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Thread: Calibrate a densitometer?

  1. #11

    Join Date
    Dec 1999
    Location
    Forest Grove, Ore.
    Posts
    3,330

    Re: Calibrate a densitometer?

    All the calibration means for Stouffer step wedges, is that they've read the steps with a densitometer that's traceable to the national standard. The readings are written down on the envelope that holds the wedge.

    Stouffer's makes an economical five step wedge (including film base plus fog) that will work fine. This wedge also includes readings near 1, 2, 3, and 4. (The fb+f reading will be about 0.05.)

    After zeroing, I adjust the slope setting so that the densitometer correctly reads the "3" wedge, and I also check to make sure that the readings of the "1", "2", and "4" steps are appropriate. After this, I may check the zero again, and if I change it at all, I would recheck the slope setting.

  2. #12

    Join Date
    Sep 2015
    Posts
    3

    Re: Calibrate a densitometer?

    Good Morning,

    I had got the standard from Tobias Associates, Inc.
    The Black and White standard was little different from the original standard.
    (Refer to attachment on the standard value)
    But I was stuck with the as I do not know how to key in the value of the standard.

    Can someone help or maybe share with me on the operating manual for this model.
    (Refer to attachment on the machine photo)


    GAM Model 144.pdf
    Attached Files Attached Files

  3. #13

    Join Date
    Dec 2009
    Location
    Pacifica, CA
    Posts
    1,493

    Re: Calibrate a densitometer?

    TKChea, you have the new standard in hand valid through September 30, 2016. This may be what you were brought in to provide: A certified standard.

    The people who use the densitometer must have been following a calibration checking procedure which would be fairly straightforward. Set the channel for Black, Yellow, Magenta or Cyan and read the white patch. Turn the knob for that color channel (knob marked "zero") until you get the reading under the zero column of the standard for that channel. For example the black channel, should zero to 0.010 on the display when reading the white patch. This is safe to do because you are not "calibrating" at this point, you are just adjusting zero which is part of normal operation. That's why it's a big knob.

    You can safely check the densitometer calibration. Read the standard black sample with the black channel selected and look for a reading of 1.610 on the display. Write down the reading you get on a report. Do the same for the other three color channels.

    I hesitate to calibrate even my own densitometers because I don't know if I will mess it up.

    To reiterate, until you get a user or service manual, change nothing inside the densitometer and just read all the samples and write all the current values displayed on the densitometer without making screwdriver adjustments...

    If the readings are only a small amount (+/- 0.100) off the samples it may not be necessary to calibrate. Remember if the shop is trying to print a standard quality and you change their densitometer, they may meet external standards after your change... but the jump in appearance may be objectionable in-house.

    If the readings are very far from the markings on the samples, this may mean somebody did play with the screwdriver adjustments. Then you might be forced into saying the machine has been tampered with and should not be trusted.

    The screwdriver adjustments are used to set the high readings to match the color sample for the color channel. But they should be done following manufacturer instructions, not an internet expert.

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