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Gage R&R on a one shot measurement system

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by Ghaleb, Jul 31, 2019.

  1. Ghaleb

    Ghaleb Member

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    Hello,

    My team has designed and tested a measurement system that quality engineering department would like to perform a Gage R&R on it.
    However, this measurement system is a one shot system. Basically it can be used once and then it is destroyed.
    Note that the part it is measuring is not what is being destroyed, the actual measurement system is.

    My questions are:
    1. Am I correct to state that a nested, crossed or minitab's expanded Gage R&R is not appropriate?
    2. What is the appropriate method to use?
     
  2. Miner

    Miner Moderator Staff Member

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    Can you provide more details on the measurement system and how it is destroyed during test? Any speculation without this information are apt to be wrong.
     
  3. Ghaleb

    Ghaleb Member

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    It is a temperature measurement system that is used during engineering/verification testing. The system consists of the Data Acquisition Unit (DAQ) and a probe that is inserted in a cavity in an enclosure.
    During the testing, the cavity is filled with a liquid that cannot be removed after the fact and damages the probe and therefore, cannot be reused.
    The DAQ portion of the system is not destroyed and is reused.
     
  4. Miner

    Miner Moderator Staff Member

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    Can the DAQ and probe be evaluated in another manner (i.e., outside of the cavity and liquid) that does not destroy the probe?

    Presumably, you calibrate/verify the probe without destroying it.
     
  5. Ghaleb

    Ghaleb Member

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    We do calibrate/verify the probe without the liquid. However, the results we will be using requires the liquid. Someone said that maybe do a capability study without the liquid and assume it is good enough to justify not running a Gage R&R
    From your question, I get the impression that you agree that the Gage R&R is not appropriate, correct?
     
  6. Miner

    Miner Moderator Staff Member

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    While I agree it is not feasible in the manner that you initially described, I do not rule it out entirely. A gage R&R does not necessarily require exact use conditions. While those conditions are certainly desirable, some information is better than no information. I recommend that you create conditions that are as close to your use conditions as possible without damaging or destroying the probe and running the study.

    What damages the probe? Contact with the liquid? Temperature? Insertion in the cavity?
     
  7. Ghaleb

    Ghaleb Member

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    One of the aspects of the system is that the liquid flows.
    After the initial test ,the liquid properties changes and therefore, the second test is not representative to the actual system.
    The liquid cannot be removed, and blocks the inlet to the cavity.
    The liquid could settle on the probe and therefore, the second test is no longer representative.
    The liquid doesn't damage the probe directly, the process of trying to clean up, removing to probe and inserting in a different enclosure, etc..all tend to result in damage to the probe
     
  8. Miner

    Miner Moderator Staff Member

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    Sorry for the delay in responding. I was off on vacation. From the sounds of your application, it is the application that is not repeatable, not the measurement system. I recommend performing the R&R study using an environment and a liquid that does not have the issues that you describe.
     
  9. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Can I confirm what characteristic is being measured? Is it the temperature of the liquid once it's injected into the cavity? I'm interested to know why this is important and how it was arrived at as being a significant characteristic.
     
  10. Ghaleb

    Ghaleb Member

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    Yes, it is temperature that is being measured.
    The customer will insert a similar enclosure with a cavity into the system and then applies the liquid into that cavity. The enclosure is actually a disposable part. The liquid is being analyzed and the results are reported to the customer. One of the requirement is that that the liquid is within a specific temperature range.
    This enclosure that is used by the customer cannot measure temperature directly so we had to come up with our own for verification testing, production final test and other activities. Quality Engineering is asking us to perform a Gage R&R on it. From my reading on Gage R&R it doesn't seem like it is appropriate since I cannot reuse it.
     
  11. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Could you use a liquid with similar viscosity and thermal properties but which doesn't "set"? Do you know the thermal properties of the cavity? Can you calculate/predict the heat transfer from the liquid to the cavity?
     
  12. Ghaleb

    Ghaleb Member

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    Miner:
    Welcome back!
    My comment earlier today (10:29 AM) is also a response to "it is the application that is not repeatable, not the measurement system."
    We still need to perform our test, the measurement system is a single use, but so is the actual application when the customer uses it. The instrument used to perform the test is not single use, but it does use a disposable which is what our measurement system is based on.
    The system being measured is can be reused. The measuring "tool" cannot, which is part of the measurement system.

    Andy Nichols:
    Could you use a liquid with similar viscosity and thermal properties but which doesn't "set"? We have tried that. Either the liquid sets, the viscosity or thermal property are not not similar, or the system, detects an error provides results too early and ends the test before we can get the results we need. Changing the control software is unfortunately not allowed
    Do you know the thermal properties of the cavity? Yes, we do.
    Can you calculate/predict the heat transfer from the liquid to the cavity? Yes, and we have done that, we had to make some assumptions but that's normal for this kind of analysis. We are also required to perform an actual test though.
     

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