In the concrete structure inspection, it is necessary to detect the position, diameter and thickness of the steel bars in the concrete. The site is usually tested by the rebar detector. This paper mainly introduces the working principle and usage of the rebar detector.

First, the rebar detector working principle

(1) According to the electromagnetic field theory, the coil is a strict magnetic dipole. When the signal source supplies alternating current, it is radiated to the outside.

The electromagnetic field is emitted; the reinforcing bar is an electric dipole that receives an external electric field, thereby generating an induced current that is distributed along the reinforcing bar. The induced current of the steel bar re-radiates the electromagnetic field (ie, the secondary field) to the outside, causing the original excitation coil to generate an induced electromotive force, thereby causing a change in the output voltage of the coil. The reinforcing bar position measuring instrument determines the reinforcing bar according to the change. The location and thickness of its protective layer. Moreover, when the reinforcing bar is directly above, the output voltage of the coil is most affected by the secondary magnetic field generated by the reinforcing bar. Therefore, in the test, during the movement of the probe, the most affected point, that is, the point with the largest signal value, can be automatically locked. The thickness value is obtained according to the correspondence between the thickness of the protective layer and the signal.

(2) The rebar detector consists of a host, a probe and a signal line, wherein the probe has a transmitting and receiving function; the host has processing data and a display function. The electromagnetic signal is emitted by the probe of the rebar detector, and the steel bar in the concrete member generates a secondary induced magnetic field, which is received by the receiver in the probe, and shows the thickness of the protective layer of the steel bar, the diameter of the steel bar and the spacing of the steel bars after data processing by the host.

Second, the rebar detector application introduction

1. Precautions

(1) It is not possible to test concrete containing ferromagnetic substances;

(2) Select the appropriate test surface, the test surface should be clean and flat, and the metal embedded parts should be avoided;

(3) For the structure and components with the facing layer, the finishing layer should be removed and then tested on the concrete surface;

2. Operation steps
(1) Preheating and zeroing the instrument before performing the test;
(2) When the test is performed, the probe moves on the detection surface until the thickness of the protective layer displayed by the instrument is the smallest, indicating that the probe center line coincides with the rebar axis, mark the corresponding position, and follow the above steps to adjacent the other The positions of the steel bars are marked one by one;
(3) Set the range of the instrument and the nominal diameter of the steel bar, select the position where the adjacent steel bars have less influence along the axis of the measured steel bar, and avoid the steel joints and the wire binding, and read the concrete cover inspection for the first test. Value, repeat the test at the same position of the measured steel bar, read the thickness of the concrete cover layer detected in the second time. If the difference between the read and output of the same place is greater than 1mm, it should be re-tested;
(4) After positioning the steel bar, record the nominal diameter of the steel bar displayed on the positioning mark. Each bar is tested twice, and the probe should be rotated 180° for the second test. Each reading must be consistent;