READING fast ADC 10MSPS - TRUE RMS WATTMETER - Page 1
Forum section: electronics / beginners

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 06, 2020, 05:35:15 pm
content: Hello everyone,i would like to ask, cause i am new into digital electronics, which parts/circuitry should i choose to achieve readings at 10MSPS?At the moment I am thinking about stages:1) voltage divider2) full wave rectifier3) analog multiplier4) What next?Some fast FPGA chip? In my first idea i though about some adder with feedback, counter and mcu that will after overflow just take number and divided by CLK cycles. But with 10bit resolution adder should be 34 bit.Thanks everyone.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2020, 12:54:53 am
content: I would start by backing up and questioning why 10 MSamples/second is required for a wattmeter.Is this for line frequency applications? Or is it for something like a solar array?

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 07, 2020, 04:23:08 am
content: Hello,Wattmeter should be also able to measure on DC side, when current reach 50khz.From my point of view it should be able to measure up to 1Mhz accetably.

author: KaneTW
author_rank: Frequent Contributor
timestamp: August 07, 2020, 06:10:59 am
content: Don't bother with an analog multiplier. Two suitably fast ADCs and then either a FPGA or MCU depending on your sample rate to filter and measure.For 1MHz, you shouldn't need more than 5MSPS imo. Probably even less depending on how steep your antialias filter is.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 07, 2020, 10:56:09 am
content: Do you think that ep2c5t144c8 could do that job? + interfacethanks

author: max_torque
author_rank: Super Contributor
timestamp: August 07, 2020, 12:16:10 pm
content: Just google stuff on "precison power analysers"IME with PPA's which i use a lot during electric motor and inverter development, the 'devil is in the details' and half the problem is actually validating what (or watt....) the true reading should be. Mearly accurately digitising the voltage and current waveforms is just the first step.https://www.newtons4th.com/products/power-analyzers/It's all well and good saying "i am able to calculate power with a 1Mhz bandwidth" but actually proving it is entirely different (Companies like N4L and Yogogawa have spent a lot of time, effort and money on proprietry calibration rigs, often with calorific validation to determing the true high frequency accuracy of their devices!(and oh yeah, if you want to use the device on any kind of switching souce/load then you need to be very very aware of the high frequency common mode rejection capabilities of your device, which make the analogue front end a complex thing)

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 07, 2020, 01:50:40 pm
content: Thanks for comment. Whats the price of that "low cost" power analyzer PPA500? I think i can not afford it as i am cheap labor -> working in czech republic, but still better than in africa...My solution should be acomplished in 150$ range. Lower - Better.

author: KaneTW
author_rank: Frequent Contributor
timestamp: August 07, 2020, 10:06:39 pm
content: Forget about getting any usable results in the $150 range. PPA500 will probably be around $6k if it orients itself around Yokogawa's entry-level models.There's a lot of difficult calibration involved. Measuring voltage and current with even just a compensatable (never mind constant) phase difference across the entire input range is not easy.It's impossible to say what size of a FPGA you need until you know what you want to do with the data and what digital filters you require.Look at the amount of effort gone into even low-speed power sensors.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 08, 2020, 10:06:33 am
content: At the moment i am interest in full wave op amp rectifier.Is MIC920 enough for 10Mhz? Slew rate should be more than 188V/us.* There would be three op amps in rectifier so bandwith is three times lower i guess.http://www.learningaboutelectronics.com/Articles/Slew-rate-calculator.phphttps://cz.mouser.com/datasheet/2/268/mic920-1099384.pdf***Update:I missed that MIC920 is out of stock.In CZ i found alternative in AD8055.https://www.tme.eu/Document/ede2c72999a483ea11da3f542ae776ee/AD8055_8056.pdf# Its not rail to rail? ehm I think i dont need it.