Circuit Design

I know the Electronics to condition any DC Signal to generate 4 - 20mA. But now I have a problem at hand where in I have to convert a 0 - 5A AC signal to 4 - 20mA. I know I can directly use a transducer for the same. But I wish to do it myself. I would like to have some circuit idea for converting 0 - 5A AC to some DC signal which I can further convert to 4 - 20mA. What are the safe and most commonly adpoted methods to achieve this.

Regards
PC

Hi, well I am not sure, but if you want to measure just the current, than you can just use a AC-DC converter, with a diode bridge a capacitor and a resistance. then you will have an equivalent DC signal that variates from 0 to 5A.

Regard
benjas

Do you want the DC signal to represent the average RMS voltage of the AC signal, or do you just want to scale and offset the AC signal so that it fits within 4-20 ma?

Robert Scott
Real-Time Specialties
Embedded Systems Consulting

Acromag offers a small and low cost AC current sensor with an output of 0 to 11.17mA-dc that could help you out. See Model 5020-350.

Basically, this is a 20Amp-Turn Current Transformer (CT) sensor that steps down the AC current and then full wave rectifies the output to create a dc current for interfacing with dc current input circuits. For 5A inputs, you simply put 4 turns thru the sensor to create 20 "amp-turns.". The dc current output from the sensor can drive a load of about 75 ohms or less. The sensor looks like a small donut and is about 1 inch in diameter.

There are many technical benefits to using a CT sensor like this if it will work for you. Accuracy is also better than 0.5 percent, Otherwise, there are op-amp circuits used for full wave rectifing of AC voltages that can be created by dropping AC currents across a resistor of very low ohms. Another technique can involve using Hall Effect sensors that yield dc outputs.

Here are two links to Acromag's Model 5020-350 AC Current Sensor Application Note:

http://www.acromag.com/pdf/AC_Current_Sensor_5020_350.pdf

http://www.acromag.com/supi_application_notes.cfm#isolators

If you have any questions or need more info, just let me know or contact Acromag.

Donald Lupo
Director of Marketing and Sales
Process Products
Direct: 248-295-0860
Cell: 248-787-3882
[email protected]