| 摘要 |
The invention relates to a method for the suppression of the effect of strong magnetic interference fields which may occur during the sensing of magnetic markings (9) provided on a web or other carrier (8) whose magnetic fields are small in relation to the interference fields. The method is based on two equal magnetic sensors (1,6) being fitted adjoining the carrier (8) of the magnetic markings (9) which are to be detected but at a slightly unequal distance from the carrier (8). The carrier (8) is led past the sensors (1,6) which each detect the markings (9) but with differently strong detecting signals, since they are located at unequal distances from the carrier (8). The interference fields, on the other hand, are so strong and their sources so remote that the detection signal from both the sensors (1, 6) will be the same. The said sensors (1, 6) are coupled in phase opposition, whereby the detection signals from the interference fields wholly extinguish each other whilst the detection signals from the magnetic markings (9) certainly are subtracted from each other, but result in a residual signal which can be amplified and made use of for the control of working operations on the carrier (8). |
