Calibration issues

Hi everyone, I'm in need of you help. I'm using this CT and I'm having some issues regarding the correct value for calibration:

I'm using an arduino, so it's 5V input, and 110~120 AC Voltage.

The value for the burden resistor I calculated was 295, using 300. (please check on this)

I'm really confused about the value for calibration, I think I calculated it wrongly, as the value is really low compared to the one here.

Thank you!

calypso_rae's picture

Re: Calibration issues

The value of the burden resistor should be chosen in order to control the size of the output signal for the amount of current that you want to measure.  Calibrating your system is a separate activity.

If you want to measure the current that is taken by your whole house, you will need a very low value of burden, maybe 18R.  But if you're only wanting to measure the current that is drawn by a single appliance, your measurements will be more accurate if you use a higher value of burden.  That's because the signal from the CT will be larger, and more of the ADC's input range will be used.

Having decided on a suitable value for your burden resistor, you will need to check the values that are recorded when various loads of known size are drawing current.  If your measured values are not as you would expect them to be, then change your calibration value(s) until they are.  The "correct" calibration values for your rig are unlikely to be the same as any published data on this site because your situation is different that the standard setup in the UK.  

When your system can display the values that you expect for voltage, current, power etc., then its calibration must be correct. 

Hope this helps.

Robert Wall's picture

Re: Calibration issues

The theory about how to work out the calibration is here (but bear in mind that there are many practical reasons why the final correct value may be different - due to component tolerances, more info is here)  and the procedure is here. You need all the information about your installation (like the max current, c.t. ratio etc, and that you haven't told us so we can't help) to work through the numbers.

(Note: the web page is totally mixed up, it gives conflicting numbers for the c.t. ratio, stupid values for other things so it's anyone's guess what is correct. You may even need to measure it to determine the correct ratio.)

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