Good day, our highest respects for the contributors here in Arduino. 
We're a group of students from a university in the Philippines. We aim to recreate a permeability apparatus and modify it by incorporating sensors in the apparatus.
We just want to ask everyone if what sensors can we use to eliminate the manometers[which read water head/ difference in pressure head in the top and bottom of the cylinder.]
Thank you and your help will help us graduate and finish the fabrication of our project!
A manometer will read differential pressure so you need to search for differential pressure gauges suitable for your application i.e. pressure range, accuracy, operating environment (intrinsically safe?), chemical resistance.
I don't believe your diagram. The pressure at the bottom of the vessel will be greater than at the top but surely the level in both manometers should be the same i.e. h=0 ?
[quote author=ardly link=msg=3878226 date=1537367019
I don't believe your diagram. The pressure at the bottom of the vessel will be greater than at the top but surely the level in both manometers should be the same i.e. h=0 ?
[/quote]
I agree both levels will stabilize over time if A is closed, but if A is big enough it will drain faster than the constant level can flow through the filter media so there will be a drop between values.
Is the goal to evaluate the condition of the filter media?
If it’s a desktop size project I would use a flow meter on A.
If it’s a waterworks project a manometer is a proven, cheap, technology that if you needed automate readings on just stick a ultrasonic rangefinder firing down the tube..
Slumpert:
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I agree both levels will stabilize over time if A is closed, but if A is big enough it will drain faster than the constant level can flow through the filter media so there will be a drop between values.
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If it’s a waterworks project a manometer is a proven, cheap, technology that if you needed automate readings on just stick a ultrasonic rangefinder firing down the tube..
I'll buy your answer if 'A' is open. I also agree keeping the manometers is a good idea as it gives a manual backup to any electronic system. Removing them does not reduce the number ofholes you need in the vessel. Keeping them you could use ultrasonics as you suggest.
The goal is to determine the coefficient of permeability. The pressure heads, in theory, if the water supply would be continuous[thus maintaining the head], would have a difference that will be measured to be used in the formula k=Q/iA where Q = V/t where V would be the volume discharged in the cylinder(say 1L), and t would be the time elapsed to fill the cylinder with a certain volume(1L), and i would be the hydraulic gradient, h/L where h is the difference in head between the manometer and L is the length of the soil specimen.
We love your opinions as they gave us an idea of the questions that our panel of examiners might ask. We'd appreciate more questions.
Please see file attached for image of our proposed apparatus. Thank you!
Your new diagram is significantly different from the original, with the water feeding into the filter at the bottom rather than the top, you have also removed several items. You are now not showing manometers, which means you could use absolute rather than differential pressure sensors if that is what you really want. Remember that atmospheric pressure does vary so your that while your reservoir may have a fixed level the input water pressure to the filter will vary (it will also vary if ambient temperature changes a lot).
If everything is airtight will the equipment act as a syphon depending on the length of the outlet pipe?
We've put the inlet pipe at the bottom because there were errors when the inlet is put on top -- since water can leak through the sides of the specimen, it might just travel down the cylinder walls and not through the soil sample. If the water inlet is at the top, we're assured that water saturates the whole layer upwards before reaching the outlet pipe.
I don't understand the siphon part sorry sir
lablacson:
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I don't understand the siphon part sorry sir
Pressures seem to be important to you. I was just thinking that if the tube into the "Discharge Cylinder" is a long one it might act as a syphon sucking water out of the soil sample and affecting pressure readings - I may be over thinking this.
lablacson:
We've put the inlet pipe at the bottom because there were errors when the inlet is put on top -- since water can leak through the sides of the specimen, it might just travel down the cylinder walls and not through the soil sample. If the water inlet is at the top, we're assured that water saturates the whole layer upwards before reaching the outlet pipe....
Thinking about this Iam not sure that what you are saying is correct. If the water can travel down the cylinder wall when the input is at the top can it not also travel up the cylinder wall the input is at the bottom?
Imagine there is a perforated tube in the cylinder against the waal. If you fill from the top water will flow down the tube, but equally if you fill from the bottom water will flow up the tube. I think if it is possible for water to flow along the wall in one direction it will also be possible for it to flow in the other.
