what frequency should i filter reading Voltage and Current on mains V and A - Page 1
Forum section: electronics / projects

author: drakejest
author_rank: Regular Contributor
timestamp: January 09, 2021, 01:43:38 pm
content: I am building an energy monitoring circuit that reads voltage and current, Before everthing the one doing the measuring is a differential delta sigma ADC that i will be setting to sample at 25kS/s - 50kS/s.Voltage is read by using the mains voltage and divided down by high voltage rating resistors somewhat shown in this.In the image i have just used a placeholder filter values. What would be the optimal frequency should i set my filter to for measuring main voltage.At the same time current is done via a current transformer and filters is done about the same way as the voltageWith the only difference is i have placed non differential filters incase i do some non differential. I am utilizing R8 and R6 as a filter resistor and a voltage divider (is this okay or should i split the resistor?). again what would be the ideal frequency shoulld i set my filters? I assume the current is set to be much higher because current waveform wont be as clean as the voltage Am i correct?

author: S. Petrukhin
author_rank: Super Contributor
timestamp: January 09, 2021, 07:09:39 pm
content: First of all, do not use the signal passing in the opposite direction from right to left on the circuits, this is confusing.It is common to use the same direction in circuit design as writing texts from left to right, Entrance on the left, exit on the right.

author: MasterT
author_rank: Frequent Contributor
timestamp: January 10, 2021, 01:48:18 am
content: For precise measurements up to 20-th harmonic, 20 x 60 = 1200 Hz

author: jkostb
author_rank: Regular Contributor
timestamp: January 10, 2021, 12:09:15 pm
content: I hope your measuring circuit is completely isolated from the remaining circuit. It is very dangerous to connect the AD converter and other parts directly to the mains without any isolation and surge protection.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: January 10, 2021, 12:41:11 pm
content: Quote from: jkostb on January 10, 2021, 12:09:15 pmIf you have a guaranteed neutral position, what is the difference between a phase wire and a Vcc wire other than voltage?

author: drakejest
author_rank: Regular Contributor
timestamp: January 10, 2021, 01:22:07 pm
content: Quote from: jkostb on January 10, 2021, 12:09:15 pmThe ADC is isolated by a reinforced isolation digital isolatorQuote from: joeqsmith on January 10, 2021, 02:55:01 amSo i would be plenty fine using my lowest setting 25kS/s, or i can go lower? also filters are vey hard to built with CP0 caps dont have a lot of values to choose from ? would increasing the resistor be alright to a few kilo ohms be alright?

author: Wolfram
author_rank: Frequent Contributor
timestamp: January 10, 2021, 01:54:12 pm
content: Beware of the phase shift introduced to the higher harmonics by the filter, if you do any calculations that depend on the phase between voltage and current. If you use the same filter response for voltage and current, this error will cancel out.

author: drakejest
author_rank: Regular Contributor
timestamp: January 10, 2021, 01:56:47 pm
content: Quote from: Wolfram on January 10, 2021, 01:54:12 pmSo what you are saying is use the same filter for both voltage and current , am i correct?

author: mikerj
author_rank: Super Contributor
timestamp: January 10, 2021, 02:26:50 pm
content: Quote from: drakejest on January 10, 2021, 01:56:47 pmThe same filterresponse. Two filters with the same response, one for voltage and one for current. You could have a single filter that you can switch between voltage and current, but if you have two ADC channels that seems a more complex way to go and you have to worry about settling time etc.

author: drakejest
author_rank: Regular Contributor
timestamp: January 10, 2021, 02:45:07 pm
content: Quote from: mikerj on January 10, 2021, 02:26:50 pmIt is actually multiple channel of the same ADC. . . Wont it have same filter response if they have the same configuration with the same values ? Apologies i have no idea what you mean by filter response,

author: rstofer
author_rank: Super Contributor
timestamp: January 11, 2021, 05:52:54 pm
content: In the second schematic, how much current is flowing to ground?