This has nothing to do with integration time or sampling rate. The device makes one reading.Paul Colby said:Okay, and Analog to digital, the modern day version of looking, has a finite integration time. When you find one that doesn't please send me the spec.
What you say make absolutely no sense to me. And, it's not the sampling rate it's the time it takes for a sample which is always finite.russ_watters said:This has nothing to do with integration time or sampling rate. The device makes one reading.
Is weight a single point or time-integrated measurement?Paul Colby said:What you say make absolutely no sense to me. And, it's not the sampling rate it's the time it takes for a sample which is always finite.
Actually it may be the latter, or it can be considered a time-integrated interaction. Weight is the interaction of mass and gravity via an as-yet-to-be discovered gauge boson, and that interaction takes time. But this is off topic...russ_watters said:Is weight a single point or time-integrated measurement?
Please review how ADC actually work. An ADC has a number in the spec called the aperture. This is the integration time for a sample. This is very much on topic.russ_watters said:This has nothing to do with integration time or sampling rate. The device makes one reading.
I've never heard of such a thing. Can you give an example of a weight measurement that utilizes a time measurement? Using what equation?Paul Colby said:Every measurement of weight I know of takes some integration time. Our theory of what weight means likely includes some notion of its time invariance. It still will take some integration time to measure it no matter how constant we think it is.
What is the equation for that?Paul Colby said:The kitchen scale I ordered on Amazon used ADCs and a load cell. Reading a voltage is alway, always always a band limited finite integration time measurement.
I'm not familiar with that equation; can you describe what it does?Edit; wait, you said ADC; analog to digital conversion, using time intervals to deconstruct waveforms. I'm not accepting that; you've already made an assumption that you are measuring a time varying signal, regardless of if it is or isn't.Paul Colby said:Well, ##f_p = \frac{1}{2\pi R C}## R is always finite and C is never 0.
I'm trying to figure out how one could ever not understand that a "single point" measurement you speak of is always an idealization.russ_watters said:I'm trying to establish here if you even recognize if there are single and multi point measurements.
Wow, I can't read a scale in 0 time. I can't take a picture of it in 0 time either. I can't use lasers or ADCs or mirrors in 0 time, ever.russ_watters said:There is no time interval involved in/inherent to the measurement. There's no clock on a spring scale.
It takes time to read a load cell. My bet is they are slow.russ_watters said:R=V/I, with (delta)R being a proxy for F.
No? How much time does it take? What's the equation for that? If I take twice as long to read a scale, does that mean I have twice the weight or half the weight?Paul Colby said:Wow, I can't read a scale in 0 time. I can't take a picture of it in 0 time either. I can't use lasers or ADCs or mirrors in 0 time, ever.
Taking a large number of readings in a small time doesn't make the readings have a time parameter. I'm betting it still read a lot of individual measurements that just said N. Not N/sPaul Colby said:This discussion of weight measurement actually amusing. Some years ago I considered using high frequency weight measurements as a means of detecting high frequency gravitational waves (RF frequencies). One would have to make a load cell that could be read out in the MHz frequency range. Not a simple nor uninteresting problem.
It's worth reviewing how they work. A mechanical meter integrates over its response time which is a function of inertia, spring constants and resistance. You can't read them at 100MHz cause they average out the variations on these time scales. It's silly to think of them as instantaneous.russ_watters said:Also, I guess I shouldn't have asked an open question: sure, you can express measurements by chopping up a continuous signal, but that doesn't mean individual measurements aren't discrete. I don't know how a digital voltmeter works, but an analog voltmeter uses magnetism to move a needle to a location; there is no time parameter involved in the reading.
This is simply not correct. There is no t2-t1 like in a traditional velocity measurement: (x2-x1)/(t2-t1)Paul Colby said:It's worth reviewing how they work. A mechanical meter integrates over its response time which is a function of inertia, spring constants and resistance. You can't read them at 100MHz cause they average out the variations on these time scales. It's silly to think of them as instantaneous.
How is this relevant? Just because it doesn't fit your narrow view of the subject? Write out the response of a harmonic oscillator (good model for a meter movement) and solve the equation for a general driving force. The meter position will be the integral of the system green function times the driving force over time. This is a time average no matter how you confuse the matter.russ_watters said:This is simply not correct. There is no t2-t1 like in a traditional velocity measurement: (x2-x1)/(t2-t1)
It's relevant because it is the subject we are discussing. You seem to want to discuss a different subject, and that's the problem. This is the first I've seen you acknowledge you are talking about a different subject!Paul Colby said:How is this relevant? Just because it doesn't fit your narrow view of the subject?
OP asked about instantaneous measurement. How is the meter movement not relevant. My point is measurement is always band limited, it always involves some finite integration time to produce a sample. How this is this a different topic?russ_watters said:It's relevant because it is the subject we are discussing. You seem to want to discuss a different subject, and that's the problem. This is the first I've seen you acknowledge you are talking about a different subject!
Instantaneous is t2-t1=0 or rather that there is no t2. You are talking about t1, t2, t3, t4...etc. As you correctly point out, they are different things (except of course yours contains mine/theOP's).Paul Colby said:OP asked about instantaneous measurement. How is the meter movement not relevant. My point is measurement is always band limited, it always involves some finite integration time to produce a sample. How this is this a different topic?
It does, but only in the sense that sample rate can't exceed the time for a single datum or sample.russ_watters said:Taking a large number of readings in a small time doesn't make the readings have a time parameter. I'm betting it still read a lot of individual measurements that just said N. Not N/s
You seem to be make up what I'm talking about. Give an example where a single sample is performed in exactly 0 time.russ_watters said:Instantaneous is t2-t1=0 or rather that there is no t2. You are talking about t1, t2, t3, t4...etc. As you correctly point out, they are different things (except of course yours contains mine/theOP's).
And not for nothing, but the OP didn't mention measurement.
Nor the measurement of energy, or weight or ... It was a pretty open-ended question. None of these things you've introduced are off topic and are certainly relevant. The difference between quantifiable and measurable was what I commented on. Instantaneous velocity is quantifiable in my view, but as a theoretical construct. The measurement of such things are very much on topic and very much limited to finite time scales.russ_watters said:And not for nothing, but the OP didn't mention measurement.
Selection of a measurement method always makes a host of assumptions. The fact is ones expectations drives the supposed time dependence the measurement method selected will be sensitive to. As I've tried to stress, this involves inferences, guesses and assumptions one must make up front. These are based on models and cost. For example, measurement of weight may well have the implicit ASSUMPTION that the weight is not varying at frequencies above a 100MHz. This ASSUMPTION then justify the experimentalist adopting a method limited by integration time to say 10Hz rather than say 100MHz, 1GHz or higher. These kind of limitations are always present in any real measurement or experiment. They certainly can't be eliminated as you have been implying and they are certainly always present.russ_watters said:I'm not accepting that; you've already made an assumption that you are measuring a time varying signal, regardless of if it is or isn't.
I've never made such a claim. I don't think I'm making up what you are talking about, I think you aren't following what this thread is about, so you are confused about what I'm saying, and why your responses are largely off topic - I think you just don't understand what an instantaneous data point is, measurement or otherwise. Here's my summary of what the thread has been about, from the question the OP asked, to its children and tangents:Paul Colby said:You seem to be make up what I'm talking about. Give an example where a single sample is performed in exactly 0 time.