BCM-MS, BCM-LS
1 Introduction
1.1 Intended Use
The BCM-MS200 and BCM-LS200 are used to measure and document changes in the properties of hydraulic and lubricating me-
dia and simultaneously measure the humidity and temperature. The respective measured values used to detect changes in the
properties as well as the temperature and humidity are detected continuously, saved and can be read out at any time using a
serial port. If the measured values deviate from a saved reference, this indicates changes which should be interpreted and in-
vestigated further.
Measured changes in the oil parameters can provide information about condition changes, e.g. oil aging, refreshing, changes or
water ingress. Damages can then potentially be detected early or even avoided. This allows taking suitable measures to avoid
serious machine malfunctions and prolong maintenance and oil change intervals. Furthermore, measured parameters and
changes in these can be used to derive and document information related to system maintenance carried out or the use of the
prescribed lubricant type.
The following chapters explain which situations changes in the condition can be detected. The sensor records the following
physical oil parameters and their time curve:
– temperature
– relative humidity
– conductivity
– relative fluid permittivity
– Liquid level (BCM-LS200 only)
Since the conductivity and relative permittivity in particularly greatly depend on the temperature, the sensor is able to convert
these parameters to a fixed reference temperature. The sensor continuously measures at various temperatures for this conver-
sion and uses this data to determine the temperature gradients of the parameters.
Determining the temperature gradient requires several temperature cycles when commissioning the sensor. During operation,
the temperature gradient is also continuously adjusted when oil is changed or ages.
1.2 Functionality
1.2.1 Temperature Measurement
A PT1000 platinum resistance sensor measures the oil temperature. The measuring range spans from -20 °C to 120 °C. Since the
resistance sensor is located directly in the oil, the conductivity of the surrounding medium should not exceed 3 µSm (-1).
1.2.2 Moisture Measurement
The relative humidity (formula symbol:
φ
) is measured using a capacitive transducer. The capacitive moisture detector detects
the relative humidity within a measuring range of 0 % to 100 %. If free water or emulsions are present, the sensor shows 100 %.
Since the moisture detector is located directly in the oil, the conductivity of the surrounding medium should not exceed 3 µSm
(-1).
1.2.3 Relative Humidity
Relative humidity
φ
means the ratio between the actual amount of free water in the oil (
ρ
W
) compared to the maximum possible
free water at the saturation limit (
ρ
W,max
).
=
ρ
.
φ
100 % (3-1)
w
ρ
w max
Since the saturation limit, i.e. the maximum amount of water it can hold
ρ
W,max
, greatly depends on the temperature, the relative
humidity changes with the temperature even if the absolute water content remains constant. As a rule, oil can hold more water
as the temperature rises before reaching the saturation limit.
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Bühler Technologies GmbH
BE150104 ◦ 03/2021
