current transformer to voltage convertor

[oreleon]

Hello all, i'm working on a project and part of it involves obtaining a current measurement, using a current transformer, from an AC circuit and converting this measurement to a proportional DC voltage in the 0-5VDC range. I'm hoping that someone can help me or point me in the right direction. I've attached a schematic, hopefully this will give you an idea of what I'm looking for. Thanks in advance, John

 

[Hero999]

You need to rectify and smooth the voltage from the using a precision rectifier and a capacitor.

What current do you need to represent 5V?

 

[oreleon]

Hello Hero999, the current transformer(CT) ratio is 20:1 so the highest current from the CT will be 5A which would correspond to 5V (The AC circuit current is 100A Max). I have a very, very limited knowledge of electronics. Thank you.

 

[Hero999]

You need to connect a resistor to the secondary of the transformer to convert the current to a voltage. A 1R resistor will convert the 0 to 5A current signal to 0 to 5VAC.

The trouble is you need 5VDC which can be obtained by connecting it to a rectifier and a smoothing capacitor. The problem is, the peak voltage is √2 times the RMS voltage so by rectifying 5VAC, you get 7.07VDC, not 5VDC. One solution is to use a 0.707R resistor but it's not a standard value so you'll need to connect other resistors in series or parallel.

Is it possible to use a different current transformer/sensor?

Here's a current sensor with the circuitry to get a 0 to 5V signal built-in.
https://www.electro-tech-online.com...ensor_Neilsen_Kuljian_Sentry_200_for_VFDs.pdf

 

[Reloadron]

When I do these circuits and I do plenty of them I use exactly what Hero linked to. Just pick you current range and you can have a 4 to 20 mA, 0 to 5 volt or 0 to 10 volt output. Just about anything you want. Using a CT just brings in too many more problems to deal with.

Ron

 

[Hero999]

When I do these circuits and I do plenty of them I use exactly what Hero linked to.

I know, I copied your idea.

 

[Reloadron]

I know, I copied your idea.

I like easy.

Maybe it is just me but there seems to be a lot of this line of question lately.

Ron

 

[oreleon]

Thank you very much for your help chaps. It seems the Transducer is the way to go. Thanks again.