Factors affecting the sensitivity of metal detectors
Effect of metal detector sensitivity and accuracy factors mainly include metal type, frequency and phase, the product effect, opening size and foreign body position, foreign body shape, passing speed, environmental factors, packaging materials and so on,
Metal inspection instrument can detect iron, magnetic, and nonferrous metals such as brass, copper, phosphor bronze, aluminum, etc.
No metal detector voltage equal when receiving the magnetic coil carrying metal in the human body, when the body carrying iron will cause magnetic enhancement, the electromotive force in order to receive the magnetic coil from the enhanced, nonferrous metal caused electromotive force decreases by magnetic repulsion, receiving field coil.
In some cases will affect, for example, magnetic induction, magnetic induction refers to the electromagnetic field caused by metal induced current, the induced current will cause the transmitter and its opposite electromagnetic field, which leads to acceptable voltage decreases, caused by the metal detector is not accurate, will produce false positives, false negatives, followed by electromotive force when receiving coil voltage below balance and acceptance of voltage transmitting voltage line
Secondly, in the traditional sense, the metal detection machine operating frequency is between 10KHz and 500KHz, the operating frequency is low, the lower the sensitivity of the metal detection machine, similarly, the operation frequency is higher, the higher the sensitivity of metal detector, metal detector when the single frequency operation at the same time should be used for the detection of dry or wet products products when the sensitivity is limited
The cell (dry / wet / electrical conductivity) of different products has a great influence on the sensitivity.
Second drying of products - such as candy, cereals and cereal products, biscuits, powder, fast food by high frequency operation, high sensitivity.
Conductivity or phase 0 of products as cheese and fresh meat, bread, jam or pickled products will produce the interference model, referred to as the product effect, must reduce or eliminate the interference signal, method:
1. Adjust the phase angle
2. Select QNR, CLX filter
3. Reduce operation frequency, or high frequency and low gain
All these measures reduce sensitivity and are particularly significant for non iron metal and stainless steel.