Submitted by TrystanLea on Wed, 13/04/2011 - 23:35
This post was moved from the old forum:
reh:
Hi
I have a circuit board to take inputs from 4 CT sensors - it is basically 4 copies of the single CT sensor circuit. I want to have different inputs sensitive to different current ranges, but am having some trouble choosing the burden resistors for low current values (i.e. the most sensitive input).
using the same CT sensor and a test 8.6A purely resistive load, i get the following results (the first column is the burden resistor in Ohm as directly measured on the board; the second is the minimum-maximum reading from the Arduino when using an RMS 8.6A current; the third is the consequent calculated maximum RMS current that can be read; the fourth is this range time the burden resistor value):
burden min-max A/D max current range range x burden
30.2 106 83 2509
51.4 157 56 2883
102.7 259 34 3492
997 340 26 25823
According to my reading of the detailed system design page, the last column should be a constant (related to the number of turns in the CT sensor and the bias voltage). The agreement is pretty good for the first couple of lines, poor for the third, and useless (out by a factor of 10) for the last.
Is there a more accurate way of calculating the burden resistor value, or should i just use trial and error?
reh: burden resistor sizing
Submitted by TrystanLea on Wed, 13/04/2011 - 23:35This post was moved from the old forum:
reh:
Hi
I have a circuit board to take inputs from 4 CT sensors - it is basically 4 copies of the single CT sensor circuit. I want to have different inputs sensitive to different current ranges, but am having some trouble choosing the burden resistors for low current values (i.e. the most sensitive input).
using the same CT sensor and a test 8.6A purely resistive load, i get the following results (the first column is the burden resistor in Ohm as directly measured on the board; the second is the minimum-maximum reading from the Arduino when using an RMS 8.6A current; the third is the consequent calculated maximum RMS current that can be read; the fourth is this range time the burden resistor value):
According to my reading of the detailed system design page, the last column should be a constant (related to the number of turns in the CT sensor and the bias voltage). The agreement is pretty good for the first couple of lines, poor for the third, and useless (out by a factor of 10) for the last.
Is there a more accurate way of calculating the burden resistor value, or should i just use trial and error?