Fermentation Temps

[thantos]

Hey all,
So I bought a new digital Ranco ETC unit for my ferm chamber. My old unit was an old Johnson analog with a capillary tube, it finally quit working. So my question is, now that I have a digital readout, how accurate is it?

I have thermometer tape on my carboys, a calibrated dial thermometer, and the Ranco all with different readings.

Is the thermometer tape reading higher because it is in direct contact with the glass, and the Ranco probe is suspended over the carboy and reading more of an ambient condition?

Ranco is set at 62deg. with a 2deg. split to come on at 64deg.

Dial thermometer is reading right at 68-69deg.

Thermometer tape is at 72deg. on the Scotch ale in active primary fermentation.

Thermometer tape is at 68deg. on the Stout in secondary fermentation.

Am I being to picky and worrying about nothing?

Or should I get a thermometer well and insert the probe of my Ranco into the active carboy and go by that temp?

Thanks, Gene

Sorry for the crappy pics!

 

[giraffe]

First off those stick on thermometers are rarely accurate. Ignore that one.
Then stick the temp probe and the dial thermometer in a glass of water. Make sure they read the same temp. (You said calibrated, so I assume the dial reads ice water at 32F)
If they read both the same, then its just ambient vs a liquid. The fermenter when actively fermenting will be a few degrees above ambient. If you are measuring ambient to set fermentation temp, you will need to figure out a fudge factor for your system and set the controller a few degrees lower than the target temp.

 

[flars]

Tape the Ranco probe to the side of the carboy. Insulate it so it can't showed a temperature reading skewed by the ambient air temperature. The fermometer strips have been tested by brewers with accurate thermometers inside thermowells. The strips have recorded temperatures within 1°F of the thermowell thermometers.

Measuring the temperature of an actively fermenting wort, with the temperature probe in contact (more or less) with the wort will be more accurate than adjusting the ambient temperature, as the fermentation progresses.

Here is a link to Thermoworks on calibrating a thermometer/probes. the trick for measuring 32°F is using crushed ice.
http://www.thermoworks.com/pdf/user_manuals/Thermapens/Thermapen_Splash_Proof_Calibration.pdf