Incorrect Hydrometer Readings

[peteru]

Looks a lot like the hydrometer that Cooper's used to ship with their kits at the beginning of 21st century. Mine reads 1.000 in 20C tap water. A friend bought the same kit about a month after me and his hydrometer was reading 1.002.

I'd suggest that with such a big error, the most sensible option is replacement.

 

[MHB]

My local Lab Supply company sells certified hydrometers for less than $40. These are OK for paying excise and come with paperwork that says so, you can be fairly confident that they are going to be spot-on.
Lets not talk about cheep arsed Chinese thermometers, seen them out by 20oC, both ways - whole batch got returned and lesson learned - good instruments cost more but at least they can be trusted.
Mark

 

[n87]

My local Lab Supply company sells certified hydrometers for less than $40. These are OK for paying excise and come with paperwork that says so, you can be fairly confident that they are going to be spot-on.
Lets not talk about cheep arsed Chinese thermometers, seen them out by 20oC, both ways - whole batch got returned and lesson learned - good instruments cost more but at least they can be trusted.
Mark

Do these lab suppliers have a website?

My hydro measures accurate at 20C (+-0.001), but I have a niggleing feeling that it doesnt read completely true at higher gravities.

 

[Lyrebird_Cycles]

If you have a decent set of scales it's pretty easy to check by making up a 20 Brix sugar solution.

Bake some ordinary sugar in your oven for a few hours at low setting to make sure it's completely dry.

Dissolve 100 grams of sugar in 400 grams of warm tap water, being as accurate as you can be.

Bring the solution to 20 oC and use it to check your hydrometer: 20 Bx = 1.083.

 

[n87]

If you have a decent set of scales it's pretty easy to check by making up a 20 Brix sugar solution.

Bake some ordinary sugar in your oven for a few hours at low setting to make sure it's completely dry.

Dissolve 100 grams of sugar in 400 grams of warm tap water, being as accurate as you can be.

Bring the solution to 20 oC and use it to check your hydrometer: 20 Bx = 1.083.

Checking a second point on the scale has always been on the cards, however, it turns out that my brain subliminally tells me I could be brewing instead... so it never really gets done

 

[user 31093]

You're just going to have to throw it out and buy a gas chromatagraph

Why not an LC/MS series then

 

[Ducatiboy stu]

Why not an LC/MS series then

Bulk buy !

 

[Ducatiboy stu]

Its only the 0 point of measurement that is the issue...and its almost irrelevant

If it is .005 out, then just adjust. It will be .005 across the scale

And it wont matter for alc% measurment as that is just a straight out subtraction of 2 values. Wouldnt matter if it was .005 or.5 out you will get the same result.

And as for when the beer is finished, this is always done over a few days until FG is stable...


I mean you can be padantic, or you could just use the ******* thing

 

[n87]

If I knew the scale was correct, it would be fine.

The problem is that if the bulb is slightly bigger/smaller, the measurement part is wider/narrower or if there are any external imperfections, it can throw the scale off.

If they were all close enough for it not to make a difference on our scale... you wouldn't have one that is .005-.008 off at 0.

 

[Ducatiboy stu]

The problem is that if the bulb is slightly bigger/smaller, the measurement part is wider/narrower or if there are any external imperfections, it can throw the scale off.

How ?

 

[n87]

How ?

Different amount of liquid displaced changes how much it floats.

 

[Ducatiboy stu]

Wont matter on a single unit

 

[Rocker1986]

I recently discovered mine reads 0.002 lower than it should in 20C water. It was throwing my efficiency calcs out even though the ABV calcs wouldn't be affected. It's a bottom meniscus reading one, and I check it every couple of months just to make sure it's still consistent and so far it has been. This isn't a big enough issue for me to replace it, I simply add the .002 to every reading. It's a Stevenson Reeves one made in Scotland, had it about 3 years now I think.

I'd only consider replacing it if the inaccuracy of it was inconsistent and it kept reading varying levels too high or low every time I used it. But when it's consistently out by the same figure it's not really that hard to simply add or subtract that figure from the reading it gives.

 

[Lyrebird_Cycles]

How ?

Because the ratio of bulb diameter to stem diameter might be off, which in turn would affect the change in stem exposure length per unit density difference which is the scale factor for the hydrometer.

I can run you though the maths if you are interested.

 

[Ducatiboy stu]

Rub it with a kitten until you get the correct stem dia

 

[n87]

Wont matter on a single unit

My bad, I was under the impression that a hydrometer worked on the displacement of media.
I am obviously completely wrong judging by your single sentence explanations.

 

[Ducatiboy stu]

well it works on buoyancy

 

[Lyrebird_Cycles]

The equation for neutral bouyancy at the zero point is

M(bulb + stem) = ρ0 (Vbulb + Vstem0) , where Vstem0 is the volume of the stem up to the zero marking.

If density changes so the new density is ρ0 + Δρ the equilibrium will shift to

M(bulb + stem) = (ρ0 + Δρ) (Vbulb + Vstem0 - ΔVstem)

Where Vstem0 - ΔVstem is the new stem volume at the eqilibrium position.

The hydrometer is calibrated for a particular ratio of ΔVstem / Δρ which is a function of the total mass and the volumes of the bulb and the stem which are logically dependent on their diameters.

 

[MHB]

Nearly as much fun as the maths behind the old
Mark

 

[n87]

And I didn't even mention the ballast, one less lead shot and it's all off.