| 摘要 |
<p>System for monitoring the resistivity of a circuit path between sense electrodes in a volume of material and providing audio pulses of increasing frequency to cut-off where cut-off is indicative of a predetermined undesired quality of the volume of material. A unijunction transistor is utilized in a relaxation oscillator circuit and a predetermined value of resistance is connected in series path with a base electrode of the unijunction transistor to provide an alarm by oscillator cut-off when the current flow between probes becomes indicative that an undesired quality of the material has been reached, e.g., that saturation of soil by moisture is imminent or that drinking water has become polluted. A particular sense probe geometry provides accurate path measurements between the probes dependent upon the particular depth to which the probe tips have been inserted.</p> |
