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CG
18-Mar-2009, 08:42
www.thermoworks.com/thermapen_privatesale.html

Looks like the sale I have needed to justify purchasing a thermapen.

PS I am not associated with them.

Lenny Eiger
18-Mar-2009, 09:01
I've been very frustrated with thermometer companies. I have 6 different glass ones that all disagree, including an old Kodak and a brand new one, bought from a photo company. I have two that I purchased that are supposed to be within .2 degree accuracy, tested against the NIST, etc. They disagree by about a degree, which means this can't be true.

When I spoke to the company that sold it to me they explained that it is accurate at "points" which usually means at 0 and 100 degrees C. In between, like near 70 F, it could be a degree or two off. What?! I specifically paid more to get a thermometer that would be accurate and got the same old minimum level of accuracy.

I would love to a have an accurate thermometer, will pay up to about $100. I've looked all over the web, spent hours trying to find one, I haven't found one yet that is accurate in the 65-100 degrees F, that does liquid measurements, is waterproof, or at least has a sensor that is waterproof. I really don't care about reading to 572 F, or down to -300. I just want 50-100 F to be reasonably accurate and I don't want to pay $500 for the privilege.

I do understand that it doesn't matter what temp something is, as long as you use the same thermometer every time. What if one doesn't, or you run out of batteries and need to go to the stored and get another, have to develop film in the meantime. While being off by a quarter or half a degree won't matter to most of us, a couple of degrees of difference clearly does. It's a shame that there isn't a thermometer co that can address this need. If anyone finds one, I'd love to know.

Lenny

Toyon
18-Mar-2009, 12:28
I wouldn't expect accuracy from a Thermapen. I too would like an accurate thermometer to use in order to calibrate all my working ones. There are "certified" color thermometers available. Maybe they are better?

John T
18-Mar-2009, 13:33
Lenny,

I don't mean this to be argumentative, but how do you know if all your thermometers are inaccurate because they disagree with each other? Could one be right at 70 degrees?

Michael Graves
19-Mar-2009, 04:39
I'm more interested in consistency than accuracy. Once I've made my tests at what the thermometer SAYS is 68 degrees, if the results are what I want, then as long as they stay the same I don't give a rats behind whether it's really 69 degrees or 67 degrees. I once had one of those stainless steels that tended to not be consistent and that was a pain.

Lenny Eiger
19-Mar-2009, 08:31
Lenny,

I don't mean this to be argumentative, but how do you know if all your thermometers are inaccurate because they disagree with each other? Could one be right at 70 degrees?

Certainly. I have picked one, and I hope I am right... I all n thermometers disagree, then the possibility of them all being inaccurate can be expressed as n-1, at minimum. In other words, one could be right. But which one?

Lenny

emo supremo
19-Mar-2009, 12:48
Hmmm, wonder if accuracy is of no concern could it be that mercury themometers are preferred over the alcohol-filled ones for precision.

John T
19-Mar-2009, 17:09
Certainly. I have picked one, and I hope I am right

Darn. I was hoping you had a solution. Do you think that there might be an industrial standard (other than the previously mentioned 0 and 100 degree standard) that can be referenced? I was thinking along the lines of the atomic clock or the 1 KG standard.

CG
20-Mar-2009, 08:07
Hmmmm, I'm sorry I passed this topic along.

Lenny Eiger
20-Mar-2009, 11:09
Hmmmm, I'm sorry I passed this topic along.

I see nothing wrong... I think it gives everyone an opportunity to learn something new. Somebody might even come up with a really good thermometer as a result....

You can't get it right every time - I certainly don't...

Lenny

John T
20-Mar-2009, 11:23
CG,

I think letting us know about possibilities is a good thing. We are always looking for equipment that works better. I don't know anything about Thermapens (good or bad) and wouldn't make any assumptions about them. At this point, my working process is fine for me, but if it helps others it is a good thing.

Did you actually buy one yet? If you do, please let us know your impressions.

CG
20-Mar-2009, 13:10
Thanks for the kind words John and Lenny.

I have two on order - at the sale price - ordered just after I posted the message online. One for the kitchen and one for the darkroom. I'll write once I have them and have had the chance to put them through their paces. Chefs and avid cooks seem to swear by them.

Drew Wiley
20-Mar-2009, 13:25
I gave up on electronic thermometers some time back because their reaction time is too slow. Get a certified standard thermometer. The Kodak process thermometer is
worth every cent (about a hundred bucks). But if you can't find one of these, any
serious scientific or lab supply house carries a selection of certified thermometers.

nolindan
20-Mar-2009, 13:56
I must be very lucky ... I have oodles of thermometers that all agree within reading resolution.

My Kodak color and process thermometers agree with a YSI cuvette thermometer to within a gnatt's arse at 37C.

For B&W photographic usage it really doesn't matter what the temperature is (to a reasonable extent). If the thermometer is repeatable and reasonably linear it is good enough. For better accuracy for color work, check the thermometer against a fever thermometer.

Most thermometer inaccuracies that I have seen are due to Weston-style dial thermometers that have gotten 'twisted' or fluid/glass thermometers that have column separation. Either twist the dial thermometer back into calibration or shake/freeze/boil/shatter the glass thermometer to get the column joined (or as an excuse to buy another).

CG
20-Mar-2009, 16:15
I gave up on electronic thermometers some time back because their reaction time is too slow. ... I hope the Thermapen is the exception to your observations. They are supposedly fast acting. I'll report in.

ghost
27-Mar-2009, 09:00
I see nothing wrong... I think it gives everyone an opportunity to learn something new. Somebody might even come up with a really good thermometer as a result....

You can't get it right every time - I certainly don't...

Lenny


I do laboratory grade thermometry and other calibration work for the biotech industry for a living. When comparing different thermometers; two critical considerations are: response time, and the uniformity of the comparison bath.

I have sent you a PM regarding thermometers and possible assistance.

ghost
27-Mar-2009, 10:17
FYI for anyone who is interested, some more info on temp. instruments:

All temperature instruments should come with an accuracy specification, expressed as +/- in Degrees. Not to be confused with RESOLUTION, which is the number of digits on the display/scale. Just because something can read in tenths, it’s often the case that the actual accuracy is much greater that 1 tenth.

Remember: ALL instruments have some error- it just depends on matching the instrument to the application-

For example To measure the critical temperature inside of a Bioreactor, we use platinum RTD’s from Hart Scientific that are accurate to within about +/- 50 mK (0.05 deg C) that cost about $5,000.
To measure the inside of his meat case, your local grocer uses a $50 Ashcroft bi-metal that is maybe accurate to about +/- 3 Degrees F. Good enough for his application.

The lab that certified a thermometer, then told you that they did not guarantee the linearity of the range between the test points…that’s BS. If I test at 0 and 50, and certify the device to +/- 1 degree- the implication is, that at 35 deg, it will read 34-36

Although these kitchen-grade consumer type thermometers are probably plenty good enough for photography- it is important to have a realistic expectation of their accuracy- probably +/- about 2 Degrees C, regardless of what the manufacturer claims- believe me I've tested a million of them over the years for lab folks trying to squeeze a dime :)

Jeff Bannow
27-Mar-2009, 10:23
FYI for anyone who is interested, some more info on temp. instruments:

All temperature instruments should come with an accuracy specification, expressed as +/- in Degrees. Not to be confused with RESOLUTION, which is the number of digits on the display/scale. Just because something can read in tenths, it’s often the case that the actual accuracy is much greater that 1 tenth.

Remember: ALL instruments have some error- it just depends on matching the instrument to the application-

For example To measure the critical temperature inside of a Bioreactor, we use platinum RTD’s from Hart Scientific that are accurate to within about +/- 50 mK (0.05 deg C) that cost about $5,000.
To measure the inside of his meat case, your local grocer uses a $50 Ashcroft bi-metal that is maybe accurate to about +/- 3 Degrees F. Good enough for his application.

The lab that certified a thermometer, then told you that they did not guarantee the linearity of the range between the test points…that’s BS. If I test at 0 and 50, and certify the device to +/- 1 degree- the implication is, that at 35 deg, it will read 34-36

Although these kitchen-grade consumer type thermometers are probably plenty good enough for photography- it is important to have a realistic expectation of their accuracy- probably +/- about 2 Degrees C, regardless of what the manufacturer claims- believe me I've tested a million of them over the years for lab folks trying to squeeze a dime :)
What would you recommend for darkroom work?

CG
27-Mar-2009, 11:15
Mine just came so I haven't had time to break them, so it will be a while to have a sense of durability. Regardless, they're fast reacting. I'm very pleased so far.

They seem to be tested for accuracy; a printout of the test of my thermometer against a lab instruments traceable to NIST and others was included with my order. Evidently mine read dead on at 32F and at 212F.

aduncanson
27-Mar-2009, 11:59
Although these kitchen-grade consumer type thermometers are probably plenty good enough for photography- it is important to have a realistic expectation of their accuracy- probably +/- about 2 Degrees C, regardless of what the manufacturer claims- believe me I've tested a million of them over the years for lab folks trying to squeeze a dime :)

Thanks for the excellent information. However, I am not sure I understand what you mean when you refer to "kitchen-grade consumer type" thermometers.

I rely on a 10 inch Kodak alcohol filled thermometer with a scale from 30F to 120F. B&H is now selling a similar thermometer from Paterson and "guarantees" an accuracy of +/- 0.3C. Is that nonsense? Mine appears to have been abused by a previous owner since there is about 1 degree's worth of alcohol disconnected and stuck beyond the top of the scale .

It seems that my purposes, processing B&W negatives and prints, would require consistency or repeatability more than absolute accuracy. Can you generalize about how do these thermometers perform in terms of consistency? The technology seems to assure pretty good stability (until it is shattered.)

Thanks - Alan

mandoman7
27-Mar-2009, 18:45
If its all relative, and you're testing your results, then it wouldn't seem to matter if your thermometer is all that accurate as long as its consistent and easy to read. I can understand wanting to be thorough however.
I used to have a darkroom that was a bit chilly, and it wasn't until developing film for several years that I started taking measurements at the end of the process as well as the beginning. What a revelation that proved to be as I was often finishing up 4 or 5 degrees colder than at the outset. Duh.

JY

ghost
28-Mar-2009, 10:58
What would you recommend for darkroom work?

Again- it depends on the accuracy you can live with. really this discussion is probably a little esoteric for most of us in the home darkroom- these kitchen thermometers or whatever Patterson is selling are probably good to a couple of degrees and thats probably plenty- good enough for Adams, Weston, et. al...

That said- nothing wrong with precision :) ...

...I would stay away from glass simply because when it comes to glass stem thermometers, the real deal mercury is the way to go- the alcohol and other replacement fluids are much less accurate, less stable offer time, and have much more column separation issues.

I would recommend getting a digital unit that consists of a readout to 0.1 and a slender probe for fast response.

These can be had for next to nothing- like $30 BUT- they will vary in accuracy all over the place, even in the same lot. So- for another $75 or so, most lab-supply companies like Cole-Parmer will certify- throughout the range of intended use (important point).

Basically, anything you see for under $50 will not have been tested, or at MOST- may have been spot-checked at a very cold and very hot point (beware of the ones that come with "certificates" showing ZERO error at the extreme ends of the range esp. for a 20$ product- extremely unlikely... sorry to be cynical but I do this for a living).

Anything over $100 probably has some decent full-range calibration built into the price.

Again- if you decide that you would like to have accurate(better than +/- 1 or 2 degrees) temp. measurement- it's like anything else- there are no "free lunches"... any manufacturer or retailer "guarantees" under that $100-125 price point are just "too good to be true"- or the pharma and government labs would not need me and my expensive gear! Believe me- they have studied this as well.

ghost
28-Mar-2009, 11:07
Thanks for the excellent information. However, I am not sure I understand what you mean when you refer to "kitchen-grade consumer type" thermometers.

I rely on a 10 inch Kodak alcohol filled thermometer with a scale from 30F to 120F. B&H is now selling a similar thermometer from Paterson and "guarantees" an accuracy of +/- 0.3C. Is that nonsense? Mine appears to have been abused by a previous owner since there is about 1 degree's worth of alcohol disconnected and stuck beyond the top of the scale .

It seems that my purposes, processing B&W negatives and prints, would require consistency or repeatability more than absolute accuracy. Can you generalize about how do these thermometers perform in terms of consistency? The technology seems to assure pretty good stability (until it is shattered.)

Thanks - Alan

Dude- your thermometer is not accurate- the little bit of fluid you describe is called "column separation"- the thermometer was designed to be accurate with ALL of the fluid in the column- it's not consistent either- because the little bit of air in the column now compresses differently at different temps.

You can probably fix it....[DISCLAIMER- no responsibility taken if you break it, etc.]

Using your stove GENTLY heat it- about 6 inches AWAY from the flame...do NOT put it in the flame...what you want to do is SLOWLY cause the fluid to rise JUST enough for the little bit that separated, and the main body of fluid to meet together at the reservoir at the top of the scale...SLOWLY...AS SOON as they meet up- take the heat away, the fluid should all be together now as it creeps back down the scale to ambient temp. I have fixed many a column separation this way...again- be gentle!

ghost
28-Mar-2009, 11:25
Yeah guys, I looked at the B&H and other stuff that is being marketed to us for darkroom work- it's pretty marked up- but I can see no evidence that the huge markups reflect any testing or calibration cost- I think it's just the "photo-use" markup ("why don't you just switch to digital anyway?":rolleyes: ) The accuracy claim is simply based on that what you can read on the scale (see my explanation of accuracy -vs- resolution)...

I guess I should not be surprised at the interest in this topic...darkroom workers should not have to be overcharged for inferior instruments.

If there is enough interest on this board or APUG- I could buy a case of digitals and have them calibrated by a technician in the thermometry lab here from say 32F to 200F at +/- 0.5 degrees accuracy up and down, and make them available for around $75 each as a break-even- it would have to be a big batch though or the CFO would wring my neck .

aduncanson
28-Mar-2009, 13:16
Thanks for the tip. Actual flames intimidated me so I heated a couple of cups of water to 160F in my microwave and then just touched the tip of the thermometer to the hot water. That brought me close but I had to nearly submerge the bulb to get the separated bit to merge. It was easy and seemed safe.

I did not really suspect I had a problem before, so I think that I will be satisfied with my fixed thermometer for a while.

Vlad Soare
1-Apr-2009, 07:36
I would love to a have an accurate thermometer, will pay up to about $100. I've looked all over the web, spent hours trying to find one, I haven't found one yet that is accurate in the 65-100 degrees F, that does liquid measurements, is waterproof, or at least has a sensor that is waterproof. I really don't care about reading to 572 F, or down to -300. I just want 50-100 F to be reasonably accurate and I don't want to pay $500 for the privilege.
[......]
While being off by a quarter or half a degree won't matter to most of us, a couple of degrees of difference clearly does. It's a shame that there isn't a thermometer co that can address this need. If anyone finds one, I'd love to know.

Lenny
Lenny, I have one of these:
Greisinger GTH 175/PT (http://tinyurl.com/ctddo6).
I'm sorry, the page is in German, but I guess it can be found in other places if you Google its name.
The measuring range is from -199.9 to +199.9 degrees Centigrade. Between -70 and +199.9 the precision is 0.1% of the measured temperature, plus-minus 0.2 degrees. For temperatures below -70C there's a correction table in the user's manual. It's accurate enough for color work.
Its response is almost instantaneous, which is why I chose it in the first place. The device itself is not waterproof, but the sensor is.
It's not cheap, but it fits your budget and is worth every penny.
As a bonus, it doesn't need some kind of weird and expensive lithium battery only stocked by specialty shops. It uses one cheap 9V battery, which can be found in any supermarket.

Lenny Eiger
1-Apr-2009, 10:17
Lenny, I have one of these:
Greisinger GTH 175/PT (http://tinyurl.com/ctddo6).
I'm sorry, the page is in German, but I guess it can be found in other places if you Google its name.

Vlad,
This device is impressive.
I didn't find it in the US, but I'm sure I could get from from the UK...
In the interim, someone very thoughtful has offered me a thermometer to test out. We shall see...

Thanks,

Lenny