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Calculating volume of fluid discharged

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mersenne31

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I have some questions about the pros and cons about two different methods used for calculating the volume of fluid used from a container.

One idea is using a flow meter to calculate the flow rate of fluid leaving the tank; the other idea is using a load cell to calculate the weight of the container before and after the fluid has been discharged.

Which one would be more accurate? Which one would be more complex to implement?
 
The load cell would help you measure fluid lost by evaporation and leaks.
I think a flow meter will read zero flow at really slow flow rates.
Which is easier? It depends. Is this a 1000 liter tank or a lab beaker?
1000 liter tank: I'd go with the flow.
Beaker: Load cell.
 
The load cell would help you measure fluid lost by evaporation and leaks.
I think a flow meter will read zero flow at really slow flow rates.
Which is easier? It depends. Is this a 1000 liter tank or a lab beaker?
1000 liter tank: I'd go with the flow.
Beaker: Load cell.

That is just a gosh darn good answer :)
 
For 150L, I'd go for the flow meter vs the load cell. If it is a plastic tank and the liquid is conductive (water based) then you could also use the capacitive approach. If you stick two pieces of foil on the tank and measure the capacitance between them you can calculate the amount of fluid in the tank.
 
Thanks for your replies. The liquid is roughly water, which is a great conductor of electricity. I guess the flow meter approach is simpler to deal with in terms of durability and functionality.
 
Ultrasonic Distance Sensor ....

Have you considered using an ultrasonic distance sensor, placed at the top of the tank, to read the height of the liquid within the tank, before and after a given process? It would be necessary for the tank to have a reasonably constant cross section .... top to bottom. Basically, ΔV=Acs×Δh.
For the cost of an ultrasonic transmitter/receiver, and a microcontroller, you might be able to accomplish your objective. ....
There is a subroutine for driving an ultrasonic range finder.
It might be in this book .... not sure, I have the first edition.:
The Quintessential PIC® Microcontroller (Computer Communications and Networks)

Amazon.com: The Quintessential PIC® Microcontroller (Computer Communications and Networks): Sid Katzen: Books
 
A hot-wire flow meter isn't hard to make, what's the application? Anything this side of industrial process control and you may want to consider sticking a nitinol wire in a pipe. Give the wire a constant current source and read the voltage. Calibrate it with a stopwatch and a bucket.
 
A hot-wire flow meter isn't hard to make, what's the application? Anything this side of industrial process control and you may want to consider sticking a nitinol wire in a pipe. Give the wire a constant current source and read the voltage. Calibrate it with a stopwatch and a bucket.
Did you really mean "nitinol"? It appears that the resistivity vs temperature curve exhibits hysteresis.:confused:
Also, I think a hot wire flow meter needs a reference element, configured in a Wheatstone bridge or some other differential scheme. The reference element needs to be of the same material, immersed in the same medium and thermal environment, but out of the flow.
Am I all wet here?
 
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No, I meant nichrome. Sorry.
Still waiting for a practical use for nitinol.
 
No, I meant nichrome. Sorry.
Still waiting for a practical use for nitinol.
Why nichrome? It doesn't have a particularly high **broken link removed**. Why not thermistors (see previous post)?
Here is another reference, with different numbers:
 
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It comes down to thermal mass. I've used thermistors in airflow meters and they work, but the physical mass and coating cause a delay. Might not be a problem here.

Yes, a reference sensor in a non-flowing part of the same medium increases the accuracy, that's a good point. I was working with air valves where we needed a fast response but not high precision, this application may be the opposite.
 
I worked in process control plant for several decades and I'm familiar with lots of different flow meters. The different types all have advantages and disadvantages, as there is no perfect flow meter, trust me. If the measurement involves custody transfer ($$ changing hands based on reading) then either a positive displacement type flow meter or a corollas mass flow meter is normally used and it's calibration is usually validated by a 3rd party calibration service periodically. If just for in house use then a integral orifice differential pressure flow meter works well for the flow rate you mentioned. The temperature probe in the pipe method is not a very accurate measurement, we used them in safety showers to give a flow / no flow alarm that someone had activated the shower.

A load cell can be a very accurate method but only works easily for batch type applications rather then continuous flow applications. Also note that flow and total mass quantity are two different measurements. A flow measurement would have to be integrated VS time to give totaled material quantity and be reset after each batch run. Using tank level drop for material added or removed can be quite complex as level instruments themselves vary in type and accuracy. Also many tanks are not perfect cylinders and have can have internal parts and structural pieces that require advance 'tank strapping' calculations to accurately compensate for measurement of material balance.

So it really comes down to defining all your specification requirements before selecting the best method.

Lefty
 
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Have you considered using an ultrasonic distance sensor, placed at the top of the tank, to read the height of the liquid within the tank, before and after a given process? It would be necessary for the tank to have a reasonably constant cross section .... top to bottom. Basically, ΔV=Acs×Δh.
For the cost of an ultrasonic transmitter/receiver, and a microcontroller, you might be able to accomplish your objective. ....
There is a subroutine for driving an ultrasonic range finder.
It might be in this book .... not sure, I have the first edition.:
The Quintessential PIC® Microcontroller (Computer Communications and Networks)

Amazon.com: The Quintessential PIC® Microcontroller (Computer Communications and Networks): Sid Katzen: Books

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.
 
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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
 
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?
 
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