Hello all,
I have implemented the current only power monitor using a SCT-013-000 as it is presented here.
All I have changed is the burden resistor, I used a 200 Ohms resistor instead of the 33 Ohms and I think I have better accuracy according to some measurements I have made in specific devices as I knew the formal power consumption from their data sheets. But, I still don't know if I have achieved the best accuracy I can.
For example, my TV, according to the data sheet has 50 W consumption on power mode while I am getting values in a range from 35 W to 45 W as consumption changes as I have noticed when I change channel.
I should mention that I have changed the 11 in the arduino code on the statement
emon1.current(1, 11.0);
to values lower and higher like 2 and 15 but the outputs were different from those I get with 11 and pretty lower from the power consumption I should have according to the data sheets .
I am a little confused but is there any way to calibrate with a different way?
Can I use an ampere meter to get the highest accuracy possible ?
I mean if I give as input 1 A, 2 A, 3 A and so on and watch the output.. Ideally I should have as output 33 mA when the input is 100 A as this is the specification for the SCT-013-000.
Maybe this is a stupid question but I really don't know how to calibrate and would like to hear your opinions.
Keep in mind that I am talking about the non-invasive current sensor and actually to the single phase supply as categorized here
Thank you!
Re: Calibration questions
You need to work through the mathematics on the calibration page that you link to to obtain the theoretical calibration, but then, because the calibration is affected by other factors such as transformer and resistor accuracy and the uncertainty of the value for the voltage reference to the ADC, you should calibrate the current against a known good meter.
But you will never read power accurately unless you also measure the voltage. Power depends not only on both voltage and current, but also on the relationship between them. Two appliances can draw the same current but consume different amounts of power. That relationship is called the 'Power factor' and you can read about it in Building Blocks.
For example, if I were to connect a 2.2 µF capacitor across the mains (don't try this), it would draw a current of 166 mA but absolutely zero power. If I were to connect a 1447 Ω resistor instead, it would draw exactly the same current and consume 40 W of power. The power factor in the first case is zero, in the second it is 1.
Calibrating current: You will need to find a load that is near to but below the maximum current that your meter can safely measure, then insert your meter in series. You can then adjust the current calibration so that the serial output from your Arduino and your meter read the same.
If your burden resistor is too large in value, you will overload the current transformer and your measurements will be inaccurate because the waveform will be distorted. The SCT-013-000 c.t has an output of 50 mA / 100 A, not 33 mA as you state (see the report, which also shows what happens when the burden resistor is too large).