Temp Probe/thermometer "hotspot"

[lonte]

OK, possibly a stupid question but I'll throw myself under the bus ...

For temperature probes and Thermometers with stems, is there a particular spot on the stem where the termperature is read? Or is it averaged across the length?

If you think of a 6" stem in the side of a MT it's quite likely that the tip (in the centre of the tun) is warmer than the edge (nearer the top of the stem).

Thoughts?

L.

 

[Adamt]

The probe has higher thermal conductivity than the mash, so the temperature range over the length of the probe will be small compared to the gradient in the mash (if that makes sense at all?). Unless there is a massive hotspot in the mash that the probe only half-penetrates, any discrepencies will be well within the measurement tolerance anyway.

 

[mr_tyreman]

i have a small coffee style thermometer, and i have found a big difference in temps based on how much of the probe is immersed into a liquid.

say its sitting in a 1L jug with 200ml of water in it, if its upright so only about 2.5cm of the probe covered it will show up to 10 degree variation, compared to the jug on its side and the probe fully immersed.

 

[seravitae]

+1 on thermal conductance with temp probes.

With 'sheathed' probes, the temperature difference across the probe is generally very small, and seeing as the actual probe element (thermocouple junction, or NTC resistor) is quite small, the probe actually smoothes out temperature.



However this is not the case for your standard glass-style thermometers. As they are not electronic, they rely on temperature difference at the bulb to push solvent up. If you immerse the thermometer more than what is expected, the temperature of the solvent up the stem will not equilibrate with the air gap above it, and give a false high reading, in my opinion..



More likely you'll see temp fluctuations where you put your probe in the mash/wash, rather than across the probe itself. Where you place your probe is ultimately up to you, however in HERMS/RIMS setups people generally suggest you put the probe close to the output stream of the wort as this is where the maximum temperature of the wort is likely to be.