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  1. #1
    erikg's Avatar
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    Can a process thermometer go off?

    I have a Kodak process thermometer that I have trusted for many years that now seems to be at least 8 degrees off from my other thermometers. Can that happen? and if so how? I developed some film last night and it was telling me that the water from the tap was well below what the thermometer on the water panel was telling me. At first I started to adjust to conform to what the Kodak thermometer was giving me and then I realized that I never have water from the tap below 70F this time of year. Something had to be wrong, I checked the water with two other thermometers that I trust and they agreed with the water panel. The developed film looks right on so that seems to be confirmed. Am I crazy? This thermometer could not have been off that much all these years, so what happens to them?

  2. #2

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    Is it mercury or alcohol? Has the thread separated? Are the graduations on the stick itself, or a separate scale that may have shifted?

    I have a small collection of thermometers going back to the 1860s, there is no correlation between the age and accuracy of the ones I have; the one from the 1860s is good within a degree over most of the scale.

  3. #3
    erikg's Avatar
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    It is glass with blue fluid, not really old enough to be mercury I don't think. the markings are inside the tube, no way they can move. No breaks in the fluid at all.

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    Quote Originally Posted by erikg View Post
    It is glass with blue fluid, not really old enough to be mercury I don't think. the markings are inside the tube, no way they can move. No breaks in the fluid at all.
    Well if it was accurate, and now it's not, something had to change. There isn't much to change in a hermetically sealed glass tube though!

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    Certainly any thermometer can go off. Column separation due to rough handling is a common problem. Take a good magnifying lens or jeweler's loupe and check the entire column. If you can get all the liquid into the bulb you can correct this problem.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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    Quote Originally Posted by Gerald C Koch View Post
    Certainly any thermometer can go off. Column separation due to rough handling is a common problem. Take a good magnifying lens or jeweler's loupe and check the entire column. If you can get all the liquid into the bulb you can correct this problem.
    Column separation is the only problem that can occur. Anything else involves breakage of the tube. The easiest way to fix it is to cool the thermometer until all the fluid is in the ball, but it can be problematic when the thing goes down to minus 40.
    An error of 8 degrees would involve a single very apparent separation, or a less apparent series of separations.

  7. #7
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    Get together a container of ice water ( ice and water with the ice no longer melting) this is 32 degrees
    After performing the ice water test then a pan of boiling water with vapor raising from the liquid this is 212 degrees
    Take the two reading and extrapolate the difference this is how you check for accuracey

  8. #8
    erikg's Avatar
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    Thank you everyone. I'll take a close look tonight, there must be a break that I didn't see. I will try the cooling method and see how that goes. Apug as always a wealth of knowledge.

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    Quote Originally Posted by rjs003 View Post
    Get together a container of ice water ( ice and water with the ice no longer melting) this is 32 degrees
    After performing the ice water test then a pan of boiling water with vapor raising from the liquid this is 212 degrees
    Take the two reading and extrapolate the difference this is how you check for accuracey
    You need to make your ice with distlled water, then make a slushy with the ice and distilled water.
    Pure water boils at 212 degrees at a pressure of 30 inches of mercury- that is sea level, normal barometric pressure. You need to correct for altitude and barometric pressure, and again use distilled water.
    The difference between these two points is then divided into 180 degrees for Fahrenheit and 100 degrees for Celsius (centigrade) thermometers.

  10. #10
    erikg's Avatar
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    I'm in Rhode Island so I'm basically at sea level so no trouble there! Looks like I need to do some preparation. Thanks again for the information, I've learned something new.

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