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> Area Under Measured Curve?
Shocker
Posted: August 04, 2014 04:46 pm
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Hi,

I have measured the current and voltage waveforms whilst powering a circuit. I want to calculate the area of the curve under both waveforms. How would i do this? Obviously if this was theoretical, i would integrate the equation between the limits.


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Sch3mat1c
Posted: August 05, 2014 04:02 am
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Er... you would integrate, of course...??

I mean, do you actually have real analytical functions to do calculus on?

Or, by "measuring", do you mean a data series, in which case you want a summation for the discrete-time equivalent (Riemann sum)? Or is this a curve written on a piece of paper, so you can cut out the paper and weigh it (assuming a paper of uniform thickness and density -- uniform paper "weight") for the same result?

Tim


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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
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Shocker
Posted: August 05, 2014 11:19 am
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I mean if i have a black box full of electronic wizardry. Whilst i apply certain signals to it and want to calculate the average current consumption/wattage. I would want to measure particular lines with current metres/oscilloscopes which would give me a set of data points. Now that i have the data points and can plot a graph, i was wondering how i would be able to measure the area under the curve.

I suppose the Riemann sum is the only way?
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Sch3mat1c
Posted: August 05, 2014 11:48 pm
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Oh ok, so you're not after the integral after all, just the average -- use an RC or LC filter and a pair of DMMs. Actually, DMMs usually smooth things out well enough on their own (the digital converter is an integrating type -- integrating repeatedly over a known time period, so the integral is always bounded).

For the AC case, you have to multiply first, and then filter. For the DC case, strictly speaking, you still should, but if the AC components are small enough in amplitude or well enough attenuated by the filter, then you will get proper DC power.

If you must use a scope (and assuming the current probe is good down to DC -- beware of hysteresis on the typical Hall sensor types, which manifests as DC offset), if you have a DSO it should have a MATH function with multiplication. Then measure the average / mean / DC value of MATH.

Tim


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Shocker
Posted: August 06, 2014 03:44 pm
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Thanks.
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