I was doing some research concerning implementing an energy meter for in house use when I ran across what seems to me to be fishy patents.

First I ran across US9588147B2(February 2015), which patents the concept of using a high pass filter to block DC as part of the required integrater circuit when using a Rogowski coil to sense current. In my mind, this would be obvious to anyone in the field with the use cases outlined. So I went looking even more.

Next I ran across US7548054(March 2006) which also has the high pass filter for blocking DC at it's core. Now I'm thinking, why would that other patent been granted?

I kept looking and that is when I ran into German patent application DE10320293A1(June 2003), which also covers blocking DC. It was not granted, but would act as prior art I believe.

As far as I can tell none of these cite each other or mention the others. If nothing else, both of the US patents should have at minimum cited the German application(and then gave it up as being prior art).

I stopped looking after the German application. None of these should have been granted to begin with. The problems that DC can cause an integrator are well known and have been for a LONG time.
As an example, Drift Free Intergrators, dating from 1998, deals with the same kind of problem. An while it is dealing with inputs from geophones(earthquake data),their correction concepts would still apply to other areas where intergrators are used.

Yes, I did have an advantage for my research with Google, but the last one granted would also have had it available. I'm not sure when Google patents came on line.

My question is: I do not understand how the US patents were granted in light of the failed German application, let alone other sources dealing with this exact problem. Nor do I see how the examiner of 2015 application failed to find the 2006 patent. A search using the primary key words finds it just fine.

EDIT: Yes, I did read the claims, as a matter of fact I read all of the patents, plus I browsed both some of their citations and those that cited them. Note, the only time you would need an intergrator in an energy measurement circuit is if your using a Rogowski coil to measure current. Left on their own, sooner or later a integrator will saturate to one of the power rails, due to the accumulation of DC on the cap.

The 054B2 patent's claim one is for an integrator for a Rogowski coil with filters. In claim two they make sure the current filter is a high pass. The 147B2's claim one is for an integrator followed by a high pass filter. In their second claim, they tie it to a Rogowski coil.

While 147B2 is fairly clear they are using a high pass filter to block DC, the 054B2 patent does not come out and say it until section 8. In both cases the primary purpose is to keep the DC levels from creating an error in the output. In the German application, claim one is a current measuring circuit using a Rogowski coil(which means an integrator) with a high pass filter before and after, which removes the DC levels as a source of error. Note, an integrator normally does not contain a HP filter, you have to reset it in some way.

So in essence, all three of them want to remove the DC bias levels of the integrator that is required when you are using a Rowokski coil to measure current. Something that is not clearly said is that you'll need to correct the current phase(because those filters will mess with it) ensure proper measurements. In the 147B2

Thank you,
GB Clark aka AE7OO

  • Are you reading the claims? You need to to understand what is actually being patented.
    – Eric S
    Jan 18, 2020 at 17:47

1 Answer 1


I am not familiar with this technology, but in my opinion your summaries about the two US patents are not accurate, or are so simple that obviously one would conclude that the patents could not have been granted. Patents are granted when the claims are directed to a technical product or process (not a concept as you put it, concepts cannot be patented) that is both novel and inventive. I have not reviewed in detail the US patents, but the claims (the independent claims too, not just the dependent claims) define several features that are not disclosed in the German patent application, which moreover seems to solve a technical problem different than those solved by the US patents. So at least the claims are novel over the German application, and about obviousness I cannot say much because I do not know much about this technology as I mentioned earlier, but if they are not obvious then the patents have been correctly granted.

Why the documents were not cited during prosecution of the different patents could be either because the examiner did not find them, or because they were not relevant for the patentability of the claimed invention; if each document deals with a technical problem of its own or the circuits are considerably different, it would make sense not to cite the documents. In any case, time is limited and searching strategies are not always perfect, thus the examiner may have not found the relevant documents, or found them but ignore their relevance.

Lastly, concerning the first of the two patents you refer to, you said "when using a Rogowski coil", which is odd because the independent claims do not even define a Rogowski coil.

  • I'm going to quote from both descriptions:
    – GB - AE7OO
    Jan 19, 2020 at 1:25
  • @GB-AE7OO With regard to '054, I am unable to find disclosure in the German pat.app. "a first analog stable filter operatively coupled to the Rogowski coil, said first analog stable filter configured to process a signal input in a current channel of the system" "a second analog stable filter operatively coupled to the Rogowski coil, said second stable filter configured to process a signal input in a voltage channel of the system.", let alone the matter of claims 7 and 10. Jan 19, 2020 at 18:20
  • @GB-AE7OO I am also having trouble finding the matter of the claims of '147 in any of '054 and German pat.app. in the very same configuration. Perhaps all that is claimed is obvious, I honestly do not know, but many times I have been in front of inventors that say "well, this is completely obvious", but they forget that when it comes to patents, certain requirements exist for determining what and why something is obvious: who is the skilled person, level of skill thereof, what the prior art documents suggest, etc. Examining an invention is not an easy task. Jan 19, 2020 at 18:30

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