Hi @dan-wachusett – I’d be interested to hear how your measurements work out.
This is what I did for acceptance testing (and characterizing) on a number of different types of depth sensors for a 2013 project – https://www.envirodiy.org/measuring-low-water-in-streams-accurately/
The update since then is the hydrologists I work with use the LT-500 for reliability and accuracy, and also been moving over from the Onset U30 to using the Mayfly.
I wonder, has anybody received a specification for the Hydros-21 Gen 2? .
Typically I find that manufactures create internal releases (generation 2?) as an internal cost reduction, with the same specification. Though every manufacturer is unique, so wondering what Metergroup changes might be :)). Insitu and Keller (and others) have different lines of depth sensors for different measurement accuracy and methods. The challenge for any manufacturer is the basic pressure sensor is similar – a pressure dependent resistor – piezo resistor. Temperature dependency of resistors is well studied, but challenging to work with when bumping up against a specific resistor technology’s limits – so different manufactures have different signal processing and manufacturing calibration for better linearity of the pressure sensor.