• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

detecting moisture in sOIL

Status
Not open for further replies.

strantor

Active Member
Do you think that one of these Vegetronix soil moisture sensors would work for detecting moisture in OIL?

From their website:
our probe measures the dielectric constant of the soil using transmission line techniques
I was reading some propaganda about handheld "On-line Impedance-type Moisture Sensors" (for petroleum/oil) and it said:
A probe senses water at a representative point of the system. The devices change capacitance as water concentration increases and decreases.
So it seems like it's the same concept but what is your prediction for "would it work"?
 

kubeek

Well-Known Member
Most Helpful Member
I can´t imagine that an electrode covered in oil would be able to detect conductivity of water, which implies it would need to detect subtle changes in impedance or more exactly in capacitance.
What are the ratios of water to oil that you are interested in? I would imagine detecting 1 part in 100 would be tricky, and in any use of oil I can imagine such number would be an awful lot and render the oil useles.
 

JimB

Super Moderator
Most Helpful Member
I have done some basic experiments and tests on capacitive oil/water probes.
From memory oil has a dielectric constant of about 2, and water has a dielectric constant of about 60.

Details of my initial experiments are in this thread, towards the end.
http://www.electro-tech-online.com/...ill-run-to-an-led-display.107910/#post-883915

As for moisture in soil, I guess that would also change the capacitance.

JimB
 

cowboybob

Well-Known Member
Most Helpful Member
Off the top of my head, I'd say no. But...

Since they explain their system's operation as:
"7... All we can say is that it's - magic. ;)... ", there's no way to tell. They do say it's "non-conductive". It's obviously self-powered.

The capacitive water/oil sensors use the properties of the oil/water fluid mix to alter the frequency of an oscillator. This is a fairly mature sensing scheme. And obviously designed for very harsh environments, i.e., not potting soil.

You may have already done this, but I did a google on "capacitance as water concentration in oil" and got a good number of relevant hits.
 

cowboybob

Well-Known Member
Most Helpful Member
Stupid site double posted on me...

At least, I think that's what happened... :woot:.
 

audioguru

Well-Known Member
Most Helpful Member
A soil moisture detector measures the resistance of the salty water in soil. When the soil is dry then there is no salty water so the resistance is much higher.
Condensation of water in the air that is in oil probably is pure water with no salts so its resistance would be near infinity, an insulator. Therefore a soil moisture detector will not detect it.
 

gophert

Well-Known Member
Most Helpful Member
A soil moisture detector measures the resistance of the salty water in soil. When the soil is dry then there is no salty water so the resistance is much higher.
Condensation of water in the air that is in oil probably is pure water with no salts so its resistance would be near infinity, an insulator. Therefore a soil moisture detector will not detect it.
audioguru / strantor
The dielectric constant of oil changes when water is added (very slightly solvable but oil/water emulsion will also change the dielectric constant as well. Here us one example of how it can be detected with a pair of plates - the changing properties of the fluid changes the capacitance of the plates.

http://www.google.com/patents/US5642098
 

atferrari

Well-Known Member
Strantor,

In tankers, to detect and measure water in oil (not as an emulsion but - we hoped - consistently settled in the bottom), we used a device that looked like a common sounding tape with a somewhat bulky "bob" at the end.

Submerged in the tank, it sounded a beeper when reached the water interface. Never had the time to look into the details. Maybe it was in line with Jim's design. With the vessel in calm water, repeatability was very good.
 

strantor

Active Member
What are the ratios of water to oil that you are interested in?
I don't need awesome accuracy or resolution. Ultimately I don't need to measure the content of water, just detect if water is present above a threshold value. Arbitrarily I pick 10%; if my volume of oil consists of 10% or more water, then output a digital high for an idiot light.
 

strantor

Active Member
I have done some basic experiments and tests on capacitive oil/water probes.
From memory oil has a dielectric constant of about 2, and water has a dielectric constant of about 60.

Details of my initial experiments are in this thread, towards the end.
http://www.electro-tech-online.com/...ill-run-to-an-led-display.107910/#post-883915

As for moisture in soil, I guess that would also change the capacitance.

JimB
I like this a lot. Thanks for the info. I think I'll try out your capacitive probe.
 

gophert

Well-Known Member
Most Helpful Member
Why don't you heat the oil to 300 degrees there wont be moisture in it then.
Because he will never notice the leak until it is large enough to overwhelm the heater that is heating the oil.

And, then he will need a big air conditioner to cool the room where the heater is located.

And, all the guys walking past the pipes full of hot oil might bet burned.

And, ...
 

JimB

Super Moderator
Most Helpful Member
I like this a lot. Thanks for the info. I think I'll try out your capacitive probe.
Thank you.

I did some more work on the two wire probe and oscillator, it is summarised here in pictures:
The oscillator:
Oscillator Schematic.JPG

Oscillator build.jpg

A calibration graph of oscillator Frequency vs Capacitance (Ctest)
Oscillator Calibration.JPG

Graphed results of probe in air and in water.
Graph 2.JPG

I hope this is helpful for you.

JimB
 

jpanhalt

Well-Known Member
Most Helpful Member
10% water in oil seems like a fairly high threshold. At that point, I suspect those methods based on physical displacement of the oil would be preferred. You could also look at light scatter for physically suspended water. At lower concentrations, you might want to consider IR. In the near IR, water shows a strong absorption around 1500 nm:
upload_2016-3-2_11-46-36.png
Surprisingly, the publication citation isn't shown on the Google link. To get it, you have to join for "free." I wasn't up for that, but here is the search header from Google:
https://www.researchgate.net/figure...ation-curve-for-the-water-content-measurement

And to tease your appetite, here is another figure showing results:

upload_2016-3-2_11-50-26.png

That apparently is dissolved water. The same IR source could be used for measuring light scatter too.

John
 

jpanhalt

Well-Known Member
Most Helpful Member
It might and is an easy test to do. While scatter and turbidity are similar in some ways, scatter offers some different dimensions. I assumed that water droplets would have different reflective properties than suspended solids, like dirt. Thus an off center detector, or even a forward detector might provide differentiation between dirt and water or other immiscible liquid.


Idea #2: can you add a small amount of water soluble dye?

John
 

gophert

Well-Known Member
Most Helpful Member
I wonder if a plain old dishwasher turbidity sensor would do the trick.
What kind of oil is it & what is it used for? Refined vegetable oil, mineral oil, used motor oil, crude oil, ... Lubricating oils change quite a bit over time. So do heat-transfer oils depending on service conditions. The expected changes during the life of the oil could be an issue.

Also, is there reservoir tank for the oil. A 10% volume change when water is present may allow a simple float switch to be used.
 

strantor

Active Member
What kind of oil is it & what is it used for? Refined vegetable oil, mineral oil, used motor oil, crude oil, ... Lubricating oils change quite a bit over time. So do heat-transfer oils depending on service conditions. The expected changes during the life of the oil could be an issue.

Also, is there reservoir tank for the oil. A 10% volume change when water is present may allow a simple float switch to be used.
http://www.royalpurpleindustrial.com/products/marine-hydraulic-oil/

It's an under water electric motor full of hydraulic oil for pressure compensation. No reservoir.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top