Calibrating Temps

[imakewort]

whats the best way to calibrate temperature controllers?

i've been taking some samples out of my fermenters lately and questioning the thermometer verses the controller temps.
same goes for my hot liq. and kettle.

i could just calibrate them using a "trusted" thermometer right?
cool or heat some water, test, compare, calibrate

what about with the fermenters? the 70-35F temperature range is more crucial obviously. my sample ports are 6-10" above the top of the cone whereas the thermocouple housing is an inch or two below the top of the cone.

seems like a simple thing but just checking if there is a proper way.
i am sure this hasn't been tested at in my brewery for years.
(also need to fill thermocouple wells with conductive putty to help)

[gitchegumee]

Your controllers are likely to use thermocouples--a twisted pair of wires in the thermowell--or a thermistor or RTD. These sensors don't require calibrations. Dial thermometers are a different story. The typical protocol for dial thermometer calibration is to boil pure water & set the temperature to 100C/212F. Likewise, an ice bath is used to set the temperature to 0C/32F. Depending on location, you may have to consider altitude adjustments. Good luck!

[Moonlight]

It is very common for there to be multiple temperatures in the same tank. Just because a thermometer or thermostat reads a certain temp, and even it is freshly calibrated, you cannot always assume the entire tank is uniform. Only the temp at that exact spot is what is you can believe. Placement of cooling jacket(s) can or does create convection flows and dead zones. I recently installed a new fermenter and only used one of the cooling jackets at first. The top of the tank fermented perhaps 10 degrees F warmer than the lower third where the active jacket was.
This is one reason why different fermenters will give different performance and/or taste.

[imakewort]

my sensors are thermistors in a stainless steel shell.
so you are saying they set themselves? you just trust the temp they are displaying?
why would the controllers have a calibration setting on them?

[gitchegumee]

I've never seen a digital controller with a calibration function. That doesn't mean it doesn't exist, but I guess would be sorta rare. Unless you refer to the PID self-tune feature that relates to the response of your control algorithm. This isn't used in small breweries as our mode of cooling is on-off via a solenoid. What controllers are you using? Can you refer to the manufacturer's literature? There are ways to calibrate thermistors, but they are most usually done by the manufacturer and left with this internal calibration for the life of the instrument. On the other hand, as long as your fermentations are consistent, does it really matter what the exact temperature is? I "calibrate" my fermentations based on taste. As Moonlight pointed out, many other factors are at play during fermentation and even with perfect temperature control you may have other more flavor-important variables that aren't monitored. Sorry I can't be of more help. Good luck!

[imakewort]

controllers are Eliwell EWPC 902s.
found a link to the manual but it just says it has a calibration setting for adjustment and that its set at 0 at the factory.

i was just thinking i could test it with an ice bath and boiling water but that seems to be the extremes and beer isn't really gonna hit those extremes.?.

[matt]

Eliwell... Maybe one of the better temp. controllers from Italy.
They use different probes, NTC, PTC(thermistors), PT 100(RTD),.... If you look on top of your controllers, they should tell you which ones they are set up for.

If you go into the programing mode for the controller, there is a setting, CA1,(you model may differ) which I believe they refer to as some sort of "calibration" Which is not actual a calibration. As mentioned before, there is no calibration for the thermistor probes, but an Offset setting to correct the difference in the digital readout and the actual temperature. The difference can be caused by a number of things, drift, length of cable between probe and controller, the probe itself, etc.

Most of the ones I have seen, used, use a 2 wire thermistor probe and have a tendency to drift over a period of time. If possible, when changing out probes, it may be worth the time and money to go to 3 or 4 wire PT100s(RTDs) for better performance.

As far as checking the temperature, I believe it would be better to have a calibrated thermometre and check the temperature in the same place as the probe.(i.e. In the thermowell)

Hope this helps.