Moisture meter vs. blood pressure monitor

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Tom ibex
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Moisture meter vs. blood pressure monitor




by Tom ibex » 29/06/20, 08:56

Hello,

in his latest book, in the chapter on water, p.325, Didier Helmstetter recommends the use of the blood pressure monitor. I wander a little compared to the price.
I can't find enough information regarding the disadvantages of the moisture meter compared to the blood pressure monitor.
The moisture meter seems more flexible, easier to use and costs less than the blood pressure monitor.

Has anyone used both and could they shed some light on this?
I am in sandy soil not far from the sea in southern Brittany

Goods.
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 29/06/20, 09:48

Hello,
I did not buy, and therefore did not read (shame on me) Didier's 2nd book, so I do not know the context of his chapter on blood pressure monitors.

One of the great advantages of the tensiometer is that it does not measure the quantity of water in the soil, but its availability. Depending on the type of soil, for the same amount of water, water is more or less easy to extract. We can therefore for the same amount of water in the soil have in one soil a plant in its comfort zone, and in another soil a plant under water stress.

Knowing the humidity of the soil is therefore not enough, it is then necessary to correlate this measurement with the type of soil to know if there is enough water for the plants or not. When you work on a single soil, once you have learned the correlation, it comes down to the same thing because the soil becomes a constant and you learn to make the link between humidity and availability.

Regarding the cost of blood pressure monitors, it depends on what you want to do. Do you want an automatic statement with data backup? or just being able to know the tension of the ground whenever you want?

In the first case, these are products intended for professionals, it is expensive! It is possible for enlightened do-it-yourselfers to make it for not too expensive, but it takes the skills for manufacturing, possible programming for the connected part and troubleshooting if necessary.

For point measurement, there are digital blood pressure monitors from € 35. The disadvantage being that the blood pressure monitor is not a mobile sensor, there is an installation procedure, and the first measurement requires a few hours (1-2) to stabilize. So if you want to make readings at several points, ideally you need several sensors.
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 29/06/20, 11:22

To illustrate the difference between the amount of water in the soil and availability:
2020-06-29_112051.png

source: https://www.latelierpaysan.org/IMG/pdf/76819159.pdf
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Re: Moisture meter vs. blood pressure monitor




by Radagast » 30/05/21, 21:01

Uncle Buzz wrote:Hello,
I did not buy, and therefore did not read (shame on me) Didier's 2nd book, so I do not know the context of his chapter on blood pressure monitors.

One of the great advantages of the tensiometer is that it does not measure the quantity of water in the soil, but its availability. Depending on the type of soil, for the same amount of water, water is more or less easy to extract. We can therefore for the same amount of water in the soil have in one soil a plant in its comfort zone, and in another soil a plant under water stress.

Knowing the humidity of the soil is therefore not enough, it is then necessary to correlate this measurement with the type of soil to know if there is enough water for the plants or not. When you work on a single soil, once you have learned the correlation, it comes down to the same thing because the soil becomes a constant and you learn to make the link between humidity and availability.

Regarding the cost of blood pressure monitors, it depends on what you want to do. Do you want an automatic statement with data backup? or just being able to know the tension of the ground whenever you want?

Hi,
You seem to have mastered the use of the blood pressure monitor. I just bought one (seltzner 20cm) and the instructions are not very precise. Could you please tell me how much water should I put inside. In the instructions, they say up to the thread without specifying what it is. What water should I put in it? They explain the results between 0 and 200 mbar, but beyond that, there is no info. Can you help me ?
Thank you very much.
Good night,
Marc
In the first case, these are products intended for professionals, it is expensive! It is possible for enlightened do-it-yourselfers to make it for not too expensive, but it takes the skills for manufacturing, possible programming for the connected part and troubleshooting if necessary.

For point measurement, there are digital blood pressure monitors from € 35. The disadvantage being that the blood pressure monitor is not a mobile sensor, there is an installation procedure, and the first measurement requires a few hours (1-2) to stabilize. So if you want to make readings at several points, ideally you need several sensors.
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 30/05/21, 23:15

I had a moisture meter - kind of stick that you push in, supposed to give pH (fancy), temperature (correct) and humidity (whatever). You might as well stick your finger in the ground! If that's what you're talking about ...

It is true that tensiometers are expensive ... But they indicate the "tension", that is to say the force with which the soil retains water. It is therefore quite faithful, whatever the soil, of what the plants have to face ...

It's expensive, but hey, a grelinette costs much more!

Sometimes, it's just choices we make ... I have two blood pressure monitors for the price of a little one!

I wonder on the other hand about the "capacitive humidity sensors", which seem precise. The "cheap" cpateurs that can be found online require to be connected to "electronic boxes" which read and record the data ... I have not advanced. If an "electronics engineer" wants to look into this ??? I can't ...

If anyone wants to get started ??? : https://how2electronics.com/interface-c ... r-arduino/
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 30/05/21, 23:42

If someone wants to "tweak", I am willing to pay for the gear and then assess the reliability. I am in the process of "calibrating" a pot with a strawberry plant with weighing and comparison with the tensions of the tensiometer ... The idea is to obtain the curve giving the humidity of the soil (quantity of water in the soil - by weighing) as a function of the tension (measured by the tensiometer). This will only be valid for my soil ...

I will be able to do the evaluation of the capacitive measurement in the same soil ...
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 31/05/21, 09:40

Radagast wrote:Hi,
You seem to have mastered the use of the blood pressure monitor. I just bought one (seltzner 20cm) and the instructions are not very precise. Could you please tell me how much water should I put inside. In the instructions, they say up to the thread without specifying what it is. What water should I put in it? They explain the results between 0 and 200 mbar, but beyond that, there is no info. Can you help me ?
Thank you very much.
Good night,
Marc


I do not know the particularities of Seltzner tensiometers, but normally for a tensiometer, you need as much water as possible, the rest being air which has the defect of being compressible (and conversely expandable) which means that its volume varies with pressure.
When we compress the air, the pressure increases and conversely its volume decreases, and in the opposite direction, when we lower its pressure, its volume increases.
In a tensiometer, initially we are at atmospheric pressure, then as the soil tension increases due to lack of water, the soil tries to suck the water from the tensiometer, which lowers the pressure in the blood pressure monitor. As the water is almost incompressible, its pressure decreases without its volume changing: the water remains in the tensiometer while the soil tries to suck it up more and more.
On the other hand, the air which is in the tensiometer increases in volume as the suction of the soil increases, therefore part of the water in the tensiometer migrates from the tensiometer to the ground since what is in the tensiometer (water + air) increases in volume while the volume of the blood pressure monitor itself remains fixed. It will then be necessary for water to return to the tensiometer when the soil humidity increases again.
So the more air there is in a tensiometer, the more water is exchanged between the soil and the tensiometer where the water would go back and forth, this is a phenomenon that must be minimized, so fill to the brim the blood pressure monitor.
I imagine that when they say up to the thread, that means to the brim (if the thread is the upper part where we screw the manometer which indicates the pressure), some have an orifice on the side to top up of water without removing the manometer, the thread being that of the filler cap, I do not know the configuration here, but roughly it should be to put as much water as possible and conversely to leave only the minimum air possible when closing.
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 31/05/21, 09:55

Did67 wrote:If someone wants to "tweak", I am willing to pay for the gear and then assess the reliability. I am in the process of "calibrating" a pot with a strawberry plant with weighing and comparison with the tensions of the tensiometer ... The idea is to obtain the curve giving the humidity of the soil (quantity of water in the soil - by weighing) as a function of the tension (measured by the tensiometer). This will only be valid for my soil ...

I will be able to do the evaluation of the capacitive measurement in the same soil ...


I have to "improve" my blood pressure sensors, in particular to protect them from humidity (oxidation of the electronics), and they are not autonomous: they are connected by radio to a "server" which records the history. It works well, but it takes "maintenance" whether hardware (oxidation fault) or software. Making it all "mainstream" to make it work without bothering to keep it running takes a lot of work.
From experience, when something works, even not successful, I tend to lose interest intellectually and move on to something else that stimulates my curiosity. 80% of the work is already done, but the 20% that is missing takes a lot more time than what has already been done, the motivation decreasing with the share of challenge remaining, this is the kind of thing that I can do but that will take an indefinite time ...

FYI, the sensor itself must cost around 15 €, the microcontroller part that reads the sensor and sends the data by radio around 30 € ready-made (with mini solar panel to keep it in perpetual operation), could be divided by 2 by oversizing it, the server is a Raspberry Pi with a radio module which should cost around € 50.

That said, I still have to make sensors protected from rain / watering no matter what.
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 31/05/21, 10:41

Uncle Buzz wrote:
I do not know the particularities of Seltzner tensiometers, but normally for a tensiometer, you need as much water as possible, the rest being air which has the defect of being compressible (and conversely expandable) which means that its volume varies with pressure.
When we compress the air, the pressure increases and conversely its volume decreases, and in the opposite direction, when we lower its pressure, its volume increases.
In a tensiometer, initially we are at atmospheric pressure, then as the soil tension increases due to lack of water, the soil tries to suck the water from the tensiometer, which lowers the pressure in the blood pressure monitor. As the water is almost incompressible, its pressure decreases without its volume changing: the water remains in the tensiometer while the soil tries to suck it up more and more.
On the other hand, the air which is in the tensiometer increases in volume as the suction of the soil increases, therefore part of the water in the tensiometer migrates from the tensiometer to the ground since what is in the tensiometer (water + air) increases in volume while the volume of the blood pressure monitor itself remains fixed. It will then be necessary for water to return to the tensiometer when the soil humidity increases again.
So the more air there is in a tensiometer, the more water is exchanged between the soil and the tensiometer where the water would go back and forth, this is a phenomenon that must be minimized, so fill to the brim the blood pressure monitor.
I imagine that when they say up to the thread, that means to the brim (if the thread is the upper part where we screw the manometer which indicates the pressure), some have an orifice on the side to top up of water without removing the manometer, the thread being that of the filler cap, I do not know the configuration here, but roughly it should be to put as much water as possible and conversely to leave only the minimum air possible when closing.


I confirm.

It is necessary to leave a minimum of air. It is also necessary to "dip" the candle before, the first time. Then put water up to the "bottom of the thread" - it is not necessary that by screwing the manometer, one puts the water - and therefore the mano - under pressure! For my part, I fill without bothering to the brim and I put my little finger to create a small water vacuum corresponding to the head of the mano ...!

We measure depressions: at the level of the porous candle, there is a "struggle" between the depression in the tensio, which would bring in the water if we soaked in a jar full of water and the force with which the soil holds the water. 'water. The tensio measures this balance. So ultimately the force with which the water is retained by the soil. And that's what we want to know. When this force becomes too great, plants cannot absorb water easily enough - their yields drop, then they wither!

The presence of a little air is not prohibitive. Even elastic, it transmits the "tension" (its volume increases, but at both ends of the air column, the depression is the same. On the other hand, if there is too much, obviously, the air reaches the level. porous candle The system defuses itself by the bottom ...
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 31/05/21, 10:44

Uncle Buzz wrote:
From experience, when something works, even not successful, I tend to lose interest intellectually and move on to something else that stimulates my curiosity. 80% of the work is already done, but the 20% that is missing takes a lot more time than what has already been done, the motivation decreasing with the share of challenge remaining, this is the kind of thing that I can do but that will take an indefinite time ...

.


Almost all of the "construction sites" on my house (or in the vegetable garden) are victims of the same phenomenon!
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