Temperature calibration

[Lutefisk]

I know that the Neptune controllers are supposed to be calibrated to NIST standards but when my new AC III keeps reading higher than any other thermometer I didn't know who to trust.

So, I did some testing which brought up some other questions.

The first thing I did was to test all my thermometers to ice water. I mixed a little water with ice chips in an insulated and stirred for quite awhile as all the temperature readings stablized. Here is what I found.

32 Deg. F. - Aqualogic single-stage temperature controller - (Does not display fractional degrees)
31 Deg. F. - Omron industrial temperature controller - (Does not display fractional degrees)
32.0 Deg. F. - Radio Shack Indoor/Outdoor thermometer - .
31.9 Deg. F. - Brand X Indoor/Outdoor thermometer -
43.8 Deg. F. - AC III - (What is this all about? :eek1: )
*** - Aquadyne Octopus - slowly approached 32.0 at which point it went "<<<<" so it apparently blanks out once it reaches 32 Deg. F.

It is strange that the Aqua Controller appears to get lost as the temperatures drop.

I considered calibrating to boiling RO/DI water but didn't want to damage any of the instruments (I'm at about 50 feet above sea level so its pretty easy)

For my next test I placed all the probes submerged to the same level into the same overflow at the same time.

82 - Aqualogic -
82 - Omron -
82.0 - Radio Shack -
81.8 - Octopus -
83.9 - Aqua Controller III -

(They don't always agree as closely as this last set of readings but all of them other than the AC III stay in pretty close agreement)

So, my question now is which to trust?

 

[IsaaX]

Mine was off 2.4 degrees. I used 3 different digital thermometers that all displayed the same exact temp with fraction. I just recalibrated my AC Probe to that.

 

[clp]

As far as the ice bath temperature compensation, I do not recommend it. First it is way outside the calibate temperature range of the controller (min is 50F), and it is about 50 degrees away from the temperature range of interest.
Our controller's are calibrated against a NIST traceable temperature probe, and should be +- 0.5 when shipped. If the offset is accidently changed by user error, init memory, etc. then it will no longer be calibrated to the NIST standard. Perhaps that is what happended on your controller.

Curt

 

[Lutefisk]

Hmmmmm,

I hadn't touched to temperature calibration function on it. If is the reason then it must have happened somewhere on its way to me.

 

[UCanDoIt]

I had the same problem. I have a Won Brothers titanium heater with digital display, 2 different digital thermometers and my sump temp read 79.0-79.2, while the AC Jr read 81.1. I just adjusted the AC Jr down 2 degrees and now everything matches, all the time.