Pulse Metal Detector. Operation Principle. ...

Описание: Pulse Metal Detector. Operation Principle. Circuit Engineering. Operation of a pulse metal detector is based on generating pulse vortex currents at the location of a metal object and measuring the secondary electromagnetic field created by such currents. In this case the actuating signal is supplied to the sensor's coil not constantly, but periodically, as pulses. Conducting objects induce the decaying vortex currents, which actuate the decaying electromagnetic field. The field in its turn induces the decaying current in the sensor's coil. The signal then changes its form and duration depending on the conducting properties and size of the object. The structural circuit of a metal detector looks like that. The device is based on a microcontroller. It is used to form time intervals controlling all the device's units, as well as to indicate data and to generally control the device. A power switch enables pulse accumulation of energy in the sensor's coil, and then termination of current, followed by a self-induction pulse that induces the electromagnetic field in the target. Another important component of the circuit is a differential amplifier at the output of the device, which is used to amplify the signal with a voltage above the supply voltage. Further amplification is performed by the receiving amplifier with a high gain factor. The first integrator is used to measure the desired signal. In the process of direct integration the desired signal is accumulated as voltage, whereas back integration converts the result into the pulse duration. The second integrator has a high integration constant and is used for DC balancing of the amplification path.