Moisture meter vs. blood pressure monitor

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Did67
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 31/05/21, 10:49

Uncle Buzz wrote:
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 all this "general public" so that it works without bothering to keep it running takes a lot of work.



I was not "mainstream" - well, it exists in full probe, but of course, a little expensive ...

I first wonder about the reliability of these measurements - does the displayed% humidity correspond in "real soil", roughly ???

For it to be "cheaper", you would need a "measuring box" and a series of probes with a "click-clack" connection. So an investment in data collection / processing and 36 3-ball probes, at each place where you want to measure. If it's reliable.
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 31/05/21, 10:58

When I say "general public" (in quotes) it means that you plug in and it works, without having to go and check in the code why it doesn't work.
For the moment, at home, I plug in, I run a few command lines to start the server, and if there is a problem I know roughly where to look to find the source of the problem, sometimes minor, but it's me who set up the system (even if everything is done by following various tutorials and I haven't invented anything) and therefore I understand how it works, send it as is to someone, if it works the first time, it's good, at the slightest glitch impossible to remotely troubleshoot or refer someone who does not know the electronics or programming.
In addition, the server is a software quite not dedicated to this use case and it is therefore necessary to know how to use it to add and register its sensors, to see how to then export the data to use them elsewhere.
And so the job so that it starts by itself just by plugging in, some automatic tests to check that everything is ok or a small manual on how to declare the sensors that are added so that the "general public" can use them, c t is a lot of work, I am not talking about a marketing target for the general public, just to allow someone who does not have the knowledge to put it all in place.
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 31/05/21, 11:49

OKAY. I understand. I actually thought that once wired / programmed, it "turned"! Quite stable. Except of course, flood, oxidation, disconnection ...

[PS: feel free !!! Don't think I'm asking ... It's one of 100 things I would try out of pure curiosity - since I have two blood pressure monitors]
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Re: Moisture meter vs. blood pressure monitor




by Radagast » 31/05/21, 14:55

Uncle Buzz wrote:
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.


Hello,
Thank you very much for this very complete answer. I'm going to test my blood pressure monitor right now.
Good week !
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 31/05/21, 15:08

Be careful though with Didier's remark, when closing the tensiometer, if there is no or very little air, as the volume is reduced as the cap / manometer is screwed in again, a times screwed enough to be waterproof (at the beginning it leaks around the thread), we end up compressing the contents, except as the water is not compressible, the variation in volume only impacts the remaining air bubble which will therefore increase in pressure, the smaller it is, the more the pressure will rise, and the manometer has a maximum pressure limit beyond which it could be damaged.

The overpressure eventually disappears as soon as the soil sucks the water from the tensiometer, so no effect on the measurement afterwards, it is just a question of not damaging the manometer when closing the tensiometer.
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Re: Moisture meter vs. blood pressure monitor




by Uncle Buzz » 31/05/21, 15:12

Did67 wrote:I actually thought that once wired / programmed, it "turned"! Quite stable. Except of course, flood, oxidation, disconnection ...


In theory: yes ... In practice, there is often a grain of sand that slips into the cog, see Murphy's law ...
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 31/05/21, 15:41

This is why it is better to live in Theory. Everything works there!
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Re: Moisture meter vs. blood pressure monitor




by izentrop » 02/06/21, 15:49

Hello,
The cheapest humidity sensors are galvanic probe (see photo) https://fr.wikipedia.org/wiki/Capteur_d ... jardiniers

My brother has one and the measurement is instantaneous. In addition, since the probe is at the end of the stem, we can suddenly obtain the measurement as close as possible to the roots. After that I did not find a doc on the precision nor on the possibility of leaving it permanently in the ground (galvanic corrosion?)
Otherwise the voltage produced could be easily processed by a Schmidt trigger system to control a sprinkler pump.
There is no galvanic probe, but the complete galvanometer sensor is so inexpensive that I ordered one for the hack.

Especially since the capacitive effect sensor does not seem to be very precise https://www.sdec-france.com/mesure-humi ... eorie.html
Professionals use the TDR (Time Reflectometry) method, but hey, we don't need such precision in our gardens. :?: :P
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Re: Moisture meter vs. blood pressure monitor




by Did67 » 02/06/21, 17:21

izentrop wrote:
My brother has one and the measurement is instantaneous. In addition, since the probe is at the end of the stem, we can suddenly obtain the measurement as close as possible to the roots.

:P


If it's the same kind as the "gadget" that I had, you might as well do without it ... Even € 7 which does not indicate much, it is € 7 thrown in a trash can!

Basically it said "Dry" almost all the time! The barely wiped out soil

The "anguished gardeners" are happy: they water, they water, they water ... How certain they have saved their vegetable garden! And proud of them ...

My ambition is to water "to the fairer extreme" - if I can, not to water ... And if not, as it should when it is necessary ...
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Re: Moisture meter vs. blood pressure monitor




by izentrop » 02/06/21, 18:36

Did67 wrote:If it's the same kind as the "gadget" that I had, you might as well do without it ... Even € 7 which does not indicate much, it is € 7 thrown in a trash can!
Basically it said "Dry" almost all the time! The barely wiped out soil
No, the one you are talking about was digital with 9 v battery, the galvanic works without battery as its name suggests :P

that that I ordered is simple, here is one with 2 probes that works on the same principle
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