Current Monitor Circuit - Filtering/Rectification?

Hi guys,

There wasn't much activity over on the sparkfun forum so I thought I'd poll the expertise, here. I have been trying to design a circuit to convert the output of the current transformer ECS1030-L72, sold by sparkfun, to a voltage usable by an ADC or arduino. I've modified the circuit discussed in this thread: to sort of work with the ECS1030-L72. Below is my LTspice simulation and diagram. As you can see, the output is still a little fuzzy. I should add that the op amp is being powered by ±5v and the current source is in place of the current transformer and output and AC signal.

How would I go about filtering that residual ac noise out?
How about other options to get this to interface with a micro controller easily?
How would I have to adapt this circuit for higher current sensors by EChun (70A, 100A)? I'm assuming no modification is necessary, it would just decrease the measurement resolution.
Any other suggestions to make this work properly?

I've seen the openenergymonitor example and others, but I'd like to have the rectification happen before the input.

I'm not sure about how it would work in real life, but in the simulator increasing or decreasing the C1 value has the effect of:

  1. increasing the ac waveform amplitude allowed to pass
  2. scaling of the overall output
  3. changing the reaction time of the circuit

All of these things are expected except number 1. Any ideas?

(Sorry, the images were sized incorrectly. Right click and open in a new tab to see the whole thing.)


My other option to consider would be using something like the Allegro ACS714: in parallel with the 10 Ohm burden resistor on the same current transformer.

Would the be a more simple option than the previous post?
Would the 5v output still be A/C with a 2.5v offset?
Would this require software rms calculations or could it be accurately rectified before the ADC?

Thanks again.

After reading the datasheet, it seems the range of the Allegro chip is too wide for for the fine measurement of the stated CT's output. :frowning:

Hi, have you tried putting a 1uF or 0.1uF cap from the output to gnd on the circuit you have posted to smooth the ripple.
In fact how mush ripple is it? And will it be a problem. The simulation is not real world, so I'd be building it in real life and checking it out.
I find I can spend my time building and trying a circuit more economically than simulating it and worrying about getting a perfect output.

Tom...... :slight_smile:

Thanks. As you can tell, I'm new at this. I tried a 1uF, 10uF, and 100uF cap to ground on the output. . It cut the 60Hz down considerably to an acceptable level with the 100uF cap while maintaining an acceptable output rise time for this application. I agree about the simulation. Now that I have a design, it's time to get some parts and try it out on the bench. Here's the improvement in LTspice: