Well I heard this in seriousness before because people get some under rated puny alibaba shunt, run it on overload and it melts and start complaining on the forums that shunts are bad.
for complying with regulation how are you gonna get something in a tight panel ? IMO its going to be extremely difficult to make something like that.I would look at some industrial metering modules. they have stuff that goes on din rail for measuring current. It is likely approved for whatever industrial standards that it might see, so it would be a good starting point.
well maybe because there is like a ground rule thats don't mess with the circuit panel.
40000:1 dynamic range is pretty readily achievable with a CT. I've designed class A revenue grade meters 3-phase and played around with this stuff quite a bit.
Choose correct core, high-permeability, low Hc/remnance, and a good simultaneously sampling S-D ADC of at least 24 bits and it's achievable.
The biggest source of error I found wasn't the core, but the input anti-aliasing filters. Use high-precision class 0 caps and it should be much easier.
The problem with CTs is that you can measure quite nicely high currents in a domestic setup, but if you use a CT that is rated for, say 100A, and want to measure below the 1A consumpion, you really will get high tolerance gibberish due to the tolerances the CT has.This is only true of low grade CTs, using poor quality cores. Modern good quality CTs can be within 0.1% for amplitude and a pretty tight tolerance for phase shift over a 40000:1 range, as uer166 noted.
There is an option to use a Hall effect current sensor. For example, used in current clamps. They can be with a built-in shunt, which reduces the influence of magnetic fields, or mounted on a cable without disconnecting.
In addition, there are many industrial current sensors with different built-in interfaces, such as 4..20mA.
There is an option to use a Hall effect current sensor. For example, used in current clamps. They can be with a built-in shunt, which reduces the influence of magnetic fields, or mounted on a cable without disconnecting.
In addition, there are many industrial current sensors with different built-in interfaces, such as 4..20mA.
For the dynamic range quoted I haven't seen any OTS Hall sensors that will be able to achieve what OP needs. If you know of one please post since I'd actually be interested in such a high performance.
I'm working on a power meter too. I tested multiple CT's. If you need something "cheap" you can search for ZMCT102 (0.35€ on Aliexpress). They have good linearity (0.2%) good phase angle error (<0.25°). Here some tests that I've done to multiple CTs.
Thanks to everyone for their input. I think I'm pretty set on a solid toroidal CT.If you are measuring mains, you will need a DC tolerant transformer. Otherwise half wave loads will give very bad results.QuoteI'm working on a power meter too. I tested multiple CT's. If you need something "cheap" you can search for ZMCT102 (0.35€ on Aliexpress). They have good linearity (0.2%) good phase angle error (<0.25°). Here some tests that I've done to multiple CTs.
That's awesome my dude! I was just planning to do exactly that.
I was thinking of testing some of these https://www.vacuumschmelze.com/products/inductive-components-and-cores/current-transformers (https://www.vacuumschmelze.com/products/inductive-components-and-cores/current-transformers)
and some of these https://www.aliexpress.com/item/1005004704546816.html?spm=a2g0o.cart.0.0.524a38daPkqjq9&mp=1 (https://www.aliexpress.com/item/1005004704546816.html?spm=a2g0o.cart.0.0.524a38daPkqjq9&mp=1)
Let me know if you would like me to share my results. Vacuumschmelze seem to use high permeability core material, and have dc tolerant models, although I suspect dynamic range will suffer.
Do you have any data for low current, less than 1% of nominal?
If you are measuring mains, you will need a DC tolerant transformer. Otherwise half wave loads will give very bad results.
A 40,000:1 dynamic range for a current transformer is pretty readily achievable?How long ago were you last looking at this? 20 years ago 4000:1 at 0.1% amplitude and a small phase variation was somewhat exotic. Now its mundane. Ferrites seem to have moved on. It might be an exaggeration to say 40,000:1 is readily achieved, but the best off the shelf parts can achieve it. If you are relaxed about phase shifts, because you are only concerned with, say, RMS current it is readily achievable. Your key issue there is not the CT, but noise giving you a residual temperature dependant current. You don't get that with power measurements, unless they are very short term, as two independent noise sources don't correlate.
Are your sure? My limited experience suggests even a 4000:1 range is very optimistic? Mains power meters seem to be not a lot better than 1%.
A current transformer relies in mechanical arrangements and stability to work, like other mechanical sensors like pressure, load etc. Not like a a resistor or even a capacitor which are mechanically robust with much less sensitivity to external events, noise, influence etc.
A 40,000:1 dynamic range for a current transformer is pretty readily achievable?
Are your sure? My limited experience suggests even a 4000:1 range is very optimistic? Mains power meters seem to be not a lot better than 1%.
A current transformer relies in mechanical arrangements and stability to work, like other mechanical sensors like pressure, load etc. Not like a a resistor or even a capacitor which are mechanically robust with much less sensitivity to external events, noise, influence etc.
I investigated hall and GMR based sensors etc.Hall probes are interesting. Hall probe chips have serious stability problems. Its hard to make things which are better than 2% accurate over a modest dynamic range with Hall probe chips. However, at least two companies have their own in house ASIC which integrates a Hall probe with power measuring electronics on a single die, and achieve really good temperature stable accuracy for power measurement in utility energy meters. Assume they have some well tune compensation on those chips.
Besides their non-linearity, my problem is that I want to get at least up to 9kHz... so ATM, I'm rather sure, I will take the shunt approach.
From my preliminary research, 24bit audio ADCs should be fine... but there are relatively affordable 32bit audio ADCs with 768kHz sampling rate around.A lot of audio ADCs do not permit the use of an external voltage reference. However, if you look around some have a pretty temperature stable internal reference, and can work well for accurate measurement. I'm not clear why they made an effort to achieve those stabilities for the audio market, where its irrelevant.
My intention is to have them isolated and floating at mains potential and doing U/I per phase with the 2 channels.
I'm not clear why they made an effort to achieve those stabilities for the audio market, where its irrelevant.
If you want 20ppm/C or better you need to make a chip by chip effort to achieve that. Been there, done that. You are talking about <20 cent chips. You really don't want to add any cost to those.I'm not clear why they made an effort to achieve those stabilities for the audio market, where its irrelevant.Well, I'm pretty sure, they just use some available standard-cell-reference (that was cheaply available from the fab) instead of inventing a poorer new one :)