Process Tank Strapping Table (PTST)
This information applies to the CompactLogix 5380P and ControlLogix 5580P controllers.
The Process Tank Strapping Table (PTST) instruction calculates the volume of product in an upright cylindrical tank, given the level of the product and the tank calibration table. The instruction can compensate for:
- Free water at the bottom of the tank, given a product/water interface level.
- Thermal expansion of the tank shell, given the coefficient of linear expansion of the shell material and product and ambient temperatures.
- A floating tank roof, given the product density is provided.
The Process Tank Strapping Table (PTST) instruction is a calculation function, between blocks.
Available Languages
Ladder Diagram
Function Block Diagram
Structured Text
PTST(PTST_tag, Cfg_CalTbl);
Operands
IMPORTANT:
Unexpected operation may occur if:
- Output tag operands are overwritten.
- Members of a structure operand are overwritten.
- Except when specified, structure operands are shared by multiple instructions.
There are data conversion rules for mixing numeric data types within an instruction. See Data conversions.
Configuration Operands
Operand | Type | Format | Description |
|---|---|---|---|
PlantPAx Control | P_TANK_STRAPPING_TABLE | tag | Data structure required for proper operation of instruction. |
Cfg_CalTbl | P_STRAPPING_TABLE_ROW | tag | Tank calibration table, level to volume. |
P_TANK_STRAPPING_TABLE Structure
Public members are standard, visible tag members that are programmatically accessible. Private, hidden members are used in HMI faceplates and are not programmatically accessible. Private members are listed in separate tables after public members.
Public Input Members | Data Type | Description |
|---|---|---|
EnableIn | BOOL | Enable input. Ladder Diagram: Corresponds to the rung-condition-in. Default is true. |
Inp_InitializeReq | BOOL | 1 = Request to initialize the instruction. The instruction is normally initialized in instruction first run. Use this request when reinitialization is needed. The instruction clears this operand automatically. Default is true. |
Inp_Level | REAL | Tank innage level, in feet or meters. Valid = any float. Default is 0.0. |
Inp_FreeWaterLevel | REAL | Tank innage free water interface level, in major level units (feet or meters). Valid = any float. Default is 0.0. |
Inp_ObsAPI | REAL | Observed density, or degrees API, at product temperature. This is used for floating roof compensation to calculate displacement based on weight of roof. Valid = any float. Default is 30.5. |
Inp_AvgProdTemp | REAL | Average product temperature input in degrees Fahrenheit or Celsius. Valid = any float. Default is 60.0. |
Inp_AmbTemp | REAL | Ambient temperature input in degrees Fahrenheit or Celsius. Valid = any float. Default is 60.0. |
Cfg_MinorPerMajor | REAL | Table minor units, in inches, centimeters, millimeters, per major unit, in feet or meters. Type 0.0 if minor units not used. Valid = any float. Default is 12.0. |
Cfg_HasCorrTempShell | BOOL | 0 = No correction for temperature of tank shell. 1 = Include correction for temperature of tank shell. Default is false. |
Cfg_HasFloatRoofAdj | BOOL | 0 = Do not use floating roof adjustment. 1 = Include floating roof adjustment to account for displacement of fluid level. Default is false. |
Cfg_HasMoreObj | BOOL | 1 = Tells HMI an object with more info is available. Default is false. |
Cfg_CalTemp | REAL | Temperature of tank calibration (typically 60 °F or 15 °C). Valid = any float. Default is 60.0. |
Cfg_ShellCoefOfExp | REAL | Tank shell linear coefficient of thermal expansion (1 per degree Fahrenheit or 1 per Celsius). Valid = any float. Default is 0.0000062. |
Cfg_K | REAL | Temperature weighting (type 0.0 for insulated tank). See API MPMS 2.2A Appendix D. Valid = any float. Default is 7.0. |
Cfg_FloatRoofLevel | REAL | Lowest level at which to add or subtract floating roof compensation (feet). Valid = any float. Default is 0.0. |
Cfg_FloatRoofCalAPI | REAL | Degrees API for which table includes floating roof data. Valid = any float. Default is 30.5. |
Cfg_FloatRoofVolPerAPI | REAL | Adjustment to table values for product density not equal to calibration density (in volume units per degree API, typically a negative number). Valid = any float. Default is -2.5. |
Public Output Members | Data Type | Description |
|---|---|---|
EnableOut | BOOL | Enable Output. This output state always reflects EnableIn input state. |
Val_TotObsVol | REAL | Raw total observed volume from Calibration Table (barrels, gallons, liters). |
Val_FreeWater | REAL | Free water volume (barrels, gallons, liters). |
Val_TempShell | REAL | Calculated tank shell temperature in degrees Fahrenheit or Celsius. |
Val_CorrTempShell | REAL | Correction for temperature of tank shell (multiplier). |
Val_FloatRoofAdj | REAL | Floating roof adjustment volume (barrels, gallons, liters). |
Val_GrossObsVol | REAL | Primary value: Gross observed volume (see API MPMS 12.1.1). |
Sts_Initialized | BOOL | 1 = Instruction is initialized. Use Inp_InitializeReq to reinitialize. |
Sts_UnderMin | BOOL | Inp_Level is below lowest level in strapping table. |
Sts_OverMax | BOOL | Inp_Level is above highest level in strapping table. |
Public InOut Members | Data Type | Description |
|---|---|---|
Cfg_CalTbl | P_STRAPPING_TABLE_ROW[2] | Tank calibration table (level to volume). |
P_STRAPPING_TABLE_ROW Structure
Members | Data Type | Description |
|---|---|---|
Major | REAL | Number of major units (feet, meters). Valid = 0.0 to maximum positive float. |
Minor | REAL | Number of minor units (inches, centimeters, or millimeters). Valid = 0.0 to maximum positive float. |
Volume | REAL | Tank volume (oil barrels, gallons, liters) at given level (feet, inches). Valid = 0.0 to maximum positive float. |
Operation
Configuration of Strings for HMI
Configure strings for HMI faceplates (FT View) and for the Logix Designer configuration dialog box. The strings are set to extended properties of tag items. Configure the strings in Logix Designer only.
- Description
- Label for graphic symbol
- Display Library for HMI Faceplate call-up
- Instruction name
- Area name
- URL link
- More Information
- Gross volume units
- Free water volume units
- Raw volume units
- Calculated tank temperature units
- Correction for tank temperature units
- Floating roof adjustments volume units
- Temperature for tank calibration units
- Temperature for API units
- Level units
- Volume units
- Temperature for tank shell linear coefficient units
Monitor the PTST Instruction
Monitor from within Logix Designer. The PTST does not have an associated operator faceplate.
Affects Math Status Flags
No.
Major/Minor Faults
None specific to this instruction. See Index Through Arrays for array-indexing faults.
Execution
Ladder Diagram
Condition/State | Action Taken |
|---|---|
Prescan | Rung-condition-out is cleared to false. |
Instruction first run | All internal statuses and calculations are reset. The instruction executes normally. |
Rung-condition-in is false | Rung-condition-out is cleared to false. Calculation values is not updated (holds last value). |
Rung-condition-in is true | Set rung-condition-out to rung-condition-in. The instruction executes. |
Postscan | Rung-condition-out is cleared to false. |
Function Block Diagram
Condition/State | Action Taken |
|---|---|
Prescan | EnableOut is cleared to false. |
Instruction first run | All internal statuses and calculations are reset. The instruction executes normally. |
Instruction first scan | See Instruction first run in the Function Block Diagram table. |
EnableIn is false | EnableOut is cleared to false. Calculation values is not updated (holds last value). |
EnableIn is true | EnableOut is set to true. The instruction executes. |
Postscan | EnableIn and EnableOut bits are cleared to false. |
Structured Text
In Structured Text, EnableIn is always true during normal scan. The instruction executes when it is in the control path activated by the logic.
Condition/State | Action Taken |
|---|---|
Prescan | See Prescan in the Function Block Diagram table. |
Instruction first run | See Instruction first run in the Function Block Diagram table. |
EnableIn is true | See EnableIn is true in the Function Block Diagram table. |
Postscan | See Postscan in the Function Block Diagram table. |
Example
In this example, the PTST instruction calculates the volume of product in a storage tank based on the measured storage tank level and storage tank strapping table information. There is no floating roof and no compensation for displacement. There are no adjustments based on temperature to account for thermal expansion of the tank.
Ladder Diagram
Function Block Diagram
The measured storage tank level connects to the PTST instruction by using the input Inp_Level. The level is in units of feet. The storage tank is four feet tall. In this example, data is in six-inch increments. The strapping table has nine rows:
Level (ft-in.) | Volume (barrels) |
|---|---|
0-00 | 3.1 |
0-06 | 136.6 |
1-00 | 264.2 |
1-06 | 402.7 |
2-00 | 541.4 |
2-06 | 692.7 |
3-00 | 844.1 |
3-06 | 990.8 |
4-00 | 1137.5 |
To store the strapping table information in the controller, the tag MyP_StrapTbl_CalTable is created as type P_STRAPPING_TABLE_ROW [9], a nine-element array.
.Major | .Minor | .Volume | |
|---|---|---|---|
MyP_StrapTbl_CalTable[0] | 0 | 0 | 3.1 |
MyP_StrapTbl_CalTable[1] | 0 | 6 | 136.6 |
MyP_StrapTbl_CalTable[2] | 1 | 0 | 264.2 |
MyP_StrapTbl_CalTable[3] | 1 | 6 | 402.7 |
MyP_StrapTbl_CalTable[4] | 2 | 0 | 541.4 |
MyP_StrapTbl_CalTable[5] | 2 | 6 | 692.7 |
MyP_StrapTbl_CalTable[6] | 3 | 0 | 844.1 |
MyP_StrapTbl_CalTable[7] | 3 | 6 | 990.8 |
MyP_StrapTbl_CalTable[8] | 4 | 0 | 1137.5 |
The InOut tag Cfg_CalTbl of the PTST instruction is modified to point to the new array MyP_StrapTbl_CalTable to provide the instruction with the strapping table information. The output of PTST is then connected to another PAI instruction. The output is the calculated volume of the storage tank.
Structured Text
MyPTST.Inp_Level := MyLevel.Val;
MyVolume.Inp_PVUncertain := MyLevel.Sts_PVUncertain;
MyVolume.Inp_PVData := MyPTST.Val_TotObsVol;
PAI(MyLevel);
PTST(MyPTST,MyP_StrapTbl_CalTable);
PAI(MyVolume);
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