Densitometer Stability

Discussion in 'Darkroom Equipment' started by CPorter, Oct 13, 2012.

  1. CPorter

    CPorter Member

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    Just a quick question, are densitometer readings more stable (for lack of a better phrase) if the unit remains on for some period of time while calibrating it periodically it prior to use? This opposed to simply turgning it on, then waiting for a few minutes, then calibrating it prior to use.

    Thanks
    Chuck
     
  2. ic-racer

    ic-racer Member

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    Depends on the unit. The Tobias I use has a regulated supply and the circuit is designed specifically to not need a warm up. One of my units did waver a little through time, but there was a poor connection in the power supply causing it. So, how well your unit behaves depends on its design and how certain you are that it is in 100% working condition.

    In practical terms, I check the calibration wedge when I start making readings, then again when I am finished. If they agree, then there probably was no change in response during the intervening time.
     
  3. Davec101

    Davec101 Member

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    How old is the denisitometer and what model? I wrote a post a few months back on the use of denisitometers which can be viewed here. Depending on your type of usage its wise to get them recalibrated every so often. Also do you have a step tablet that came with the unit to compare against?
     
  4. CPorter

    CPorter Member

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    I have an X-Rite 301 B&W Transmission densitometer and yes I do have a calibration tablet. It does calibrate to the desired reading after I have powered it up and nulled it properly. I turn it off when I'm done, sometimes the next time I go to use it, power it up, null it, then insert the calibration tablet, it seems to always have to be adjusted again, i.e., it is more than .02D units off. I was just wandering if this has to do with the power and perhaps I should turn the unit on let it remain on for a good while before use.
     
  5. gmikol

    gmikol Member

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    I know that both my Xrite 361 and my Speedmaster tr-90 recommend a warmup period, though I don't remember exactly how long offhand.

    It's not surprising to see a small drift from a warmed-up unit to one that has cooled back to ambient temperature. Electronic components warm up, and their values can change slightly with temperature. How sensitive a device may be to those component changes is a function of the circuit design.

    If you only need to make a single reading or two, then there's no harm in turning on, calibrating and taking your readings in a fairly short period of time, the thermal state of the unit won't change much in those couple of minutes. If you're going to be taking a number of readings over a period of time, especially those which need to be compared to others, it's probably best to allow a warm up period prior to calibrating and to leave the unit on until you're done with all your readings. For critical work, you should check against the calibration plaque prior to making each set of readings, re-calibrating as necessary.

    --Greg
     
  6. CPorter

    CPorter Member

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    This is what I've been doing since I've had it, but I was curious as to how extended periods of being "on" may or may not improve things.

    Thanks
    Chuck
     
  7. gmikol

    gmikol Member

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    Allowing it to warm up fully (10-30 mins.) will not hurt it from an accuracy standpoint, and probably help it, longer than that, you need to balance that against lamp hours. Leaving it on all day for one set of measurements probably doesn't make sense. The replacement lamp for my Xrite costs almost $100. Some densitometers bulbs may only cost $5 or 6.

    Hope that helps...

    --Greg
     
  8. Chan Tran

    Chan Tran Member

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    My X-Rite 801 doesn't turn the light on until it does the measurement so I could leave it on all day without hurting the lamp. It does seem to drift a bit so I calibrate it before use. The calibration routine is pretty much automated and can be done in a minute.
     
  9. gmikol

    gmikol Member

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    My 361 and my TR-90 are both lit the whole time, at least in transmission mode. I think the tr-90 on lights the lamp on demand in reflection mode.

    --Greg
     
  10. Saganich

    Saganich Subscriber

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    Last time I checked my MacBeth TR524 didn't waiver between short start-up measurements and prolonged warm-up.