shushikiary
Well-Known Member
So I'm putting together plans to build an automated all grain system using 3 kegs I have. I'm building the keggle right now and will use it for a while before finishing the build, but I'm thinking ahead.
I've seen that many people like to stop their sparge after gravity of the sparge wort hits 1.010 - 1.008. However doing this typically means pulling a sample and taking a reading by hand or buying a VERY expensive inline gravity reader (lowest I've seen a sensor was 1200 bucks).
So I got to thinking... what if there was a better way? Using a refractometer and an excel table you can even get the SG without an ATC device, thus all you need is the refractive index and the temperature of the sample to get your SG.
Well... step 2... refractive index is DIRECTLY proportional do dielectric constant. Sense the tubing I'll use will most likely not be metalic, we can assume a magnetic permeability of 1, thus making the index of refraction equal to the square root of the relative permittivity.
(see http://en.wikipedia.org/wiki/Refractive_index)
Given this is the case we CAN measure this easily. We simply take some silicon tubing, or PEX tubing, and put two halves of a copper pipe we cut down center around the tubing and solder a wire to each. Now the capacitance of the two copper "plates" will change as the dielectric material changes in permittivity....
Given a capacitor with 2 dieletrics of different permittivity it acts like two caps wired in parallel, so it's very easy to pull out the dielectric of the silicon (which is also constant, and thus very easy to simply calibrate out if you dont want to remove it mathematically).
Thus, as the permittivity of the wort changes with SG we can measure it and get refractive index, and then also take a temp measurement as close as possibly to where the "sensor" is and then we can use the excel sheet equations to get our SG with a cheap sensor.
The cheapest way to measure the capacitance would be to wire the cap as the oscillator tuning cap for a digital counter chip, allowing us to get a different count given the same period of time as the capacitance changes... giving us a digital count directly proportional to the permittivity, and should have linear response as the frequency of the oscilator circuit is fairly linear as the cap changes, and the capacitance changes linearly with permittivity. (see http://en.wikipedia.org/wiki/Capacitance)
Thus, we simply calibrate the sensor to see what counts correspond to what SG at what temperature by backwards calculating the excel equations, and BAM we have a cheap working SG sensor for in line wort measurements, allowing us to automate our sparge! (assuming you can already control your pump speed (and thus sparge rate) with the controller you have)
Am I crazy or would this work?
I've seen that many people like to stop their sparge after gravity of the sparge wort hits 1.010 - 1.008. However doing this typically means pulling a sample and taking a reading by hand or buying a VERY expensive inline gravity reader (lowest I've seen a sensor was 1200 bucks).
So I got to thinking... what if there was a better way? Using a refractometer and an excel table you can even get the SG without an ATC device, thus all you need is the refractive index and the temperature of the sample to get your SG.
Well... step 2... refractive index is DIRECTLY proportional do dielectric constant. Sense the tubing I'll use will most likely not be metalic, we can assume a magnetic permeability of 1, thus making the index of refraction equal to the square root of the relative permittivity.
(see http://en.wikipedia.org/wiki/Refractive_index)
Given this is the case we CAN measure this easily. We simply take some silicon tubing, or PEX tubing, and put two halves of a copper pipe we cut down center around the tubing and solder a wire to each. Now the capacitance of the two copper "plates" will change as the dielectric material changes in permittivity....
Given a capacitor with 2 dieletrics of different permittivity it acts like two caps wired in parallel, so it's very easy to pull out the dielectric of the silicon (which is also constant, and thus very easy to simply calibrate out if you dont want to remove it mathematically).
Thus, as the permittivity of the wort changes with SG we can measure it and get refractive index, and then also take a temp measurement as close as possibly to where the "sensor" is and then we can use the excel sheet equations to get our SG with a cheap sensor.
The cheapest way to measure the capacitance would be to wire the cap as the oscillator tuning cap for a digital counter chip, allowing us to get a different count given the same period of time as the capacitance changes... giving us a digital count directly proportional to the permittivity, and should have linear response as the frequency of the oscilator circuit is fairly linear as the cap changes, and the capacitance changes linearly with permittivity. (see http://en.wikipedia.org/wiki/Capacitance)
Thus, we simply calibrate the sensor to see what counts correspond to what SG at what temperature by backwards calculating the excel equations, and BAM we have a cheap working SG sensor for in line wort measurements, allowing us to automate our sparge! (assuming you can already control your pump speed (and thus sparge rate) with the controller you have)
Am I crazy or would this work?
.
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