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Moisture Meters |
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Conductivity Meters
An electrical circuit through the meter is completed by placing two probes, (electrodes), on the surface, or by embedding them in the
depth of the wall. The electrical resistance of the wall, hence the circuit in the circuit, and the meter’s reading are influenced by
the moisture content in the wall.
Capacitance Meters
Either the meter itself (carrying adjacent conducting plates) or separate head (carrying conducting concentric rings) are placed on
the surface whose moisture content is to be measured. The meter readings measure the fringe capacitance in the sensor, which is influenced
by the moisture content in the wall. Some instruments (of both types) use a flashing light, or audible tones to indicate changes in moisture
content, either instead of, or as well as the conventional meter dial.
Both types electronically indicate or illustrate moisture content by the difference in the “charge” going through or across the surface of
the wall. Should the meter be held constantly against a wet surface and monitored, any active changes in moisture content will be illustrated
by the active changes on the meter or led indicator.
Electrical moisture meters and other methods of determining the presence of moisture in building materials cannot differentiate between
dampness from one source and that from another. Neither can they differentiate between surface dampness and in-depth dampness unless used with
long insulated deep-wall electrodes.
Hand held electrical moisture meters are non destructive and readings are taken easily and quickly. In the majority of walls which are of
uncertain composition, the electric method does not provide a percentage reading of the moisture content since readings may vary from material
to material. Readings are usually recorded on a relative or arbitrary scale which enables the pattern of moisture to be established. The
electrical method does not give a direct reading of moisture content and its value depends much upon the ability of the user to interpret the
results obtained by its use. In experienced hands it is a useful tool but it can give rise to confusion and incorrect diagnosis,
particularly where hygroscopic ground salts are present or where the dampness is due to condensation.
Electrical methods are not satisfactory in order to check the efficacy of a new dpc in a building that has suffered from rising damp. In such
cases, salts will be present, to a greater or lesser extent, whether the new dpc is effective or not. The presence of these salts alone can
produce high readings.
It is therefore necessary to consider all potential causes of dampness before arriving at a final conclusion.
The Lectros System incorporates a permanent moisture meter. The electrical charge is displayed illustrating the current passing from
the anodes, installed deep inside the wall to the cathode, buried deep in the ground a minimum of 2 metres from a treated wall. The readings
illustrated will vary with the changes in the walls moisture content similar to a hand held moisture meter.
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