When selecting a submersible level sensor for measuring liquid levels, it’s essential to understand the differences between absolute and sealed gauge sensors. Choosing the wrong type of sensor can lead to reduced accuracy and resolution, which can impact the reliability of your measurements. Let’s break this down in simple terms.
Absolute Sensors and Their Limitations #
An absolute pressure sensor measures pressure relative to a perfect vacuum (absolute zero pressure). While this might sound ideal, it introduces challenges when measuring liquid levels in typical applications. Here’s why:
- Atmospheric pressure at sea level is approximately 1 bar, equivalent to the pressure exerted by a 10-meter water column (10mH2O). This means that an absolute sensor starts measuring from a vacuum (0 bar) and only begins to register positive pressure once the pressure exceeds atmospheric pressure (typically 1 bar or 10mH2O).
- To measure a liquid level of 10 meters using an absolute sensor, you would need a sensor with a range of 0 to 20mH2O. The sensor must account for the 1 bar/10mH2O of atmospheric pressure and the 10mH2O of liquid level pressure.
- With a standard 4-20mA output signal, the sensor would output 4mA at absolute zero pressure (vacuum), 12mA at atmospheric pressure (1 bar/10mH2O), and 20mA at an actual liquid level of 10mH2O. This effectively doubles the range of the sensor, reducing its resolution and increasing potential inaccuracies.
In simpler terms, using an absolute sensor for liquid levels of 10 meters or under means using a sensor with twice the actual range you need. This reduces the precision of your measurements and makes the sensor less effective for your application.
The Advantage of Sealed Gauge Sensors #
To overcome these limitations, a sealed gauge sensor is a better choice for most submersible-level measurement applications. A sealed gauge sensor works similarly to an absolute sensor but with one key difference: it is calibrated to account for atmospheric pressure.
- A sealed gauge sensor with a range of 0 to 10mH2O is designed to output 4mA at atmospheric pressure (1 bar) and 20mA at a liquid level of 10mH2O. This means the sensor’s range perfectly matches the fluid level you’re measuring without the need to account for atmospheric pressure separately.
- The sensor provides a more accurate and higher-resolution measurement by trimming the zero point to atmospheric pressure. The full range of the sensor is used for the actual liquid level rather than being split between atmospheric pressure and fluid level.
A sealed gauge sensor simplifies the measurement process and ensures that your readings are more precise and reliable, especially for liquid levels 10 meters and under.
Why Sealed Gauge Sensors Are Recommended #
For applications where the liquid level is less than or equal to 10 meters, sealed gauge sensors are the preferred choice because they:
- Eliminate the need to account for atmospheric pressure in the sensor range.
- Provide higher resolution and accuracy using the entire sensor range for the liquid level measurement.
- Simplify calibration and interpretation of the sensor’s output signal.
Choosing a sealed gauge sensor prevents the drawbacks of absolute sensors, such as reduced resolution and increased inaccuracy, making it the ideal solution for most submersible level measurement applications.
For recommendations of submersible level sensors, please review some of our options here: https://stork.solutions/level/submersible-level-sensors-and-level-transmitters
