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water level sensor

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duncan webster02/03/2021 21:46:22
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Way back in 2016 there was some correspondence n the Model Boats forum about a water level sensor which clipped round the gauge glass. sensor

I've tried pm'ing the author Jens Eirik Skogstad with no response, and tried (and failed) to post on the Model Boats forum. Does anyone have any info/experience? I'm not after probes which go into the boiler, I can sort that out for myself. I think Cheddar models used to supply similar, but I've looked at Clevedon (who took over from Cheddar) website and it isn't mentioned

noel shelley02/03/2021 22:22:22
527 forum posts
18 photos

The circuit diagram and component list is there. It should be possible to build it from that info. I fancy it would be an interesting project and could be made fail safe with a servo gas valve. Noel

duncan webster02/03/2021 22:29:40
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I'm particularly interested in the sensor. Does it just shine a light straight through the glass tube, in which case why does having water in it make any difference. The industrial ones I've seen shine a narrow beam off centre through a much bigger gauge glass, and when there is water present it acts like a prism and deflects the beam. If this is how Mr Skogstad's sensor works having some more onfo could save me a lot of experimenting. I don't intend to use any of the circuitry, a processor will be much easier.

Michael Gilligan02/03/2021 22:53:51
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I suspect that the water filled tube acts as a cylindrical lens [rod lens] and spreads the light from the LED into a fan-like line.

MichaelG.

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Edit: Ref. https://www.comaroptics.com/components/lenses/cylindrical-lenses/rod-lenses

Edited By Michael Gilligan on 02/03/2021 23:03:03

not done it yet02/03/2021 23:15:14
5870 forum posts
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Not all ‘transparent’ materials are actually transparent to other frequencies of electromagnetic waves. IR is absorbed/attenuated by water.

Perhaps think here of microwaves, which are readily absorbed by water in the food/drink..

fizzy02/03/2021 23:22:50
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hey Duncan....jerry who is a good mate of mine has just perfected a new line (clevedon steam), email him for details...we might all learn something

duncan webster03/03/2021 00:05:39
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Posted by not done it yet on 02/03/2021 23:15:14:

Not all ‘transparent’ materials are actually transparent to other frequencies of electromagnetic waves. IR is absorbed/attenuated by water.

Perhaps think here of microwaves, which are readily absorbed by water in the food/drink..

IR doesn't penetrate glass either, at least according to the interweb

Martin Connelly03/03/2021 09:17:25
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1713 forum posts
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Duncan, I thought greenhouses worked by letting the IR in then when it hit the inside surfaces it turned into heat energy in those materials and heated the greenhouse up.

Martin C

duncan webster03/03/2021 11:32:42
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Just shows you can't believe everything on the interweb. Further googling says some infra red gets through, some is absorbed. Depends on frequency. More go searching needed, but the original used a visible red led.

Bazyle03/03/2021 12:10:40
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Greenhouses. They let the high energy UV from sunlight in and block the IR getting out. They do also let a lot of the IR from the sun in because it is still fairly high frequency (hot) compared to the mere 25C inside the greenhouse.
The original probe type level control used in boats was invented in the early '70s by Beak&Verden who are still on the St Albans DMES committee.

duncan webster03/03/2021 12:56:16
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As far as I can determine, short wavelength IR (800 to 2000nM) passes through glass, longer doesn’t.
However, according to Wikepdia, in this range, water has a low attenuation coefficient, with a minimum at 940nM, which is a popular value for IR LEDs

Attenuation coefficient - Wikipedia

Electromagnetic absorption by water - Wikipedia

which means that IR can get through that as well. Absorbtion coeff of water vapour seems to be very frequency dependant.
I suspect I’m going to use a probe and continuity, a lot easier, and as long as I make the probe AC relative to the shell I gather that deposits won’t be a problem.

I’ll try to contact Messrs Beak and Verdon and Clevedon steam
Thanks for all the input, in these lockdown times a sounding board keeps me sane.

not done it yet03/03/2021 13:57:54
5870 forum posts
20 photos

They let the high energy UV from sunlight in ....

Funny that. People working under glass don't get tanned....🙂

not done it yet03/03/2021 13:57:56
5870 forum posts
20 photos

They let the high energy UV from sunlight in ....

Funny that. People working under glass don't get tanned....🙂

Grizzly bear03/03/2021 18:22:36
278 forum posts
8 photos

Duncan,

Would a solid float work, sitting on top of the water?

Good luck, Bear..

Michael Gilligan03/03/2021 19:08:44
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17886 forum posts
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This may be of interest to those still contemplating attenuation as the ‘mechanism’

**LINK**

https://manoa.hawaii.edu/exploringourfluidearth/physical/ocean-depths/light-ocean

MichaelG.

Ian P03/03/2021 20:37:06
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2497 forum posts
102 photos

Unless I have the wrong end of the stick, Duncan is looking for a system that can measure the level of water in the boiler. I single sensor can be made to detect the presence of water at a particular level in the tube but I would think several sensors would be needed at different heights if this system is going to control a water valve or whatever.

Noel S mentioned 'servo' in his reply, that might need some type of analogue sensing rather than just one 'above' and one 'below' sensors. I can see quite a bit of development being needed before one could be confident that the water meniscus was actually between the two sensors and not below the bottom one (or above both). That bit might be trickier than the optics.

Ian P

Michael Gilligan03/03/2021 20:57:03
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Posted by Ian P on 03/03/2021 20:37:06:

[…]

Noel S mentioned 'servo' in his reply, that might need some type of analogue sensing rather than just one 'above' and one 'below' sensors. […]

.

The video demonstrates a ‘radio control’ type of servo being driven by the circuit.

If my understanding is correct, then the sensor is detecting the presence or absence of water at one particular location in the tube ... which is not quite the same as sensing the position of the meniscus.

MichaelG.

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P.S. __ Here is the, very brief, datasheet for the ‘Kingbright photo-transistor:

https://www.bitsbox.co.uk/data/L7113P3C.pdf

Edited By Michael Gilligan on 03/03/2021 21:00:16

Joseph Noci 103/03/2021 21:20:30
913 forum posts
1100 photos

As usual,discussion run amuck and we wonder what it is that Duncan Actually asked...

Duncan, are you wishing to know if there is water in the gauge glass tube, or do you want to know the level of the water in the tube?

Joe

Michael Gilligan03/03/2021 21:37:53
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17886 forum posts
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Posted by duncan webster on 02/03/2021 22:29:40:

I'm particularly interested in the sensor. Does it just shine a light straight through the glass tube, in which case why does having water in it make any difference.

.

Joe ^^^

MichaelG.

.

My immediate response was explicitly to that question.

Edited By Michael Gilligan on 03/03/2021 21:39:29

duncan webster03/03/2021 21:56:45
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3186 forum posts
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I just want to know if the water is above a set height in the glass. The sensor in the Model Boats article has a LED and a phototransistor. It looks like a simple red LED, see photo below. This is positioned around the gauge glass, and detects water level on a simple on/off basis. It uses lots of components which can all be replaced by a processor (I think), but I'm trying to understand how the sensor works. As the original electronics has adjustment for 'photo sensitivity' I suspect the water attenuates the light and the signal is fed to a comparator, it would be a lot neater if the actual sensor was on/off, which can in principle be done by shining a thin beam offset through the glass, with water in you get much more deflection (refraction) but I've only seen this on much bigger glass tubes in industrial environment. I'm hoping to avoid having to miniaturise it myself (idle b*gger)

Once I know that water had dropped I propose to turn on the pump, which will pump at a higher rate than the fire can evaporate the water, and if after a set time (short enough that the water can't get dangerously low if the pump doesn't work) the water level has not risen it will kill the gas.

This is a long term project, I haven't made the burner for the boiler yet, that's been on the to-do list for a long time, too many distractions. I have however ordered a photo-transistor, that might kick start something

Edited By duncan webster on 03/03/2021 21:58:14

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