2 Visual Components Manuals

Introduction to Visual Components 2.3
Since VC 2.2 Runtime supports m68k targets in addition to i386 targets, the imprecise floating decimal data type
"double" should be avoided when calculating scaling internally. Calculation takes place with int32 data types
instead.
To prevent problems with value overflows, actual calculations are processed with the aid of Assembler routines
which allow 64−bit operations.
When scaling in VC 2.2, the slope 'k' from the linear function is made up of the PLC−Min, PLC−Max,
Display−Min, and Display−Max parameters. These configurable values (fixed or dynamic using PVs) result in
the slope 'k' whereby either x or y is represented depending on the scaling direction.
k = (ymax ymin) / (xmax xmin)
d=ymin−(xmin *k)
This results in the following scaling formula, whose scope is general:
y = (ymax ymin) / (xmax xmin) * x + (ymin −(xmin*(ymax ymin) / (xmax xmin)))
Example:
Following configuration:
PLCmin=2
PLCmax=4
SCALmin=−10
SCALmax=100
Needed: Displayed value when PLCValue=3
k=(100−(−10)/4−2))
k=55
d=−10−(2*55)
d=−120
Y=55*3 −120
Y=45
The parameters defined above in detail:
Parameter Description
PLC Min Permitted lower limit of the values of a PV on the target
PLC Max Permitted upper limit of the values of a PV on the target
Display Min Permitted lower limit of the displayed values of a PV on the display
Display Max Permitted upper limit of the displayed values of a PV on the display
4.13.2.3 Restrictions
Using scaling, even unsigned PVs (on the target) can accept a signed value range on the display. PVs of data
type float are normally excluded from scaling because their special properties and non−linear cardinality would
cause unforeseen side effects for the user. The following table shows all data types which can be scaled:
PV Data Type Display Value Range
BOOL DINT
USINT DINT
SINT DINT
UINT DINT
INT DINT
UDINT UDINT
DINT DINT
4.13.2.3 Restrictions 439