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  • Essay:

    moisture content measurement with built in probes

    Brandt, E.,1993, Nordtest Method, NT Build 420 (1993), Building Materials, Wood: Moisture Content.

    Nordtest is an institution under the Nordic Council of Ministers and acts as a joint Nordic body in the field of technical testing

    The moisture measuring disc consists of a 12 mm plywood disc with a diameter of 50 mm, or dowel's made of beech wood. Two electrodes are inserted in the plywood. Besides, the disc is equipped with a thermocouple, which is used for temperature registration as well as for temperature compensation of the resistance. Before use the moisture measuring disc's are calibrated by being placed in turn under different, controlled humidity conditions.

    Guideline for measurement by means of discs, dowels or built-in electrodes

    - use insulated electrodes (nails) to apply the method for measuring in certain depths,

    - for an ordinary contact plug meter and a 3-light terminal block

    - Knowledge of building physics is a prerequisite when interpreting the results exceeding ordinary moisture control.

    - The moisture conditions in a construction may vary considerably from one area to another and consequently several measurements are necessary to give a clear picture of the conditions.

    - The moisture conditions may vary considerably over the year and an assessment of the results should take this fact into consideration.

    - As with hand-held moisture meters measurements should be made along the grain. It should be avoided to measure near cracks or nails or in impregnated wood.

    The advantage of built-in probes

    - inserted permanently, able over a period of time, possible to detect any abnormal changes

    - the electrodes can be built in right from the beginning so that measurements can be carried out in inaccessible places

    intermediary link in the form of disc or dowel

    - adv: it assures that measuring is taking place in relatively homogeneous material with well known properties and that a direct relation exists between the measured resistance and the moisture content. Practical experience also shows that more stable measurements are obtained.

    - disadvantage of using probes is that it is necessary to calibrate and that, consequently, the price is relatively high.

    CRDBER, at CBS, BCEE, ENCS, Concordia,