Tank sensors are an important part of industrial automation. MaxBotix Inc., recently performed a liquid level measurement test at our facility. This test ran from July 13, 2012 until July 16, 2012. The test was conducted by filling a bin with water and recording readings from the ultrasonic sensor using the serial connection while the liquid was allowed to drain.
The graph below shows the range reported by the sensor in millimeters as the tank was drained. The plotted graph is the first 100,000 readings that were reported.
Readings were very stable, rarely changing by more than 1-mm (except where secondary reflections from the sides of the tank caused acoustic phase cancellation and readings from the tank sensor were
+/- 2mm). The raw data collected during the test is available to the public here: Tank Sensor Draining Test.
The HRXL-MaxSonar-WRM sensors are the recommended ultrasonic sensors for tank level measurement. The MB7369 and MB7389 sensors ignore smaller targets and only reports the range to target with the largest acoustic return. The Most-Likely filter is designed to report the distance to the largest acoustic return while ignoring smaller targets. When targets are of similar amplitude reflections, preference is given to the closest target.
Pictures of our test set up can be seen below.