Hey all, I'm new here. I came across a video which seemed to discredit PPV as a method for monitoring structures, but I'd love to get other opinions. Does anyone defend the practice and why do people who oppose it do so?
So you're saying that the problem is really in the design of the sensors themselves and not using PPV to measure this? What is the basis for this view, Kelly?
As a general scientific principle, if a method doesn't always work, it can't be relied upon. That was my concern.
The video did not demonstrate that there was a problem that needed to be solved...
I will let Kelly give her own direct respnse to your direct question to her; but, here is my simple input on the issue.
The application of all "reliable" principles even when mathematically determined are dependent upon the accuracy of the observations of those principals and therefore the applicability of the instruments and observation methods utilized in those observations as well as the background priniciples that determmine what method/instrument are appropriate for the observation.
What I fail to see in the presentation is any statement or display of the amount of error that has been shown to occur from the application of currently available instruments and their application methods; which, brings us to the "close enough" view of measurement applications. As an example, exactly how many decimals of accuracy in a series of calculations are necessary to consider a mathematical solution "accurate" i.e should we abandon the use of PI because we cannot determine its unknown final value as the number of decimal points approach infinity? That is why making statements such as presented based purely upon theoretical arguments of accuracy are of little use in real world applications of science and engineering.
Really? Did you not notice the simple demonstration in high frequency and the problems therein? Surely, if a model does not work in all cases, it needs a rethink. A new model even. Did you even watch the video? What do you use PPV for Kelly? It might work in the majority of cases but if it doesn't then you've got some pretty big problems. I'm sure we can agree on that.
This is what specifications and competent engineering is about. Set the range of operation, temperature requirements, etc... If the end item utilized in the application meets functional requirements then we are "Close enough".
I don't care how much money the product costs - perfect does not exist in the products we design, engineer and build.
Last edited by Kelly Bramble; 11-01-2014 at 05:09 PM.
Actually, neither Kelly nor I are overlooking “safe practices”. If you think that safety standards are based on “absolutes” and not on "best practices" you have been seriously misled.
In 40 years of engineering I have worked under the most stringent regulations and standards in practice; and, in the development and applications of all standards there still remain discussions about some of their elements.
What is most important in applying standards is recognizing the limits of those standards. That is what good engineering practice is based upon. There are no absolutes in science or engineering.
As for this particular case, I repeat: "the speaker makes only a general statement about limits of accelerometers; for example, his statement about their lack of ability to measure the "0" point of resonance, as though that has any applicability in designing structures to avoid the critical resonance region for safety. I also repeat: "the lecturer does not give any evidence to indicate that current "best practices" and equipment used have failed to provide a safe basis for structural design". If one is going to refute a standard or practice, evidence of their lack of effectiveness is mandatory.
There is not a single thermometer that is accurate from absolute zero to 10,000 degrees K but that does not mean that there are no thermometers that can accurately measure the safe temperatures for food storage or the safe range of operating temperatures for super heated steam systems.