How to measure small AC current

[mufthas]

measuring ac current

I want to measure AC current from differential current transformer (or zero current transformer) in the range of 0-1 A using PIC16F series. I dont no exactly, how to interface this AC current to PIC.
Can I directly interface to PIC by a resistor? or are there any IC's to measure AC current and interface to PIC?

I need your your HELp. Im stuck stuck with this. plz help me

 

[Awarapunshee]

how to measure ac current

If you are using current transformer, then voltage across the secondry winding should be rectified and filter and then give it to ADC and then PIC.

 

[laktronics]

measure ac current

Hi,
You can convert the current to AC voltage using the resistor as you said. Then you rectify it using an active rectifier and apply the volatge to PIC ADC input. Since your input is a sine wave, you can even avoid filtering and use PIC to measure the peak volatge and calculate the RMS volatge which is proprtional to your current.

Alternatively, after converting into AC voltage, use an RMS to DC converter IC ( source Analog Devices) and apply its output to PIC's ADC.

Reagrds,
Laktronics

 

[mufthas]

measuring current with pic

Hi,

I am designing a automatic Residual Current Circuit breaker (RCCB) for household circuitry. If there is an unbalance in the circuitry current transformer will induce a residual current. I want to measure this current accurately and if the residual current is more than 30mA, i want to interrupt main power supply to the house circuitry. The maximum that can flow through the House circuitry is around 40A.

my question is, how to measure the current accurately and protect my PIC from higher residual current. I have few ideas, but i don't no whether these are correct?

1. interfacing current transformer and PIC (ADC port) using a resistor
2. interfacing through a current measuring IC ( still don't have one) to Digital input or PWM input of PIC


Plz help me.

 

[laktronics]

how to measure small current

Hi,

Do you think it is necessary in such cases to measure the current accurately? A simple comparator driving a contactor may do the job? Have you studied how the commercially available Earth Leakage Circuit Breaker (ELCB) works?In any case as regards protection of PIC from over current is concerned, you can use a fuse along with Resistor-Zener combination clamping circuit at the input to ADC/ DC conversion circuit.

Regards,
Laktronics

 

[FvM]

measure ac with pic

Short circuit currents even in a home power distribution must be expected in the kA range and an RCD is required to withstand it without loss of safety function. Fuses in the measurement circuit thus won't be a good idea.

 

[Siniša]

pic current transformer

Your transformer has two primary coils and one secondary. One end of that secondary place on input of ADC, and other end on 1/2 of Vcc made by two identical resistors, let's say 4,7kΩ. Couple of diodes from input of ADC to Vcc and 0V will insure safety of MCU. Only thing remaining is loading resistor on secondary that depends on transformer and capacitor on input of ADC to limit bandwidth. Transformer design and loading resistor should be selected such that ADC is used in whole dynamic range.
Maximum positive peak should be close to Vcc and maximum negative peak should be close to 0V.
This way no rectifier circuitry is needed, offset compensation is easilly automated if needed, and part count is low.

 

[madicalphy]

ac current measure

some operationa amp should be included here to solve the problem

 

[Micro_brain]

ac current measurement circuit

good idea
Thanks Sinisa
Micro_brain