Hi, I am looking for information that discusses the various methods for A and V acquisition hardware design.
I am specifically wondering how decisions were made for some of the designs out there, like IotaWatt and OpenPowerQuality.
E.g. why use an isolating current transformer vs. a voltage stepdown transformer vs. an integrated isolated single chip solution for current sensing.
E.g. what is the impact of using a transformer when wanting to measure at a high sample rate for e.g. will the inductive transformer suppress high frequencies like transient spikes and harmonics.
E.g. what are the various requirements for certification, inside a panel, outside a panel.
E.g. are there any reference implementations in the open hardware community.
I know, lots of questions, inquisitive minds want to understand the why in the designs.
Any pointers appreciated.
We cannot answer for those. You need to ask the respective design authorities.
The law, as it applies in the UK and the EU. Using bought-in “certified” articles that are separate, to handle mains voltages, means that the ‘low voltage’ parts do not need to meet the same standards and persons with no experience, knowledge or training in working on live parts can at least construct a system with minimal risk to their personal safety, and the safety of those around them.
I would have though that the choice of whether to use a current or voltage transformer was, to say the least, obvious.
That depends on the bandwidth of the transformer in question.
You need to obtain the relevant documentation for the country or countries where you expect to sell the product. Generally, the requirements for “CE” marking apply to any item that falls within the scope of the legislation that is “offered for sale” in Europe, while the former “British Empire” countries generally have a national standard that is closely aligned to the old British Standards.
What will apply if or when European standards are no longer relevant in the UK is open to question.
When you say “I would have though that the choice of whether to use a current or voltage transformer was, to say the least, obvious.”
It is not that obvious to me, I could imagine using either?
I will ask the projects directly, as none have published the decision making or component math, I was hoping for more general purpose resources.
A current transformer transforms current.
A voltage transformer transforms voltage.
Many energy monitoring I.Cs expect a c.t. for the current input, but a galvanic connection for the voltage input. That automatically implies that the front end must be designed to withstand (if not work or measure properly) mains transients, that isolation must be provided further down the signal path, and that the front end must not be accessed by inexperienced and untrained users.