Sight Glass Calibration

[Belter]

I'm sure this has been discussed at length in the past but I had a quick search and couldn't find anything.

I want to accurately calibrate my sight glass for my 100L HLT. I measured 500ml of water in a measuring jug and weighed it. It came in at 486g. I don't have large accurate scales that I can put the HLT on and I don't really want to measure 2L at a time. That is if my measuring jug is accurate. I assume my scales are out as they are cheap dunelm mill scales.

I want to stick the stickers I got from MrLard on and I only want to put them on once in the right place.


How did you do it?

[Fil]

OK another dumb Q on this .. as we are interested in water at strike and sparge temps, should we be calibrating at these temps too??
sorry Belter my Q is dumb not yours..
think your onto something validating your incremental measure as it its off at 1l by l50 the error is going to be exaggerated

[Hogarth]

Belter, I've always found scales more accurate than measuring jugs. One way to calibrate them is to use coins. You can find out how much they weigh on the web, then just bung a load on your scales and see if they measure up. Whenever I've done this I've been surprised at how accurate my scales are, even the cheapo one from China.

[Belter]

Cheers Hogarth I'll give that a try.

[Horatio]

I use this
http://www.regaltanks.co.uk/calculator/
Can work out what measurement in millimetres equals any given volume.

[Belter]

I tried pennies. My scales appear to be out my a Gram, but when I add more the difference increases.


@Horatio surely that relies on exact dimensions of your tank and for it to be entirely cylindrical... i.e no curve in at the bottom?

[Martin G]

Interesting point about the heat. Found this;

http://mobile.engineeringtoolbox.com/wa ... d_595.html

Looks like about 3% different at 80C. It is probably best to calibrate at 20C though as it is the cool volumes that matter in the end? Can make a correction for heat when required?

BTW if people work out boil evaporation loss based on a hot volume at start and cold volume at end then on a 25l batch it would account for about three quarters of a litre.

On calibration I think it is best to calibrate using as large a volume as the scales can manage first.

[Horatio]

I tried pennies. My scales appear to be out my a Gram, but when I add more the difference increases.


@Horatio surely that relies on exact dimensions of your tank and for it to be entirely cylindrical... i.e no curve in at the bottom?

Yes it does but as its my HLT I never worry about it. I always prepare more water than I need and always use a salifert test after adding CRS. I base the amount of CRS on the volume shown on my sight glass and it is bang on. In fairness I have weighed the water using digital scales before and even though you cannot guarantee the uniformity of the pot curves the weight when compared with my sight glass markings is spot on. I suppose each pot will vary though so good point.

[darkonnis]

Just calibrate at room temp.
If you want a quick way, put 10L in and mark it. Then fill the pot (with a known volume ie 80L) and mark that. Measure the difference with a ruler and break it down into 10L intervals and place your stickers, job done.
Water does expand as it is heated, and it is by more than you'd think. Realistically I'd not worry, as long as you do the same thing every time you'll not have a problem with things like repeatability.

[Belter]

I won't be doing the same brew length every time and want it to be pretty accurate. I'm going to try and get access to some large scales that will weigh say 120kg and mark every ten grams up to 100

[barneey]

I`ve gone down a slightly different route, calibraten the sightglass at say 20c, I`ve then placed a permanent set of scales under the MT and the boiler.

[darkonnis]

I was meaning that if you use the same scale every time and appreciate it might be a 100ml or so out you won't go far wrong if you ever decide to repeat a recipe

[Fil]

@Horatio surely that relies on exact dimensions of your tank and for it to be entirely cylindrical... i.e no curve in at the bottom?

isnt your hlt a 98l french pot? so apart from the bottom curve it is cylindrical. your gonna have some dead space.. so use the curved bottom bit as deadspace and pick up from above that point. ergo the volume used is stored in a cylinder... avoids lots of probs such as not having the sightglass low enough to read the last few litres out, and may even allow you to butcher a meter rule for graduations on your scale..

[Belter]

It is one of those. I hadn't thought about the dead space below the pickup as was going to put the pickup on the bottom. Saying that like you say the sight glass won't cover that as it isn't bottom draining.

[Fil]

Thats the bit im scratching my head over still, how to maximise the usefulness of the sightglass as whatever volume lies below the visible aspect of the tube is effectively dead-space, Or at best a known single drop volume of Xl and looking at the fittings i have already we are looking at a good 6cm up the pot side. thats over 10% of capacity??
My original plan was to level the drain pick up with the sightglass bottom so now im trying to figure out my maximum hlt volume demand as i may need to fit a second sump drain to dump the final Xl of deadspace.