Thermometers

[PeterB]

My 'master' is a mercury-in-glass Brannan that agrees with another, identical, Brannan to 0.1 C.

Roger,

The digital clock in my car agrees with my bedside radio clock too.

They are both 2 minutes slow.

regards
Peter

 

[Jerevan]

I don't know if this rings true to you but for me; use what you use, and as long as it is consistent from session to session and gives me the results I want, I don't bother with it.

You'd need a laboratory and a bunch of test engineers to be even remotely sure about anything. But even then, we are talking about shutter times, developing times, agitation schemes, temperatures, and so on and so forth - all the ways to mess up the ideal, perfect process, from making the photograph until it hangs on the wall. Listen to anyone but choose for yourself.

 

[Roger Hicks]

Roger,

The digital clock in my car agrees with my bedside radio clock too.

They are both 2 minutes slow.

regards
Peter

Dear Peter,

Well, I did say that consistency matters more than accuracy...

Cheers,

Roger

 

[j-fr]

It is always a good idea to have two thermometers, preferably identical, in the darkroom, and compare them once in a while. If one is broken, you can just pick up the other without having to bother about any possible change in process. Just remember to get a new second thermometer and test it against the one in use, so it is ready when the next mishap occurs.

j-fr

www.j-fr.dk

 

[photomc]

Interesting thread, and your comment here Roger. On this side of the pond, the ideal would be to obtain a thermometer certified by the NBS (National Bureau of Standards) and compare all others to it - the master/slave thing. However, not sure we need that extreme in our darkrooms (the NBS thermometers, like everything else are quite pricey).

Like most things darkroom, we can cater to the analytical side and spend all of our time checking, calibarting, etc. NOTE:I am as bad about this as anyone, so I do not think it is a bad thing. On the other hand we should consider what we can do - in this case trying to match at least 2 "good" thermometers and keeping one as the master, then always match to it should work very well.

One question, those that use the digital thermometers, have you noticed any changes in readings when the battery starts to go? I would think that at some point the readings would become "off" just prior to the battery failure.

What surprises me is that no-one has suggested the 'master/slave' model.

The master thermometer does not even need to be accurate, merely consistent, though accuracy is nice if you can get it. Mercury-in-glass lab thermometers (incliding the Kodak ones) are probably the most reliable; bimetallic dial drift most in my experience; and electronics may do almost anything without warning, no matter how reliable. Most don't, it's true, but they can.

All 'slaves' are calibrated to the 'master'. Let's say you have three thermometers, one 'master' and two 'slaves'. When the 'master' reads 20, one slave reads 19,5, the other, 20,5. For a standard 20, you therefore use the slaves accordingly.

Break a slave; replace it; recalibrate against the master. This one's 19.7. Fine. Still the same temperature...

My 'master' is a mercury-in-glass Brannan that agrees with another, identical, Brannan to 0.1 C. My 'slaves' vary widely for different purposes: spirit-in-glass, dial (for water baths), digital... Digital and dial are checked periodically; spirit-in-glass only when I acquire them.

Cheers,

Roger (www.rogerandfrances.com)

 

[Phong]

> On this side of the pond, the ideal would be to obtain a thermometer
> certified by the NBS (National Bureau of Standards)

In case you didn't know, NBS has been NIST (National Institute of Standards and Technology - mentioned in some of the earlier posts) since the late 1980s.


- Phong

 

[photomc]

> On this side of the pond, the ideal would be to obtain a thermometer
> certified by the NBS (National Bureau of Standards)

In case you didn't know, NBS has been NIST (National Institute of Standards and Technology - mentioned in some of the earlier posts) since the late 1980s.


- Phong

LOL Figures, been longer than that since I had to deal with them. But then I still remember the Atomic Energy Commission and Bureau of Biologicals. Thanks for the 'old' update.

 

[BOSS565]

I vote for the kodak glass thermometer.

 

[Claire Senft]

I must say the thought that a mercury thermometer enclosed in etched glass
being able to go out of calibration to be very surprising news that I find hard to fathom.

How could this happen?

 

[Brian Jeffery]

Hi all,

thanks for your input.

I must admit that I agree with your comments in that it's not accuracy that's most important, but consistency. That' was my reasoning for going for a digital thermometer as I'm less likely to break it. However, the Kodak thermometer that was mentioned in many posts looks just the ticket as it is housed in a metal sleeve.

A couple of points though. When trying to ascertain the best development time for a particular film/developer combination it is probably advisable to start of with the manufacturer’s development times. However, if you’re working with a thermometer that's two degrees out you are going to under/over developing your film by nearly 20%. It'll definitely make things harder Hence it’ll be good to get a reasonably accurate thermometer.

As to the resolution/accuracy debate. In a previous existence I was an electronics engineer and it was a common misconception that because a particular digital meter had three decimal places it was more accurate than a meter with two decimal places. It may or may not be, it depends on the quality of the meter and whether or not it's been calibrated.

Another misconception was that a digital meter was always more accurate than an analogue one. Again, it depends on the meter.

Anyway, I've managed to purchase a Kodak Processor Thermometer Type 3 for £5 (including postage) of Ebay. So with a bit of luck this will be my work horse for the next x years.



Thanks again,

Brian

 

[Roger Hicks]

I must say the thought that a mercury thermometer enclosed in etched glass
being able to go out of calibration to be very surprising news that I find hard to fathom.

How could this happen?

Dear Claire,

Puzzles me too.

Cheers,

R.

 

[glbeas]

Surprising as it sounds, I've heard stories that mercury has the ability to wick through glass, very slowly. This may account for a glass thermometer getting out of calibration in it's grizzled old age.

 

[jovo]

I have my dad's mercury in glass thermometer (Kodak, I guess...I haven't looked at it in years), but the mercury separated from itself, i.e. it's in segments. Is that common? Is there a simple fix? I'd love to use it if it were usable once again. (It must be 60+ years old.)

 

[glbeas]

You have to heat the theremometer enough that the mercury column rises all the way to the top and then some, forcing the bubbles together at the top. On cooling the column will retreat as on piece. Needless to say you need to be very careful not to overheat and break the thermometer in the process. Storing the thermometer in an upright position will help prevent this from recurring.

 

[jovo]

You have to heat the theremometer enough that the mercury column rises all the way to the top and then some, forcing the bubbles together at the top. On cooling the column will retreat as on piece. Needless to say you need to be very careful not to overheat and break the thermometer in the process. Storing the thermometer in an upright position will help prevent this from recurring.

Thanks, Gary...I'll try that. It'd be great to use that piece of family antiquity again.

 

[PeterB]

Quote:
Originally Posted by Claire Senft
I must say the thought that a mercury thermometer enclosed in etched glass
being able to go out of calibration to be very surprising news that I find hard to fathom.

How could this happen?

Dear Claire,

Puzzles me too.

Cheers,

R.

Roger and Claire,

I posted a URL above where you can read all about LIG thermometers going out of cal. Maybe you missed my reference. I'll post it here again.

http://www.icllabs.com/whyrecalibrate.html

One time a thermometer was found to be out by 10 degrees:

"We have had, on rare occasions, thermometers submitted for a periodic re-calibration which at first examination appeared in excellent condition, but did not function properly; an examination under the microscope revealed a nearly invisible stress crack in the bulb through which a quantity of mercury had escaped - changing the reading of the thermometer in excess of 10 degrees C "


regards
Peter

 

[Claire Senft]

Thank you.

 

[Roger Hicks]

Dear Peter,

Good Lord! Thanks. Sorry I missed the previous url.

Cheers,

Roger

 

[Thomas Bertilsson]

I know this is a really old thread, but as I went to develop some film yesterday, the chemical bottles felt warm to me. So I checked my darkroom thermometer against three other thermometers in the house, and found that my bi-metal dial thermometer was showing a whopping 11 degrees Fahrenheit too little.

So now I'm looking at Kessler in NY state. They quote you on the spot when you want to buy thermometers, and seem to start around 80 bucks and go as high as the sky...

I'm glad I caught it before I started developing film.

 

[John Wiegerink]

Tom,
I had something like that happen with an Omega digital LED read-out type with the coil probe. Things started going slowing South with my film processing and I was looking at several possible problem areas(developer, time, etc.). My thermometer unfortunately was not the first place I looked. I wasted time and money before I checked my fancy super-accurate digital thermometer against an old liquid FR I had sitting around. Yup, same problem you had. I've also had problems of the bi-metal thermo's be off by a couple of degrees from one time to the next. Well, I now have a Kodak No.2 process thermometer and all is well. I found out that sometimes newer/modern technology isn't always better. And to stop anybody else's grief that Omega wonder is at the bottom of some landfill in Michigan right now. Lesson learned! You are very lucky you caught it before you took that roll off the reel and said "What the.............". I'll let you fill in the blank. JohnW