DIY refractometer?

[gturner6ppc]

Has anyone built their own refractometer?

Currently I'm playing around with the idea. I got a bunch of microscope slides from the hobby store and glued them into 60 degree prisms. I did some quick ray tracing and four to seven of them laid side by side and filled with wort, with the other space filled with distilled water, should give me a really good deflection.

My purpose is to make an auto-cutoff for sparging that automatically detects a predetermined gravity (such as 1.010).

The idea is that the tubing from the lauter tun branches to feed wort through the inside of each glass prism, while the box they're in is filled with either water (for a slight deflection) or a controlled 1.010 sugar solution in which case no-deflection signals that the wort has hit 1.010 or so. The detector would be a laser pointer aimed through all the prisms with a photodetector directly across from it.

The ends of the prisms, where they meet the tubing in and tubing out, would be sealed with silicone or epoxy. In theory, by the time most of the wort has run through and is getting anywhere near the endpoint, it's already warmed up the reference solution to the same temperature as the wort so thermal compensation wouldn't be required.

 

[Revvy]

WOW!!!!

I don't know if it would work or not, nor if it is more difficult than spending 30 buck to get one. But in terms of sheer DIY balls I wanted to acknowlege your thread, so it wouldn't drop into obscurity.

And to tell you that nothing like this counts unless you post pictures.

 

[sudbuster]

Has anyone built their own refractometer?

Currently I'm playing around with the idea. I got a bunch of microscope slides from the hobby store and glued them into 60 degree prisms. I did some quick ray tracing and four to seven of them laid side by side and filled with wort, with the other space filled with distilled water, should give me a really good deflection.

My purpose is to make an auto-cutoff for sparging that automatically detects a predetermined gravity (such as 1.010).

The idea is that the tubing from the lauter tun branches to feed wort through the inside of each glass prism, while the box they're in is filled with either water (for a slight deflection) or a controlled 1.010 sugar solution in which case no-deflection signals that the wort has hit 1.010 or so. The detector would be a laser pointer aimed through all the prisms with a photodetector directly across from it.

The ends of the prisms, where they meet the tubing in and tubing out, would be sealed with silicone or epoxy. In theory, by the time most of the wort has run through and is getting anywhere near the endpoint, it's already warmed up the reference solution to the same temperature as the wort so thermal compensation wouldn't be required.

I'm with Revvy on this. More power to you dude. If you are into optics and get it working, Pix are great, that is unless you decide to sell it.

 

[gturner6ppc]

Thanks.

But at this point all I've done is use some super-glue from Lowe's to make four prisms out of microscope slides.

The change in index of refraction isn't all that much, which is why I'm using bunches of them to keep on bending the beam. I have the CRC handbook tables and wrote a little ray trace program to check (Snell's law of refraction, high school stuff), and five or so prisms should give me a 3/4 inch swing on the last prism from for a gravity swing of 1.000 to 1.080.

My worry is that the prisms will require too much wort to respond quickly, or something along those lines, or that particles in the wort will disperse the beam too much, or something along those lines. I'd prefer a smaller setup with less volume, or maybe something a bit more optically clever than using $4.00 worth of slides.

But I'll give it a try and see what happens.

 

[Rushis]

How long is your pathlength for each prism? I figure with mircoscope slides you have roughly 2cm on edge and you were mention 5 prisms, giving you effective pathlength of 10 cm. The scattering from small particles in the wort is going to be a big problem as is molar absorptivity of the wort itself. Where you considering a pen laser as a light source or something with more balls?

 

[gturner6ppc]

The slides I got were exactly 1" wide, so yes, the path length might be a problem. I wish I had something smaller for the front prisms. As it stands, cutting through the top of five prisms is going to give me about an inch and a half of path length through the wort. I was thinking of using a pen laser and hoping that by the time the lautering is nearly finished the wort would be clear enough that scattering doesn't throw it off.

If it doesn't work, perhaps I could using the pen laser and a single surface of a slide to make a grazing angle refractometer, such as the kind they use to measure slurries, but I don't think I can do that with much accuracy. I could try ray tracing such a setup and see what I come up with, though. Perhaps using part of a barcode scanner to give a sweep across the surface and then reading where the lines end up on the other side, or something.

But I'd like to keep it simple enough that every DIY'er could build one.

 

[annasdadhockey]

And I was excited when I built my own wort chiller. :cross:
Sounds like a cool project if you can get it to fly. Good luck to you.

 

[conpewter]

Sounds very cool. Would you basically have it set so that as the wort changes in gravity it would make the beam bend more and eventually hit a photosensitive eye to stop the sparge?

Does the amount of sugar in the wort change it's index of refraction? (I've not actually looked in to how a refractometer works)

 

[gturner6ppc]

Well, the prisms are hollow, made of slides, so they don't bend the light unless the inside fluid has a different index of refraction than the outside fluid. By putting them in a box filled with pure water I eliminate most of the refraction relative to wort so my beam can travel a fairly straight path. If the wort dropped to SG 1.000 then the beam wouldn't deflect at all.

The index of refraction of pure water at 20 degrees C is 1.3330. As you add sugar it goes up, but not by very much. At an SG of 1.011 it's 1.3374, and at an SG of 1.082 is 1.3639.

So the change isn't very big at all, but it is measurable.

On the downside, the index of refraction drops with temperature, (because the water expands) so pure water at sparging temperature (170F) is 1.32376 instead of 1.3330

I figured I'd try using multiple prisms because these changes are so small.

 

[conpewter]

Cool! Thank you for the explanation. I do wonder if the water will heat up to the same temp during the sparge or not, depends on the amount of water and possible insulation (except where the beam goes through.)