Improper R&R Test? Downdraft Velocity in Automotive Spray Booths



We have two different instruments to measure the downdraft velocity in automotive spray booths. Our customer decided to perform an R&R study on the two measurement instruments to determine their capability. They selected 12 different locations in the booth and had two operators take two measurements at each location with each piece of equipment. The operators moved around the booth performing their measurements at different locations, i.e. operator 1 may have been at location 1 while operator 2 may have been measuring at location 7.

Our concern is that this study does not seem to be correct. The downdraft at any point in the spray booth is continuously fluctuating. You can measure 85 fpm and then seconds later a second measurement may read 101 fpm at the same location, for example. If you take a sufficient number of measurements around the booth, the average of a one set of readings will be close to the average of another set of readings but the readings at each location can vary significantly between any two sets of measurements.

We believe that the test as conducted isn't reading the same "part" as the measurements were made at different times and the actual downdrafts are varying continuously and is therefore different for each measurement. We think that unless a study with a very large number of measurements at each location was conducted the results will be meaningless. Can an expert on R&R studies comment? Thanks.


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Not sure anyone would call me an "expert on R&R studies"...but I'll chime in anyway...

The purpose of the downdraft is (I presume) to remove particulate from the area.

That said, it seems that the most pertinent reading is the MINIMUM airflow...not the average.

Presuming these things, perhaps it might be fruitful to measure in each location for 60-120 seconds and record the minimum reading in that area during that time.

Conversely...if what you are after is "Do these gages read correctly?"...put them in a more controlled air flow that doesn't fluctuate so much.


Our understanding of an R&R study is that each operator measures the exact same widget. In this booth downdraft study the operators are not measuring the same downdraft as it is constantly changing. (The downdraft measurements every second are shown on the attached photo - the downdraft numbers are on the left which vary from 91 fpm to 63 fpm).


  • smaller downdraft.jpg
    smaller downdraft.jpg
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