Reply To: HYDROS 21 no longer vented… any idea when this changed?

Are you using a sensor with bare wires at the end, or with the molded stereo plug?  Is it a red cable or a black cable?  We’ve bought hundreds of CTD-10 and now the Hydros 21 sensors (only the name changed when the company changed from Decagon to Meter, and there was no design change).  We bought a bunch earlier this year, and every one we’ve ever used has a small Gore-Tex sleeve about a foot from the end of the cable that provides the vent used for the pressure sensor atmospheric reference.  Even their new Generation 2 Hydros 21 sensor (due to be released soon) that we’ve been testing recently has the vent.  If your sensor doesn’t have a vent somewhere along the cable, then either it’s an error and it’s missing, or you’re using a bare-wire terminated cable and the end of the cable allows the air into the jacket to provide the reference (the newer cables have a dedicated air tube inside the cable whereas the old cables relied on the airspace between the wires).   Either way, I recommend contacting Meter Group tech support, they’ve always provided great customer support for us over the past 7 or 8 years that we’ve been using their sensors.  Did you try putting the sensor in a bucket of water at a constant depth and then logging depth over a few days to see if you see atmospheric pressure affecting the data?