Design of DC Current Comparator

Hello all,

I wanna make a current comparator circuit which compares two incoming the currents.

One input is constant current of 12mA and other is variable current coming from the meter according to the flow passes through the pipe...

So which IC can be useful to design this application...

And other thing is i want decision making also if the current is below of above the 12mA then the further system will automatically tripped off.... Can NC relay will do..???

Please help ASAP....

When you say 'compare' do you mean (1) just detect if the variable current is above or below 12mA or (2) measure (and display?) the difference between the two?
An NC relay might form part of the circuit.

There are many ways to skin a cat............

You could pass the two current thru a pair of identical resistors, and then compare the voltage difference across the resistorswith a simple voltage comparator.

Another way would be to use a hall sensor, those with a hole in the middle. Then pass one of the currents in one direction, the other in the opposite direction. The output will swing above or below the cell's quiescent point (usually Vdd/2) depending of which current is larger.