Reply To: Hydros 21 CTD sensor calibration question

<div class=”bbp-reply-author”> @rogers1313</div>
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<div>I have used the Hydros-21 for several years now and can add a bit to what Neil has mentioned. I also asked the engineers at Meter Group about temperature compensation and found their response unhelpful. My Hydros21 sensors output water depth that is highly affected by temperature (I can be more specific if you like). I run most of my Hydros21 sensors side-by-side with HOBO sensors (made by Onset Computer Corp) and I have come to the conclusion that a post-processing temperature compensation results in a much tighter match with the HOBO output and nearly eliminates the sinuosity imposed by the diurnal temperature fluctuations.   If you are running these in small streams where small change in water level can result in a large percent increase in flow, then these fluctuations can really make a difference in the measured discharge. As for conductivity, we clean off the electrodes regularly and perform corrections for drift due to fouling and apply offsets to match regularly calibrated YSI sensors which provide sanity checks a few times per month. We find the Hydros21 performs fairly well with conductivity so long as it is cleaned regularly.</div>