| 摘要 |
<p>The oscillator provides an output signal, of frequency f0, whose phase is shifted by 45 deg. to obtain a test signal which is coupled by a first cable to a bridge circuit located in proximity to a sample box and interconnected with an active, centre electrode of that sample box. In response to the test signal, the bridge circuit provices a bridge output signal whose frequency is identical to that of the test signal and whose phase, relative to that of the test signal, and whose amplitude are related to the electrical admittance of particulate material within the sample box. The oscillator output signal is also applied to a phase-shifting network which provides four signals respectively in-phase, 90 deg. out-of-phase 183 deg. our-of-phase, and 270 deg. out-of-phase with the test signal. A switching circuit couples the four signals to its output in a predetermined sequence and at a frequency of fa, where f0 is much greater than fa. This develops a reference signal which is coupled by a second cable to a first input of a double-balanced mixer located in proximity to the bridge circuit.</p> |
