Environmental Engineering Reference
In-Depth Information
where
F
is frequency measured [Hz],
w
water content in percent,
A
the constant
representing the sensitivity of the measurement and
B
the constant linked to the
oscillator.
Figure 11.1.
Calibration of a capacitive sensor
on the Lavoux Stone (F = 50w+ 5,096)
11.1.2.2.
Experimental set up
The capacitive sensors used for this study are two cylindrical electrodes made of
stainless steel, with a diameter of 6 mm and length of 80 mm placed within Lavoux
stone blocks (150 x 10 x 10 cm) in two parallel holes 20 mm from each other. A
graphite bearing grease allows the electrodes to be in electrical contact with the
stone.
The inside facing wall, receiving the instrumentation, is made of limestone
blocks sealed with lime mortar. The stones bearing the electrodes are moistened up
to 6% and inserted into the core of the masonry, along a vertical transect at heights
of 0.5, 1, 3, 4 and 5 m.
The output signals of the oscillators connected to the electrodes are transmitted
to a data logger fitted with a modem and a cellular phone, thus allowing remote
collection of the data. The data originating from the six sensors are collected every
90 minutes.
At 3m height there is a box inside the wall containing a sensor measuring
relative humidity of the air in equilibrium with the surrounding masonry.
Meteorological data (air temperature, relative humidity, pluviometry, wind direction
and intensity) are provided by Poitiers weather station.
