You know that the voltage of a load cell is relatively small... can I connect the load cell directly to a PLC??? or Shall I make an amplification stage ???

 

hi,
You will require to amplify a load cell signal before using it with a PIC.

A LC has an output in the order of 0 thru 10mV or 20mV at full load.

If you use the PIC's adc with the internal 5Vref, the LC signal will require 5000/10 = *500 gain for the max adc value.

What resolution in weight are you planning, also whats the max weight.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Thanks alot for your reply .. but I'm using a PLC ( programmable Logic Controller ) not a PIC

 

hi,
Does the PLC you are using have any ADC inputs.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

well, not an integrated ADC .. but I will use an ADC module .... it has 12 bit resolution ( values from 0 to 4095 ) .... the load cell's output is 2mv/v

 

hi,

Is that 2mV/Volt or maximum output.?

What the weight range of the Load Cell.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

No this is the output voltage per each volt of excitation voltage ... the cell weight range is from 0 to 100 kg

 

hi,
So IF the Vx=12Vdc then the 100kG FSD would be 24mV.
The Vext should be marked on the cell.?

Which external ADC do you plan to use.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

as I've told you before I'm planning to use an ADC module .... it has 12 bit resolution ( values from 0 to 4095 )

 

hi,
Thats what I said

I know its a 12bit, whats the model number, some have inbuilt amplifiers.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

the model is Al-1116 .... it's a product from ALTUS company
This is the website of the company:
www.altus.com.br

 

hi,
I have downloaded the datasheet.
I would suggest the 0 to +5V input option.

The LC output will require to be amplified from its 2mV/Vx upto 0 to +5V, also a ZERO and SPAN control pot for the amp.

Are you using all 8 input channels.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Thanks Eric ... Why do I need to amplify the signal ? ... The LC output is from 0 to 2mv/vx this values are inside the range 0 to 5v

 

The ADC will only give the full 12 bit output for +5V input.

That means to get a count of 4096 requires a +5V input.

If you say had a 10mV input the all you would get from
the ADC is 0.01 * 4096 =40 [40.96] counts,,, which is no use, the resolution is far too low.

If for example the LC had a 100Kg weight on it and gave say 10mV out, then
the LSB of the ADC would be 100Kg/40 = 2.5Kg

Do you follow OK.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

ok eric ... What type of amplifiers can be efficient to use with PLCs??