Help interpreting a design for power management unit

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Discussion Overview

The discussion revolves around interpreting the specifications of a power management unit (PMU) design, particularly focusing on the sampling rates mentioned in the documentation. Participants explore the implications of these rates for domestic applications, addressing potential discrepancies and their understanding of sampling theory.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant questions the statement that "AC signals are measured 30 times per cycle and 1200 times per second," suggesting that for a 60Hz supply, this should result in 1800 samples per second.
  • Another participant agrees with the first, noting inconsistencies in the sampling rate and the time axis of a referenced figure, which is in hours.
  • Concerns are raised about the high sampling rate of 1200ksps, with one participant suggesting that this may be excessive compared to other devices that operate in the KHz range.
  • There is speculation about whether the 1200 samples per second figure is a typo, and participants seek clarification on its origin.
  • One participant expresses interest in the project, sharing their background in theory and the challenges of applying that knowledge practically.
  • Questions arise regarding the necessity of reconstructing the waveform from sampled data versus directly reading binary values from the ADC output.

Areas of Agreement / Disagreement

Participants generally agree on the calculation that 30 samples per cycle at 60Hz should yield 1800 samples per second, rather than 1200. However, there is no consensus on the implications of the high sampling rate or the necessity of waveform reconstruction.

Contextual Notes

Participants express uncertainty regarding the specifications and their practical implications, particularly about the sampling rates and their relevance to the intended application. There are unresolved questions about the accuracy of the documentation and the requirements for effective signal processing.

Who May Find This Useful

Individuals interested in power management unit design, signal processing, and practical applications of theoretical knowledge in electronics may find this discussion relevant.

jendrix
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Hello,

I have been looking to build a pmu similar to this device, it will be for domestic use.

https://www.digikey.com/en/articles/techzone/2014/jan/low-cost-microcontroller-based-phasor-measurement-units-improve-smart-grid-reliability

I am having a bit of trouble with the sampling part and was unsure whether it was a typo. It says "AC signals are measured 30 times per cycle and 1200 times per second"

If this is from a 60Hz supply then wouldn't it end up 1800 times per second?

There is also this part later on

"The microcontroller receives a filtered analog signal as input to the A/D. These signals are converted at a minimum sample rate of 1200 ksps"

Wouldn't 1200ksps be too high, surely that would be a sampling rate of 1.2MHz, I have seen other devices which sample in the KHz range.Regards
 
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I agree with you. They also refer to figure 1 as showing how sampling at 1200 samples per second helps show up oscillation, yet the time axis on figure 1 is in hours.
 
jendrix said:
Wouldn't 1200ksps be too high, surely that would be a sampling rate of 1.2MHz, I have seen other devices which sample in the KHz range.
As far as I know digital postprocessing (especially filtering) requires quite an oversampling. But 1.2MHz indeed is a bit too much. Guess somebody there strongly believes in marketing...

CWatters said:
They also refer to figure 1 as showing how sampling at 1200 samples per second helps show up oscillation, yet the time axis on figure 1 is in hours.
In the context of the graph it's OK.
 
Thanks, so was probably a typo?

So where does the 1200 come from? Wouldn't it be 1800 samples per second?
 
I agree, 30*60=1800, not 1200.

jendrix said:
I have been looking to build a pmu similar to this device, it will be for domestic use.

Now that's interesting. Do you have any plans? any hopes? for what to do with it when it is complete?
 
anorlunda said:
I agree, 30*60=1800, not 1200.
Now that's interesting. Do you have any plans? any hopes? for what to do with it when it is complete?

It's actually for a fun project believe it or not, I'm finding it quite challenging as I have mainly done theory in the past, so transitioning that knowledge to a real life application should be fun.

If the aim were 30 samples per minute does that mean I would need to sample at 30x the mains frequency or would I be able to sample lower, reconstruct the wave and get the data from there? I was confused whether I would need to even reconstruct the waveform or could I merely just take the output from the ADC and read the binary values on a microcontroller? Regards
 

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