modicon weight scaling

Hello,
I have a momentum that I want to add weight to from a Metler
Toledo scale. My scale goes to 20,000lbs. and my signal is 4-20ma.
Im not sure how to make the logic,as far as math. can you help?

Scaling analogs in a Momentum is HORRIBLE


Anyways, heres how it works:
First thing is to converty all your values to Float using ITOF instructions.
This gives you alot better resolution.

Map out registers for Raw Input Value, Eng Unit Hi Scale, Raw Counts Full Scale.
Keep them at least 1 register apart as Floats take up 2 registers.

I use SUB blocks to hard code the following values into the math registers and while not strictly necessary it helps prevent any issues if the PLC is ever powered down.

Eng Units Hi = 20,000
Raw Count Full Scale = 32,000

Use a ITOF to convert all your values to floats.
Using an EMTH DIVF (Instruction 21) divide your Raw Counts Full Scale (float) by your Eng Full Scale (float) to give you counts/pound.
Put this in a 'Scaling Factor' register pair.
Then divide your actual analog input raw counts by the 'Scaling Factor' and put the result in a 'Scaled value' register pair.
Finally use an FTOI to change your scaled value back to an integer if required.

One thing worth noting - putting in a SUB block so if the analog value goes negative it just moves a Zero into the Raw Counts register is a good idea otherwise it'll screw up your math.

I have used Concept to program all the Momentums I have used. If yours is a Concept compatible unit then don't use 984LL use IEC and then you dont need to worry about registers

Geoff

Stewy,

I have a DFB that you can import into your program that emulates the SCP (scale with parameters) that AB has come up with in recent years.

It has Min and Max input and Min and Max scaling factor. It takes these and scales to an output.

Let me know if you need some help still

-J