| 摘要 |
<p>A system for determining a property, such as conductivity, of a material (18) in which a sensor (15) provides a square wave sensor output signal the value of which is selected to the proper in response to a square wave driver signal. The sensor (15) output signal is compared with a feedback signal to produce an error signal. A forward circuit (21) responds to the error signal and provides an in-phase component thereof which is integrated to provide an integrated DC output signal. A feedback signal provides an in-phase square wave feedback signal the peak-to-peak amplitude of which has a precisely selected relationship with the integrated DC output signal for comparison with the square wave sensor output signal to reduce the error signal to zero. The integrated DC output signal can be digitized and suitably processed to provide a signal which represents the property of the material (18) to a high degree of accuracy.</p> |
