Time Domain Reflectometry (TDR)

Thread Starter

shibin_varghese

Joined Jan 14, 2019
57
Hai Friends,
I would like to design a soil moisture sensor using TDR technology since TDR based moisture sensors are more accurate than capacitive or resistance-based moisture sensors.
But I don't have any idea about it.
Can anyone help me in finding a solution for it?
 

Thread Starter

shibin_varghese

Joined Jan 14, 2019
57

haresfur

Joined Oct 13, 2019
7
You have probably figured out by now that this is not a simple project. I am not aware of any step-by-step instructions for constructing a TDR soil moisture probe with parts lists, etc. You might consider looking into TDT, which has similar accuracy and precision to TDR and similar lack of interference from soil type. My understanding is that the electronics are simpler. Good luck!
 

Thread Starter

shibin_varghese

Joined Jan 14, 2019
57
You have probably figured out by now that this is not a simple project. I am not aware of any step-by-step instructions for constructing a TDR soil moisture probe with parts lists, etc. You might consider looking into TDT, which has similar accuracy and precision to TDR and similar lack of interference from soil type. My understanding is that the electronics are simpler. Good luck!
Thank You @ haresfur, TDT and TDR have the similar working principle, and I would like to know more about TDT so that I can make a soil moisture sensor.
Can you help me???

Moderators note: Please stop creating new threads on this subject..
 
Last edited by a moderator:

DJordan

Joined Nov 26, 2019
1
I'm coming to this thread from a completely different angle. I'm a soil physicist and I understand the interactions of water, soil and electric charge pretty well (I hope). But I don't have enough electronic expertise to really understand these circuits, though I do understand the measurement itself. So I can respond to questions about the strengths and weaknesses of different means of soil moisture measurement (complicated, as others have commented on this forum).

It's very helpful to see this low-cost TDT design because the measurement of soil water content is actually of very great importance in using soil well and protecting it from the loss of fertility and organic matter. TDT is one of the better methods. The problem is that most commercial instruments which can measure soil moisture accurately are very expensive (like hundreds of dollars expensive) so a low-cost design which ordinary mortals might be able to build could make a really valuable contribution to protecting our environment and food sources.

So thank you for bringing this to our attention, Danko. Comments welcome.
 

haresfur

Joined Oct 13, 2019
7
I'm coming to this thread from a completely different angle. I'm a soil physicist and I understand the interactions of water, soil and electric charge pretty well (I hope). But I don't have enough electronic expertise to really understand these circuits, though I do understand the measurement itself. So I can respond to questions about the strengths and weaknesses of different means of soil moisture measurement (complicated, as others have commented on this forum).

It's very helpful to see this low-cost TDT design because the measurement of soil water content is actually of very great importance in using soil well and protecting it from the loss of fertility and organic matter. TDT is one of the better methods. The problem is that most commercial instruments which can measure soil moisture accurately are very expensive (like hundreds of dollars expensive) so a low-cost design which ordinary mortals might be able to build could make a really valuable contribution to protecting our environment and food sources.

So thank you for bringing this to our attention, Danko. Comments welcome.
That's the situation I am in. IMO it is important to have some understanding of the soil physics and the sensor technology to come up with a solution. I'm having difficulties understanding enough of the electronics to see what is possible to construct and what the limitations will be compared to the commercial units.

I appreciate Danko's post above, but am afraid I can't read the design well enough to build one. Looks like it would be a great project, though.
 

Thread Starter

shibin_varghese

Joined Jan 14, 2019
57
I'm coming to this thread from a completely different angle. I'm a soil physicist and I understand the interactions of water, soil and electric charge pretty well (I hope). But I don't have enough electronic expertise to really understand these circuits, though I do understand the measurement itself. So I can respond to questions about the strengths and weaknesses of different means of soil moisture measurement (complicated, as others have commented on this forum).

It's very helpful to see this low-cost TDT design because the measurement of soil water content is actually of very great importance in using soil well and protecting it from the loss of fertility and organic matter. TDT is one of the better methods. The problem is that most commercial instruments which can measure soil moisture accurately are very expensive (like hundreds of dollars expensive) so a low-cost design which ordinary mortals might be able to build could make a really valuable contribution to protecting our environment and food sources.

So thank you for bringing this to our attention, Danko. Comments welcome.
Thank you for your response.
I would like to know more about the behavior of soil to high frequencies (in the range of GHz).
Some people say it is not recommended to use low frequencies to measure the moisture content of the soil since low frequency is more responsive towards electrical conductivity and salt content of the soil.
 

haresfur

Joined Oct 13, 2019
7
My understanding is that you are correct in that higher frequency systems are affected less by soil properties and salinity, but I haven't delved into the underlying theory.

For what it is worth, there is a new commercial TDT probe with a circuit board design, similar to the cheap capacitance probes. I am not affiliated in any way with the ITC or the manufacturer and don't know the details but here is a link: http://www.ictinternational.com/products/smt100/smt-100/?from=/products/soils/moisture-sensors/
 
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