Form my simple test with the clamp as I said in the first email I received:
0.023v from 1000w load
0.046v from 2000w load
All I really want to do is convert the small AC to DC and then after that conversion amplify the signal so it is between 0 and 5v - so something like a 100X Multipler.
The article I referred to in the first post http://www.crmagnetics.com/Products/Assets/ProductPDFs/Precision%20Rectifier%20Circuit%20for%20CT%20Signal%20Conditioning.pdf shows the following diagram:
I am just not sure on the final two components a resister and capacitor I assume to filter the signal, but I do not know how to calculate this.
The pdf has this text
- The CT secondary current is applied to the resistor R1, which generates a voltage equal to the primary current
divided by the turns ratio and multiplied by the value of R1. This AC voltage is rectified by the first op amp,
and then amplified by the second op amp.
- The gain of the first stage is always kept at 1 or unity (R2 = R3) to guarantee symmetry of the rectified
waveform. R2 should be chosen at least 10 times greater than R1 for proper accuracy.
- The gain of the second stage is R5/R4 + 1. This gain is chosen to get the desired output DC voltage for the
designed input voltage.
- The main advantage of this circuit is the removal of the diode drop as a variance in the signal. DC can be
generated directly from R1 by applying the AC voltage to a diode bridge. However, the AC voltage required to
do this must be greater than 2 diode voltage drops, or over 2 VAC. This limits the designer to use a silicon steel
core that can generate enough voltage before going into saturation. By using the above circuit, the AC voltage
input can be very low (10-100 mV) and then amplified to the level desired. This then allows the designer to
choose smaller core devices and nickel core devices which saturate at low voltages. Accuracy and cost are both
- Use standard op amp design guidelines when setting up this circuit. Keep resistors at 1 M ohm or less, and
keep gains to 100 or less.
- The output must be filtered for pure DC. The RC output network shown should be designed with a time constant
at least 10 times greater than the period of the waveform sensed. For 60 Hertz, use a time constant of 1/6.
For 400 Hz, use a time constant of 1/40, minimum.
So for me I am thinking of using
Z1, Z2 = 1N4735A - not sure if this Zener is OK, 6.2v 1W but I assume it is.
R1 = 10 Ohm
R2 = 100 Ohm
R3 = 100 Ohm
R4 = 1k Ohm
R5 = 100K Ohm (to give a 100 x multipler)
R6 = ?
C1 = ?
Technically with my 100 times multiplier I believe:
0.023v * 100 = 2.3v
0.046v * 100 = 4.6v
So I should be able to read this on an analog in on the arduino?