Measuring Moisture in Oil0 pages

/ APPLICATION NOTE
Measuring Moisture in Oil
Frequently asked questions
1.
Where should I install the probe for the best measurement?
2.
What is the maximum flowrate the sensor can withstand?
3.
What is the response time of the sensor?
4.
Can the sensor measure
% water by volume in oil
(free or emulsified water)?
5.
What does the water activity (aw) output indicate?
6.
What is the benefit of measuring aw versus ppm?
7.
Does the sensor need to be programmed or calibrated to each specific fluid you are using?
8.
In which fluids can the sensor be used?
1. Where should I install the probe for the best measurement?
The probe should be installed in a location that provides a representative sample of your entire oil system (e.g. a high flow feed line, or return line to reservoir). The sensor can only read what it is directly in contact with. Locations to avoid include the bottom of oil reservoirs where
Water contamination in lubricating oil deteriorates both the lubrication performance and the ability of the oil to protect the machine from corrosion. On-line monitoring of moisture in oil is an important step in avoiding costly failures and unscheduled downtime. free water may settle out and areas where air bubbles could form due to turbulence caused by pumps or agitators.
2. What is the maximum flow rate the sensor can withstand?
The flow limitation of the sensor is affected by the shear force applied by a high flow oil with significant viscosity. If high enough, this force could bend or damage the sensor contacts. We recommend a maximum linear flow rate of 1 meter/second.
3. What is the response time of the sensor?
The Vaisala thin-film polymer capacitive sensor is extremely responsive to a small step change in moisture level. This can be demonstrated by grasping the probe in your hand. The moisture from your skin will be detected within 2-3 seconds. However, this response time is diminished due to the viscosity of the oil and the slow rate of travel of water through the oil. In still oil at 20 ¢ªC, 90% of the reading will be reached in ten minutes. This response time dramatically improves by installing the probe in a flowing oil line – remember, the sensor can only measure what it is in direct contact with.
4. Can the sensor measure % water by volume in oil (free or emulsified water)?
No. The Vaisala HUMICAP® sensor is designed to measure only water that is in the dissolved state (below the saturation point).
5. What does the water activity (aw) output indicate?
Water activity (aw) is a measurement which indicates moisture (water) content in a fluid based on a scale from 0…1 (0 being completely dry,
1 being completely saturated).
Vaisala HUMICAP® Hand-held Moisture Meter MM70