| 摘要 |
<p>System for detecting a magnetic field emanating from a VDT (101) in which a current induced through a sensing element (L1) is amplified then rectified to convert the induced current to DC. The DC is one input to a comparator, the other input set by a potentiometer (P1) to provide a threshold input voltage differential representative of harmful magnetic field radiation level. The threshold comparator output triggers a driver (A4) connected to a battery powered solenoid. The solenoid actuates an indicator (102) in presence of a magnetic field exceeding the threshold magnetic radiation level. To conserve battery energy, the solenoid also functions as a relay to break contact between itself and batteries (B1, B2) simultaneously with actuating the indicator. In another embodiment a radiation detector includes astable multi-vibrators (250, 256) respectively producing audible and visual warning signals. The detector is calibrated by defining ELF and VLF frequencies and sequentially applying each of these frequencies to the detector (200).</p> |
