Why are my Tank Level readings inaccurate?

Rowan Chase

Created: ; updated: .

The Observant C3 and Solo Tank Level solution uses the Senix ToughSonic Ultrasonic Sensor.  This sensor transmits ultrasonic pulses that reflect off the water surface back to the sensor.  The time between transmit and receive is used to calculate the distance.

With this in mind, there are are some installation and operation considerations to be taken when resolving inaccuracies in tank level readings.


Water Level Readings have spikes or noise

Spikes and 'noise' in tank level readings (as below) may be induced by 'echoes'.erraticSenixLevels.png

This can be caused by the sensor being installed too close to the side of the tank.

The sensor should be a minimum distance of 15% of the "tank height" (see above) away from the edge.


Water Level Readings are consistently inaccurate

To calculate the water level, Global uses the distance to the water surface measured by the sensor in conjunction with the measurements of the tank provided.  

If tank level readings are consistently inaccurate then it's likely the measurements provided are not correct.  This often results in reported water levels greater than 100% or reported water levels that never reach 100%, even when the tank is full.

To revise your tank measurements, see the Managing Tank Level Settings article.


Sensor Reports 'Under-Range'

You will see this error on the Monitor Card :


It will also be reported in Manage Equipment :


Generally this is due to an obstruction on the sensor diaphragm.  Often spiders and other insects may have nested on the sensor, or there is a build up of dirt.  A site visit is required to clean the sensor face.

Another common reason for this error is the water level reaching too close to the bottom of the sensor. Since the sensor cannot measure any surface closer than 4", if the water level in the tank reaches within 4", the sensor will report an under-range error. Because of this, the bottom of the sensor should be at least 4" above the highest level that might be measured.

The 'Under-range' error can also be caused by the ultrasonic pulse not being received back to the sensor.  This is discussed more in the next section below.


Tank is empty but Water Level Readings are not 0%

Firstly, ensure that your tank measurements are correct and see the Managing Tank Level Settings article.

Some other possible causes are :

  • The distance between the bottom of the tank and the sensor is beyond the maximum distance of the sensor.  The most commonly used version of the Senix ToughSonic has a maximum range of 4m.
  • If the sensor is installed above a dam then the floor of the dam may not be a flat surface when it is dry.  This results in the ultrasonic pulse being scattered and not returning to the sensor.

In both the above cases, the reported readings may be close to 100% or in some circumstances the sensor may report 'Under-Range' (as above).


Tank is full or overflowing but Water Level Readings are 65-85%

This observation suggests the sensor is fully or partially submerged.  It is further characterised by a sudden drop, with high tank readings either side of the incorrect readings (as below).

The Senix ToughSonic will continue working when submerged, however due to the speed of sound being 4x faster in water, it reports a distance 1/4 of the full depth of the tank.  This results in a reported water depth of 3/4 of the full tank ie. about 75%.





If you have further questions about Water Level Readings, feel free to send your inquiry to the HelpDesk

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