Friday 21 October 2016

pic - Current Transformer with pic16f877a


I am currently working with a current transformer (CT) to measure the load current of a system. I am connecting the CT with a pic16f877a microcontroller using a basic circuit I found on the internet. I have implemented this circuit pictured below and connected the CT but it did not work. The value is not being changed by CT. Please suggest any changes in the diagram below or provide help regarding how to connect CT with the PIC. I have provided pics of the specific CT as well.


Circuit to connect CT with Pic16F877a CT CT CT Circuit


I need to measure AC Current. actually am software engineer by profession and don't know much electronics but are learning and implementing things. My purpose is to measure load on three phases of our company which is provided to us from Grid. So I will pass AC wires from CT to measure load on every phase. Can you help me to provide solution as I can read ADC value from pic because I have measures temperature successfully using LM35 but don't know how to connect CT with Pic, neither any manual or data sheet is provided by CT supplier. Can you help me to connect CT with pic16F877a.




Answer



Your circuit doesn't make much sense. The two resistors attenuate whatever signal is produced by the CT by a factor of 2 and shift it up 2.5 V. Is this really what you intended?


What current range do you want to measure, and therefore what is the expected output voltage of the CT? Without knowing that, it's impossible to say whether it's doing what it's supposed to or not. Start by just putting the load resistor on the CT and measuring the voltage. Do you get what is expected? If so, work forwards thru the circuit to see where you are not getting the expected signal. If the signal seems right at the PIC pin, then any remaining problems are in the firmware.


I'd expect you would want to amplify the CT signal before it drives the PIC pin, but you also have to make sure a current spike can't cause a voltage outside the PIC Vss to Vdd range.


A TL082 is inappropriate here. Look at its overhead voltage. It's not going to do anything useful with a 5 V supply.


The power is connected backwards to the opamp, or you labeled the pins backwards. Either way something is wrong since you have the more positive power at the bottom of the opamp symbol.


You realize a CT can only measure AC current, right? You won't get any response out other then a short blip if you put DC current thru the hole, regardless of how much current.


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