CONSIDERATIONS ON ELECTROMAGNETIC HUMIDITY MEASUREMENT IN SIMPLE MASONRY WALLS

Abstract

Humidity measurement in thick walls indicate under what conditions is exploited a building. Any type of moisture walls, superficial or deep, give information about possible cracks or infiltration of water. The electromagnetic techniques for measuring soil humidity (by resistivity) has been known for a long time. It can be used to measure walls moisture. Conductivity is preferable in inductive techniques, as instrumentation readings are generally directly proportional to conductivity and inversely proportional to resistivity. The operating principle of this method is: a Tx coil transmitter, supplied with alternatingcurrent at an audio frequency, is placed on the wall. An Rx coil receiver is located at a short distance, s, (on the wall) away from the Tx coil. The magnetic field varies in time and the Tx coil induces very small currents in the wall. These currents generate a secondary magnetic field, Hs, which is sensed by the Rx receiver coil, together, with primary magnetic field Hp. The ratio of the secondary field, Hs, to the primary magnetic field, Hp, (Hs/Hp) is directly proportional to wall conductivity. Measuring this ratio, it is possible to construct a device which measures the wall conductivity by contactless, direct-reading electromagnetic technique (linear meter). This technique for measuring conductivity by electromagnetic induction, using Very Low Frequency (VLF), is a non-intrusive, non-destructive sampling method. The measurements can be done quickly and are not expensive.

Keywords

• electromagnetic
• wall humidity
• conductivity
• contactless.