I hope you have already put the cursor on an SCP instruction and hit F1, or otherwise consulted the Help Files and Instruction Set Reference. Given that much, here is some amplification:
The SCP instruction helps you convert an input value to a value in different engineering units, as long as there is a linear relationship. For example, if you wanted to convert Fahrenheit to Celsius, you could enter 32 and 212 as the Input Min and Max, and 0 and 100 as the Output Min and Max. Those parameters in an SCP instruction would convert a Fahrenheit value in the Input register to a Celsius value in the output register. Note that neither the Input nor the Output are limited to be within the scaling parameters (-40 Input will yield -40 Output in the example), and floating point arguments are supported in processors that support that data type.
The SCP instruction was created mostly to aid the implementation of the original SLC500 analog modules, which did not support onboard scaling to engineering units. It has since become very popular for simple engineering unit conversion.
Scale with parameters simply lets you do the equivalent of the common analog operations of summing an offset and scaling the input (gain,
span) to a new set of values.
I have used the SCP to convert counts, read in from an analog input card, to an engineering units value. One application I was reading in a 4-20 mA signal from a temperature sensor that represented 0-200 Deg.F. My input min was 6242
which represented the counts associated with 4 mA or 0 Deg.F (scaled min). My input max was 31208 which represented the counts associated with 20 mA or 200 Deg.F (scaled max). Hope this helps.
The SCP is an easier to use version of the Scale instruction.
You provide the SCP with the input value (typically from an analog input module), it's raw range (min/max) and it's range in engineering units (min/max) and the SCP outputs the normalized (in engineering units) value of the input.
There are lots of uses for this instruction. For example, if you want to sum a set of flow meters which have different ranges you run them through the SCP. The results can be added together since they're now in engineering units.
The instruction can be applied wherever you need a linear relashionship between two data. The data are the variable (t or x) and the function of that variable F(t) or y. the min and max data are the domain of x, the min and max of the function, are the range of it. If you use scale with parameters, you have not to deal with slope, nor the equation y=mx+b. ...But, if it is not clear, keep reading...
In order to understandt it the easiest way. Draw a two axis plane over a sheet. Identify the axis as x and y. Then mark: 1. the origin (where both axis cross each other) 2. Over the "x" axis, mark the years, considering it a timeline.
3. Over the "y" axis, your birth-year, and your actual age.
4. draw a line, that matches your age against the timeline.
5. Did you got a line that has a slope of 45 degrees?, you followed me the right way, otherwise, start again on step 1.
6. Once you succeed, getting the right plot, draw a rectangle that has the lower left corner over that line, and other upper right corner over same line (the one that has a slope of 45 degrees).
Now, you got the limits:
The lower line of the rectangle (bottom) starts on the minimum variable value, and ends on the maximum value.
The vertical side of the rectangle starts on the minimum scaled value, and ends (up) on the maximum scaled value.
As you can see, you can drawed any rectangle over that line. The same way you can scale any two valuess that are related by a linear function by this method. The rockwell guys are smart!, they do other peolple life (the PLC programmers) easier. I Love htem!
Remember that the line (function) can have any slope, not only 45 degrees. Anyway, the method works. Try the same example above, splitting the timeline in years, and your age in months.
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