Prevention is better than a cure, and condition monitoring is an essential part of a healthy hydraulic or lubrication system.

The contamination monitoring sensor measures and quantifies the numbers of solid contaminants in hydraulic, lubrication and transmission applications. The CMS is designed to be an accurate instrument for permanently installed applications utilising mineral oil as the operating fluid. The unit can operate using any of the international standard formats ISO 4406:1999, NAS 1638, AS 4059E and ISO 11218.

Operating principle of the contamination monitoring sensor

The instrument uses a light extinction principle whereby a specially collimated precision LED light source shines through the fluid and lands on a photodiode. When a particle passes through the beam it reduces the amount of light received by the diode, and from this change in condition, the size of the particle can be deduced.

Water Sensor

CMS-W models measure water content using a capacitive RH (relative humidity) sensor. The result is expressed as percentage saturation. 100% RH corresponds to the point at which free water exists in the fluid, i.e. the fluid is no longer able to hold the water in a dissolved solution. This is also normally the point at which damage occurs in a hydraulic system, so is an ideal measurement scale that is independent of the fluid characteristics. The water saturation point (100% RH) is temperature dependent, so the temperature is measured at the same time.

This enables results to be compared meaningfully. The water sensor output is affected by pressure, so the accuracy will be proportionally degraded above 100 bar operating pressure.

Measuring Water in Hydraulic and Lubricating Fluids

In mineral oils and non aqueous fire resistant fluids water is undesirable. Mineral oil usually has a water content of 50-300 ppm which it can support without adverse consequences. Once the water content exceeds about 500ppm the oil starts to appear hazy. Above this level there is a danger of free water accumulating in the system in areas of low flow. This can lead to corrosion and accelerated wear. Similarly, fire resistant fluids have a natural water content which may be different to mineral oils. (Source: North Notts Fluid Power Centre)

Saturation Levels

Since the effects of free (also emulsified) water is more harmful than those of dissolved water, water levels should remain well below the saturation point. However, even water in solution can cause damage and therefore every reasonable effort should be made to keep saturation levels as low as possible. There is no such thing as too little water. 

As a guideline, a recommendation is to maintain saturation levels below 50% in all equipment.