Temp probe fluctuation

[SirJoshuaIV]

I finally got around to changing over my gas system to electric the other day. After some struggles with faulty SSR's in my panel, I finally have everything up and running. All seems to be working greatly, with one exception.

At or near a rolling boil my temperature probes jump around greatly. I live at a high elevation so my boiling point is a bit low, coming in just a hair over 208. Just prior to reaching a boil my temp reading will jump around ranging from 202 to 206, up and down constantly. When I reach a rolling boil it will fluctuate up and down from 208 down to 203, but rarely above 206. The boil will be so vigorous that it will be shaking the keggle, yet the probe wont read a steady temp. I have the same issue in both my boil kettle and HLT. Any ideas? My dial thermometers read constant.

System details:
3 vessel system. 2 converted kegs, one 15 gallon stainless kettle.
5500 element in BK and HLT
BCS-460 Controlled
6 inch BCS Temp Probes in all vessels, located 4 inches above elements and perpendicular to them.

 

[lesw]

I had a similar problem that I solved by hooking up a pump and having continuos wort circulation. Same in the HLT. There are hot spots in the pots and the pumps smoothest them out. My RTD probes are positioned same as yours and I was really surprised by the temp difference in just inches horizontal and vertical. Give it a try.

 

[BadNewsBrewery]

I could understand the fluctuations in the HLT being fixed with a pump - I recirculate my HLT and get steady temps. The boil kettle, especially during a rolling boil, should have PLENTY of mixing action taking place within the kettle.

That being said, I have no thoughts on what would be causing the issues with your temperature readings. I get a pretty steady 211* read out during my boils... Is there a way to adjust the sampling speed within the PID? I could see there being minor changes, or steam bubbles hitting the RTD and a higher-than-needed sampling rate might pick up those fluctuations and try to display them. If you sampled at a lower rate, it would smooth that out - sort of like your analog thermometer.

-Kevin

 

[SirJoshuaIV]

The problem seems to be worse when the boil is more vigorous. Really, this is not an issue of any kind because the boil is intense, and controllable. The temp reading of it is not much of a concern.

However, with that being said I did brew a batch of an imperial amber rye ale today. 10 gallons in total. I tried recirculating everything via my march pumps and I had the same issue with the readings. I think I will buy some new temp probes. Any recommendations? What temp probes do you have kevin?

 

[alien]

Boiling point will vary with the local air pressure which changes from day to day. I wouldn't sweat a couple of °C.

To measure the boiling point accurately, set up a thermometer over the liquid. It will show the correct boiling point when there is water condensing on the bulb/probe.

You don't have to worry about mixing in a boiling liquid unless it is extremely viscous. If it is not up to temperature throughout, it won't boil - steam rising through the liquid will condense in any cold patches.

 

[BadNewsBrewery]

I use the liquidtight RTDs available from Auber - http://www.auberins.com/index.php?main_page=index&cPath=20_15 - they sell them in various lengths. I think the one in my BK is a 4" model?