How Ultrasonic Water Depth Sensing Works
In a nutshell, water depth sensing is using a sensor to measure the depth of water in a tank or container. Although various sensors can be used for this application, we will talk about ultrasonic sensor application.
With ultrasonic sensors, we can find the water depth calculation by finding the distance between the transceiver and the surface of the water. The sensor will transmit a short ultrasonic pulse, and we can measure the travel time of that pulse to the liquid and back. We can then subtract that distance from the total depth of the tank to determine the water depth.
This method of measuring with ultrasonic sensors is more accurately described as water level measuring. In a tank or container, this will produce the same results. It is important to note, you would need to position the sensor at a fixed point above wherever the water is stored. This can have benefits over underwater submersion, including greatly increasing the overall lifespan of the sensor.
As mentioned above, to truly measure water depth rather than water level with an ultrasonic sensor, we must submerge the sensor in water. We do not recommend this because our sensors were not designed for underwater use, and they have not been properly tested in this environment. Even though the MaxSonar-WR and MaxSonar-WRC lines are IP67 rated and can be submerged up to one meter, this goes against their intended function and will void the manufacturer’s warranty. We cannot guarantee proper function if submerged.
Although this is not covered under our warranty, you can take a look at our article designed to help with underwater ranging. We can’t necessarily support outside, underwater testing of our sensors, but we would love to hear about the results. Click here to take a look at our MaxSonar-WR and MaxSonar-WRC product lines.
Ultrasonic Depth Sensors aren’t limited to only water detection and are used in a variety of applications including:
- Tank level measurement
- Diesel fuel gauging
- Irrigation control
- Stream or River level monitoring
- Wet well and pump controls
- Sea or Tide level monitoring and Tsunami warning
- Liquid assets inventory
If you are interested in measuring tank levels, check out our Guide to Tank Level Monitoring with Ultrasonic Sensors that might help answer some questions. We also have an article about using an ultrasonic sensor inside of a pipe that might provide some useful information on the above applications.
Mounting an Ultrasonic Level Sensor
When mounting the sensors in a tank, there are things to take into consideration.
The dimensions are important to be able to choose the proper sensor beam pattern for your application.
If the tank walls are corrugated, it is important to take that into consideration when selecting your sensor, the sensor may not range past the walls to the surface.
Note: The MB7389 comes with the most likely filtering to help resolve this issue. The sensor will search for the largest acoustic return, instead of the closest. This helps to hide the side walls of the tank from the sensor.
Sensing Lake Levels with Ultrasonics
While all of our sensors can detect liquid levels, none of our sensors were designed for bathymetry. The only way you could use our sensors to measure the depth of a lake would be to mount it a known height above the lake bed and subtract the reported distance to the water (the sensors reading) from the known distance to the lake bed. (Same concept as measuring levels/depth in a tank or container).
Take a look at our recommended sensors for tank level monitoring:
Features of the weather resistant MB7052, XL-MaxSonar-WRM1, include small target rejection providing range information to the target with the largest acoustic return, a stability filter, centimeter resolution, short to long distance detection, range information from 20cm to 765cm, a 6.7Hz read rate, and various output options: pulse-width, analog voltage, and RS232 serial.
Features of the weather resistant MB7369, HRXL-MaxSonar-WRM, include millimeter resolution, short to long distance detection, range information from 300mm to 5000mm to the target with the largest acoustic return, a 6.7Hz read rate, and various output options: pulse-width, analog voltage, and RS232 serial.
Features of the weather resistant MB7389, HRXL-MaxSonar-WRMT, include millimeter resolution, short to long distance detection, range information from 300mm to 5000mm to the target with the largest acoustic return, a 6.7Hz read rate, and various output options: pulse-width, analog voltage, and TTL serial.
If you would like help selecting a sensor for any application, please email us at [email protected].
Common Questions about Water Depth Sensing with Ultrasonics:
– Do I have to seal the back side of the sensor where the pinout is?
Yes, the front side of the sensor is IP67 rated, however, the user is still required to seal the pinout section of the sensor. We can easily do that for you if you add the shielded cable attach option when selecting your sensor. You can check out our article about weatherproofing the pin out.
– If the sonar is not meant for underwater use, how can you outfit it to work underwater?
If you use the analog envelope output, you could use the waveform and look for the underwater reflections in the waveform detected by the sensor. This would require an AD converter that sampled at regular intervals and then this data would show the distance to the target. Some users reported that they used the analog voltage output with success (it reported the wrong distance because ultrasonic sound waves travel at different speeds under water, but they were able to use the measurements with lookup values).
If you have any further questions or need assistance with sensor selection, contact our tech support team at [email protected].