| 摘要 |
If an inductively acting proximity switch is to be used to detect railway wheels running past on a travel rail, the problem occurs, at least whenever the proximity switch is directly attached to the travel rail, that part of the high-frequency alternating field, to be influenced by the vehicle wheel, of the switch penetrates the rail head. Since the permeability of the rail material may vary in the case of high rail currents, the proximity switch may respond at an unsuitable time if no counteracting measures are taken. The invention avoids this by means of a screening plate (8) which is positioned between the proximity switch (4) and travel rail (1) and is made of a material which is a good electrical conductor but a bad magnetic conductor. As a result of the formation of eddy currents, this screening plate forces the high-frequency alternating field (10) of the proximity switch out of the rail head so that the response behaviour of this switch is dependent upon the influence of passing vehicle wheels only. The screening plate is advantageously part of a housing (8,9) which holds the proximity switch. <IMAGE>
|
