Temperature Measurement

[dpnicol]

In one of the other forums here there was a question or two in relation thermometers etc. as I am suitably qualified in this area I replied. I thought it might be a good idea to post this information in the appropriate forum for all to see.

Different types of temperature measurement and their pro's and con's

Please find below the main body of text:

Firstly, NEVER use a "mercury in glass" thermometer ( stuff in glass appears silver ) for any food orientated work whatsoever. Repeat NEVER!

Whereas an alcohol filled thermometer ( usually red or blue dye ) is OK and actually often more accurate and more reliable over a long time than many digital thermometers. FACT. Most digital temperature systems involved with Quality Assurance systems ( ISO9001 and the like ) are required to be calibrated every 3 to 12 months, most "liquid in glass" thermometers merely verified ( checked ) every 3 to 6 years or more!

The "glass" that your thermometer is made out of, I would hope is probably "Pyrex" which is rather tough and quite reliable even when sitting on the bottom of a boiling wort. You would have to work extremely hard to damage a Pyrex thermometer by heat alone ( one for an oxy-torch ). Pyrex is much tougher than glass when it does come to shock and extremely tough when it comes to heat.

I actually prefer "liquid in glass" thermometers for these reasons:

1. You can easily see the rate of change as the liquid creeps up or down the glass
2. Pyrex is excellent when it comes to changes in chemistry, pH and temperature etc.
3. As the thermometer only senses at the bulb in the bottom ( or within a short distance of the bulb ), you can move it up and down in a wort and check the temperature gradient through the wort ( around 5 to 15 Deg C depending on the brew and size of the pot ). Digital thermometers do not do this as well as the metal sheath over the sensor slows down the response ( due to added mass ) but a "liquid in glass" thermometer will "chase" just fine.
4. Pyrex is food grade! not all digital thermometers are food grade, to be food grade it must be the appropriate grade of stainless steel i.e. 316 etc.

The other thing to watch is what type of sensor you digital thermometer uses. RTD's ( resistance temperature device/detector ) are the best, and the best of these is PT100 or Platinum 100 Ohm, they are reasonably stable and usually accurate to about 0.1 Deg C in the right application ( some even 0.01 deg C) .
Be aware of digital thermometers that use thermocouples ( T/Cs ) usually described by type: J, K, T or S etc. as these are much less accurate ( +/- around 2 Deg C ). I would not recommend using a thermocouple type at all unless you are able to calibrate the measuring device accurately.

At this point I am going to make an admission: I do have a digital system on my fermenter of all things but this system is not something most people can get easily and, even if they did they would have trouble justifying the $1000 for said temperature measurement system ( mine came free from an instrumentation company's sales dept. ! Really ). I use this +/- 0.01 Deg C instrument for seeing the rate of change in temperature of the fermenter purely so I can make decisions early in relation to ensuring I keep the temperature under control. I am not going to automated temperature control yet, but when I do - watch this space.

Back on subject

The other thing to watch with "liquid in glass" thermometers is that sometimes a little liquid can get stuck up the top of the glass, or a bubble may appear within the tube. The way to resolve this is to heat the thermometer up all the way along it's range ( very near the top of the tube but not quite the end - to avoid bursting the bulb ) then remove and gently settle into dry ice or even slowly lower in to liquid nitrogen ( i.e. stuff well below 0 Deg C ). This should suck all the liquid into the bulb.

Just in case you are wondering where I get my thermometers. It is simple: Laboratory suppliers ( sorry Danny, and other brewing equipment retailers ). You are always guaranteed they are accurate and the quality is excellent, you can even buy them in a "strip" of 5 or 10 etc.
Now look, even I broke a thermometer the other day ( I recommend every one carries a spare ) but as always, I broke it cleaning-up not brewing.

... but I still prefer them.

Now look if any one has any particular questions in relation to instruments for brewing feel free to ask.

 

[brettprevans]

since your qualified to comment...
how about commenting on 'dial/bi-metal thermometers' or other electric/digital type termometers? like this, this or this

they are no where near $1000 and do the job fine. so im interested in your comments.

edit: good reminder for newbies about mercury thermometers

 

[QldKev]

If you could provide feedback on the other thermometers it would be great.

I BIAB and have 3 vessles I use, 2 x singles and 1 x double size. I have been using a floating electronic thermometer but recently have not had much luck with them; dying from moisture.

So for me I want something that wont get in the way of the bag, and portable between pots.
I was thinking an electric controller and just hanging a water tight probe into the pot.

QldKev

 

[gjhansford]

Yes ... I have a question that I was pondering only on Saturday when I was using my 'red liquid in a glass tube' thermometer to check the temp of the mash.

I also have a fixed metal probe near the bottom of the mash tun with a dial gauge on the outside ... and there's always a bit of a difference between the reading on the dial and the reading on the tube. Can be as much as 5 degrees (with the dial always the low one) which is quite a concern ... the dial says the mash is at 64 degrees but the thermometer says 68-69 degrees! Not good!!

When submerging the tube thermometer into the mash I get an increase in the reading. When I just immerse the bulb I get one reading (of the mash at the top) but when I immerse more of the tube the reading goes up. Does this mean the temperature of the mash is higher at the bottom (I don't add any external heat) or does it mean that the liquid in the thin part of the tube (above the bulb) is also expanding and giving me a high reading when I lower the bulb?

Your post seems to suggest that that's not the case ... which means my probe/dial unit needs recalibrating ... how do I do that?

Thanks for sharing your experience and knowledge ... :icon_cheers:

 

[brettprevans]

if you have a bimetal dial thermometer there should be a little screw type thing at the back that a screw driver will fit into. that will adjust the position of the indicator. use that and another thermometer to calibrate.

I used a digital stick thermometer and a 'red liquid in a glass tube' cooking thermometer to calibrate my bi-metal thermometer. used near boiling water and cold water. seems to have done the trick

 

[dpnicol]

since your qualified to comment...
how about commenting on 'dial/bi-metal thermometers' or other electric/digital type termometers? like this, this or this

they are no where near $1000 and do the job fine. so im interested in your comments.

edit: good reminder for newbies about mercury thermometers

OK, firstly I am not going to knock "Craftbrewer" and their gear, craftbrewer make quality equipment at a good price - end of story.

However, the Bi-metallic thermometer you placed the link for is excellent, as a guide. The downfalls of these devices are:

1. Zero only adjustment ( i.e. "offset" adjustment ), no Span or Linearity adjustments.
2. Should be mounted in what is called a thermowell which is basically a sealed tube which is designed to contact the very end of the element ( rod - looking part )
3. Are quite exposed to the elements which, in the case of boiling a brew can be awfully steamy and sticky type stuff ! Even though they look sealed, they often aren't.
4. 304 Stainless steel ... not what I'd like for food grade. I'd prefer 316SS. But, in the retailer's defence, these measuring devices are meant to be installed in a thermowell which, will be made of the appropriate material, but unfortunately add mass to the measuring point ( slows down and/or delays readings )
5. The stated accuracy of the device is +/- 1% FSD which means that the reading has confidence level of around 2 Deg C. Keep that one in mind.

Look these are still usable devices, but if you really want to nail a particular temperature for mashing I would recommend using the "Dial Indicator" to get you close, then use a "liquid in glass" manually at various depths to be precise. Problem solved.

2nd link

Micro-controller

These type of units are generally quite good, but to nail that temperature I would recommend moving away from NTC sensors and go for PT100 ( they rock and p.s. have you ever heard of platinum "rusting" - I think not ). I would also recommend "calibrating" the whole unit this as I will post this arvo ( soz, gotta order Turkey and ham for wife and I for chrissie, and put on 2 brews: 1 x sima and 1 x mellow mexicana ).
The other thing to watch with these controllers is: they really should be installed and maintained by suitably qualified electrical worker as the unit you linked to is 240VAC supply. To avoid this you can actually get ones that will work on 24VDC and the like ( a lot safer for the home brewer ). Also look through the instruction manual and see if you can calibrate the input i.e. change type of sensor and even apply offsets/adjustments.

Finally the Infra-red thermometer

Benefits are that these units are quite stable over time but seem to have problems in my experience over the last half of the battery life, run one off an external supply if possible ?
Apart from this keep in mind that the error may be 1% of range but the range might 0-1000 Deg C ! which equates to 10 Deg C ! Be careful, once again I would use it as a guide, and once again I will probably rely on my good 'ol "liquid in glass" thermometer, but that's me.

Sometimes simple really is better after-all

 

[brettprevans]

great info man.

glad ive got my dial themometer in a thermowell.
my 'micro controller' is only controlling hlt so thats not too bad if my waters a few degrees off.

completely agree with mash temp issue though. i might keep this in mind and upgrade at some stage.

another problem is that you'll get uneven temp distribution in the tun so a 'liquid in glass' thermometer might not completely accurate. i guess thats what you were talking baout when you said to use a couple of peices of equipment.

 

[dpnicol]

Yes ... I have a question that I was pondering only on Saturday when I was using my 'red liquid in a glass tube' thermometer to check the temp of the mash.

I also have a fixed metal probe near the bottom of the mash tun with a dial gauge on the outside ... and there's always a bit of a difference between the reading on the dial and the reading on the tube. Can be as much as 5 degrees (with the dial always the low one) which is quite a concern ... the dial says the mash is at 64 degrees but the thermometer says 68-69 degrees! Not good!!

When submerging the tube thermometer into the mash I get an increase in the reading. When I just immerse the bulb I get one reading (of the mash at the top) but when I immerse more of the tube the reading goes up. Does this mean the temperature of the mash is higher at the bottom (I don't add any external heat) or does it mean that the liquid in the thin part of the tube (above the bulb) is also expanding and giving me a high reading when I lower the bulb?

Your post seems to suggest that that's not the case ... which means my probe/dial unit needs recalibrating ... how do I do that?

Thanks for sharing your experience and knowledge ... :icon_cheers:

Firstly G'day to TBA my birthplace! I betcha it's cooler there than where I am in Brissie.

It's completely normal to get a difference between the top and bottom of the vessel in which you are boiling, here's a few tips.

Most glass thermometers have what is called an immersion depth etc. on my thermometers ( Brannan U.K. -10 to +110 Deg C ) this is 76mm ( etched on back ) so effectively if you have the first 76mm of the thermometer in liquid you should be reading about right.

Temperature effects on the materials is negligible ( expansion or contraction of pyrex etc. ), in fact that's why pyrex and alcohol are used.

To measure the very top temperature lay the thermometer over on it's side so the nominal 76mm is still wet ( this should allow you to measure about 20mm below the surface and still read the graduations ). Your thermometer is reading the right temperatures as it goes further down in the wort, this is normal due to the heat at the base.

Last but not least, calibration...

There are a few standards and most of them involve water.

Most common is an ice slurry ( water and ice ) should be around 0 Deg C within 0.25 Deg C use this and check with your glass thermometer to check, record the result.
Second most common is boiling water, once again within about 0.5 Deg C of 100 Deg C, interestingly, being at Toowoomba you might have to go with about 99.8 degrees due to your altitude ( One reason why there is no such thing as a good cuppa at K2 basecamp - so I've been told ), record this as well.
Now one thing I would do is do your best to make up a 50 Deg C pot ( maybe in a small esky ) to calibrate in as this will be the most important region for your protein rests, and once again record the figure.
Note: the best way to do this is with three pots, each with the different temperature water in it, and ensure you really give the dial thermometer time to settle ( >5 Mins ), also give it a bit of a "flick" or tiny tap with the finger to remove any friction from the movement prior to taking a reading or making an adjustment, and after making an adjustment.
Now, if you are lucky the figures will just be what one would call a "zero" error or offset, i.e. the three points will read say +2, +52 and +102 respectively, in which case you only have to adjust the little screw in the back as previously mentioned, however if you have a "span" error such as -2, +50 and +102, then you might have to compromise your adjustment to where you want the instrument to be accurate. That is, adjust for 50 Deg C, which in this case would still be -2, +50 and +102 Deg C. If however you are unlucky enough to have a linearity error then you might be looking at something like 0, 55 and 100 Deg C then I would either run off a graph of errors or replace the instrument ( In more expensive instruments all of these adjustments may be present ).
Oh, and one other thing, whenever you buy a temperature device, check it against the water or some reliable standard, you would be surprised how often new gear can have errors out of the box!

 

[dpnicol]

If you could provide feedback on the other thermometers it would be great.

I BIAB and have 3 vessles I use, 2 x singles and 1 x double size. I have been using a floating electronic thermometer but recently have not had much luck with them; dying from moisture.

So for me I want something that wont get in the way of the bag, and portable between pots.
I was thinking an electric controller and just hanging a water tight probe into the pot.

QldKev

OK, I reckon I can help with this but firstly, unfortunately, pardon my ignorance, but what is BIAB ? Yes, it's ok to laugh.

 

[Online Brewing Supplies]

I wonder why we dont see brewers running around micro's with little red bulb jobbies ? I guess they are only practicable on 20l brew's where you can push it in a few cm. Oh and I have seen them explode before hey PP :huh: I have found my fixed temp sensors (Dallas) to be very accurate.
GB

 

[alexbrand]

Hey folks,
just to widen the list of possible thermometers.

I prefer the (digital) DS18S20 (or similar) from Maxim-IC. They're accurate enough for us homebrewers. Those of us which know on wich side site the soldering iron is safe to touch can build their own circuits to read the thermometer or even take action at certain readings (such als relays).

Cheers,

Alex

PS: For my fermentig and lagering fridge the PT100 is good enough.

 

[dpnicol]

I wonder why we dont see brewers running around micro's with little red bulb jobbies ? I guess they are only practicable on 20l brew's where you can push it in a few cm. Oh and I have seen them explode before hey PP :huh: I have found my fixed temp sensors (Dallas) to be very accurate.
GB

The Hanna pH and temperature gear you sell is second to none, and I believe the best bang for the buck, about time I saw brewing equipment retailers selling lab quality gear, there may be a purchase or two coming your way... do you also sell buffer capsules and / or solutions for calibration of the pH probes?

 

[Stubbie]

Excellent info. I particularly like the advice on how to remove air bubbles. There's 2 retired Brennan 110 deg C glass thermometers in my drawer, hoping that some day I'd come across some info on how to correct the problem. FWIW - one I dropped, the other I left upside down for too long.

Will try CTB's fix later on tonight.

Stubbie.

 

[Online Brewing Supplies]

The Hanna pH and temperature gear you sell is second to none, and I believe the best bang for the buck, about time I saw brewing equipment retailers selling lab quality gear, there may be a purchase or two coming your way... do you also sell buffer capsules and / or solutions for calibration of the pH probes?

Coming from a brewing science background I also though it was time to bring in some professional quality lab gear for the Micro and craftbrewers.There is more gear on the way including calibration satchels etc , but things are a bit slow for deliveries being close to Chrissie , thats why I offer to condition (the probe) and calibrate any of the units before shipping. I have got a really cool pH Data logger coming real soon which you connect to your PC and in theory you can log the pH all the way through the brewing and fermenting stages. Ive got to have a play with this, sounds like my idea of fun .
GB

 

[Zwickel]

....snip.... I have got a really cool pH Data logger coming real soon which you connect to your PC and in theory you can log the pH all the way through the brewing and fermenting stages. Ive got to have a play with this, sounds like my idea of fun .
GB

Personally Ill come over to pick up one of these toys :icon_cheers:

 

[Online Brewing Supplies]

Personally Ill come over to pick up one of these toys :icon_cheers:

Graphs and settable temp compensations all on a full size screen, we could have a ball ! I have wanted to log pH and its affect on flocculation of different yeast strains, this is the toy to do it with. I have read that yeast use pH as an "indicator "(for want of a better word) on when they flocculate.Mate its turned summer here and you would love it

GB

 

[dpnicol]

I wonder why we dont see brewers running around micro's with little red bulb jobbies ? I guess they are only practicable on 20l brew's where you can push it in a few cm. Oh and I have seen them explode before hey PP :huh: I have found my fixed temp sensors (Dallas) to be very accurate.
GB

If I was running a micro this is what I would use to control it ...

http://www.yokogawa.com/dcs/centumvp/dcs-v...-en.htm?ID=prvp


Just in case anyone is interested, not cheap, but it kicks!

 

[Damian44]

conon_the_beerbarian i was wondering what your thoughts are on these. http://www.hannacan.com/fiches_techniques/...98509-98510.pdf

They have a calabration test built in. Mine says its out by .1.

TYVM Damian

 

[dpnicol]

conon_the_beerbarian i was wondering what your thoughts are on these. http://www.hannacan.com/fiches_techniques/...98509-98510.pdf

They have a calabration test built in. Mine says its out by .1.

TYVM Damian

Yeah,it looks ok, I reckon there would be adjustments inside. probably one marked Z (zero) and another marked S (span), please note: I will take no responsibility for you breaking your thermometer ! :unsure:

Here is all the manual I could find for it:
http://www.hannainst.com/manuals/manHI_98509_98510.pdf

Personally I would still check it at around 0, 50 and 100 Deg C. So easy and so much confidence. :icon_cheers:

 

[katzke]

I wonder why we dont see brewers running around micro's with little red bulb jobbies ? I guess they are only practicable on 20l brew's where you can push it in a few cm. Oh and I have seen them explode before hey PP :huh: I have found my fixed temp sensors (Dallas) to be very accurate.
GB

I use a glass stick with a stainless sheath because when my dial was found to be wonky I called the local micro and they use the glass stick with a stainless sheath. Not sure what their barrel capacity is but they are not the big boy in the next town that is the number 13 craft brewer in the USA. I am sure it would be hard for Deschutes to use a stick thermometer in their big brewhouse/factory but I bet they have stick lab thermometers in the lab for test work. But most micros do not have full labs and quality control chemists. I have also found that not all micros take a scientific approach to brewing. One reason why a beer will be great one batch and the next time you go to the pub it is not as memorable. Some of them are always fooling around with the recipe, and not in a good way. I am sure some home brewers have better process control then the average micro uses.

One thing I like about my glass thermometer is I never have to give it a flick to see if it is reading correct. Also every time I have checked it it is spot one. Maybe that is why they do not have to put little screws on the back to adjust it all the time.