-2 to +2 mA AC Current sensing

Rasool,

There are many possible ways to measure AC current. The best way for your situation may depend greatly on the details of your application. One common way is to allow the current to flow through a resistor and measure the voltage across the resistor.

Please provide more details:  What is the frequency of the leakage current? What is the source of the leakage? What voltage level is the current flowing to? If you can provide a diagram of the measurement conditions it would be helpful.

Regards, Bruce.

Dear Bruce,

The project is to sense the leakage current of the surge arrester.

It is mainly a 50 Hz sinusoidal which is greatly capacitive. The magnitude is -2 to +2 mA peak to peak and has a very low magnitude 150 Hz harmonic.

The source is a several kV supply.

The sensing is being done at the earth terminal of the surge arrester.

I search for the method that the measurement would be less depend on the temperature and ageing.

The current finally would be converted to digital by TMDXDOCK28069.

Best regards,

Ras Sharif

Ras,

I think that you do not want to acquire and convert the AC signal but want to detect its amplitude. Correct? The circuit below may be a solution. Leakage current from the surge arrester would be routed to the resistor R1 and allowed to flow to ground. D2 and D3 clamp the voltage input to U1 and allow large surge currents to flow without damage to R1.

U1 is a positive peak-hold circuit with gain of 10. Output would be 2V for a peak AC current of 2mA. I could not find details of the analog input of the TMDXDOK2869. This circuit may require a G-1 buffer to drive the input to the a/d converter.

Would this circuit meet your needs?

Regards, Bruce.

Dear Bruce,

No, I need the instantaneous current; since the main problem is to calculate the power.

I design to sense the current by a suitable sensor less depended on temperature and ageing.

Then to isolate, filter and digitize it.

Finally to measure temperature for compensating the effect of it by a processor.

Like a dedicated current transducer.

Best regards,

Ras Sharif

Ras,

Is the method I've shown for sensing the current suitable? This includes R1, D2, D3.

Is is okay to only recover the AC component of the leakage? The voltage on R1 can be AC coupled into an amplifier that drives the a/d converter.

Regards, Bruce.

Dear Bruce,

Thank you for the attention. I likely use of resistor method.

Regards,

Ras Sharif

Hi Bruce,

The circuit is a good solution. The current is partly isolated; and is clamped if over happened; and finally buffered.

I should to work on this point to improve the circuit; fully isolated, and more importantly to access the less phase shift, etc.

I glad to know if I can use of your advise.

Very thanks,

Ras Sharif

Hi Bruce, 

I want to measure AC current from 230V AC source directly using a micro controller. The current is in the range of 50-100mA. Please suggest me how to proceed? 

Thank you, 

Rahul Shah