Where does power meter sense current?

In summary, the power meter takes readings of the voltage and current in each phase of the transformer and uses that information to calculate the power.
  • #1
Evil Bunny
241
0
I've been trying to determine how a power meter (like a utility company attaches to your house to determine your bill) works, but I can't find anything that explains exactly where the meter is taking it's readings.

On a center tapped transformer, you have L1, L2, and Neutral, but the loads aren't always balanced. Are they sensing total current on L1 and L2 and then averaging that total? I suspect this is how it works... Anyone know for sure?
 
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  • #2
Evil Bunny said:
I've been trying to determine how a power meter (like a utility company attaches to your house to determine your bill) works, but I can't find anything that explains exactly where the meter is taking it's readings.

On a center tapped transformer, you have L1, L2, and Neutral, but the loads aren't always balanced. Are they sensing total current on L1 and L2 and then averaging that total? I suspect this is how it works... Anyone know for sure?

The current in each phase is sensed (either with a shunt or a current transformer), and the current and voltage of each phase are used for the total power calculation.
 
  • #3
Right... the voltage is known, but the current must be the average of the sum of L1 and L2, correct?
 
  • #4
Evil Bunny said:
Right... the voltage is known, but the current must be the average of the sum of L1 and L2, correct?

No. The power in each phase is calculated separately, and added up to give the whole power. You need to sense both the voltage and current in each phase -- the voltage is not "known". The voltage in each phase can vary quite a bit, and the actual voltage needs to be used for the power calculation. The waveforms are sampled at a fairly high rate, to get accurate power numbers.
 
  • #5
The 240 Volts coming into my house varies quite a bit? I did not know that... Interesting.

So they're using neutral as reference and then calculating 120V (or whatever the "actual" voltage is) times the current in L1 and then 120V times the current in L2 and adding them together... I guess that makes more sense than averaging the current off the two hots and sensing the total voltage between them.

Thanks! Could not find that information out there...
 

Related to Where does power meter sense current?

1. Where is the power meter placed in a circuit to sense current?

The power meter is typically placed in series with the circuit element that you want to measure the current for. This means that the current passes through the power meter, allowing it to sense and measure the current.

2. Can a power meter sense current in both AC and DC circuits?

Yes, there are power meters that are designed to work with both AC and DC circuits. However, some power meters may only be designed for one type of circuit, so it is important to check the specifications before use.

3. How does a power meter measure current?

A power meter measures current by using a shunt resistor or a current transformer. The shunt resistor creates a voltage drop proportional to the current passing through it, which is then measured and converted into a current reading. The current transformer uses the principle of electromagnetic induction to sense the current and produce a current reading.

4. Are there different types of power meters for different current levels?

Yes, there are different types of power meters for different current levels. Some power meters are designed for low currents, while others are designed for high currents. It is important to select a power meter that is suitable for the specific current level in your circuit.

5. Can multiple power meters be used in the same circuit to measure current?

Yes, multiple power meters can be used in the same circuit to measure current. This can be useful for measuring current at different points in a circuit, or for measuring the current in multiple branches of a circuit. However, it is important to ensure that the power meters are properly calibrated and do not interfere with each other's measurements.

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