Digital Thermometer Recommendation

[Ken Lee]

Can anyone recommend a digital thermometer that is reliable, accurate, unbreakable, and affordable ?

The Thermapen (http://www.thermoworks.com/products/thermapen/splashproof_thermapen.html) looks attractive, but... why not ask those in the know ?

(I do know about traditional thermometers. I am looking for a digital thermometer :))

[kmack]

I have been using a ML 4052 (http://www.marketlabinc.com/products/details/440) lab thermometer for a few years now. Works fine for me.

[Shen45]

The digital one I got from DSE is very accurate and cost $24.00. I've put a couple of people on to it. I'm not certain about unbreakable but that part is up to us to "attempt" to be careful. Perhaps treat it like it is filled with mercury.

[nolindan]

I use a "Taylor 9842 Commercial Waterproof Digital Thermometer", $14 from Amazon. Single point calibration so you can get multiple thermometers to read within a 1/10th C of each other.

Take the 'waterproof' part with a grain of salt. Water does get in; it just has a hard time getting out. If it stops working chances are it just needs to have its innards dried out.

And if you can't find the kitchen thermometer and the turkey's in the oven...

[Struan Gray]

The Thermopen makes sense for people who want to prod their test objects and not lose or crush the sensor cable, but for darkroom use I would prefer a model which has its sensor on a cable.

If you want reliable and robust, Fluke are a standard for carry-round measuring instruments. Their 50-series thermometers are great, and have a wide range of usable probes. Not cheap, but all-round good. The fluke.com site will only show me pages in Swedish, so I can't give you a link, but the thermometers are not hard to find.

If you already have a decent voltmeter (which can measure to 0.01 V) you can save money by buying only a probe (a 'Type K' thermocouple is what you want) and using a table to convert the voltage readings to temperature.

Otherwise, there are cheaper brands than Fluke. Ninety-nine times out of a hundred it's the sensor cable that goes bad with use. Really cheap ones don't have the proper temperature-compensated connectors (the odd square yellow things with two different-sized prongs), so they can drift with the ambient temperature.

[bsimison]

DeltaTrak traceable pocket probe, $35 from professionalequipment.com. Link: http://www.professionalequipment.com/deltatrak-flash-check-pocket-probe-thermometer-11024/thermometer/

I find it inexpensive and accurate. I regularly check it against my lab-grade Fisher glass thermometers and it's always spot-on.

[Dave Dawson]

I use a cheap digital thermometer intended for a tropical fish tank. It has an lcd display and a sensor on the end of about 4 ft of wire. It is within 0.1 degree C

Cheers Dave

[Nathan Potter]

Like Struan I use a couple of Flukes; Model 52 digitals with flexible thermocouple extension leads so I can keep the electronics away from the chemistry by mounting on the darkroom wall. Don't know current price but mine are 10 years old or so and work fine. They are for type K or J couples and have the temperature compensated connectors.

The Thermapens look pretty good though.

Nate Potter, Austin TX.

[Ken Lee]

I use a cheap digital thermometer intended for a tropical fish tank. It has an lcd display and a sensor on the end of about 4 ft of wire. It is within 0.1 degree C

Same equipment, but different pricing... I love when that happens :)

[sanking]

Same equipment, but different pricing... I love when that happens :)

I picked up a few digital thermometers from Harbour Freight for about $3 a piece. They are all within 0.5 degrees F of my standard mercury thermometer and another much more expensive digital thermometer.

Sandy King

[ki6mf]

I just got a Taylor Waterproof Digital with a range from 40-200 degrees F. Cost was around $14 at a local cooking store. The key is a WATERPROOF case!!!! I checked it against a color photography thermometer and it is accurate at 68 degrees F. Google Taylor Commercial Waterproof Digital Thermometer. Cost was around $14.00 I normally use my Samigon adjustable and test it against the Color thermometer to set.

[bsimison]

Those little $5-$10 digital cooking thermometers *are* pretty good, especially for the price. They're accurate and precise (enough) for the job. The ones I've used often disagreed with each other by about 1-2 degrees C, but as long as you stick to one unit and judge your results by its reading, you're good.

The problems I always ran into was that they break down so easily. I literally have a pile of dead ones in a box in my darkroom. That, and I was never really happy with how fast they provided a reading. Some were slower than my glass thermometers, and I'm just not that patient of a guy. :-)

[Robert Hughes]

I confess, my digital thermometers are on the end of my hand. "Cool to the touch" seems about right. If the developer's too cold, I warm it up. If it's warm, I cool it down.

PS - Why are half my negatives too dark? Hmmm...

[Ken Lee]

Place one hand in ice water, and another hand in hot water.

Then place both hands in tepid water. One hand will tell you it's hot. The other will tell you it's cold.

Can both be right ?

[Bruce Watson]

Place one hand in ice water, and another hand in hot water.

Then place both hands in tepid water. One hand will tell you it's hot. The other will tell you it's cold.

Can both be right ?

Yes. Relatively.

[ic-racer]

Ok, so I can just plug a 'type K' thermocouple into my Fluke DMM and use this table and I have a digital temp probe. The Fluke probes are somewhat expensive. Wonder if a cheap generic probe will work.

If I am reading this correctly, then at 25 degrees Centigrade, with my meter set to millivolts (not ohms?) it would read a perfect "1.0" correct? Or do I need to find out how many volts my meter applies in the OHM mode and use that to calculate ohms it should read at the target temp?

http://srdata.nist.gov/its90/download/type_k.tab

[Struan Gray]

The thermovoltage (aka contact potential) gives the difference in temperature between the sensor and the ambient room temperature. So if you get a reading of 1.000 V your junction is 25 °C above room temperature.

The handheld reader units have an internal reference which measures the ambient temperature. They vary in quality - it's one reason good ones are more expensive.

You can always use an ambient thermometer to measure your darkroom's temperature. They integrate over much longer times (and use different physics in their sensors) so you are only partially stuck in a chicken and egg situation. Otherwise, you can provide a reference bath for your sensor. A bath of ice and water give a fairly reliable 0°C - it varies with pressure (see here (http://en.wikipedia.org/wiki/File:Melting_curve_of_water.jpg)) but not as much as the boiling point. For continuous monitoring, it's standard to have two sensors, one in a bath of known temperature, and one in the test solution. You can connect them in series (get the polarity right :-) or just measure voltages one after the other.

It sounds complex, but with a probe, voltmeter and home-thermometer to measure ambient you should be able to measure temperatures with far more accuracy than photographic precision requires. Repeatability and reliability are more important than absolute accuracy.

PS, if you're handy and can find a source for the wires without having to buy whole reels, the cheapest way to get a sensor is to make it yourself by spot-welding chrome-nickel and aluminium-nickel wires together. You only need a low-power spot welder.

[bsimison]

It sounds complex, but with a probe, voltmeter and home-thermometer to measure ambient you should be able to measure temperatures with far more accuracy than photographic precision requires. Repeatability and reliability are more important than absolute accuracy.


With this method, your readings are only as accurate as the thermometer you use to measure the ambient temperature. Why not just simplify and buy an inexpensive waterproof culinary thermometer?

I don't mean to criticize, but this sounds very complex for the results you get.

[Struan Gray]

With this method, your readings are only as accurate as the thermometer you use to measure the ambient temperature. Why not just simplify and buy an inexpensive waterproof culinary thermometer?

I don't mean to criticize, but this sounds very complex for the results you get.

You're right. And not quite.

It's easier to make a cheap thermometer that accurately measures the temperature of a room. Integrated circuits with a calibrated built-in sensor are available pre-packaged, and the intrinsic voltage output of their temperature-sensitive diode circuits is a thousand times greater than a thermocouple. Their physical size and thermal mass make such sensors less useful for probe-style applications, but measuring the ambient temperature of a room on a timescale of minutes is a doddle.

Probes at the end of a wire suffer from all the problems of trying to measure small voltages at a distance. Thermocouples are robust, cover a wide temperature range, and can be made with very small thermal masses, but they only put out microvolts per °C of temperature change. You have to get right issues like noise shielding, contact integrity and the piezo response of the insulators round the wires, or the measurement becomes unreliable.

I have used cheap digital probe-based thermometers (in a lab, not a darkroom) and learned to avoid them. They are less reliable and are too sensitive to things I cannot control, like whether the local radio station is running it's signal compressors full tilt or not. For my personal darkroom use I see no need over the many good conventional thermometers I already have, but if I were to buy one I would get a good one that I know I can trust - or, a good sensor and a multimeter.

FWIW, thermometers for tropical fish aquariums are supposedly better made and more reliable than those sold as kitchen or general home gadgets. Perhaps that's a halfway house.

[Ken Lee]

Why not just simplify and buy an inexpensive waterproof culinary thermometer?

The $3 aquarium thermometer I just purchased at a pet supply store, seems just as accurate as the $20 digital culinary thermometer I just purchased.

The digital thermometer may be more precise - giving readings in the 1/10 of a degree - but it's hard to know if it's any more accurate.

The aquarium thermometer is smaller, requires no batteries, and even has a suction cup to hold it against the inside of an aquarium or a... dish-rack film washer (http://www.kenleegallery.com/html/tech/dishrack.html). :rolleyes:

[BetterSense]

Walmart sells a small Acu-Rite wide-range digital thermometer that has a small pot on the side for calibration. It costs about $15, and responds very fast. I have two which I calibrated via the screw to a $$$ lab thermometer from work, and they still agree to within +-.05*C. They are NOT waterproof, but if you accidentally turn the light on to find that you set it down in the stop tray, you might be able to revive it with a good soak in 99% rubbing alcohol.

[Paul Kierstead]

I really liked the idea of the digital aquarium thermometer; seemed cheap and accurate, so wandered down to my local pet store and bought one. I'll compare it to my thermopen to get some idea; I'm hoping that it is consistent at least (E-6, which I do mostly, is somewhat sensitive to temp). In the long run I want to hook up a PID controller to my CPP-2 to make it easier to dial up a temp...

Great tip!

[Ken Lee]

What I like about digital thermometers, is their fast response time.

[domaz]

I have a couple culinary thermometers and they seem to read a bit low. I think they do this intentionally because they'd rather you overcook than risk undercooking and someone suing them. So keep that in mind using anything made for the kitchen.

[Andrew ren]

just called this company, apparently its a quebec based one.

http://www.prolabscientific.com/Digital-Lab-Thermometer-p-18644.html

all i am concerning is the "for Lab" use. a must.
so I ordered one.:D

Andrew