Float with rodIs not practical if the rod is 4m long, it will move with wind, birds will use it and the structure of the sensor will be more than 6m with high water, a pulley and a string don't increase the height.I've found only expensive underwater pressure sensors , I can experiment using a cheaper one inside a jar, but I have to compensate temperature and air pressure.IR emitter/sensor with ping pong ball.The IR range sensors that I know work for less than 24cm, do you know any that could work with 4/5 meters?Laser timing:Measuring flight time seems to be hard, expensive and for some reason the cheap measurement devices are closed blackboxes that you can't hack and they are also heavy I don't know why.Laser triangulation:This is easier, laser diode and webcam but for 400cm I would need more than 40cm diameter in the pipe if the laser dot is around 1cm, I think the dot is less than 1cm but I have to experiment. Laser triangulation + ultrasonic could work together in the same pipe.Ultrasonic:is it possible to protect the sensors from humidity ? I tried different materials but none of them are transparent to the sound.what about using some kind of encoder without a rod or pulley? ideas?thank you very much everybody!
For the price, I personally would have to give this one a try -(Pressure/Altitude sensor)https://www.sparkfun.com/products/11084It claims down to 30cm accuracy (about 1 ft). I ran across a few others which claimed slightly better precision (20-25cm). Just hook it up, attach it to a buoy....?
@tigger: Excellent information, thank you. Could you give me more details and/or links for each sensor?1. why do calibration is complex? Because sound speed changes with temperature or something else?2. I didn't understand how the heating oil tank gauges work from the pictures I found3. Triangulation with reflective surface, do you have more info ?4. Why have you decided to use pressure or mechanical and why do you think that floats are bomb proof compared to other methods?5. I think calibers use encoders but I would need a long rod to implement the same idea for 4mthanks again
A pressure sensor can also be used for this. Inexpensive pressure sensors are not made for contact with water, but that can be overcome by enclosing the sensor in an air filled container (e.g. a jar with a rubber membrane for a lid)