The use of a 3rd U/S or D/S sensor in Salt Dilution Flow Measurements

Abstract

<p>Salt Dilution flow measurement is relatively accurate and easy way to measure flow in turbulent waterways.&#160; However, it&#8217;s accuracy and precision are governed by the Signal to Noise (SNR) Ratio, which can be very low in urban, sub-urban, and rural waterways due to a highly variable BackGround specific Electrical Conductivity (BG ECT) signal.&#160; Conventionally, more salt is added to the waterway to overcome the noise in the BG ECT.&#160; The &#8220;noise&#8221; is a combination of random noise, which is amplified by the typically high BGECT (>500 uS/cm), but also lower frequency noise that changes on the same time scale as the salt breakthrough curve.&#160; To compensate for the changing BG ECT, we have employed a 3^rd UpStream (U/S) probe to track the BG ECT, along with algorithms to transform the signal in 3 domains: magnitude (ECT offset), time (transit time of pulse), and frequency (to compensate for storage in the waterway).&#160; Additionally, we have tested the use of a 3^rd DownStream (D/S) probe to measure cross-channel variance when mixing is not complete in order to achieve a reasonable flow estimate.&#160; Results are compared and discussed.</p>