How Accurate doe you need it to be

a normal nivau meter (with a extra measure inputs and contacts in the tank) can give you already a a good visual indication how much you did use

150L is not that much to store in my opinion so if you have 20 points that takes a level spaced evently from each other than you have a 7.5 liter acuracy of the closing of one contact/input

you make these spacings smaler than you get in a sertain range even a bigger acuracy

easyest to make and cheap (use some logic gates to couple the sensor wires in the tank)

is it a hobby project or a comercial project where the info is used for $ calculations????

Robert-Jan

Originally Posted by ssylee

After taking a look at the prices of a variety of flowmeters, I'm not entirely sure if this solution would fit ideally in terms of cost considerations.

For the ultrasound liquid level meter method, what are other limitations to take into account other than needing a container with roughly constant cross-sectional area?

My specification is that I know about the change in water level after a feeding session (i.e. amount of water before feeding - amount of water after feeding). I hope this specification helps.

Thank you all for your input.

About the only factor that you need to consider is accuracy.
.... seem like this was an end-of-chapter problem in the book ....
I will have to check on it.

I get the impression that the ultrasonic transducers are reasonably durable, and immune to corrosion .... They might require occasional cleaning if there is a buildup of dirt, sludge, or other residue.

... Not surprised at the cost of flow meters .....

This is more like an industrial project for research purposes. The solution needs to be able to withstand quite caustic environments, aka ammonia. In terms of accuracy, the change in liquid would be in the neighborhood of 100 mL per feeding session. If the cross-sectional area of the bin is small enough, the change in distance would be quite noticeable. What do you think based on this new information that I have missed out earlier?

If your number .... 100 mL .... or 100 cubic centimeters .... per actuation ...is correct, then the ultrasonic T/R might not be the best choice. A graduated cylinder, or anything of such a small dimension might have peripheral interference from the container walls ....The idea is to detect a distinct echo pulse from the fluid surface .......
A larger diameter cross sectional area would be better....have more of a chance of working properly. ...Apparently there is a dispersion of the ultrasonic wave from the transmitter ..... at some acute angle.

If you were to place a transmitter at some point above a 1 cm diameter cylinder, not within it, and generate a pulse, it may be that there would not be sufficient energy in the reflected wave to be picked up by the ultrasonic receiver.

Originally Posted by ssylee

This is more like an industrial project for research purposes. The solution needs to be able to withstand quite caustic environments, aka ammonia. In terms of accuracy, the change in liquid would be in the neighborhood of 100 mL per feeding session. If the cross-sectional area of the bin is small enough, the change in distance would be quite noticeable. What do you think based on this new information that I have missed out earlier?

It may be that you want to find a means to determine the height of the fluid column by measuring the pressure at the lowest point .... the base of the fluid column. The pressure of a fluid column is equal to:
(fluid density) * (g ... a gravitational constant) * (height)
or P=ρgH.
The great thing here is that there are a wide variety of pressure sensors to choose from. You should be able to find one that will have enough 'resolution' .... smallest measurement interval ... to be able to detect the 100 mL increments that you anticipate. You will have to decide what form you want the data to take .... Voltage A/D conversion .... or whatever, but that should be a trivial problem.

n.b. : technically, the first sensor parameter that you will want to consider is the 'resolution' or the smallest increment that can be measured.
The term 'accuracy' is related to the consistency of repeated measurements.

Originally Posted by user_88

It may be that you want to find a means to determine the height of the fluid column by measuring the pressure at the lowest point .... the base of the fluid column. The pressure of a fluid column is equal to:
(fluid density) * (g ... a gravitational constant) * (height)
or P=ρgH.
The great thing here is that there are a wide variety of pressure sensors to choose from. You should be able to find one that will have enough 'resolution' .... smallest measurement interval ... to be able to detect the 100 mL increments that you anticipate. You will have to decide what form you want the data to take .... Voltage A/D conversion .... or whatever, but that should be a trivial problem.

n.b. : technically, the first sensor parameter that you will want to consider is the 'resolution' or the smallest increment that can be measured.
The term 'accuracy' is related to the consistency of repeated measurements.

Sorry for getting "accuracy" and "resolution" mixed up. For accuracy, of course I would want the system to be as consistent as possible. For the resolution, the change in liquid could go anywhere between 20 mL to 200 mL, but for operational purposes, the smallest liquid mass change should be about 10 mL.

Originally Posted by ssylee

Sorry for getting "accuracy" and "resolution" mixed up. For accuracy, of course I would want the system to be as consistent as possible. For the resolution, the change in liquid could go anywhere between 20 mL to 200 mL, but for operational purposes, the smallest liquid mass change should be about 10 mL.

Just as an initial approximation...say you have a cylindrical container of
1 cm diameter, and using water as the fluid of interest:
Then a 10 mL change in the volume of the container would equal about 10 cm of vertical height change. The pressure change due to this same height change would be in the neighborhood of 1 kN, or 0.01 bar, or 0.15 lb/sq. in., or equivalently, about 4 in. of water.
This would be the approximate resolution to look for in a pressure transducer.
....just using water in the column.

Do you have a value for the density of the liquid that will be used?

The density of the liquid is remarkably close to water, so assuming that it's water would be fine. Are you suggesting a pressure sensor to sense the pressure change due to the change in the amount of liquid? The container used is around 150 L, while the bin is around 25 cm high, so the cross-sectional area is quite large.

Originally Posted by ssylee

The density of the liquid is remarkably close to water, so assuming that it's water would be fine. Are you suggesting a pressure sensor to sense the pressure change due to the change in the amount of liquid? The container used is around 150 L, while the bin is around 25 cm high, so the cross-sectional area is quite large.

... Given this information, the question is: what will the change in vertical height of liquid in the bin be, if the minimum liquid volume amount is removed from the container?

I am guessing that the minimum Δh of the fluid will not be a very great quantity.

Consequently, the ΔP of the fluid at the bottom of the container will hardly change at all...

So, the pressure sensor method is not likely to work.

.... Going back to the ultrasonic transducer, I have doubts about using any sort of home made / microcontroller unit, due to the lack of resolution....
As I recall, the home brew version could only measure to within a few centimeters ....Maybe a commercial ultrasonic level meter could give the desired results for your application.... would cost more though.

There is a type of low flow rate pump that works by repetitive squeezing of a flexible tube. The tubing comes in various types .... depending on what chemical resistance is required. You would have to set up some sort of counter mechanism to measure amount of fluid delivered ... and some way to turn the pump on and off... Not sure about the economics ....
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I actually got some new information about the apparatus. Even though the tank is 150 L, the ideal flow rate is actually around 1 to 2 L/min. So the change in liquid volume would be much larger than I thought. Given the new information, I guess the change in liquid level would be much more significant that ultrasound may fit as a suitable solution now. The current apparatus uses a pump to pump the liquid out, with the time that the pump is on translates into the amount of liquid consumed.

Originally Posted by ssylee

I actually got some new information about the apparatus. Even though the tank is 150 L, the ideal flow rate is actually around 1 to 2 L/min. So the change in liquid volume would be much larger than I thought. Given the new information, I guess the change in liquid level would be much more significant that ultrasound may fit as a suitable solution now. The current apparatus uses a pump to pump the liquid out, with the time that the pump is on translates into the amount of liquid consumed.

To use either the ultrasonic or the pressure method, you have to have a significant change in the height of the fluid level. Even a Δh resulting from 1 or 2 liter effluent from the container may not be sufficient for these methods to work...If your value of 25 cm for the container wall height is correct, then for 150 L of fluid, you would have about 0.6 m² of container area....quite a large area, considering the height of the container wall.