How to get that elusive 68 degrees

[bobwysiwyg]

I also have the Harbor Freight IR unit, $19.95 as I recall and have determined it is accurate to within 1 degree at least. Couldn't you just point it at the liquid surface to determine temp?

 

[Paul Verizzo]

I also have the Harbor Freight IR unit, $19.95 as I recall and have determined it is accurate to within 1 degree at least. Couldn't you just point it at the liquid surface to determine temp?

That's what I do. My little cheapo unit has a wide 45 degree read pattern, so for some things you need to put it up real close or even right on the subject to be metered.

I do just what you suggest to confirm the water temperature for mixing chemicals, for instance. I was doing some fixer formula testing the other night and was using only 100ml. A typical darkroom thermometer would not have been usable. After mixing the hypo in, I put the beaker in the freezer to get it down to room temperature. The IR thermometer was easy and quick to check the diminshing temperature.

How did you confirm the accuracy of your unit?

 

[bobwysiwyg]

How did you confirm the accuracy of your unit?

I did it a couple of ways. One was against the house thermosat, the second using a therm. used to check temps of cooking items (electronic fork thing) which has a plug in probe and finally against a Davis weather station with a +/- one degree accuracy. Matched all three and figured that was good enough for me.

 

[Paul Verizzo]

I did it a couple of ways. One was against the house thermosat, the second using a therm. used to check temps of cooking items (electronic fork thing) which has a plug in probe and finally against a Davis weather station with a +/- one degree accuracy. Matched all three and figured that was good enough for me.

Great. Yeah, ultimately it's only critical on development and one should work the developing time to the thermometer, not the other way around.

I'm sure you realize that anything +/- 1 degree could be off as much as two degrees when you are dealing with two units. But, hey, we aren't doing qualitative analysis of biochems here.....

 

[bobwysiwyg]

You raised a couple of good points. First being my poor choice of words. Actually the Davis instrument claims accuracy 'within one degree.' All three displayed accuracy well within my humble needs.

 

[Paul Verizzo]

You raised a couple of good points. First being my poor choice of words. Actually the Davis instrument claims accuracy 'within one degree.' All three displayed accuracy well within my humble needs.

"Within one degree" is "+/- one degree" AFAIK.

But you are right, it's close enough for our kind of work.

For some very interesting observations on this matter and other things photograhic, go to http://www.geocities.com/ResearchTriangle/Thinktank/5693/photogra.html . You will have to scroll down for the "Thermometers: Unreliable assistants!" It does not have a stand alone URL.

 

[PhotoJim]

Accuracy "within one degree" is just one aspect of thermometers.

What about consistency?

If the same temperature could read at 19 one day and 21 the next, accuracy is still within one degree, but consistency is poor.

On the other hand, a thermometer that constantly read three degrees high, but was constant, would be a very useful tool.

Incidentally, which degree? Within 1 degree C is 80% worse than within one degree F.

 

[bobwysiwyg]

Paul, thanks for the link. Very interesting and again points out the fact that consistency and repeatability are the keys rather than absolutes.

 

[Paul Verizzo]

Accuracy "within one degree" is just one aspect of thermometers.

What about consistency?

If the same temperature could read at 19 one day and 21 the next, accuracy is still within one degree, but consistency is poor.

On the other hand, a thermometer that constantly read three degrees high, but was constant, would be a very useful tool.

Incidentally, which degree? Within 1 degree C is 80% worse than within one degree F.

My gut sense is that liquid filled thermometers would be very repeatable. Mechanical, like the famous 3" dial on a stem thermometers, probably not.