Specific gravity transducer?

Spectre

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I've tried searching but haven't found a cheap solution for measuring specific gravity digitally. I have seen people determining their alcohol volume using a CO2 calibrated flow meter but they don't seem too readily available either.

I want something I can submerge in a demijohn or other fermenting vessel along with a thermistor or RTD for temperature so I can estimate alcohol content and see when fermentation has finished.


@MH, you know about process control and such :), have you seen anything small and cheap that works around 1.500 and lower?
 

MH

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To be honest I have not, but I do know brewery's still use the tried and trusted method of the hydrometer.
You will ideally be looking for a density meter, however as a guess most will be self contained units that go inline with the flow or measured on a per sample basis.
The process control part is easy, as its essentially apply heat until density equals x. I don't get involved in the actual instrumentation, just the highlevel stuff. Well I don't anymore as there are underlings for that now ;)

TT
 

Spectre

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Simple, effective and cheap. No need for anything more complicated.
I do have one :).

I fancied making a logger though it seems measuring the gravity electronically isn't trivial.
 

Him Her

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I do have one :).

I fancied making a logger though it seems measuring the gravity electronically isn't trivial.
Keep an eye on the BrewPi and BeerBug projects although I don't think there's anything in 'near-sight' yet!

In the meantime, unless you build it yourself, it's fermometer and hydrometer - you only use the hydrometer two or three times surely?

:)
 

Spectre

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Keep an eye on the BrewPi and BeerBug projects although I don't think there's anything in 'near-sight' yet!

In the meantime, unless you build it yourself, it's fermometer and hydrometer - you only use the hydrometer two or three times surely?

:)
I'd seen those but the details of the SG probes are somewhat sketchy. Not sure why BrewBit (another one) went with a thermocouple, that requires cold junction compensation. They could have used absolute devices like thermistors.

Once my major clean-up is done and I can actually sit at my workbenches I might have a closer look into this.

It's not a massive hardship getting the glassware out but I can't sit at work and look at temperatures and SG from a networked logger then :D.
 

MH

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I would like to see his PID controller in more detail in the BrewPi project. Little amazed that he is using the integral action though, as the expectation would be for a linear/predictable curve. Along with a positive and negative gain factor as I assume cooling v heating will NOT be equal.
 
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