Which Circuit is Best for Sampling Voltage and Current in the 250V, 30A Range?

In summary: If the required sample rate is low then I would suggest a DMM with a (isolated) digital output (so it can be connected to a PC).That would provide you a safe framework to work with.If cost is also a concern then some (cheap) DMMs has DIY mods to provide (isolated) digital output.
  • #1
core7916
56
3
Hello,
Please help me to create the sampling processing circuit.
i have to create the voltage and current sampling processing circuit, Then the output of circuit will be fed to processor to further operation.
output voltage of my original circuit will be maximum 250v and current is 30A(peak, not mean) which i have to sample.
can any one suggest proper which will do the current and voltage sampling with this range, or provide circuit.
Thank you.
 
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  • #2
You can always try to use voltage divider to scale the voltage down to 0/5 V range, trivial to deal with with any microcontroller.
 
  • #3
Borek said:
You can always try to use voltage divider to scale the voltage down to 0/5 V range, trivial to deal with with any microcontroller.
ok sir , but i need the proper micro controller which can do the sampling, please suggest any.
 
  • #4
core7916 said:
output voltage of my original circuit will be maximum 250v and current is 30A(peak, not mean) which i have to sample.
250Vac or 250Vdc? What processor will the sampled data be fed to, and what interfaces do you have available for that interface? (Ethernet, USB, Parallel IO, SCI/SPI, etc.)

If the voltage is AC, you should use a standard power monitoring module. Something along the lines of a Kill-A-Watt module, but a little higher power capability and with the appropriate interface for your processor.

1685970900485.png

https://www.harborfreight.com/kill-a-watt-electric-monitor-93519.html
 
  • #5
core7916 said:
output voltage of my original circuit will be maximum 250v and current is 30A
What kind of sample rate is needed?
If the required sample rate is low then I would suggest a DMM with a (isolated) digital output (so it can be connected to a PC).
That would provide you a safe framework to work with.
If cost is also a concern then some (cheap) DMMs has DIY mods to provide (isolated) digital output.

Ps.: if high(er) sample rate is needed then you might try to look for USB 'oscilloscopes' with probes for the required voltage range.
Isolation or a proper diffprobe might be required.
 
Last edited:
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  • #7
By specs , for example instant Power is not Average power = Vrms*Irms, so how many samples per cycle do you want to compute RMS per cycle. You cannot do this with just undefined samples. When you try to design something before you understand the requirements or how commercial equipment works, you end up learning the slow way.
 
  • #8
Yeah, this is all very subjective. The simplest answers have been given, but we don't know what the constraints are. My idea would be to investigate the use of potential and current transformers first. Go from there.
 
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  • #9
It needs to be changed from a subjective to an explicit task with well defined specs. What is your purpose? What are the goal? minimum and ideal expectations? (must haves & nice to haves). Trial and error learning step?
 
  • #10
Sometimes to help to understand the question (while trying to keep the one asking safe) is part of the job.
Sometimes it is the job.
 
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  • #12
TonyStewart said:
Canada has a regulation of 3% maximum error in power meters.
Holy cow, 3%?! That seems huge! Part of my company used to do commercial power meters, and I'm pretty sure that they needed to be calibrated (across power levels and temperature) for more like 0.1% max error. I'll need to find some references, though. A recent device that I helped to design and qualify (including my calibration program) had to meet 0.5%...
 
  • #13
core7916 said:
ok sir , but i need the proper micro controller which can do the sampling, please suggest any.
1. What microcontrollers have you experienced in the past ?
Arduino ? Cortex-M0, such as the STM32 Blue pill ?

2.a. Is the power you want to sample DC ?
2.b. or what is the AC frequency ?
 
  • #14
berkeman said:
Holy cow, 3%?! That seems huge! Part of my company used to do commercial power meters, and I'm pretty sure that they needed to be calibrated (across power levels and temperature) for more like 0.1% max error. I'll need to find some references, though. A recent device that I helped to design and qualify (including my calibration program) had to meet 0.5%...
we have -40 to 40 'C ambients and this includes low p.f. impulse loads. but I was also in AMR biz too for 5 yrs so this surprises me too.
 
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  • #15
berkeman said:
250Vac or 250Vdc? What processor will the sampled data be fed to, and what interfaces do you have available for that interface? (Ethernet, USB, Parallel IO, SCI/SPI, etc.)

If the voltage is AC, you should use a standard power monitoring module. Something along the lines of a Kill-A-Watt module, but a little higher power capability and with the appropriate interface for your processor.

View attachment 327438
https://www.harborfreight.com/kill-a-watt-electric-monitor-93519.html
output voltage is dc and sampled data will be fed to fpga. so what micro controller wil do the sampling.
 
  • #16
Baluncore said:
1. What microcontrollers have you experienced in the past ?
Arduino ? Cortex-M0, such as the STM32 Blue pill ?

2.a. Is the power you want to sample DC ?
2.b. or what is the AC frequency ?
i want to sample the dc power, i dont have much knowledge about arm, or stm32, can you suggest any ic which can be used for sampling.
 
  • #17
core7916 said:
output voltage is dc and sampled data will be fed to fpga. so what micro controller wil do the sampling.
You can measure the current with a low value resistor near ground, or a Hall effect current sensor. The DC voltage will need to be attenuated with a resistive divider before conversion. The speed and accuracy required of the sampling will depend on the application, which you have not yet identified.

core7916 said:
Hello,
i am programming pga970evm module and the core is of arm cortex m0.
You met Cortex-M0 and C in February. I would suggest you stay with that. Get yourself an ST-LINK V2 programmer and an STM32F103C8T6 Blue pill. Total cost should be less than $20. There are many instructional videos on the web that will show you how to program the 12 bit A-D converter(s) in C to sample, and then write the data out to your FPGA.
https://www.ebay.com.au/itm/304767925985
https://www.ebay.com.au/itm/364207488111
 
  • #18
core7916 said:
output voltage is dc and sampled data will be fed to fpga. so what micro controller wil do the sampling.
What cutoff frequency will you set for your anti-alias filter? Which polynomial will you use for that filter?
 
  • #19
What design criteria are you familiar with regardless of the hardware used.
 
  • #20
berkeman said:
What cutoff frequency will you set for your anti-alias filter? Which polynomial will you use for that filter?
Let's get something happening that can be built on to empower the future. Perfection is the enemy of progress. Exploration is good here.
 
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  • #21
Baluncore said:
Exploration is good here.
Sort of. Based on this poster's past history, I'm worried about them (again) asking about designing circuits with high voltage and high power. :wink:
 
  • #22
berkeman said:
Based on this poster's past history, I'm worried about them (again) asking about designing circuits with high voltage and high power.
Let's encourage them to program low-voltage logic circuits, then build on that success. I might learn something.

They will be more careful, if they need to avoid blitzing and having to reorder, a complete 32 bit processor development system, that does 70 MIPS and costs almost $5. It is the cost of postage, and the delivery delay that will slow them down, not high-voltage excitement.
 
  • #23
The best tool is the one you know how to use to perform the task you define.
 

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