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That sensor will probably work. It will need a power supply that is separate from your emonTx (or Arduino), that will give ± 12V - ±18V, and the 0 V from that power supply will connect to the emonTx GND. The output is a current of 50 mA (for 20 A primary current), therefore you calculate the value of R_M to give 3.3 V (5 V for Arduino) or a little less at 25 mA.

Hello Robert

I want to use Arduino to 5 v, for interfacing the sensor with arduino I have to use some circuit?

or I can use this:

http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface

calculating the different resistances

No, you cannot use the circuit for a CT. It is for a CT only. Use the standard Arduino circuit for measuring d.c.

You connect the GND of your Arduino to 0 V of your dual power supply, and you connect pin 3 of the sensor to the Analogue input of your Arduino. Do not forget the resistor R_M.

Then in the sketch, you use analogRead(x) to get the current. ('x' is your input pin). The number you get should go from 0 to 1023 for 0 to 10 A, but of course it will not, exactly.

There might be an offset, meaning you read a non-zero number with no current. To correct that you add a constant value.
There might be a scale error, meaning that you need to multiply the number you read by a correction factor so that when you have 10 A, you read 10 A.

Your code within setup( ) might look like this:

double m = 1.0 // change this to adjust the scale calibration
double c = 0.0 // change this to remove any offset

Your code within loop( ) might look like this:

double dcAmps = analogRead(x) * 10.00/1024 * m - c;
Serial.println(dcAmps);

 Hello Robert, 

what is the resistor RM??

thank you