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RSLogix 5 Analog Scaling
Trying to replace 4 proximity switches with a laser using a 4-20mA signal.

Hello there!

I am just a few minutes into this and here is my first post. Hopefully this works out! I am very new to Allen Bradley programming.

Anyway, I am trying to replace 4 proximity switches with a laser. The laser needs to be able to tell the RSLogix5 to execute at 4 different positions.

System Information:

16 channel analog input card
Input card: 1771-IFE Series C
4-20 mA signal scaled to 0"-50"

I’ve done some digging and can’t seem to find a great way to scale an analog signal in RSLogix5. So far, all I’ve come up with is to make 4 different 'LIM' blocks to create a range that matches the existing proximity switches.

Any help is great help! Hopefully I provided enough information. If more is needed please let me know!

Raw data for this module should be 0-4095. I would just DIV the raw data integer by 81.9 to a float for 0-50 inches value. Four LIMs is a fine way to get the positions.

By David Ferguson on 6 February, 2019 - 2:54 pm

You can scale the raw signals right in the logix 5 software.....

I'm not at my computer, and it's been a while, but you scale them in the analog card setups....

It is in the IFE manual. If you can't find it, I can when at a computer...just let me know. Did many many cards this way for ages. Haven't done PLC5 in a while though other than to convert them :-).

Dave Ferguson
Control Systems Engineer

By Steve Myres on 6 February, 2019 - 3:00 pm

SLC has SCP, which would work nice, can't remember if the PLC-5 does or not.

I think the 1771-IFE will scale to engineering units internally. I know some 1771 AI modules did. You BTW to some registers for EU min & max. Now the output will still be integer, so you probably want to do implied decimal, like 0-500 or 0-5000 rather than 0-50.

Also check the filter rate in the module if you're moving fast.

By David Ferguson on 7 February, 2019 - 7:31 am

It does; this is what I was trying to get at saying you can do it right in Logix 5......

Dave Ferguson
Control Systems Engineer

By Steve Myres on 7 February, 2019 - 11:08 am

My post wasn't in response to yours. With the moderation delay, both of us submitted our responses to the OP before either of ours were showing on the thread.