How to block an AC current and only get the DC componant of a signal

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How can I measure only the DC component of the current through a resistor when an AC current is also present?

Measure the combined current as a voltage across R3 with an op-amp or similar, then use a low-pass filter to remove the AC component and leave the DC part [#21683367] If the measurement point is at a high voltage, use an op-amp that can withstand it or add a resistor divider first [#21683367] A simpler passive option is an inductor, which behaves like a short at DC and presents high impedance to AC because XL = 2πfL [#21683372] A direct DC-amps multimeter was also suggested as a practical alternative [#21683367]

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#1 21683364 23 Oct 2019 19:04

Wissal Han Wissal Han

Anonymous

Post #1
21683364 23 Oct 2019 19:04

Hello,
I have a currant AC source (about 100A)connected to a load, this same load is in parallel with a 12VDC voltage source and a resistance.How can I get the DC part of the current signal crossing the resistance?
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#2 21683365 25 Oct 2019 05:25

Elizabeth Simon Elizabeth Simon

Anonymous

Post #2
21683365 25 Oct 2019 05:25

Wissai,
A diagram of this circuit showing the connections and where you want to measure would be helpful.
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#3 21683366 28 Oct 2019 18:40

Wissal Han Wissal Han

Anonymous

Post #3
21683366 28 Oct 2019 18:40

Hi Elisabeth,Thank you for your answer.A would like to block the AC componant from de current measurement at 'mes' .
Measure combined current then low-pass filter AC
#4 21683367 29 Oct 2019 20:31

Elizabeth Simon Elizabeth Simon

Anonymous

Measure combined current then low-pass filter AC
Post #4 21683367 29 Oct 2019 20:31

The approach I would take for this is to measure the combined current using an op-amp or similar (using the voltage drop across R3) Make sure you get an op amp that can withstand the voltage or use a resistor divider. Then once you have the combined result you can use a low pass filter to remove the AC.Or depending on how many you have to build and how you need to use the output, you could get a cheap multi-meter and insert it in the circuit with it set to DC amps.
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#5 21683368 30 Oct 2019 14:56

Wissal Han Wissal Han

Anonymous

Post #5
21683368 30 Oct 2019 14:56

Thank you very much, I am going to try that.I also want to
know your opinion about this system. I added the circuit circled in the
schematic to be able to detect if there is a cable disconnection in the
resistance R2.Do you think it could work by measuring the DC current accross R3
Need open-circuit detection for current source cable
#6 21683369 04 Nov 2019 15:31

Wissal Han Wissal Han

Anonymous

Need open-circuit detection for current source cable
Post #6 21683369 04 Nov 2019 15:31

Hello,To explain more the system and my need :I am trying to find a way to automatically stop de current source in case there is an open circuit somewhere between de current source and the load R4.R2 represents a simplified model of the resistance of the cable between I1 and R4.My problem is that I couldn't find a way to detect the open circuit.Also the current source generate a AC current with multiple harmonic from a few hertz to few hundred hertz that have the same amplitude. Which makes it harder to detect a law current crossing R4.Could you please help me to find a way to detect a cable disconnection that is reliable and fast?
#7 21683370 05 Nov 2019 05:24

Elizabeth Simon Elizabeth Simon

Anonymous

Post #7
21683370 05 Nov 2019 05:24

The easiest way to detect an open circuit in R2 would be to measure the voltage on R1 (in parallel with current source). If R2 is disconnected then current from I1 will go through R1 instead of R2. When the peak or RMS voltage measured across R1 exceeds a certain value (say 2x normal) then shut the circuit off.
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#8 21683371 05 Nov 2019 20:15

Wissal Han Wissal Han

Anonymous

Post #8
21683371 05 Nov 2019 20:15

R1 and I1 represent an audio power amplifier. I just used this model to make some simulations.
#9 21683372 07 Nov 2019 23:27

Faisal Maache Faisal Maache

Anonymous

Post #9
21683372 07 Nov 2019 23:27

Hey Wissal Han, you can simply use an inductor that will act as a short circuit in dc and bock the AC current because the impedance will be very high for the ac as we all know XL= J(2pi*f )L.
#10 21683373 16 Dec 2019 15:54

dazzy12 kafe dazzy12 kafe

Anonymous

Post #10
21683373 16 Dec 2019 15:54

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Topic summary

The discussion addresses the challenge of isolating the DC component of a current signal in a circuit where a 100A AC current source is connected in parallel with a 12V DC voltage source and a resistance. The goal is to measure only the DC part of the current crossing the resistance while blocking the AC component. Suggested solutions include using an operational amplifier to measure the voltage drop across the resistance combined with a low-pass filter to remove AC harmonics. Alternatively, a DC ammeter can be inserted in the circuit for direct DC current measurement. To detect cable disconnection in the load path, it is proposed to monitor the voltage across a parallel resistor; a significant increase in voltage indicates an open circuit. Additionally, using an inductor in series can block AC current due to its high impedance at AC frequencies while allowing DC current to pass, exploiting the frequency-dependent reactance XL = j2πfL. The circuit model includes components representing cable resistance and an audio power amplifier for simulation purposes.
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How to block an AC current and only get the DC componant of a signal

How to block an AC current and only get the DC componant of a signal

How can I measure only the DC component of the current through a resistor when an AC current is also present?

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