Reply To: Depth measurement using MaxSonar

Hi James, thanks for the agupubs reference – very nice to see the LiDar work.
I had talked to a LiDar guy some years ago and they had said they didn’t think it would work for streams, but that ref is showing it very nicely.

I’ve used 20mA depth sensors with Onset loggers, and had a couple of UL6a https://www.utopsensors.com/pressure-measurement/level-transmitter/liquid-level-sensor.html
It depends on what accuracy you want and over what temperature range. As the pressure sensor is the most critical cost component, a low cost resistive element, usually has an uncompensated temperature range. If you are pretty confident in little water temperature range for the stream depth when you need the most accurate readings then they are very useable.
If, as I’ve blogged and mentioned above, you need accuracy at low stream levels when the water temperature may have a large (10C?) diurnal swing then too much error can creep in.
For ground water situations, the temperature may hardly vary and there can be a large range in water levels.

For a stream loading looking at peak flows seems like range of interest are at the upper end, and the rating curve probably has the most error in it. 🙂 Just a guess.

One way to try it would be to use RS485 wingboard that can take a switched +12V generator, and screw terminals, with an appropriate high accuracy and stable temperature 50ohm resistor 0.05%, (0.020A * 50ohms = 1V) feeding via plug-in lead into the ADS1115 ports on the Mayfly you can get a reliable accurate conversion (0.1%)of the 4-20mA to a digital reading.
The 4-20mA is valuable, as only two wires, and if the loop breaks ~0mA ~ its an error condition. If the line short circuits, then its typically over 20mA and again error condition.

I did give up on Utop when I got one of their sensors with a combined temperature sensors in it, and the temperature calibration was way off. I queried about it, and didn’t get a very satisfactory answer.