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3. DEVICE AND PRINCIPLE OF OPERATION
3.1. The principle of operation of the metal stress
scanner is based on the measurement of the magnetic field
strength over the surface of the residual magnetized area of the
metal (the field strength of the residual magnetization of the
metal).
3.2. The block diagram of the stress scanner is shown
in Fig.3.1.
Fig.3.1. Block diagram of IN-02 the metal stress scanner
1 – magnetic measuring unit, 2 – integrated Hall effect
sensor chip, 3 – pulse voltage stabilizer, 4 – scaling amplifier
combined with a low-pass filter, 5 – microcontroller, 6 – travel
distance sensor, 7 – memory card, 8 – liquid crystal display.
The stress scanner works as follows. Magnetization of
the metal of a steel product or metal structure is carried out by
a constant magnetic field in the process of translational
movement of the magnetic measuring unit 1 along the
inspected surface of the metal.
The sensor with the integrated sensor 2, which is
located in the housing of the magnetic measuring unit 1, is
4
5
7
2
1
3
6
8
8
powered by a constant electric current from the pulse voltage
stabilizer 3. The electrical voltage from the output of the
sensor 2 is supplied via a scale amplifier combined with a low-
pass filter 4 to the input of the analog-to-digital converter of
microprocessor controller 5.
To tune out the effect of random changes in ambient
temperature on the stress scanner readings, the amplifier 4 has
an automatic gain control unit inspected by an electrical signal
coming from the output of the temperature sensor, which is
located inside the housing of the the sensor 2.
In the case of the magnetic measuring unit 1, a travel
distance sensor 6 is installed, the output of which is connected
to one of the logical inputs of the microprocessor controller 5.
One of the outputs of the microprocessor controller 5 is
connected to the electronic memory card slot 7, the other
output of the microprocessor controller 5 is connected to the
input of the graphic liquid crystal screen 8.
Fig.3.2. Appearance of IN-02 the metal stress scanner
1 – magnetic measuring unit, 2 – electronic unit.
1
2
