| 摘要 |
Detection system for detecting imperfections in EMP shieldings, a rotating magnetic (or electric) field being generated outside (or inside) the shielding (2) by means of for example pairs of Helmholtz coils (13, 15 respectively 14, 16), which are at an angle (of for example 90 degrees) with regard to each other and which are driven by a modulated signal, the modulation phase of the respective pairs of coils differing with respect to each other with a value which is equal to the difference between the respective angles of those pairs of coils. The field penetrating through the shielding (2) is detected in various directions by detecting means (10). In those directions in which the field intensity is relatively high, the shielding can be closer examined by local measurements. In co-operation with an alarm element the detection system can ber used as a protection system against damage of a room shielding (22), caused by for example burglary. When it is detected that the field penetrating through the shielding increases (due to damage of the shielding), an alarm will be given.
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