The TEM is based on electronic measurement of chemical reactions that reveal the penetration of corrosion inside the concrete.
The TEM sensor inserted into the concrete structure through a small hole, injects a solution and measures the half-cell potential with respect to a counter electrode of liquid junction of the type Cu/CuSO4 (sat. sol).
It analyses two parameters:

1. Chlorides concentration and distribution
2. Concrete pH and carbonation depth