Scale (SCL)
This information applies to the
CompactLogix
5370, ControlLogix
5570, Compact GuardLogix
5370, GuardLogix
5570, Compact GuardLogix
5380, CompactLogix
5380, CompactLogix
5480, ControlLogix
5580, and GuardLogix
5580 controllers.The Scale (SCL) instruction converts an unscaled input value to a floating point value in engineering units.
Available Languages
Ladder Diagram
This instruction is not available in ladder diagram logic.
Function Block
Structured Text
SCL(SCL_tag)
Operands
Function Block
Operand | Type | Format | Description |
SCL tag | SCALE | Structure | SCL structure |
Structured Text
Operand | Type | Format | Description |
SCL tag | SCALE | Structure | SCL structure |
See
Structured Text Syntax
for more information on the syntax of expressions within structured text.SCALE Structure
Input Parameter | Data Type | Description |
EnableIn | BOOL | Enable input. If false, the instruction does not execute and outputs are not updated.
Default is true. |
In | REAL | The analog signal input.
Valid = any float
Default = 0.0 |
InRawMax | REAL | The maximum value attainable by the input to the instruction. If InRawMax  InRawMin, the instruction sets the appropriate bit in Status and stops updating the output.
Valid = InRawMax > InRawMin
Default = 0.0 |
InRawMin | REAL | The minimum value attainable by the input to the instruction. If InRawMin  InRawMax, the instruction sets the appropriate bit in Status and stops updating the output.
Valid = InRawMin < InRawMax
Default = 0.0 |
InEUMax | REAL | The scaled value of the input corresponding to InRawMax.
Valid = any real value
Default = 0.0 |
InEUMin | REAL | The scaled value of the input corresponding to InRawMin.
Valid = any real value
Default = 0.0 |
Limiting | BOOL | Limiting selector. If true, Out is limited to between InEUMin and InEUMax.
Default is false. |
Output Parameter | Data Type | Description |
EnableOut | BOOL | Indicates if instruction is enabled. Cleared to false if Out overflows. |
Out | REAL | The output that represents scaled value of the analog input.
Valid = any real value
Default = InEUMin |
MaxAlarm | BOOL | The above maximum input alarm indicator. This value is set to true when In> InRawMax. |
MinAlarm | BOOL | The below minimum input alarm indicator. This value is set to true when In < InRawMin. |
Status | DINT | Status of the function block. |
InstructFault (Status.0) | BOOL | The instruction detected one of the following execution errors. This is not a minor or major controller error. Check the remaining status bits to determine what occurred. |
InRawRangeInv (Status.1) | BOOL | InRawMin InRawMax. |
Description
Use the SCL instruction with analog input modules that do not support scaling to a full resolution floating point value.
For example, the 1771-IFE module is a 12-bit analog input module that supports scaling only in integer values. If you use a 1771-IFE module to read a flow of 0-100 gallons per minute (gpm), you typically do not scale the module from 0-100 because that limits the resolution of the module. Instead, use the SCL instruction and configure the module to return an unscaled (0-4095) value, which the SCL instruction converts to 0-100 gpm (floating point) without a loss of resolution. This scaled value could then be used as an input to other instructions.
The SCL instruction uses this algorithm to convert unscaled input into a scaled value:
Alarming
Once the instruction calculates Out, the MaxAlarm and MinAlarm are determined as follows:
Limiting
Limiting is performed on Out when Limiting is set. The instruction sets Out = InEUMax when In > InRawMax. The instruction sets Out = InEUMin when In < InRawMin.
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See Common Attributes for operand-related faults.
Execution
Function Block
Condition/State | Action Taken |
Prescan | EnableIn and EnableOut bits are cleared to false. |
Tag.EnableIn is false | EnableIn and EnableOut bits are cleared to false. |
Tag.EnableIn is true | EnableIn and EnableOut bits are set to true The instruction executes. |
Instruction first run | N/A |
Instruction first scan | N/A |
Postscan | EnableIn and EnableOut bits are cleared to false. |
Structured Text
Condition/State | Action Taken |
Prescan | See Prescan in the Function Block table. |
Normal Execution | See Tag.EnableIn is true in the Function Block table. |
Postscan | See Postscan in the Function Block table. |
Example
The SCL instruction is typically used with analog input modules that do not support on-board scaling to floating point engineering units. In this example, the SCL instruction scales an analog input from a 1771-IFE module. The instruction places the result in Out, which is used by an ALM instruction.
Function Block
Structured Text
SCL_01.In := Input0From1771IFE;
SCL(SCL_01);
ALM_01.In := SCL_01.Out;
ALM(ALM_01);
Provide Feedback