alternating current measurement using pic microcontroller. In this artcile I will discuss how to measure alternating current using current transformer and pic microcontroller. After reading this, you will be able to design AC Ammeter using PIC16F877A microcontroller. It is very important task in pic microcontroller projects. I have already posted a dc current measurement circuit with code. you can also read it.
Current transformer for AC current measurement
It is used to measure alternating high current of the order of thousand Amperes. It steps down ac current to lower value so that it can be easily read with the help of microcontroller. Step down ability of current transformer depends on the rating of current transformer and its current step down ratio.Suppose you have a current transformer with current ratio of 100:10 Ampere .Its mean primary current of transformer is 100 Amp and secondary current is 10 Amp.you can not use this current transformer to measure current more than 100 Amp.By measuring secondary side low current, we can easily convert it into primary current value by using current ratio formula. I will discuss in later part of this discussion how to use this step down ratio in programming part.
How to measure secondary side current of CT
There are many methods to measure low alternating current you can also measure it using AC ammeter. But if you want to perform some control operation and want to send measured current value to other place.You have to use some kind of intelligent system.
For example you want to make a current protection circuit and circuit specification are followings
if current flowing through a line is greater then 100 Ampere, a control action should be performed to operate a rely
if current is greater than 100 Ampere relay=open
if current is less than 100 Ampere relay=close
To make such kind of intelligent system, we may use analog and digital electronics,but its better to use digital electronics as far as cost issue is concernIn this tutorial tutorial we will use PIC microcontroller to measure alternating current.
Hardware components of alternating current measurement:
AC current measurement circuit working
To measure this current with pic microcontroller,we have to use ADC module of PIC microcontroller.To use ADC module we will convert current into voltage form by using a .1 ohm shunt resistor across CT and we will measure this voltage drop across shunt resistor.Then this voltage drop can be easily converted into current again.For example
voltage drop across .1 ohm shunt resistor =8v
then current according to ohm law
but the problem is ADC of pic microcontroller can never measure voltage greater than 5 volt.so to solve this problem we can use difference amplifier.By adjusting gain of difference amplifier we can reduce voltage lower than 5 volt.Following diagram shows the circuit of CT and difference amplifier.For more information about difference amplifier how to adjust its gain etc, you can search on Google.