A detailed comparison study of the Atago and VST refractometers - Page 13

Coffee preparation techniques besides espresso like pourover.
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AssafL
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#121: Post by AssafL »

Peppersass wrote:PAL-COFFEE units? (BTW, at one time their website had an optional certification of the 0.15% accuracy to a NIST standard for an extra $140, which I believe would put the price over $500.) The specs of instruments like this are based on things like circuit noise and the expected tolerances of the components used. In many cases it's possible to comb through the production line to find a unit that performs to tighter specifications. I'm not saying that was done in Socratic's case, but it would be good to know the source of the unit they used.
The 0.15% is for the entire temp range. One cannot compare 0.15% over 100C to 0.01% over 30C. Can't compare the two. Now that VST took off the calibration solutions from their website, one cannot make any comparisons....
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TomC
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#122: Post by TomC »

It's very tempting for these discussions to wander into the same old waters of patent infringement talk, water cooler lawyer-ese, etc. And these all end up ending the same way with the thread getting locked or participants deleting their posts. Let's try to avoid that this one time... Please keep the discussion about what's stated in the thread title, the two different refractometers and how they compare to each other.

I for one, am a bit tired of seeing every VST or refractometry thread ending the same way and it would be nice to avoid it for once.
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AssafL
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#123: Post by AssafL replying to TomC »

Very true. Edited my wayward remarks on a previous post.

So I guess this inability for anyone to touch this subject with a 10 foot pole means that we are now left comparing our coffee to the flavors preferred by 1960's America. I am running off to a barnyard sale to find me a genuine percolator and a coil heater to match (wouldn't work on my induction cooktop). About time these awful devices make a comeback!

That was a cynical remark and I apologize for it. The real problem is scaring Anton Paar, Atago, Reichert, and everyone else (including forum readers) from this subject means that we are left with crap science for 20 years. One cannot really make a remark without questioning if they hit a crumb on that awfully murky patent. Why should one even attempt to go to length to try to improve the current state?
Scraping away (slowly) at the tyranny of biases and dogma.

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TomC
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#124: Post by TomC »

On the contrary, I hope you continue to talk about the science of refractometry. Your posts have been some of my favorites in the past month. I just get sick of seeing the same old dog, people start interpreting intent, hashing out the law and crap, and it detracts from the discussions. And unfortunately that's usually the fatal blow to these discussions.
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Peppersass
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#125: Post by Peppersass »

AssafL wrote:Are these legal in the USA?
I couldn't find the text you quoted. Can you post the link?

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Bob_McBob (original poster)
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#126: Post by Bob_McBob (original poster) replying to Peppersass »

Chris

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AssafL
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#127: Post by AssafL »

Reference solutions were taken down off of the VST website. Now one cannot compare other refractometers (nor verify the accuracy of their VST branded Misco).

Which I guess is good enough because VST products didn't fair better than run of the mill Atago....
Scraping away (slowly) at the tyranny of biases and dogma.

jpender
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#128: Post by jpender replying to AssafL »

I think this is just speculation. We don't really know how well the Atago compares to the VST in any general sense. The notion that the specifications would line up if the temperature ranges were the same may be true but it's based only on faith.

Furthermore, the insinuation that VST took their reference solutions off their website in order to prevent honest comparison is also speculation. They may simply be out out of stock.

While their reference solutions are useful they aren't the only way to check the calibration of the refractometer. If you have the skill you should be able to create an accurate sucrose solution to use as a reference. The nD of various sucrose solution concentrations is not a secret and the nD to %TDS formula is there for anyone to see in the VST patent application. You don't even have to do the calculation yourself. Vince Fedele provided a recipe for a sucrose based reference solution that correlates with 2.00% TDS at 20°C on coffeegeek several years ago.

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Bob_McBob (original poster)
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#129: Post by Bob_McBob (original poster) »

jpender wrote:While their reference solutions are useful they aren't the only way to check the calibration of the refractometer. If you have the skill you should be able to create an accurate sucrose solution to use as a reference. The nD of various sucrose solution concentrations is not a secret and the nD to %TDS formula is there for anyone to see in the VST patent application. You don't even have to do the calculation yourself. Vince Fedele provided a recipe for a sucrose based reference solution that correlates with 2.00% TDS at 20°C on coffeegeek several years ago.
The equations disclosed in the VST patents rely on several undisclosed constants to give a TDS value, so they're a "secret" unless you test a few samples in a drying oven and derive your own equation for the physical relationship (like Randy Pope in 1995 and Alan Adler and Joseph Rivera in 2005). They note the essentially linear relationship at lower values that was observed in now-deleted posts comparing Brix and TDS values. It's all the same as any other refractometer scaling: a few constants and some standard temperature compensation math. Here's a 1970 equation for Brix at 20°C, for instance.

B = 0.0087 + 699.82353(ri - 1.3330) - 1801.9215(ri - 1.3330)^2 + 4696.422(ri - 1.3330)^3 - 6427.26(ri - 1.3330)^4
Chris

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#130: Post by jpender »

Bob_McBob wrote:The equations disclosed in the VST patents rely on several undisclosed constants to give a TDS value, so they're a "secret" unless you test a few samples in a drying oven and derive your own equation for the physical relationship...
Look again. The constants are in the application.