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Message: <blockquote data-quote="waparc" data-source="post: 14132525" data-attributes="member: 72022"><p><img src="http://i46.tinypic.com/othv7p.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">use above circuit for your ct coil.</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">for R82 and R83 you have to do some calculation. as you mentioned, you use 30:5 CT coil. so 5A rms current will flow through R82 and R83 when maximum of 30A flowing through it. </span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">PIC16F877 can only measure voltages between 0 and 5V.</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">so there should be maximum of 5V peak from IAP.</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">to have 5V peak, </span></p><p><span style="font-size: 10px">x * square root of 2 =  5</span></p><p><span style="font-size: 10px">x = 3.54 V rms</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">according to V=IR,</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">3.54=5*R</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">R =0.708 ohms</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">Since the input signal is differential for each channel, the </span></p><p><span style="font-size: 10px">burden resistor is split in two to yield 0.354 * 2</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">according to E12 resistor value range you can use 0.33 ohms 10 watt resistors as R82 and R83. </span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">for R15 and R17 use 560 ohms resistors. for C16 and  C17 use 0.056 microfarad ceramic capacitors.</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">input only IAP to pic16f877 analog pin. do the A/D conversion. </span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 10px">since you are using 30:5 CT, accuracy will be low. for high accuracy, use CT coils like 1000:1 or 2000:1.</span></p><p><span style="font-size: 10px"></span></p><p><span style="font-size: 15px"><span style="color: Red">Check above circuit with proper testing equipment before connecting it to pic16f877. make sure that voltage from IAP should not exceed 5V.</span></span></p><p><span style="font-size: 15px"><span style="color: Red"></span></span></p><p>based on source - <a href="http://www.analog.com/static/imported-files/application_notes/2698536550528608457AN641_0.pdf" target="_blank">http://www.analog.com/static/imported-files/application_notes/2698536550528608457AN641_0.pdf</a></p></blockquote><p></p>

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