Load cell-How it acts as Analog I/O module

Thread Starter

Lala Lulu

Joined Jun 5, 2017
4
Hello. Im still confused on this transducer whether it can be output or input module. lets say..i am using the load cell to monitor a weight.i might be using 0-5v,so,between 200<w<500 the motor will slow down after w=600 it will stop.How should i make the ladder logic?Just a direction is fine.Should i use MOV the weight set values into hexa bit and use CMP to trigger the output?Thank you.
 

Reloadron

Joined Jan 15, 2015
7,580
.i am using the load cell to monitor a weight.i might be using 0-5v,so,between 200<w<500 the motor will slow down after w=600 it will stop.How should i make the ladder logic?Just a direction is fine.Should i use MOV the weight set values into hexa bit and use CMP to trigger the output?Thank you.
I am not sure what you are asking? Do you have a link to the load cell data sheet. You mention w200 and w500 that would be 200 and 500 what? Pounds Kg.

You also mention 0 to 5 Volt so may we assume the output of your load cell zero to full scale is converted to 0 to 5 Volt? Now the 0 to 5 volts is going somewhere, where is it going and if it is going to an analog input of an ADC (Analog / Digital Converter) what is the ADC bit count as in a 10 bit or 12 bit converter?

Maybe you are only using a comparator? Please provide accurate information, data sheets and a schematic of what you have to get good help.

Ron
 

Thread Starter

Lala Lulu

Joined Jun 5, 2017
4
I am not sure what you are asking? Do you have a link to the load cell data sheet. You mention w200 and w500 that would be 200 and 500 what? Pounds Kg.

You also mention 0 to 5 Volt so may we assume the output of your load cell zero to full scale is converted to 0 to 5 Volt? Now the 0 to 5 volts is going somewhere, where is it going and if it is going to an analog input of an ADC (Analog / Digital Converter) what is the ADC bit count as in a 10 bit or 12 bit converter?

Maybe you are only using a comparator? Please provide accurate information, data sheets and a schematic of what you have to get good help.

Ron
Thanks for responding..I appreciate that..ok.I'm trying to do a ladder logic from a load cell-filling machine that i found on Futek website.So,I'm still learning about plc..and I kind of confused when an analog input/output situation question showed up..

The weight is in kg..0-5V..lets say I use 12 bit converter which means 4096..how should I proceed with that.My boggling problem is only at the load cell...can I directly use the value or needs to use Scaling function SCL or I can just use MOV(21) but change it to hexa..before use CMP of the weight sets given.I'm using Siemens by the way.
 

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Reloadron

Joined Jan 15, 2015
7,580
OK, so we can assume a 0-5 volt signal represents a weight in Kg. Now some PLCs allow the scaling and some don't but here is what is going on. 0-5 Volts actually is equal to 0 to 4095 bits in a 12 bit ADC. So then 0 - 4095 would be 0 to full scale weight. Now if the PLC lets you scale it we can figure if I have a 0 to let's say 100 Kg transducer then 0 - 5 volts would be equal to 0 to 100 Kg. so 4095 / 100 = 40.95 bits per Kg. We can call it 41 bits per Kg.
Your Analog input to the PLC in code would look like:
(4095 / Analog In) x 100 = Wt 'Wt represents your actual weight.

So with a full scale input you would get 4095 / 4095 = 1 and then 1 X 100 = 100 Kg.

The reason we used 4095 is a 12 bit converter has 4096 quantization levels so including zero the maximum count would be 4095.

Knowing that we can apply our logic be it Ladder Logic or whatever we are working with or coding. We could also say for example:

If Wt >something Then
do something
EndIf

This part all depends on what you actually have. Even knowing the bits we could use the bit count rather than Wt. Does this help and make sense to you? :)

The image is a bit dark but you did a good job!

Ron
 

bertus

Joined Apr 5, 2008
22,305
Hello,

I used the automatic white balance function of the GIMP on your image to make it a little brighter:

lala_1496677589583290648984_wb.jpg

Bertus
 
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