| 摘要 |
<p>A circuit for measuring the conductivity of a solution by applying a known ac current source across a pair of electrodes in the solution and utilizing an analog-to-digital dual slope converter (50), such as those of the integrated circuit type which include capacitor sampling of the signal input, for conversion of the ac voltage drop across the electrodes. The circuit includes means for synchronizing the ac current to the clock to time the sampling so that the same polarity of signal input is always obtained. Where the known ac current source consists of switching the sense of the electrode connections to a combination of a dc source in series with a known resistor, used for supplying the reference input to the converter (50), a dc signal input, instead of ac, is obtained by including the voltage drop of the switch (64) with the drop across the electrodes in the signal sampled. With this arrangement, higher cell constants can be used to minimize the effect of the voltage drop across the switch (64).</p> |
