Lavan:
If I keep the ultrasonic sensors (40KHZ/25KHZ) in a sealed plastic container, will they still measure the distance? I want to measure the water level in a tank about 10ft depth and I don’t have the water proof ultrasonic sensors available at my place. Any suggestions are welcome.
I don't know your exact usage, but maybe instead of measuring the depth of the water from the surface down, you could measure the distance from above the surface to the water's surface. Then, with a known surface level and depth, you could easily calculate the depth.
In other words, put the ultrasonic sensor let's say 1 foot above the surface of the water. The sensor would measure the distance as 12 inches. You then measure the distance from the sensor to the bottom of the tank, lets say it's 132 inches. So, when the sensor reads 12 inches, you would do 132-12=120 inch water depth. When the sensor reads 15 inches, 132-15=117 inch water depth.
While the ultrasonic sensor won't work under water, the ping will reflect off the water's surface. Not knowing your exact usage maybe this won't work. But, if it's a tank, it has a static depth and probably a place to mount the sensor above water. If you do choose to use an ultrasonic sensor, may I suggest the NewPing library which has a ping_median method that would work nicely to filter out noise and get an accurate measurement with something like this that's probably not moving quickly.
Tim