Smart WiO - Water in Oil Sensor

The working principle is a capacitive measurement operating on absorption of water in oil. The physical measured value is % Humidity. New oil has the ability to hold a certain amount of dissolved water. The maximum water amount oil can hold is called “saturation point”. Above the “saturation point” free water will fall out which can cause corrosion inside of the engine. The “saturation point” is influenced by temperature and other different factors like the composition of oil mineral or synthetic, formulation of additives and will change during the lifetime of the oil. The Water in Oil Sensor (WiO) is not measuring free water or emulsion, which is detectable by regular Water in Oil test kits, it measures the absolute water content in oil.

The PAV (Pre Alarm Value) is set to 50% humidity.

The MAV (Main Alarm Value) is set to 90% humidity.

More than 100% humidity means free water is present. From this point regular Water in Oil test kits begin to measure.

Normally in the field, the water in oil content is measured by a Water in Oil test kit. The results are mostly <0.02% (or 100.02% humidity), this value means free water content. If the WiO Sensor shows the main alarm, the value is higher than 90% humidity and damage could be caused to the engine if 100% humidity is reached.

Controller Specification 

Power Supply

18…32 VDC

Current Consumption


Polarity Protection


Alarm relays

Pre-alarm at 50% humidity

Main alarm at 90% humidity

Output Current


Operating Temperature

-25 to +85 0C

Protection Degree


Analog Output: Water in Oil

4…20 mA (equiv. 0…100% Humidity Linear)

Analog Output: Temperature

4…20 mA (equiv. 0…1000C Linear)


125mm x 80mm x 57mm

Local Indication

LED Indicators



Sensor Probe Specification

Wong Polarity protection


Operating temperature

-25 to 85 0C

Protection degree


Pressure resistance against medium

10 bar

Connection type

G3/4” Male Thread


Stainless Steel AISI 303; 1.4305


50mm x 187mm

Cable Length to Controller


Insertion Length 


Local indication

LED Indicators




Indicator Dial Temperature 


Indicator Dial Humidity

Indicator Dial type

Analog needle type

Indicator Dial type

Analog needle type

Unit of Measurement

Degrees Celsius

Unit of Measurement

% Humidity


0 – 1000C 


0% - 100% Humidity


96mm x 96mm x 77mm


96mm x 96mm x 77mm