A good plan is to start by drawing a graph. If you start by assuming the ADC is OK, then a graph will tell you what sort of offset, gain, polarity you have. Just whacking the first few numbers you posted into a spreadsheet, and doing an XY graph, yields this.
The general equation for a straight line is y=mx+c. A good ADC will have a straight line relationship between the input voltage and the output code.
The spreadsheet has two columns, one the actual input voltage, the other y=mx+c, where x is the ADC reading. I've roughly adjusted m and c to give a reasonable fit over part of the curve. I've left the offset off a bit so you can see all of both traces.
You will notice that you need to multiply the ADC reading by a small floating point number. Whether you can do this with your particular compiler, and exactly how, is a programming exercise for you.
As you see, the points do not fit a straight line. It might be the ADC is non-linear. It might be your voltage measurements are non linear. You will need to investigate which before you put your trust in this system.
I would suggest swinging the voltage from -FSD to +FSD (is it designed to go between +/- 5v ?) in a dozen or so steps, and then drawing a similar graph. When you can see what's happening on the large scale, examine smaller ranges. Notice where the ends of the valid range are, and see what code it outputs when it overloads. Try to understand where any discrepancies from linear are coming from.
I experimented this fairly extensively as a mOhm meter set-up here: https://dannyelectronics.wordpress.com/2015/10/25/a-hx711-based-milliohm-meter/
1) Is there a simple way to reduce fluctions ? What can I try ?
you can try filtering, either in hardware or software. or using a different adc.
2)what can be done in software to reduce noise ?
filtering.
3)if the output of load cells is same (0-20mv) why does this issue arise ? is it due to multiplication factor ? lower range load cells work fine ..is it due to stable first bits of ADC output ?
not sure what you meant by "this issue". noise is inevitable, especially for high resolution adc. sometimes that noise can be a very useful feature in some applications.
4)I read somewhere that fluctions can be reduced using some hardware peripherals like resistors .
how to do it ?
in some applications, yes. cannot see how resistors alone can help here.
Best Answer
I had a problem with wiring (Tx and Rx not making contact), Note- the voltage adjuster doesn't seem to start until communications from the MCU have taken place.