understanding Loadcell, instrumentation amplifier

[varuntejavarma]

Hello,
I want to build a weight scale with 0.1 gram resolution. But i have some problems in my initial stage.
I am using a load cell with sensitivity of 1mv/v and excitation voltage of 3 v.
1. With no weight, the load cell output shows -0.089 mv and with full load(500gms) it shows 2.895 mv. Is -0.089 mv the noise of my load cell. If so, how could i solve this problem. why is my load cell mot showing an output of 3mv for 3 v of supply.
2. I have connected the load cell to IN amp ( PMI AMP04FP) with a gain of 100, with no load, i get an output of 3.203 mv and with full load i am getting an output of 278 mv.
my q: why is the inamp showing an output of 3.203 mv. is it the offset voltage. if so how could i solve the prob. why am i getting 278mv instead of 300mv
I have gone through the basics.But couldnt get my mind clear because of lot of information in small time. I know that my questions are basic and need some reading. I would be glad if someone could explain me what is happening and how to proceed. I am willing to learn . So, any kind of help( links, books etc) is appreciated. kindly go easy on me

 

[JimB]

I am using a load cell with sensitivity of 1mv/v and excitation voltage of 3 v.

Do you know what this means?
The full scale output of the cell will be 1mV for each volt of excitation.

and with full load(500gms) it shows 2.895 mv

Which looks like you got more or less what you would expect. No Problem.

With no weight, the load cell output shows -0.089 mv......
Is -0.089 mv the noise of my load cell.

No, it is the zero offset.
You will have to zero this out by some means or another. There are several ways to do it.

As for the amplifier, it seems to be doing more or less what I would expect.
The zero and gain may need a bit of a tweek, again there are several way to sort those problems.

kindly go easy on me

No chance!

JimB

 

[varuntejavarma]

does the input offset or the output offset voltage change of INamp with gain??

No, it is the zero offset.
You will have to zero this out by some means or another. There are several ways to do it.

As for the amplifier, it seems to be doing more or less what I would expect.
The zero and gain may need a bit of a tweek, again there are several way to sort those problems.


JimB

How could i zero the offset of Load cell and the INamp.

 

[JimB]

How could i zero the offset of Load cell and the INamp.

I was rather hoping that you would attempt to find that out for yourself.

JimB

 

[varuntejavarma]

I have just added some weights on loadcell untill it reads 0. Is this the right way to remove offset..

My load cell outputs from 0mv(0 load) to 2.987mv(full load). With a gain of 100 I get 3.112 mv(0 load) and 279 mv(full load). how could i remove offset in INamp. I mean, should i add any components to my circuit or any measures to be taken to reduce noise.

what should i do to read small weight changes. upto 0.1 gm.

 

[willeng]

Don't mean to but in here, some time ago Eric basically gave me an excellent Tutorial on how to setup a load cell that is working & has been working flawlessly, accurately & reliably since I built it, it would be worth reading. Do a search for "Load Cell Output" not sure how to link it?


The Credit goes to Eric not me & if I can do it believe me you can!

Thanks again Eric!

Cheers

Mod edit..
Link... https://www.electro-tech-online.com/threads/load-cell-output.130249/#post-1081074