I'm designing a wavemeter. One that measures wave height in a lagoon along with water depth. (What were you thinking, audio wave, radio wave? )
This is verson 3 or 4, I lost track. This attempt will use a pressure sensor located near the bottom to measure the pressure of the water column above the sensor. Knowing the water column I know the wave height. And, since I know its distance to the bottom and the height of the water column, I know depth.
I thought things were coming along nicely until I held the pressure hose in my hand and noticed a sharp rise in pressure readings. Let me back up a bit... the sensor is a Honeywell ABP2LANT001PG2A3BB. 1 PSI gauge full scale, i2c interface, 24 bit. 1 PSI is about 27" water, sufficient for my use. I have a 5 foot flexible tube plugged into the barb on the sensor. The thing is here on my desk with a bucket of water while I play around with it to learn how to make it do what I want. I see numbers going up & down as I dip the end of the hose into the water. So far so good. But then I discovered that if I hold the end of the hose in my hand (while out of the water), the pressure readings go up by about 5%, taking around 15 sec to stabilize. When I let go the pressure drops to what it was before, taking about a minute to stabilize. I'm not blocking the end of the hose in any way. (But it seems like I am, doesn't it?)
This is totally baffling. Why does the sensor care about me holding the end of the 5' tube? HOW can it know? Quantum entanglement? Spooky action at a distance?
Suggestion: post the required details, as described in the "How to get the best out of this forum" post. A wiring diagram and a picture of the setup would help to spot missing ground connections, for example.
not attempted to use a pressure sensor measuring water height on a tidal river
in a river monitoring system I used The Things UNO with a BMP280 temperature/pressure sensor, a SR04M ultrasonic transducer and a DS18B20 DallasTemperature sensor uploading data over LoRaWAN to the myDevices/cayenne desktop
Yes, I saw your work a while back when I was attacking my problem with sonar. I almost got that to work. It's one thing to use ultrasonics to detect the surface of the water to compute water depth, but something else to catch the crests and troughs of 2-foot waves. The water surface is so irregular and the ultrasonic transducer beam is so wide that what you get is pretty much unusable. So, I eventually wound up with this:
Transducer in the PVC pipe looking down at the buoy; buoy has a plastic pipe through its center; buoy rides up & down with the waves along a SS cable anchored to the bottom with a 10# weight. Not shown in this picture but I added a corner reflector to the top of the buoy.
This worked for a few months until the barnacles took over and nearly sunk the buoy. Before that could happen the whole mess was crushed by hurricane Milton. (I'm on the Indian River Lagoon in Titusville FL)
So this time I want to try measuring the water pressure at the end of a tube positioned a few inches from the bottom. The other end of the tube will be attached to the transducer pressure port up on the dock. I can already see a problem with this. When I lower the end of the tube into the water, the water level inside the tube will rise to some degree. I'm having trouble wrapping my head around what will actually happen here and how that will effect my measurements.
So here is where I am when this weirdness arrived and put a stop to my plans. Need to figure out why just touching the tube gives me a 5% pressure reading.
This morning I got a clue. Holding the tube in my hand did absolutely nothing. So, what's changed? What's changed is there is no water droplet clinging to the end of the tube. A water droplet at the open end of my narrow tube effectively seals off the tube so the heat of my hand causes the air pressure inside the (sealed) tube to rise. If I make sure there is no water in the tube then it works as expected.
You need a low volume air pump to make up for air leaking out of the tubing, a "bubbler". Run the pump a couple of seconds every 30 minutes or so to keep water purged from tubing.
Bubblers are a common form of air-pressure type water level gauges. The pressure in the system is limited by the height of the water column, and the fouling is limited since you are pushing clean air into the system.
To review where I'm headed, imagine this: I have a pressure sensor located on the dock. There is a small diameter hose from the sensor pressure port to about 2 ft under water. I'm trying to measure the water pressure at that depth.
The air in the line just ruins everything. A changing air pressure due to temperature changes just obliterates my measurement.
OK, so if I fill the tube with water from the sensor down to the 2-ft depth then that should take care of air pressure changes. Or not. It gets worse. With the tube full of water and gravity being what it is, that will create a negative pressure at the sensor.
So how on earth can I measure the pressure at a 2-foot depth?
You would also need to know the instantaneous barometric pressure... so throw the carcass out with the pondwater.
Pewpew a LASER down a tube fixed to a pier, and smooth the high and low measurements. D is the known depth of the pier to the top of the tube and C is the high and low of the water in the tube.
You can discourage biological growth by turning your float into a part-time electrolysis cell (like a pool chlorinator).
Industrial consumers of sea water do this on a large scale to keep intakes clear.
Aside from that I don't see where I would attach an electrode to the sensor. It's plastic.
Barnacles are a real problem where I live. It pretty much ruined my last attempt at this project (using sonar to determine distance from dock to water surface). If I do put this sensor under water I plan to build a container for it made from copper mesh. Copper is supposed to be kryptonite to a barnacle.
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