Trotec T500 Manuel D'utilisation page 60

thus the measured value appear to be higher. The measuring
device interprets the increased measuring current as a lower
resistance and thus a higher measured value.
• Note the disruptive influence of electrically
conductive materials:
If a building material or a multi-layer wall or ceiling
construction contains an electrically conductive material, a
lower resistance value is obtained which simulates a high
moisture value. This leads to false measured values being
displayed. It is usually impossible to visually ascertain whether
or not electrically conductive materials are present in the
structure. The largest sources of error in particular are
B - 27
reinforcements, metal laminations and conductive insulating
materials such as cinders in wood beam ceilings. In particular
in the case of insulating materials with metal laminations, the
measured values from the resistance measurement are often
falsely interpreted.
Operating manual – English