Overview

The Observant C3 and Solo Tank Level solution uses the Senix ToughSonic Ultrasonic Sensor. This sensor sends ultrasonic pulses that reflect off the water surface back to the sensor. The time between sending and receiving the signal is used to determine the water level.

The under-range error can occur if:

• Something is blocking the sensor's diaphragm
• The sensor is not exactly vertical
• The water level is too close to the bottom of the sensor
• The distance being measured is beyond the maximum of the sensor
• The tank/dam is empty
• The sensor has become damaged from water contact
• The sensor is in direct sun

You can identify the Under-range error on the Monitor Card :

It will also be reported in Manage Equipment :

Resolving the Error

Obstruction

The under-range error is generally caused 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:

Sensor is not exactly vertical

The 'Under-range' error can also be caused if the sensor is not pointing directly at the water surface at a clean 90º angle.  If this is the case the ultrasonic signal can end up bouncing a number of times around the tank before returning to the sensor and therefore creating inaccurate readings.  Ensure the sensor is pointing straight down.

Water level too close to sensor

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 10 cm, if the water level in the tank reaches within 10cm, the sensor will report an under-range error. Because of this, the bottom of the sensor should be at least 10cm above the highest level that might be measured. It should also be positioned so that no water splashes reach it. 

Water level too far from sensor

The 'Under-range' error can also be caused if the distance from the sensor to the water level (or bottom of the tank) is beyond the maximum distance the sensor can measure. The most commonly used version of the Senix ToughSonic has a maximum range of 4m. 

Tank is empty

If a tank or dam is empty, the ultrasonic pulse might be scattered by the floor and not return to the sensor causing the 'Under-Range' error.

Sensor damaged from water contact

If the sensor's diaphragm comes into contact with water for a period of time, scaling can develop on the diaphragm and it can become damaged. The sensor will need to be replaced in this case. The replacement sensor should be placed higher so no water reaches it.

Sensor is in direct sun

For the temperature compensation to work correctly the body of the sensor needs to match the ambient temperature as close as it can, so it's important that it's shrouded from direct sunlight.

If you've checked the above and are still unsure of the issue, please email us photos of the sensor's diaphragm and some shots of the tank installation:

Please include a photo of the sensor's serial number if possible: