Hydrometer calibration changing over time?

[501irishred]

Anyone had a hydrometer fall out of calibration? I noticed the last couple batches finishing a little higher than expected, so I double checked the last one with a second (and finally a third) hydrometer only to find out that my "primary" hydrometer was off by .003. Not a huge deal, but I go through great pains to check out newly purchased hydrometers and I KNOW this one was on the money ~6 months ago. Verified offset with distilled water at 60 deg...suspicion comfirmed...

 

[progmac]

i once had a hydrometer that developed what i think was a small hairline crack. everything was off by about 0.01

 

[501irishred]

i once had a hydrometer that developed what i think was a small hairline crack. everything was off by about 0.01

Yea, I expected to find a crack of some kind, but it is still solid as a rock...

 

[ChuckO]

Did the paper scale shift? Most of them that I've seen are just held in place by friction to the glass.

 

[Stevo2569]

Did the paper scale shift? Most of them that I've seen are just held in place by friction to the glass.

This has happens to one of mine. I made a mark on the last one to verify whether it has moved or not.

 

[501irishred]

Definitely can't rule that out. Good idea adding the marks at least for a sanity check!

 

[hanson95]

I just noticed my hydrometer changed. I calibrated it (or rather, checked it's accuracy) with distilled water when I bought it - .003 low. Now, about 6 months later, I checked it again and it's .009 too high! It changed by .012 I didn't think to check the paper movement, but when I get home I'll see if I can get it to move by shaking it...

 

[firerat]

Did the paper scale shift? Most of them that I've seen are just held in place by friction to the glass.

I can't think of any other way a weighted floating piece of glass would go out of calibration.

 

[passedpawn]

Note that even when they read correctly at 1.000, they can still be off at the high end. You should do a 2-point calibration check.

I had 3 hydrometers and one of them had this linearity issue. It was easy to verify against the other two, as well as a refractometer. It was close to 10 points off at 1.100

 

[hanson95]

I can't think of any other way a weighted floating piece of glass would go out of calibration.

Good point. Although I wonder if something changed with my distilled water? I bought it and used it for the first calibration several months ago, then stored some of it in a grolsch bottle. Could the distilled water properties have changed?

 

[501irishred]

Note that even when they read correctly at 1.000, they can still be off at the high end. You should do a 2-point calibration check.

I had 3 hydrometers and one of them had this linearity issue. It was easy to verify against the other two, as well as a refractometer. It was close to 10 points off at 1.100

Interesting. Never even crossed my mind to calibrate at the high end......

 

[501irishred]

Good point. Although I wonder if something changed with my distilled water? I bought it and used it for the first calibration several months ago, then stored some of it in a grolsch bottle. Could the distilled water properties have changed?

I would think the only way it would have changed is if the bottle had residual sugars (beer) left in it before adding the water. Did you use the same thermometer for your comparison?
Other than that, you could do like I've done and simply blame it on the gremlins....