I'm trying to build one and learn a few things in the process. When i try to google it I get the wrong question answered (like how to read a electric meter, etc.). AC just looks like a sine wave on an oscilloscope so what characteristics of that sine wave are measured to determine wattage used? If that's not what is looked at, then what is? Standard AC voltage and current units of measurements are given in equivalent DC RMS values such that if your were to power a 120 ohm resistor from both a 120 vac power source and another time with a 120 vdc battery, both are said to create 1 amp of RMS current and the resistor is dissipating 1 RMS watt of power. AC voltage can be measured in other units like average voltage, peak voltage, peak to peak voltage, all derived from the same indentically sized AC voltage wave form. The measurement of true AC power consumption (as measured by your billing meter) involve other additional factors like Power Factor (phase angle difference between voltage and current for loads other then pure resistance) and dealing with non-sine wave current flows ( the AC voltage provided to you is always in sine wave form, but some of your loads don't draw current as a pure sine wave and must be converted to true RMS current to obtain true power consumption). But before advancing you first should nail down voltage/current/wattage measurements as they apply to AC and DC circuits and what the units of measurement really mean. This seems to be a good article on the subject: http://www.allaboutcircuits.com/vol_2/chpt_1/3.htmlSecondly, if a 1:1 transformer is used between the meter and the load, would the meter still read correctly?Yes, the 1:1 ratio tells you the voltage and current levels with be equal between the primary and secondary minus a few percentage power loss in the transformer core in the form of heating of the iron core due to eddy currents.Lefty
We studied phase angle in my college physics 2 class. Is the phase angle what is used to measure current?No, phase angle is the relationship between voltage and current at an given instant of time and if not 0 degrees then simply multiplying voltage X current won't give you the true RMS power consumption. The phase angle must be measured so it's effect can be calculated for true power consumption as in billing rate.When using a 1:1 transformer, I don't understand how the meter can still tell how much current is used. The wires providing power aren't actually connected to the load in any way.Not directly connected but effectively connected by the transfer of power via constantly changing magnetic coupling from primary to secondary windings, the iron core of the transformer makes this a very efficient transfer of power. This only works for AC as DC will not pass power through a transformer as there is no changing magnetic field as in AC. AC power transfer is effectively constant (minus small transformer losses) such if the step up voltage ratio is 1:2 the current ratio transfer will be 2:1 making the actual power transferred constant.
Secondly, if a 1:1 transformer is used between the meter and the load, would the meter still read correctly?
AC just looks like a sine wave on an oscilloscope so what characteristics of that sine wave are measured to determine wattage used?
This is for a college project. We are supposed to figure out a way to power a load without the meter registering it :/ Some students were thinking you could draw a really small amount that maybe wouldn't register. Another idea was to suck up a huge amount faster than the sampling rate and dissapate that slowly to power the load. Another idea was the 1:1 transformer but that I guess wouldn't work. Any ideas? The school allocated the funds for us to build it.
Not be able to measure it in what way, current or voltage?
Simple attach/wire your load to the input side (upstream) of the metering point rather then output side (downstream).Lefty