Parrt sourcing: Power Measurement ADC IC - Page 1
Forum section: electronics / projects

author: drakejest
author_rank: Regular Contributor
timestamp: August 09, 2023, 06:20:30 am
content: Hello i seldom borrow a Fluke Norma 6004 from a friend to do some power measurements, its great! but recently i had the need to keep on borrowing, although my friend is alright with me borrowing it whenever i want, i could not keep on borrowing on good conscience. I also could not afford to buy one cost about the same as a car. It is here i got the idea of why dont i make one myself. I think it would be a fun project to do. Most of the features the fluke have i really dont need, all i need are the basics power quality measurements (voltage, current, freq, real, apparent, reactive, etc), I dont even need a screen.the biggest hurdle for me would be finding the best ADC chip. So far here are the ADC that caught my interestFrom Texas Instruments:ADS131E08SFrom Analog Devices:AD7768It would seem that these two are the best offerings from their manufacturer.Any advice which of the two IC i should use (or other better recommendation). I really dont have great meteorology experience. I think the first question i should ask is at what sampling rate is required for power analyzing, as that would affect the noise, dynamic range, and bandwith. It would seem that the chip from analog device is better in every regard.. Any points why i should choose the texas instrument one?

author: uer166
author_rank: Super Contributor
timestamp: August 09, 2023, 06:29:59 am
content: You haven't mentioned what accuracy and dynamic range/standards you need to comply with.I have designed revenue grade meters and evaluated the ADS131. The ADC mattersvery littleonce you get to 24 bit metrology dedicated S-D ADCs. >90% of the error budget will be in the passives, sensors, and one of the biggest ones is calibration quality.Sounds like you're trying to design a tool that will cost you probably >$5k in development parts, yet you can buy something for <1k that will do the job just as well.

author: drakejest
author_rank: Regular Contributor
timestamp: August 09, 2023, 08:19:38 am
content: Quote from: uer166 on August 09, 2023, 06:29:59 amthe ADS131 seem relatively easy to design maybe around 100$ - 150$ in components not including the mCU circuit as i would like to start making the ADC portion first , with the ads131 chip @15$ as the most expensive and maybe the voltage reference , op amps and the digital isolator. Which other components could inflate it to 5k$ or 1k$?Anyway babystepsone of my difficulties in choosing the adc is as you have mentioned i do not know the accuracy or dynamic range that i need. I simply lack the experience to know what is enough... Most of the time the reason i borrow the fluke from my friend, is to measure the power consumption of a specific device over a period of time, to be able to calculate the Cost To Operate of a specific device. With that i guess what im going to make should be atleast as accurate as a good Electric meters. Of course if need anything more than that i would borrow the fluke.You have mentioned that you have evaluated the ads131, can you share what you think about it? Do you think its good enough ? I read thistypical applicationfor the ads131, this application looks good enough for my use-case. what do you think?One of my main question though, do sampling rate matter? I mean im pretty sure it is but i dont know if the noise and dynamic range penalty is worth it. In your experience what sampling rate do you use?

author: uer166
author_rank: Super Contributor
timestamp: August 09, 2023, 08:58:50 am
content: You shouldn't need opamps or external reference with the ADS131. It's called an AFE for a reason since it can handle bipolar inputs directly and has a good reference and PGAs on inputs.I guess I'm confused since on one hand you are talking about a 15$k piece of test equipment and in another a way to measure appliance energy over time. For the latter you can get a Kill-a-watt or something for $40 and forget about spending months of your life on a power meter project.The cost isn't just the components themselves, but more the rest equipment you'll need to develop, the test loads to validate, a decent reference meter (although your friend had you covered here), and patience to work through the crazy silicon bugs you encounter with high performance ADCs.You're fixated on sample rate, but that's one of many knobs to turn. Sample rate in sigma-delta isn't like in a SAR ADC, but the ultimate effects are similar: higher modulator frequency means higher possible bandwidth due to higher possible anti-aliasing filter cutoff, but at a reduced effective number of bits.What specs are you after? What load nominal power? What power factor are the loads? If you're doing power analysis you want to measure harmonics of 60hz, if so how high? What is the lowest power you need to meter and at what accuracy? Do you want to use current transformers? Shunts? Are they 1-phase of 3-phase loads? Do you need reinforced isolation? Do you need galvanic isolation? So many questions to answer, but don't get stuck in analysis paralysis since this could be a fun project (although with little utility compared to buying something).Since you're fixated on ADC output frequency, just go with whatever defaults the datasheet mentions since you get the most amount of data for those. Something like 3-10kHz sample output rate is a good start (note that this is not the S-D modulator frequency, that'll be in the MHz).

author: ArdWar
author_rank: Frequent Contributor
timestamp: August 09, 2023, 08:59:19 am
content: Quote from: drakejest on August 09, 2023, 08:19:38 amYes, can even be *very*. Depends on what you intend to do, you probably want to measure up to at least 10th harmonics, which require at least 2ksps.

author: drakejest
author_rank: Regular Contributor
timestamp: August 09, 2023, 10:34:34 am
content: Quote from: uer166 on August 09, 2023, 08:58:50 amof course i need something more than a kill-a-watt meter, i want to able to log the consumption to see if the wattage increased/decreased at certain times. most of the other stuff can be done in software anywaySo i guess that settles it then im going for the ADS131 since its simple and does not need more complicated components such as opamps. has an 8 channel option so i can do 3 phase if i want to. Also can do more than 10khz sample rate.Now the question is which one is better theADS131E08orADS131M08. Aside from the E version having 64kHz sampling rate to the 32kHz of the M version which do you think is better? The E version has more pins to manage but better dynamic range at lower sampling speed, the M version has better dynamic range at higher sampling rate.Do you think its worth the trouble to use the E version? How significant is that extra 32kHz sampling rate?

author: uer166
author_rank: Super Contributor
timestamp: August 09, 2023, 06:56:19 pm
content: You haven't answered a single question when it comes to the specification of the final product, yet are trying to specify a parameter that depends entirely on those specs and implementation details. I recommend taking a step back and writing a list of specific parameters (at the minimum bandwidth/harmonics measurements required, power factor of the loads, dynamic range, and accuracy at that dynamic range). Higher sample rate is a tradeoff like anything else, so more is not better, it's just different.

author: coppice
author_rank: Super Contributor
timestamp: August 09, 2023, 07:04:27 pm
content: If you simply want to build something to measure the power consumption of an appliance to good accuracy, a 50 cents energy measurement chip will give you 0.1% accuracy over 1000:1 dynamic range, if you use it properly. Its consumption is low enough to power it from a simple RC supply. Use some opto-isolators to galvanically isolate it from the rest of your circuitry, and you are done. Cheap. Simple. Accurate.

author: drakejest
author_rank: Regular Contributor
timestamp: August 10, 2023, 09:09:15 am
content: Quote from: coppice on August 09, 2023, 07:04:27 pmOh wow i did not know there are dedicated energy measurement chips... I also noticed that the use different units for dynamic range compared to adc, it is like you said 1000:1 or 10000:1 over 20 seconds accumulation for energy measurements(ADE9430) . Can help me understand what does this ratio mean ?Am i able to extract the highest surge currents from these energy measurement ICs? I guess it would have to be mathematically extrapolated from enegry readings unlike with ADCs where you have the raw readings. It basically does the tracking instead of doing it in software correct?

author: coppice
author_rank: Super Contributor
timestamp: August 10, 2023, 03:46:13 pm
content: Quote from: drakejest on August 10, 2023, 09:09:15 amIt depends which chip you choose. The simplest ones simply give pulses at some X pulses per kWh rate that suits domestic meters. Those are 20 cent (in volume) parts. The 50 cent parts can output a full range of measurements - active and reactive power, voltage, current, accumulated energy, etc. - suitable for smart meters. Some will give you readings down to per mains cycle. Most give you readings more like once per second.They accuracy ratio is based on using most of the input swing of the voltage ADC, and the current ADC at their maxima. Then when the current input drops to 1/1000th or 1/10000th of that you should still be measuring active power to 0.1% accuracy, if your external circuitry is well implemented. The current inputs normally have enough gain for a single phase meter to use a low value shunt connected to them with nothing more than purge protection. Three phase meters get more complex, because of isolation requirements.You found ADI. Look around. There are several makers of these types of parts. Energy meters are a big market, so there are lots of players.

author: drakejest
author_rank: Regular Contributor
timestamp: August 23, 2023, 03:55:26 pm
content: Quote from: coppice on August 10, 2023, 03:46:13 pmCan you share what is your favorite/go to IC? i mostly stick to the popular manufacturers just because they have better documentation and typically have dedicated forums for their products.

author: coppice
author_rank: Super Contributor
timestamp: August 23, 2023, 04:50:36 pm
content: Quote from: drakejest on August 23, 2023, 03:55:26 pmIf you want a fixed function metrology chip ADI and Cirrus Logic are big. Microchip, ST, and others also have offerings. If you are happy dealing with Chinese suppliers, who might not have the best English language support, there are players like BeiLing and ReEnergy. If you want a programmable part that includes a metrology front end, TI, Teridian and Renesas are key players. There are actually a lot of people in this business, but most people are also rans. There are a few big meter makers, like Landis and Gyr, who make a lot of meters with their own ASIC for the metrology part.If you just want a metrology part, I'd start with ADI. They have a big range from very simple single phase active energy measurement parts to 3 phase parts making a fairly comprehensive set of measurements.