| 摘要 |
The invention relates to a method and a device for contactless thermal detection of metal objects in magnetic field. According to the invention, the detection method is intended to measure the increase of temperature due to the heating of a foreign body and consists in determining the rate of temperature variation detected by some sensors, calculating the average value of last "n" samples and multiplying this value with the value of the sample prior to the average value calculation, comparing the rate of temperature variation between two sensors or between a sensor and a reference sensor and ascertaining the presence of a foreign body if the difference resulting from the comparison exceeds a certain threshold. According to the invention, the detection device comprises one or more resistive sensors (5) and an electronic control circuit (8) which includes a control unit (9), a programmable current source (12) injecting a constant current into the resistive sensor (5) such that the modification of the resistance thereof with the temperature leads to a variation of the voltage at the sensor output, the resulting signals being analyzed and selected/filtered by means of multiplexer (10) and transmitted to a controlled amplifying unit (11) wherefrom they are transferred to the control unit (9) where a detection algorithm is generated and implemented, then the signals being transmitted to an electronic block (18) where the signals corresponding to the rate of temperature variation between two sensors (5) or between a sensor (5) and a reference sensor (26) are analyzed in a comparator (19), the resulting signal being transferred to a decision and display unit (20) where the presence of a foreign body is marked out and is communicated via an interface (24) inbuilt in a logic block (21) which has also the role of adapting the electronic circuit (8) depending on the external parameters. |
