How do you calibrate a Johnson digital A419 controller...

[Beavdowg]

I'm out of beer in my keezer so I decided to use it as a fermentation chamber on a batch I just brewed last night. I have it set at 65*F and that is what it is currently reading. I thought I'd check it against my digital thermometer that I just calibrated yesterday and the Johnson controller is about 3* too high. My thermometer read 62* while the Johnson read 65*. How can I calibrate the Johnson controller so it's reading accurately?

thanks

 

[Beavdowg]

Anyone, anyone?

 

[Brewsncrabs]

Not sure if you can other than "lie" to it and adjust to compensate. If you're not using a thermowell you may be off more than you think. Is the probe just dangling in the air?

 

[Beavdowg]

Yes, I just have the Johnson probe dangling in the keezer. I had no idea these can be off that much, I just assumed they were more accurate. Do you know how to calibrate it?

 

[Brewsncrabs]

I'll read the manual when I get home. I bet your problem is because its dangling in the air. Put it in a thermowell.

 

[Beavdowg]

I guess I don't understand why there would be any significant difference in the temperature readings of the Johnson controller vs. my digital thermometer. Both of them were reading the air inside the keezer. I could understand if one was inside a thermowell but if they're both sitting in the same "medium", in this case air, I should get similar readings.

 

[GilSwillBasementBrews]

The probe just dangling in air will be more susceptible to temp swings as the air in the fridge cools and heats during its normal cycling. You should either submerge the temp probe in a container if water or thermowell in the fermenter or I've read people taping it to their fermenter with a bit of insulation on the outside to get closer to the liquid temp as possible. The liquid temp will be more consistent than the temp of the air.

 

[Beavdowg]

GilSwill,

I understand what you're saying but my point is that the temperature of the Johnson controller was not the same as the temperature of my digital thermometer and they were both sitting in the air of the keezer. I left my thermometer in there for 10-20 seconds with the door closed before I read the temp. Shouldn't the controller read the same temp as my thermometer if they're both sitting in the air of the keezer?

 

[Barnesie]

Did you try checking calibration on the Johnson by using freezing water as well? What I'd be doing is calibrating both in the same solution at the same time to be sure you actually have a variance, otherwise I'd assume you're seeing possible temperature swings from a more accurate/rapid measurement on one and not the other.