Analog Input Card 1769-IF4 Channel Read

Hi, I need some help reading the value of Channel 0 of a 1769-IF4 card.
The analog card is in slot 1. So the Input value should be: Local:1:I.Ch0Data. The card has been configured in RSLogix 5000.

What instruction should I use to retrieve this channel 0 value and converted to a real value. It will be between 4-20mA, so it will require decimal points. I was thinking of using the COP instruction, but I am not sure what data type the destination tag should be to accept numbers with decimal points.
The plc is L35E.


Thanks in advance.

Your scaled data type should be REAL.

As for the scaling itself, you will need to do some calculations to convert the raw analog value to your scaled value.

I usually do it in function block as there is a SCL instruction already available (there is in structured text as well) however you need RSLogix 5000 Pro to use these languages.

If you want to do it in LAD you will have to roll your own scaling but you will have to figure out your rate and offset first.

There is a good example on the AB Knowledge Base here but you need TechConnect access to view it: https://rockwellautomation.custhelp.com/app/answers/detail/a_id/38286

Otherwise here is an excellent post by Ron B explaining the formulas:

http://www.plctalk.net/qanda/showthread.php?p=101766&postcount=1

There is also a SCP (Scale With Parameters) AOI available on the RA website. I have used it and it seems to work good.

Brendan, thanks for the response. I will take a look at the interesting post you pointed to. I think is worth reading through it. I believe using the REAL data type is my answer.
Thanks a lot!

Bullzi, thanks for the reply. I think the SCP instruction is very useful, but it is only available for RSLogix 500. Thank you.

caleno said:

I think the SCP instruction is very useful, but it is only available for RSLogix 500. Thank you.

Click to expand...

See link below.

http://www.plctalk.net/qanda/showpost.php?p=434919&postcount=2