Overview oil condition sensors

Bühler Technologies oil condition sensors reliably monitor:


  • Particles according to ISO4406 and other standards
  • Ferromagnetic particles
  • Relative humidity
  • Temperature


  • Permittivity
  • Conductivity
  • Liquid level

A hydraulic system or lubricating system working properly among other things essentially depends on the fluid choice and quality. Both subtle processes such as the ingress of moisture through air or even sudden errors in the system along with contamination with foreign substances can cause the fluid quality to deteriorate, resulting in costly damage to the unit or tool.

Continuous oil condition monitoring is therefore of utmost importance to extend the system life and optimise oil change intervals. Bühler Technologies offers a wide range of stationary measuring instruments which remain in the system for a variety of oil and lubricant quality parameters.

The devices remaining in the system presents significant advantages over cyclical oil sampling and laboratory testing. It generates a continuous picture of the oil quality to obtain specialised information about the system. Problems in the system can be detected in a very short time and appropriate preventive action taken. So the system meets all requirements of modern maintenance at a go and opens up all possibilities for digitalisation according to I4.0.

Laboratory testing, on the other hand, merely shows a specific point in time. When in doubt, the system is operated with inadequate lubricant quality for many operating hours until the next oil sample is taken. This could be a costly mistake.

The technology

Particle monitoring

The BPM sensor in the particle monitor uses the optical principle of light obscuration. A laser shines through the measuring cell that oil flows through. The shadow of a particle flowing through causes an intensity reduction on a photodiode. The larger the particle, the greater the reduction in intensity. Too many or too large of particles in the medium can clog valve seats, dull edges in hydraulic system components and roughen seal surfaces. This will inevitably cause internal leaks and performance loss in the system.

Ferromagnetic particles

Ferromagnetic particles can e.g. be a measure of abnormal wear in gearbox applications. The BMD sensor collects ferromagnetic particles using a permanent magnet on the sensor and inductively monitors particle quantity. The interval between the individual automatic sensor cleanings can be a measure for progressing wear. The sensor can also distinguish between coarse and fine particles. The automatic self-cleaning feature is a unique function of the BMD.


Bühler Technologies primarily uses PT100 & PT1000 resistor elements to measure temperature. Some oil quality parameters are directly related to temperature, e.g. relative humidity, permittivity, viscosity and conductivity. Correlating the temperature to precisely these parameters as accurately as possible is therefore essential. In addition, every system is designed for a specific temperature range. Monitoring the temperature is therefore necessary at any rate.

Moisture measurement

Moisture is an undesired parameter in oil-based hydraulic systems. If the temperature-dependent saturation point of the oil is exceeded, free water in the oil settles out, causing corrosion damage, and in temperatures over 100°C can cause dangerous malfunctions due to degassing. The BCM sensor measures relative humidity using a capacitive transducer. If free water or an emulsion is present at the measuring element, the sensor shows 100 %.


Relative permittivity means the capacity to store electrical energy when voltages are present. In the case of fluids, this is a measure for the polarity of the fluid. The polarity can vary in different base oils and additives. Meaning the permittivity can be used to determine if e.g. the correct oil was used in an oil change. Oils also change their polarity as they age. So permittivity provides information on the degree of ageing and the oil type. This measuring technology is used in the BCM-MS and BCM-LS.


Fresh oil has a specific conductivity. Since every oil has a specific conductivity, this is a good criterion to distinguish oils. Conductivity can also be used to determine if oil has been mixed with foreign substances. Measuring conductivity is therefore a good tool for monitoring the oil with respect to oil changes, oil mixing and contamination.

Liquid level

The liquid level in the hydraulic oil tank should be monitored to prevent the pump from running dry. A continuously dropping liquid level can also be used to detect a leak in the system and prevent major damage to system components as well as reduce pollution. Monitoring the max. liquid level is also relevant to avoid overfilling.

The BCM-LS uses capacitive measurement to measure the liquid level. Bühler Technologies further also offers measuring instruments with float in section liquid level measurement.

Particle detection    
Ferromagnetic particles    
Relative humidity  
Temperature •* •*
Liquid level    
Compressive strength50 bar420/600 bar20 bar50 bar50 bar
Voltage12-30 VDC9-33 VDC22-33 VDC9-33 VDC9-33 VDC

*The temperature is measured inside the sensor and therefore only serves as a reference point for the oil temperature.

Oil moisture sensor BCM-W

This sensor can be used to measure the relative moisture in oil, before the saturation point of the oil is reached and free water is formed. It is available as a pure transmitter as well as with a local display. Operating pressure up to 50 bars / 725 psi.

Particle Monitor BPM

The BPM-100 particle monitor was designed specifically for monitoring particles in oil. Continuously monitoring the fluid for solid particles can extend oil change intervals, thus significantly reduce maintenance costs. This makes the BPM-100 particle monitor an essential part of your condition monitoring system.

Metal Detector BMD

The BMD is a smart sensor and based on the inductive measuring system to properly sort the ferritic particles in the respective fluid. It can distinguish between fine and coarse ferromagnetic particles. It has analog and digital output signals.The BMD also features an automatic cleaning process..

Condition Monitor BCM-LS

The Bühler condition monitoring liquid level sensor (BCM-LS) was designed specifically to continuously monitor the relative humidity, temperature, permittivity, conductivity and liquid
level in oil tanks. By continuously monitoring the fluid, sudden and subtle level changes, deterioration or changes in oil quality can be accurately detected and the oil change intervals
extended or planned accurately.

Condition Monitor BCM-MS

The Condition Monitoring Multi Sensor (BCM-MS) was designed specifically to continuously monitor the relative humidity, temperature, permittivity and conductivity in oil. By monitoring the fluid, sudden and subtle deterioration or changes in oil quality can be accurately detected and the oil change intervals extended or planned accurately. Maintenance costs can be reduced significantly. This makes the Bühler Condition Monitoring Multi Sensor an essential part of your condition monitoring system.