By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

water level sensor

All Topics | Latest Posts

Search for:  in Thread Title in  
duncan webster04/03/2021 22:41:59
3457 forum posts
63 photos
Posted by Michael Gilligan on 04/03/2021 22:08:55:

Posted by duncan webster on 04/03/2021 21:58:33:

[…]

I'm beginning to think that Michael's idea of cylindrical lens might be the answer, if the water makes it splay out like a fan it would cause a step change in intensity, same amount of light in a wider beam.

.

Using my arbitrarily chosen numbers: The empty tube splays it more than the water-filled tube; but yes, there would be a step-change in intensity.

If you can give me actual diameter, bore, and refractive index ... I can demonstrate.

MichaelG.

.

Edit: Here’s a little taster

.97637b52-f450-4e55-a4b6-ed3ad3c28147.jpeg

Edited By Michael Gilligan on 04/03/2021 22:26:26

OD 6mm, ID 3.8mm, refractive index no idea!

Michael Gilligan04/03/2021 22:55:45
avatar
18746 forum posts
918 photos

Posted by duncan webster on 04/03/2021 22:41:59:

.

OD 6mm, ID 3.8mm, refractive index no idea!

.

Not a bad guess then ... I chose OD 6mm, ID 4mm

Do you have a name for the glass ?

... if not, I will assume it to be borosilicate [i.e. Pyrex or similar]

I will adjust things tomorrow

MichaelG.

Edited By Michael Gilligan on 04/03/2021 23:00:57

duncan webster04/03/2021 23:31:22
3457 forum posts
63 photos

It's what is sold for gauge glasses, I'd guess borosilicate but no evidence

Michael Gilligan05/03/2021 08:42:04
avatar
18746 forum posts
918 photos

Here we go, Duncan ...

Tube OD 6mm, ID 3.8mm, Material = botosilicate glass

Red light from a point-source 3mm from the tube surface

Tube filled with Air / Water / Glass

.1169289d-df60-47b3-884b-4a28883b2cd8.jpeg

.

b0337b45-5625-45fd-bef6-40f07f5bb6f5.jpeg

.

e1922c93-705e-46ec-b628-6e941263777e.jpeg

.

Q.E.D.

.

MichaelG.

Chuck Taper05/03/2021 08:54:41
30 forum posts
1 photos
Posted by Michael Gilligan on 05/03/2021 08:42:04:

Here we go, Duncan ...

Tube OD 6mm, ID 3.8mm, Material = botosilicate glass

Red light from a point-source 3mm from the tube surface

Tube filled with Air / Water / Glass

[Snip, Snip, Snip]

.

Q.E.D.

.

MichaelG.

I'm intrigued - how, what etc??

What software is that?

Regards.

Frank C.

Michael Gilligan05/03/2021 09:11:23
avatar
18746 forum posts
918 photos
Posted by Chuck Taper on 05/03/2021 08:54:41:

.

I'm intrigued - how, what etc??

What software is that?

Regards.

Frank C.

.

RayLab, by Kamyar Ghandi ... Running on iPad Pro 9.7”

**LINK**

https://apps.apple.com/gb/app/raylab/id710190065

... I gave it a rave review

MichaelG.

Andy Stopford05/03/2021 09:34:05
92 forum posts
9 photos
Posted by duncan webster on 04/03/2021 21:58:33:

I quite like Noel's capacitance idea, but it's beyond my electronic expertise. Are we talking relaxation oscillator and phase locked loop chip? If so I've just bought some of those for another project, but I can't find them either!

Here's a fairly simple device for capacitive sensing, using a 555 timer and an ATMega 328 microcontroller (as in an Arduino). The schematic, MaquinaSafetyLevel.sch, is in the PCB folder, and is a KiCAD file.

https://github.com/andystopford/SCRAM

It works in the opposite sense to what you want, i.e.it switches on if the water is above a pre-determined level (to power a heater element).

The level probe is a commercially available one intended for espresso machines, though it seems to be just a stainless steel rod, with all but the last 10mm or so sheathed with acetal or something similar.

In main.ino, at line 10, I've commented it as voltage, however I think the values are arbitrary - it certainly doesn't carry 600 volts (I hope). These values were determined experimentally, and take a while to settle down; I'm not sure why, but I had to change them several times in the first few weeks of operation. They always drifted towards the 'safe' condition though, with shutdown occurring even when there was water in the boiler.

Michael Gilligan05/03/2021 10:48:27
avatar
18746 forum posts
918 photos
Posted by Michael Gilligan on 05/03/2021 08:42:04:

Here we go, Duncan ...

Tube OD 6mm, ID 3.8mm, Material = botosilicate glass

.

.

Oops ... Arthritic finger problem

botosilicate should read borosilicate blush

MichaelG.

duncan webster05/03/2021 11:28:33
3457 forum posts
63 photos

Michael's ray plots are extremely interesting. While I get my head round them, I've done what I should have done right at the beginning, got off my backside and done some investigating

first photo shows a 5mm LED, no glass, just to get a baseline

no glass small.jpg

then with just the empty glass tube, note how the LED appears much narrower, and there appear to be 2 red edges

 

glass only small.jpg

Then with water in the tube, the image fills the tube and seems much brighter, at least to my eye

 

 

glass and water small.jpg

I'll have to wait for the phototransistors to arrive now, but at last I'm beginning to see what is going on. I have a feeling that if Michael widened the beam slightly on his with-water plot he'd get total internal reflection on the inner glass/air interface, which might explain the side bands on the second photo.

Now to delve into Andy's capacitor scheme.

Thanks to everyone who has contributed, quite a bit learned. And the good news is I've found the PLL chips, but not the slotted opto

Edited By duncan webster on 05/03/2021 11:31:46

Michael Gilligan05/03/2021 20:01:15
avatar
18746 forum posts
918 photos

At Duncan’s request ... here are three more ray-traces, with the source at different distances from the Water-filled glass tube.

Sorry, I really can’t do dozens of these ... but if anyone can give me the dimensions of the original sensor arrangement, I am happy to try these in my model.

MichaelG.

.

dcb8823c-1873-47c8-88a9-29c3c4007980.jpeg

.

312a76d3-398a-454d-8e30-520e62ae125b.jpeg

.

2c30cb84-be0c-4c63-8c10-d8fc6d5b38fa.jpeg

.

The generation of the traces is easy ... but getting them onto the forum is tedious !!

Edited By Michael Gilligan on 05/03/2021 20:04:13

duncan webster05/03/2021 21:06:34
3457 forum posts
63 photos

That looks like explaining the rugby ball shape. The distance from the outside of the glass to the actual source of light is not the same as the distance to the end of the LED, but when the water filled glass is touching the LED the image fills the tube as I pull away at about 6mm distance the image is round, then becomes more rugby ball same as empty tube.

More news when the transistors arrive, I'll bet you can't wait!

John Baron05/03/2021 21:14:32
avatar
487 forum posts
189 photos

Hi Duncan, Guys,

An old computer mouse will provide you with at least four IR pairs. Two on either side of the slotted wheel !

Michael Gilligan07/03/2021 11:56:35
avatar
18746 forum posts
918 photos
Posted by duncan webster on 05/03/2021 21:06:34:

[…]

More news when the transistors arrive, I'll bet you can't wait!

.

Meanwhile ... I thought interested readers might find this diagram helpful:

.

46b12330-fe47-4454-a90f-e750f2939525.jpeg

.

It shows the typical beam pattern for a common ‘5mm LED’

... and, by implication, it also represents the acceptance angle for the specified photo-transistor.

MichaelG.

.


Note: I linked the data-sheet for the PT in an earlier post.

duncan webster14/03/2021 14:26:06
3457 forum posts
63 photos

well the phototransistors turned up, so I've made a lash up test rig. The voltage display is just the drop across the transistor. 15mA current through a red LED, no idea of its part number, it was in the bits box.Low water gives high voltage drop and vice versa. I can easily knock up some electronics to switch a pump etc, and to notice if a wire has dropped off. However, following Fizzy's suggestion I contacted Clevedon Steam. He is working on bringing back the sensor which Cheddar used to supply, and is working out how to cope with the heat from the gauge glass. No point 2 of us competing, and I don't want to undercut his sales possibilities, so this will now go on the back burner for a bit. It's getting pretty crowded back there, but at least it might get me enthused to finish off the stationary boiler it's intended for

low water (small).jpghigh water (small).jpg

Michael Gilligan14/03/2021 15:21:42
avatar
18746 forum posts
918 photos

Thanks for the update, Duncan

... looks like a clear and convincing demonstration yes

... Did you ever hear back from the originator ?

MichaelG.

duncan webster14/03/2021 15:30:38
3457 forum posts
63 photos
Posted by Michael Gilligan on 14/03/2021 15:21:42:

Thanks for the update, Duncan

... looks like a clear and convincing demonstration yes

... Did you ever hear back from the originator ?

MichaelG.

I joined the RCME forum and sent him a pm, but he seems to have gone to ground

thanks for your help everyone

Grizzly bear14/03/2021 20:32:59
282 forum posts
8 photos

Duncan,

That poor multimeter, please give it a bath, I'm sure it will appreciate it.

Bear..

duncan webster14/03/2021 20:57:01
3457 forum posts
63 photos

OK so I've given it a bath and now it doesn't work. Seriously I've wiped it down with IPA and it does look a lot better, (and it still works)

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Dreweatts
Warco
walker midge
cowells
JD Metals
Eccentric July 5 2018
emcomachinetools
rapid Direct
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest