Non-Invasive Current sensor SCT-013-000

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Circuit to connect SCT-013-000 to Arduino.

Circuit to connect SCT-013-000 to Arduino.

Previously we talked about this sensor and made an example of how to use it you can see here. But if you want to create your own circuit for measuring different values of maximum power, you can use this guide to help you to assign the values of R1 and RBURDEN.

First we must establish what are the characteristic values of the signal power that will measure the SCT-013-000 sensor. These values are VRMS and frequency.

Country VRMS Frequency
Argentina 220 V 50 Hz
Australia 230 V 50 Hz
Canada 120 V 60 Hz
Chile 220 V 50 Hz
China 220 V 50 Hz
France 230 V 50 Hz
Germany 230 V 50 Hz
Italy 230 V 50 Hz
Mexico 127 V 60 Hz
Netherlands 230 V 50 Hz
Russia 230 V 50 Hz
South Korea 220 V 60 Hz
Spain 230 V 50 Hz
United Kingdom 230 V 50 Hz
United States 120 V 60 Hz

Next we need the values of the sensor SCT-013-000.

  • Output Mode:  It gives us the relationship between the signal measured by the sensor and the signal is giving us at the output.
  • Input Current: range of values of current sensor can measure.
SCT-013 specifications.

SCT-013 specifications.

This values are:

\text{Input Current} = \frac{ \text{Output current}}{33m} \text{ A, when Input current = 100A max}

This means that the maximum current that can be measured is 100 AIf we have a 120V VRMS maximum power will be 8485.28 Watts (15556.35 Watts in the case that the VRMS is 220V). If you need to measure values above these we have to opt for another sensor.

In addition to the maximum current that can be measured (100A), the sensor will give us 3.3A this leads to other limitations. For example as normal it is that we opt for a resistor 1/4 Watt, where:

R_{BURDEN} = \frac{(V_{REF})^2}{P}

R_{BURDEN} = 100 \Omega \text{ If Vref = 5V}

R_{BURDEN} = 43.56 \Omega \text{ If Vref = 3.3V}

This limits the maximum power that can be measured with this type of resistance to 117.85 Watts for a 5V Vref (178.56 Watts for a 3.3V Vref).

P_{MAX} =V_{RMS} \frac {\frac{V_{REF}/2}{R_{BURDEN}}/33m}{\sqrt{2}}

The value of the resistors R1 must be much higher than RBURDEN around 100 times, if opted for a RBURDEN 100 Ω then R1 will be 10ΩK.

This value causes that the voltage divider Vref is not affected by RBURDEN, being R1 a much greater value, but in turn R1 must be much smaller than the input impedance of the ADC we use, in the case of Arduino recommend not exceed 10kΩ impedance to avoid erroneous measurements.

To calculate the minimum power we have to consider the number of bits of the ADC .

P_{MIN} =V_{RMS} \frac {\frac{V_{REF}/(2^{Nbits})}{R_{BURDEN}}/33m}{\sqrt{2}}

 

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