Hey there;

I want to build up a circuit which I can easily see the voltage change in mVs. To be honest, I have an IC which gives about 40 mV as output and in order to take feedback I need to measure clearly this output voltage. Thus, when it jumps up from 40 mV to 70 mV I want to see this 30 mV change in Volts so that I can measure it easily.. Until now I tried to use basic amplifier circuits, but in practice I couldnt achieve what I want to do.Even if the gain seems to be OK, I cant get my desired output. To put it simply i want to increase this 30 mV DC output to change into 1-2-3 Volts level so that I can see it on CRO etc.

Cheers..

 

Can you post a image of your circuit. These low voltages probably require some precision when it comes to selecting op-amp and resistor values.
Posting the circuit will help us identify your problems.

 

by the circuit image what do you mean? If u mean the ones that I used to amplify ,those outputs, were just basic negative feedback OpAmp circuits in which the gain is (1+Rf/R1) where Rf is the resistance which is on the Vout side. On the other hand if u mean the circuit which I get output in mVolts range it is just a sensor which is called MPX200. I want to read its output clearly

Thank you for paying attention..

 

That would be the schematic of the circuit, with values of the components.

 

Here is the exactly same basic circuit which I tried to use.

http://www.wiringdiagrams21.com/2009/12/17/basic-inverting-op-amp-circuit-diagram

I used regular OpAmp u741 and for Rf i used 50K and Rin 1k Ohms supposing that I will have a gain of 50..

 

This is what you are looking for

I'd use something a bit more modern than a 741 op amp though. Something with low noise and rail to rail abilities. There are many to choose from, depending on if you have single supply or +/- supplies.

 

I think you want a non-inverting amplifier.

If you have a positive voltage that is referenced to ground, in the range of 10 to 100 mV or so... and you want to amplify it to 0.5 to 5V or so, then this is what you want.

Like "thatoneguy" said, you want to use a better op amp than 741 -- one with rail to rail input and output. Things can get dodgy when you're near the ground with a single-supply op amp. You could use a dual rail if you have the power supply both - and +.