Sensor positioning

[Touchstone]

I've seen many posts about the position of the sensor in a fermenting fridge. I've tried it on the side of FV with insulation , hanging in free space , in a thermo well immersed in the wort all seemed to work equally well. So, I've installed a dial thermometer about half way up the FV , set my temp to 20c on the controller ,the sensor is hanging in free space at the side of FV and the dial indicated temp is smack on 20c. So it seems inside temp of fridge = temp of wort. Another point, I've read discussions about the yeast generating it's own heat , it may do but it doesn't seem apparent on my dial . What do you think ?

 

[mabrungard]

Fermentation does generate some heat. However given the large surface area of many fermentation vessels, there isn't a huge temperature differential between the beer and the surrounding air. So it's not surprising that you see little difference.

With that said, I prefer to keep the temperature sensor wedged tightly against my fermenter with a small block of foam insulation over it to help reduce the temperature fluctuation it sees and improve it's sensing of the fermentor temp.

 

[morethanworts]

Seconded!

 

[Touchstone]

Update on yeast generating heat. The brew has now almost finished it's ferment or is tailing off & the temp indicated on the thermo has dropped about 2c to 18c, so it seems that this was the temp that the yeast was generating . I've increased the controller temp to 21c

 

[Kevin Wood]

Positioning the sensor on or in the FV serves two purposes, IMHO:

1) Any heat generated by the brew will be picked up and this will avoid the FV heating above the ambient air temperature in the 'fridge

2) It adds a bit more thermal mass to the sensor, which reduces the tendency for the controller to cycle between heating and cooling as the air temperature inside the 'fridge inevitably responds quite rapidly to the heater coming on or external influences such as the door being opened. I find with the sensor in free air I have to increase the hysteresis on my PT1000 to 1 degree or more to avoid it cycling between heating and cooling. With the sensor taped to the FV it's fine at 0.5 Deg. C or less.

 

[PaulCa]

As I am using a hardware chip temp sensor I found some of these things can be programatically removed by using a sliding average temp window which removes spikes and fluctuations. That said, as I have wiring troubles with making the sensor remote to the breadboard, when I put it in the fridge attached to the complete breadboard the behaviour changed completely. All that thermal mass of the breadboard smooths it right out, although it also gives an indicated temp about 1C warmer than it actually is. Open the door and it takes about 5 seconds for the relay to respond and in my case bring on the cooler.

 

[peteoc]

I have 3 temp sensors - 1 in the FV, 1 in "free air" inside the brew fridge and one sat on top to get room temperature. I'm able to keep my fermentation within 0.1 degree constantly using all 3 sensors to calculate diffs and running times.

 

[morethanworts]

I have 3 temp sensors - 1 in the FV, 1 in "free air" inside the brew fridge and one sat on top to get room temperature. I'm able to keep my fermentation within 0.1 degree constantly using all 3 sensors to calculate diffs and running times.

That's just cheating, and spoils our usual fisty-cuffs about where the sensor should go! Mods, please remove the post for sheer smugness, and let's just all agree that it's better under a couple of layers of bubblewrap, half way up the FV. :thumb:

 

[peteoc]

just to rub it in even further, after reviewing the most recent data from the sensors I'm able to keep my temp within 0.06 of the required temp :) :

 

[morethanworts]

If you have a 4th sensor, I can think of somewhere for it! :shock:

 

[peteoc]

If you have a 4th sensor, I can think of somewhere for it! :shock:

haha - do you not think I'd have trouble with some sort of power supply? :P

 

[Touchstone]

Joking apart, it doesn't matter how many sensors you have or where you place them , you still don't know the actual temp of the wort unless a thermo is fitted. This was my problem before I started my experiment. I've increased temp to 21c , thermo now indicates 19.5c, with sensor in free space.

 

[peteoc]

Joking apart, it doesn't matter how many sensors you have or where you place them , you still don't know the actual temp of the wort unless a thermo is fitted. This was my problem before I started my experiment. I've increased temp to 21c , thermo now indicates 19.5c, with sensor in free space.

So you're saying I'm not currently aware of the temperature of my brew - even when a sensor is currently sat in the middle of the brew..... :wha:

 

[winelight]

I have 3 temp sensors - 1 in the FV, 1 in "free air" inside the brew fridge and one sat on top to get room temperature. I'm able to keep my fermentation within 0.1 degree constantly using all 3 sensors to calculate diffs and running times.

Would love to see some figures (graphs, even) showing how these vary/compare.

For example, what is the free air temperature doing while the wort stays within the 0.06?

 

[nobyipa]

Fermentation does generate some heat. However given the large surface area of many fermentation vessels, there isn't a huge temperature differential between the beer and the surrounding air. So it's not surprising that you see little difference.

With that said, I prefer to keep the temperature sensor wedged tightly against my fermenter with a small block of foam insulation over it to help reduce the temperature fluctuation it sees and improve it's sensing of the fermentor temp.

:thumb: same here the temperature of the wort and temperature difference can be worked out
what i did was get a fermenter full of water into my fridge then took temperature readings of the air temp the fermenting bucket temperature external and the actual water
so i know with the thickness of my fermenter and the probe on the fermenter under polystyrene the temperature difference is less than 0.6C


So if i want to ferment at say 18C I set the stc1000 to 17.4

 

[peteoc]

 

[Aleman]

It is so simple

Measure the temperature of what you are controlling . . . if you are controlling the fridge then measure the air temp, if you are controlling the wort measure the wort temp.

The issue comes in that air is a bad conductor of heat, so you need a fan to ensure that the heat is distributed. This will prevent swings in the air temp.


The thermal mass of 5 gallons of mostly water is also large and so if the thermal environment outside is at a constant temp then eventually the temp of the wort will be the same as the external temp. The issue comes when you want to change the temp (up or down) your fridge will stabilise quite quickly, but the wort will lag behind by several hours.

For this reason, I measure the fridge temp . . . and control that with an STC1000. That gives me a constant environment.

I also measure the temperature of the wort (again using an STC 1000) cooling being provided by a Maxi Chiller and a cooling coil in the wort, heating is via a heat belt attached to the base of the cone and insulated from the fridge.

I've not bothered to log the temp differences and swings in the two environments, but generally I see +/- 0.5C in the air temp and +/-0.1 to 0.2C in the wort temp. Obviously when running the STC's are set to the same temperature.

Once I've got some time to play, I will be coding a couple of Arduinos, and linking them to a RasPi for logging purposes.

 

[Wezzel]

Surely if you are going to be so anal as to stress over less than half a degree you need to treat your whole brewing process the same way.

For instance you would need to have Murphy's test every batch of water. Weigh your grain and check your water quantity, boil off rate etc. super accurately. Might as well factor in barometric pressure, ambient temperature and humidity too. Where will it end and can you taste the difference?

I brew to the "near enough as dammit" rule. I make good beer and don't stress about it. ;-)

 

[Aleman]

Temperatures . . especially fermentation temps have a huge effect on the yeast (and yeast provide up to 80% of the flavours in beer!!), so it is worthwhile being "anal" about them . . . although I would be more than happy with a +/- 1C swing about the set point.

One thing I've learned in over 30 years of work and brewing . . . Good Enough rarely ever is!

 

[morethanworts]

Nice graph. It would be interesting to see a similar graph plotting probe readings over a few hours while the temperature was raised and then lowered few degrees.

I think we are allowed to be a bit 'anal' sometimes - if we can't be on here, then when can we? It's good to exhaust all the avenues at least once (at least in the theory). That said, when I used to discuss audio-capture/recording on a specialist forum, there was a similar position (to Wezzel's) that went something like... "By the time you're recording in 96/24 quality, then there is no point going up to 192/24 until your mic leads are of supremely high quality." In other words, I would agree to some extent with Wezzel. If you're keeping your wort within 0.5C, then something else in your process is likely to have a greater effect on the quality of your beer than reducing that further.