4-20ma scaling and Vfd to HMI Scaling

Hello,
I have looked through the archives and haven't had any luck on the basics of scaling. I'm trying to refresh myself and what formulas I can use to scale inputs and output's. Anything from HMI controls for vfd's. To level indicators ,computing pump speeds to a HMI, etc. I can do most of my scaling needs in the Analog card itself , but I still would like to have information to read through. Do you have any recommended text books or websites? Any thing would help. Thx

For basic scaling try this thread:
http://www.plctalk.net/qanda/showthread.php?t=109295&highlight=basic+scaling

Depending on Platform, there may be built in scaling tools, that do the scaling for you, such as the SCP in the SLC-500 platform

Hi, Mavrick
I don't have too many thoughts on books or websites, but I have done a lot of programs this last 2 years that required a LOT of scaling. The very first reference I used was another rs5K program, and the person that wrote it used a function block routine for scaling. The analog I/O had the proper limits, current or voltage ranges, but then he used a SCL instruction with the input and output blocks for the scaling.
At first I was a little leery of it because I'd never used it or seen it, but I've really gotten to like it and I'm really used to it now. I have like 24 analog I/O in one of my programs and it works good. Easy to change on the fly. Looks nicer than big CPT blocks on a rung. Hope this helps.

I wish had function block abilities but unfortunately I only have ladder logic. Thank you for the info.

Mavrick
Add a routine, like I call mine "Scaling" and in the drop down, pick FBD (function block) when you create the routine. It usually defaults to "ladder" but you can change this, and I think get ST also. Hope this helps.

If you have only the LAD editor go to Rockwell's Sample Code Library,search for 'SCP' and download the AOI to your PC; Import the AOI into your project, add the AOI to your code and then you'll be able to Scale with Parameters in LAD editor.

A little more info..

https://www.ronbeaufort.com/y=mx+b_part1.pdf

https://www.ronbeaufort.com/y=mx+b_part2.pdf

And another formula.. And a helpful tool..(you can edit the zero/span and units to suit your needs)

Thank you for the help I have added the SCP.

Mickey, thanks for the spreadsheet.

mavrick said:

Mickey, thanks for the spreadsheet.

Click to expand...

Your welcome. The chart is not mine, I dowloaded it from this site.

See below for credit.

[B said:

John Soltesz[/B];283466]That's me. Check the Excel file properties.
I use it for calibration checking charts when I have the techs install instruments. What is handy is the PLC counts. If you are looking at the raw value in a register just check the chart. Or don't have a MA meter but have a voltmeter to check the loop and it has a 250 ohm resistor check volts in the chart. I carry a pencil type VOM and a 250 ohm resistor for quick checks. I also have a version of the Excel chart running on my pocket PC.

Click to expand...

If I was wanting to control a valve or motor from a HMI screen Ex. Open a valve to 65% or operate a pump at 35%. Is there a good formula/standard to use for that application?