Hi,

You have all probably answered this one before but how do I export analogue values from a running plc into a excel spreadsheet to help with process control of a two variable PID loop? its been bugging me for ages and I really would like some form of idiots guide on how to do it.

Any help would be very grateful.

Cheers,
Bill Pritchard

 

the first question is this: Do you have a copy of RSLinx which is NOT the RSLinx “Lite” version? ...

basic idea: the “Lite” version will handle the communications necessary to program a PLC ... but the “Lite” version will NOT do the DDE/OPC transfers that you require ...

RSLinx “Lite” is free ... anything else costs money ... see your Allen-Bradley distributor for various versions and their prices ...

but let’s assume for discussion that you already have a “non-Lite” version of RSLinx up and running ...

first click the “DDE/OPC” feature on the RSLinx main menu ... select “Topic Configuration” from the drop-down menu ... highlight your PLC ... click the “New” button at the bottom of the window ... type a name for the new topic ... example: “BILL” ... click “Done” and close the configuration window ... leave RSLinx running ...

now go to Excel and click a cell ... we’re almost done ...

type the following formula ...

=RSLINX|BILL!’S:42’

now cross your fingers and hit Enter ... if you’re lucky (I prefer to say “blessed”) then you should have a number which changes once each second and ranges from 0 through 59 ... note that S:42 is the seconds reading from the real-time clock in MOST SLC processors ... it USUALLY makes an excellent “just getting started” test ... you didn’t tell us what model PLC you’re using ... if the S:42 address doesn’t work, don’t panic ... substitute another address that you KNOW exists in your processor ...

finally ... you should be able to go from there ... but ... since PUNCTUATION IS EVERYTHING! I’ll go one step further and nail down the formula for you step-by-step...

EQUAL SIGN

RSLINX

STRAIGHT UP-AND-DOWN-LINE “DOS PIPE” CHARACTER (shift backslash on most keyboards)

BILL (or the name of your topic)

EXCLAMATION POINT

SINGLE QUOTE MARK (apostrophe)

S

COLON

42

SINGLE QUOTE MARK (apostrophe)

and NO SPACES anywhere in the string

like I said, punctuation is EVERYTHING! ... if you miss one character then it usually won’t work at all ... and yes, I'll agree ... this can be a source of MAJOR frustration ...

hope this helps,
Ron