| 摘要 |
A probe (20) for measuring the hardness of concrete comprises a body (22) which is adapted to receive a retainer (26) such that the combined body and retainer can be held in an aperture extending through a wall of a mould (8) for the hardenable material, with the body extending from the inside of the wall. A sensor circuit (90) comprises detector elements supported by the body and disposed, in use, in the concrete, and circuit terminals which, in use, face the exterior of the mould wall and are accessible through the retainer for connection to terminals of an external instrument. The detector elements are conductive portions (72,74) of a printed circuit board (33), and form a resonator (100). The instrument can operate a switch in the probe which interconnects the terminals to indicate a good connection. The instrument measures the impedance of the resonator at multiple frequencies.
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