Tag Scaling Properties
Configuring a tag's scaling properties will condition the data for use within the Ignition Designer.
For example, if the capacity of a tank is 5250 Gallons but the tanks fill level is better represented in the Designer as percentage of 0 through 100, configuring the tag's scaling property will result in the tag displaying 0 through 100 while the actual tank fill moving is between 0 and 5250 Gallons.
Numerical properties of tags can be scaled allowing automatic bi-directional conversion outside of the PLC. Scaling types include Linear scaling, Square Root scaling, and Exponential Filter scaling.
The numerical properties are available to OPC, DB, and Client tags whose data types are numeric.
Property |
Binding |
Name Description |
Scale mode |
ScaleMode |
If and how the tag value will be scaled between the source, and what is reported for the tag. |
Raw Lo |
RawLow |
Start of the raw value range. |
Raw Hi |
RawHigh |
End of the raw value range. |
Scaled Lo |
ScaledLow |
Start of scaled value range. Raw low will map to Scaled low for the tag. |
Scaled Hi |
ScaledHigh |
End of scaled value range. Raw high will map to Scaled high for the tag. |
Clamp mode |
ClampMode |
How values that fall outside of the ranges will be treated. "Clamped" values will be adjusted to the low/high scaled value as appropriate. |
Scale Factor |
ScaleFactor |
For single parameter modes (currently only for Exponential Filter), the factor parameter for the equation. |
Deadband |
Deadband |
A floating point value used to prevent unnecessary updates for tags whose values float by small amounts. |
Deadband Mode |
DeadbandMode |
There are two modes to choose from: Absolute or Percentage. |
Linear Scaling
The value will be scaled linearly between the low and high values, and clamped as appropriate.
The linear equation is:
ScaledValue = ΔS * (Value-RL)/ΔR + SL |
Square root Scaling
The equation for square root scaling is:
ScaledValue = ΔS * √((Value-RL)/ΔR) + SL |
Where:
ΔS = (ScaledHigh-ScaledLow)
ΔR = (RawHigh - RawLow)
RL = RawLow
SL = ScaledLow
Exponential Filter Scaling
This mode implements a simple linear recursive filter to smooth values. The scale factor corresponds to the weight of the smoothing effect, and is a value between 0.0 and 1.0. The smaller the factor, the greater the degree of smoothing.
The equation for the filter is:
y(t) = (1-f)*y(t-1)+f*x(t) |
Where:
y(t) = the output at time t
y(t-1) = the previous output
x(t) = the input value (current value)
f = the scale factor, with 0.0<=f<=1.0
Note: Only good quality values are considered for the filter. Bad quality values are ignored.