RSLogix5000 Analog input scaling

Hi Everyone,
I am currently reverse engineering a hydraulic unit with a CompactLogix L35E and I have an issue with a Differential Pressure transmitter as I need to scale the analog input in the PLC. I am a long time user of AB software however the scaling I'm trying to achieve with the analog has me stumped, the transmitter is not a smart or hart compatible, therefore I need to do the scaling within the PLC.
Ok this is the situation.
1. Diff Pressure Transmitter 0-5000psi
2. Re-scaled range in PLC 255-3000psi
3. Then convert the above into 0-100% (255-3000psi)
I have set the AI channel configuration as,
- 4mA to 20mA
- 50Hz
- Engineering Units
I have also created a CPT instruction to scale the 4-20mA with the equation (DPT1-4000)/16
If anyone can provide some assistance, it would be much appreciated.
Thanks in advance
James

Sorry guys, I missed some significant key points;

1. Diff Pressure Transmitter 0-5000psi
2. Used range in PLC 255-3000psi
3. Then convert the above into 0-100% (255-3000psi), as this diff pressure is represented as torque 0-100% for operations.


Unfortunately because I am using a 1769-IF4, I don’t have the ability to manipulate the AI channel configuration as per a 1756-IF8.

Thanks
James

Use a real for the analog input engineering unit

0 psi = 4 mA.......5000 psi = 20 mA .....Difference = 16 mA

From the engineering unit real subtract 4 to give you the scaled input scaled across 16 mA
use a real for this result

5000 divided by 16mA =312.5 per mA

Get the scaled input real and multiply it by 312.5 to give you your wanted Psi real value

The difference in your Psi scaling is 3000 minus 255 = 2745 for your % answer
Get the Psi real and subtract 255 to get a differential real for your % answer

Now all you need to do is

100 multiplied by the differential real for your % answer divided by 2745

There are many ways you could set this out to get your result
but this gets you what you have described

Thank you, works perfectly