I am uploading the pic of circuit without load and supply

 

@JMac3108: I agree 3cmm is long so I changed later and that u can c in the picture i uploaded. The actual load draws current of 0.68 A without sense resistor (direct from dc supply). I agree its not with the max4080, its something to do with the circuit.

 

@Kubeek: Yes, i noticed that the output for 1 ohm resistor is getting stucked at 11.66v. but i cant use such a high voltage with microcontroller ADC, as i have to measure the current value and keep monitoring. Its like a diagnostic system.

 

You do realize that the resistance of your bread board connections will play an important part in the operation of your circuit. Try soldering the shunt resistor directly to the IC pins.

 

@Kubeek: Yes, i noticed that the output for 1 ohm resistor is getting stucked at 11.66v. but i cant use such a high voltage with microcontroller ADC, as i have to measure the current value and keep monitoring. Its like a diagnostic system.

Mark ... do you understand what Kubeek is telling you? He's pointing out that the 1 ohm sense resistor is too large and because of this the input voltage is so high that the MAX4080 with a gain of 60 is trying to put out more voltage than it can output.

You need to do what Bill said - solder the sense resistor directly to the IC pins.

 

@JMac3108: k i will do the same as Bill said and let me check. thank u

 

Thank u every one guys for ur help

 

So did it work the way expected after moving the resistor??

 

@BillB3857: yes it did work, but still there is some difference in reading from the actual load current value. That is + or _ 0.08A when measuring load current of 0.68A.

 

How are you making your measurements for comparison? Is there a way that you can make both measurements at the same time?

 

@BillB3857: yes it did work, but still there is some difference in reading from the actual load current value. That is + or _ 0.08A when measuring load current of 0.68A.

What make and model of DMM are you using? Are you using more than one to measure both current and voltage concurrently?

That alone could explain many of the issues in this thread.

 

The normal DMMs use 0.1 Ohms in series to convert current into voltage for measurement in 2A range. When you are measuring current, this 0.1 Ohms alongwith probe resistance is coming in series with your load. So the measurement of current with the meter is only that much accurate, or inaccurate!
As for as wires to MAX4080, they can be longer provided that they dont carry the load current. That is, with the load connected in series to 0.1 Ohm sense resistor normally, take 2 wires from the ends of the 0.1Ohm resistor to MAX4080. After all, internally, there is a 20k res in G=60 MAX4080.

 

So I take it you aren't using Fluke, Agilent, or similar brand/re-branded (not clone) meter?

If so, your measurement accuracy is essentially about ±5% after throwing out the last digit of the display. Example is if you measure 3.859V, the actual voltage is ±5% of 3.85V, or somewhere between 3.75 to 4.04 V. Similar with current measurements, resistor measurements, etc.

Your processor and this setup may be giving a more correct value than your meter if your meter was a low end model from Radio Shack, or a clone with a bunch of features from a random brand in SE Asia. Some will be as close as ±1% after throwing out the last digit, but hoping for more than that is futile.

If you are using a precision sense resistor, and at least 10 bits of ADC on the uC, while the uC has decoupling capacitor and a clean power supply, I have seen them give more accurate readings than a $20 no name DMM.

Just ensure your sense signal output voltage is within the limits of the silicon of both the sense IC and uC (usually < 5V), with over-voltage protection such as a zener clamp (which triggers an overload LED so you can disable the power), and you should be good to go.

 

Try leaving the external current meter in series with your load while measuring current with your micro. This way any effect of the series resistance of the meter is included in both measurements.