I am trying to finalize the AC voltage and current measurement circuit using a differential amplifier. I have designed two circuits for each. In the high side current measurement circuit 2 and voltage measurement circuit 2, I have connected multiple resistors in series to the inputs of the op-amp. However, in the high side current measurement circuit 1 and voltage measurement circuit 1, I have connected a single resistor to the inputs of the op-amp. I am planning to use 0603 package resistors. As I know that op-amps have very high input impedance, I used a single input resistor in circuit 1. I am confused about which circuit to follow for voltage and current measurement, respectively.
I think you have to use both plus and minus power supplies for the op amp to have symmetrical measurements.
Those circuits are totally unsafe for household AC measurements (as in absolutely deadly).
Safe circuits with complete galvanic isolation can be found at the OpenEnergyMonitor web site.
Please state the voltage, current and frequency of the AC signals you actually intend to measure.
With 311 volts (peak) in the diff amp at a gain of 1 would try to put 311 volts out. Not gonna happen.
Secondly as @jremington mentioned. Having any hobby circuit connected directly to mains is going to really really hurt you if it doesn't kill you.
Third, if you use an Arduino connected to the USB of a laptop you can say goodbye to your laptop. The mains voltage will go right through your diff amp to your arduino to your laptop.
I read VA=311 on the schematic, which usually means VoltsxAmps = 311, or about 300 Watts.
Yea but it looks like a spice source, unlikely to have a VA rating.
hi there, 311V is a peak voltage, I am trying to measure 220V rms voltage and high side current. I tested circuit 2 of voltage and current measurement and it worked. My doubt is why should I consider using multiple resistors in series to the inputs of opamp as showed in circuit 2 rather than using single equivalent resistor as shown in circuit 1.
Because 0603 resistor is not rated for 300 V. Be VERY careful with this circuit. You can easily kill someone or cause a fire. Your questions show very little understanding.
What was your test like? Is your testing a simulation or real parts?
Keep in mind the simulation is an "ideal" situation. Real life is not.
Stop right now, before you kill yourself with circuits like the ones you posted.
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real parts
The smart way to do it is to use a step down transformer and a divider if needed to measure the AC voltage. Transformers have a turns ratio that will drop the voltage and isolate you from the mains.
Consider using a split core sensor for the current.
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This the only way to do this. I use old wall warts the have a AC output.
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Photos please.
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