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Water In Oil Monitoring// Water In Oil Monitoring System for Engine Control Room
SELMA Water In Oil Monitoring System for Engine Control Rooms is designed for the detection of Water Contamination in any kind of Oil or Fuel in the marine industry.
An oil system can contain water in three phases depending on the chemistry of the oil whether mineral or synthetic. Every oil has a degree of water solubility and its specific water-saturation point past which additional water becomes either emulsified or free. Therefore, different oil systems may contain dissolved, emulsified and/or free-water.
Water solubility in oils is mostly exponentially dependent on temperature. Higher temperature oils can absorb more water from the air, with airborne moisture being the most common source of water.
In new oils water solubility is mainly determined by the type and amount of additives, while in aged oils oxidation products have the most significant effect. The aging of oil is a function of activity of water rather its absolute content due to the chemical reactions of the process.
Over-saturated water content in oil results in a two-phase system where excessive free water is formed and co-exists separately from the oil. Free water can then cause corrosion and cavitation type damages to the system.
Moisture measurement
Conventionally, water in oil has been measured by a method determining the moisture content of a sample and expressed in ppm, which is the total absolute water content, thus not giving any indication whether water is dissolved or free. However, due to differences in oil types and difficulty in predicting aging effects, ppm values are often not sufficient for setting alarms in control systems and relative values like water activity (expressed in aw) is used instead.
Water activity is the partial vapour pressure of water in the oil or fuel divided by the standard state partial vapour pressure of water.
Principle of Operation
Water In Oil Monitoring System Capacitive Sensors provide the value of water activity without temperature corrections or oil-type calibrations. A membrane of the sensor absorbs water molecules, which change its dielectric constant (i.e. a measure of the ability of a material to resist the formation of an electric field within it). The absorption is proportional to the equilibrium relative humidity of oil, thus indicating the margin to saturation.
The Water In Oil Monitoring System generates an alarm at a Pre Alarm Value (PAV) of 0.5 aw or a Main Alarm Value (MAV) of 0.9 aw.
The state-of-the-art Water In Oil Sensor / Transmitter System is perfectly suited for Marine applications. The high accuracy measurement and excellent long-term stability make it ideal for online monitoring of moisture in transformer, lubricating and hydraulic oil, as well as diesel fuel.
Technical Specifications
With its compact design and rugged stainless steel housing the Water In Oil Detection Sensor provides the solution of a space-saving installation in the most demanding applications. The Water In Oil Detection Sensor measures water activity (aw), oil temperature (t) and calculates the absolute water content (x). The measured values are available on two 4-20mA outputs and one digital output with MODBUS RTU interface.
The heavy duty design of the Monitoring – Recorder System is based on Marine Approved Colour Touch Screen
| Display | Colour Touchscreen Type |
| Alarm | Audible / Visual |
| Alarm History | Included |
| Modbus RTU Input | 1 (Wa Water Activity in Oil Activity Monitor) |
| Digital Inputs | 4 |
| Digital Relay Outputs | 6 |
| Output Communication | 1 Ethernet / 1 CAN Open / 1 RS232-485 for connection to Ship’s Network |
| Recorder Function | USB Stick 16 GB |
| Power Supply | 24 V DC |
| Alarms (Adjustable) | Water Activity / Temperature / Sensor Circuit Failure |
| Panel Mount | Flush Mounted Prewired with Terminals / Glands |