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My Hydros21 CTD-10 sensor depth output is highly affected by the diurnal stream temp fluctuations by upwards of 15 mm sometimes. This issue was noted in forum post # 13557:
I recently got a quote for the CTD-10 (10m or 30′ – they only do the 10m now) with a fixed accuracy at 20C of 0.05% Full Scale or +-/5mm and no statement of how it varies with temperature (called temperature compensation). UpdateJan9th: I got a reply from firstname.lastname@example.org “We typically evaluate this from 0 to 50C and we see somewhere around +/- 2 cm in that range. It does vary sensor-to-sensor and some sensors have lower sensitivity.” So practically they are saying temperature compensation is challenging, and they could have the readings varied by ±25mm or 0.25% of scale – and they wouldn’t take the instrument back. https://www.metergroup.com/environment/products/hydros-21-water-level-monitoring/ Quote $491 per sensor and with a 10-meter cable.
I started a new thread since the original topic of that post was about something else. Has anyone else experienced this with their Hydros21 CTD-10? We used to have the CTD-5 which did not have this problem. This unit was damaged during cleaning and replaced under warranty with a CTD-10. The replacement unit showed this problem and we returned it thinking that it was defective – Meter acknowledged that this was a “known” issue. The second replacement sensor is experiencing the same issue (illustrated in the attached plot). If anyone has any insight into this or a method to fix the problem I would be interested in hearing about it. From the quoted thread above it seems like this output is normal and expected.