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Old May 22nd, 2020, 01:14 PM   #1
bigLee
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1771 IFE to 1794 IF4I Scaling Dilemma

Hello. Wanted to ask you seasoned vets out there about a scaling issue I'm having. Controller migration. A 1771 IFE 0-5VDC analog signal, configured for 0-16533 in BTW. 1794 is configured for -10V to 10V signed 2's.

I'm figuring I'll have to scale the new voltage input to correspond to the old voltage scaling?

At 5VDC, the eng value in the PLC5 is 2340. That doesn't make much sense to me as to why it wouldnt be 16533 but, moving along.

My new 5VDC eng value is 4860. I tried scaling the 0-4860 to 0-2340 but it doesn't track accurately. It's always off by an unacceptable range. This is for a flow setpoint application to bump valves to match flow.

Does anyone have any guidance or tips on how to rectify this problem? I don't want to rewrite logic if I don't have to. This program was created when I was 8 years old.

Any info is as always appreciated!

Thanks,

Ben
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Old May 22nd, 2020, 02:39 PM   #2
drbitboy
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what are your four bit settings from table 4.8 on page 61 here: https://literature.rockwellautomatio...pdf#G8.1048069


?
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Old May 25th, 2020, 03:59 AM   #3
JohnCalderwood
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Quote:
I don't want to rewrite logic if I don't have to. This program was created when I was 8 years old.
If you wrote the logic when you were 8 years old, you were doing well...!!

What is the configuration setup for the 1771-IFE card?
My understanding on the 1771-IFE was that the input range was always 0-4095.
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Old May 26th, 2020, 08:41 AM   #4
bigLee
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Bit configuration

Please see the screeenshot. I to had the conversion planned for 0-4095, but the values are not that as configured with voltage into the channels. 0 vdc is 970 eng and 5 vdc is around 4860 eng.
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