data loggers and interfaces that utilies the SDI-12 protocol means that applications are becoming more widespread.  For this reason Impress will consider the integration of this technology into other products upon request.  Please get in touch if you have such a requirement to discuss in more detail.

Datasheet: SDI-12L Submersible level transmitter

Products Page: Submersible hydrostatic level measurement

For more information on the SDI-12L submersible level transmitter please contact us at sales@impress-sensors.co.uk The hydrostatic submersible level transmitters can be found here.

Tags: hydrostatic level sensor, Hydrostatic level transmitter, level measurement, Level Transmitter, SDI-12 sensor, Submersible level transmitter

This entry was posted on Sunday, June 21st, 2009 at 11:43 am and is filed under Hydrostatic level transmitter, Level Transmitter, Submersible level transmitter. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.