| 摘要 |
<p>The system uses a transmission appts. which includes a power amplifier which is coupled to two electrodes located at a distance apart in contact with the ground to inject a low frequency signal. A number of measuring electrodes are located in parallel with the transmitting electrodes and are coupled to amplifiers. The amplified signals are filtered and applied to a difference amplifier from which the phase and quadrature components are separated. These signals are recorded graphically and measured by voltmeter (17) to indicate presence of a discontinuity. In order to prevent false detections, a further filter is connected to a circuit which consists of a reference signal generator.</p> |
