Accurate digital thermometer for chemicals

[Bormental]

I have been looking for a DIGITAL thermometer suitable for C41 processing to supplement my accurate but hard-to-read spirit thermometer made by Paterson. B&H and the usual suspects don't really have anything. Amazon is full of $12 meat thermometers with crazy range and no accuracy specs, plus "lab" thermometers with a stated accuracy of 1C supplemented by customer photos showing inaccurate readings in iced water.

Does it exist?

I don't even care about accuracy that much. As long as I know what the delta is (or can calibrate it) vs my Paterson, I will be happy. What I care about is speed, consistency and reliability. The oral medical thermometer work really well (super accurate and fast enough) but it is designed to take a reading and then stop, which is annoying. I'm basically looking for the same thing, but with a continuous-mode measurement.

Thoughts?

 

[beemermark]

Nothing beats a real mercury thermometer- if you can find one

 

[grat]

Nothing beats a real mercury thermometer- if you can find one

You probably believe that the "normal" body temperature for humans is 98.6... a number arrived at by a doctor named Wunderlich in the 1800's. A doctor in the early 90's discovered that his patients, on average, ran 98.2 degrees, so he started investigating:

His "aha" moment came when he learned that one of Wunderlich’s thermometers was at the Mutter Museum, in Philadelphia. Tests showed that the thermometer, a mercury-filled glass instrument about nine inches long, ran 2.9 to 3.2 degrees higher than modern digital thermometers

A mercury thermometer, like a modern digital one, is entirely dependent on it's calibration. And modern thermometers aren't laced with heavy metals that are known to be seriously poisonous.

 

[Michael Teresko]

I found a used one of these for $20 on EB. Waterproof, works great.

 

[Deleted member 88956]

Sure there is, search for Termoprodukt DT-1and be sure to search for english site. I have it. It can be had with cal certificate too. High precision, fast response. I spoke about it some time back on this forum, so if you search it here it should come up too.

 

[AgX]

I found a used one of these for $20 on EB. Waterproof, works great.

Do not let you fool by that decimal. It does not tell anything on precision.

 

[AgX]

Cheapest great precision digital ones are digital medical stem-thermometers. (Over here you even get them with official calibration seal). (about 2.50€)
As with the fluid-stem medical thermometers their disadvantage is that they only show the maximum value. Thus one cannot follow a temperature gradient at blending water of different temperatures, but need to repeat in such case metering runs. And they only have a very limited temperature range. But as one would use such typically only with 100°F colour processes, that would not matter.

For a full range great precision digital thermometer you have to pay about one magnitude more. The cheapest here by far are the ones from Greisinger (about 80€).

 

[bdial]

a general-use kitchen thermometer should be fine. There are some which can be calibrated by putting it in an ice water bath.

 

[AgX]

Putting a thermometer of unknown origin in ice-water does not tell you much about 100°F.
Furthermore a generic kitchen thermometer does not even yield the resolution needed to comply for coulour processing industry standard.

The OP is explicetely asking for thermometers with given specifications.
The medical stem thermometers (fluid and digital) got that, as the Greisinger digital ones, as the fluid stem thermometers from for instance Schmidt.

 

[foc]

I used to use a food hygiene thermometer to check the C41 tank dev temp in my Fuji film processor against the software temp reading.
It was accurate to + 0.5C.
It did the trick for me.

 

[Deleted member 88956]

a general-use kitchen thermometer should be fine. There are some which can be calibrated by putting it in an ice water bath.

Temperature calibrations are done in oil bath and never heard of doing it at cold levels either

 

[Arvee]

I've been using this one for about 10 years; it consistently reads about 0.2C high as compared with my Taylor Metrology Lab mercury thermometer (18-28C).

https://www.amazon.com/Cooper-Atkins-DFP450W-Digital-Waterproof/dp/B00VV1HDGQ

 

[AgX]

Temperature calibrations are done in oil bath and never heard of doing it at cold levels either

Calibration at water in temperature equilibrium wit ice is a calibration standard, but it tells only about those low readings. To extrapolare to 100°F one need to know about the precision of both the capillary and the scale.

 

[Donald Qualls]

Calibration at water in temperature equilibrium wit ice is a calibration standard, but it tells only about those low readings. To extrapolare to 100°F one need to know about the precision of both the capillary and the scale.

There are other calibration points available, though some of them are annoying and some involve some cost. Commercially sold low-melting alloys have well characterized solidus and liquidus temperatures (solidus is the point below which the alloy is fully solid; above liquidus it's fully liquid, and in between it's "slushy" -- and a few alloys, known as eutectics, don't have a liquidus or solidus but a single-temperature melting point), and are available in a wide range of melting temperatures. There's a gallium/indium eutectic that melts at below room temperature, pure gallium melts at about palm temperature (79F?). Glacial acetic acid freezes at, IIRC, 68-69F (but I'd rather deal with gallium, thank you). Wood's metal will melt in hot tea or coffee (it's sold as gag spoons, with a silicone mold for recasting the spoon after your joke), well below 100C.

With that assortment, it ought to be possible to calibrate over a good range close to our usual working temperatures (20-40C).

For myself, given I use a hand inversion tank and water bath tempering for C-41, my developer will cool slowly over the process time. I use a sous vide in the tempering bath and a bimetal dial thermometer in the solution itself to confirm that everything has equalized. They agree to within the limits of the bimetal (about reads to 1/2F), and that's good enough for me, at least until/unless I have trouble with RA-4 prints.

 

[Deleted member 88956]

Calibration at water in temperature equilibrium wit ice is a calibration standard, but it tells only about those low readings. To extrapolare to 100°F one need to know about the precision of both the capillary and the scale.

Well, every calibration I've gone through in petroleum and engineering industry is always done in oil bath as considered far more stable and homogenous than water, so the chances of skewing what medium probe is in are minimized.

 

[Deleted member 88956]

Termoprodukt DT-1, actual link to the produkt I am proposing. Link is to one with long 300 mm probe, shorter probe costs a little less. Accuracy is 0.07 C (resolution 0.01), calibration certificate comes with it.

They also have a nicely made yet cheap wall mount if that is something that fits your set up. It holds the meter plus has bracket for the probe, so all is out of the way yet at hand when needed. I've owned this for some 3 years and it does what they say it does.

 

[Deleted member 88956]

Nothing beats a real mercury thermometer- if you can find one

And for that nothing better than Kodak Type 3, often enough available on ebay. But it does have a rather large form factor so won't fit into tighter openings, if that is part of the user's need.

 

[AgX]

Nothing beats a real mercury thermometer- if you can find one

If you want a new one and are able to obtain it (prohibition) than you likely pay about the same as for a good digital one. And the mercury one is not more precise than the digital one, so using it as reference only makes sense in the long run, as the mercury one will be as precise in decades as now

I rather would buy the digital one now and wait to come across a cheap, used precision fluid one of known manufacturer to be used as reference.
Moreover the digital one is more forgiving in handling.

 

[Bormental]

@Witold that's exactly what I need, too bad it's not available here in the US. We live in a strange world, where brands have no meaning. For example I found this $81 thermometer with stated accuracy of 0.2C, on a corporate site of Fisher Scientific. And then I see exact same thing for $24 on Amazon, branded as "General Tools". This is annoying.

 

[AgX]

Well, every calibration I've gone through in petroleum and engineering industry is always done in oil bath as considered far more stable and homogenous than water, so the chances of skewing what medium probe is in are minimized.

The point with an ice/water mixture in equilibrium is that the bath itself forms the reference. With your oil baths you need a second thermometer acting as reference, the oil only being the medium.

 

[Deleted member 88956]

@Witold that's exactly what I need, too bad it's not available here in the US. We live in a strange world, where brands have no meaning. For example I found this $81 thermometer with stated accuracy of 0.2C, on a corporate site of Fisher Scientific. And then I see exact same thing for $24 on Amazon, branded as "General Tools". This is annoying.

If you really want one of those DT-1 and UK site does not ship to you, then I can help. PM me if that's something you would want to consider. No charge outside of whatever it costs me including PayPal fees. I would guess snail mail would not add a lot to its price, some extra $20 would probably cover it. I can check on that. Possible customs at your end is another matter. This thing comes in a cardboard box. Quite light overall, but even in a buble envelope it would take a larger one.

 

[AgX]

@Witold that's exactly what I need, too bad it's not available here in the US. We live in a strange world, where brands have no meaning. For example I found this $81 thermometer with stated accuracy of 0.2C, on a corporate site of Fisher Scientific. And then I see exact same thing for $24 on Amazon, branded as "General Tools". This is annoying.

For that thermometer on Amazon by no word is hinted at its precision, only at the resolution of 0.1°

 

[Bormental]

For that thermometer on Amazon by no word is hinted at its precision, only at the resolution of 0.1°

Yep, but notice how every other spec matches: the range & stem length, not to mention appearance. I am going with the (seemingly) original, will see if it's worth it.

 

[MattKing]

I have a Kodak Type 3, which serves as my calibration standard.
It is carefully stored standing up (as required) in the back corner of a closet.
My everyday user is a mid-priced kitchen digital thermometer, which I check against the Kodak Type 3 regularly.
The digital thermometer has been consistent for the 3+ years I've been using it.

 

[Steve Goldstein]

About 10 years ago I bought one of these:

https://www.mcmaster.com/3569K58/

I checked my other thermometers against it - all were within 1/2 degree F - but this is the one I use most often except for the small submersible in bottom of the print developer tray, because I don't have to squint. The on-off switch has become slightly flaky over time, but if I wiggle it a little in the "on" position it stays on.

I've never bothered to have it recalibrated as it doesn't seem to drift relative to my mercury thermometer, against which I compare it when I think of it. The price has gone up around 30% since I bought mine.