Why this Simple Watt Meter for 220 Volt Circuit works?

Thread Starter

henriquevpp

Joined May 12, 2020
1
Hello!

I'm just a begginer student. I found this circuit of a wattmeter that works only with resistors. Can someone explain to me how the 33k resistor give a voltage of 1 mV to 1 Watt? I did not understand why these resistor values has been chosen and why the it measures only in the 33k resistor.


Link: https://everycircuit.com/circuit/5290189996163072/simple-watt-meter-for-220-volt-circuit


I made a version (only changing one resistor value) at Fasltad: http://tinyurl.com/y7uqu8n4 (the url was too big).

Can someone help me? Thank you!
 

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Audioguru again

Joined Oct 21, 2019
1,503
Two parallel resistors are 470m ohms each. That is 0.47 ohms each. They make what is called a "shunt" in a current meter. They pass most of the current and the 33k and 7.5k voltage sensing resistors pass only a small current.
 
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