Engineering task and calculation objective
The TABI module provides user-defined value tables for calculations: the user stores tables of X values and associated function values Y, optionally dependent on an additional parameter (family of curves). For a current X value and a current parameter value, the module reads out the interpolated function value; multipliers allow input quantities and result to be scaled, for example for unit conversion. The final value Y determined in this way is then available for further calculations.
Such table modules are needed in engineering practice wherever relationships exist not as a closed-form formula but only as a diagram or value table: performance curves of pumps and valves, coefficients from code diagrams, material- or manufacturer-specific curves. Instead of reading values off the diagram anew for every calculation, the curve is digitized once and then evaluated reproducibly.
TABI thus serves as a flexible utility module in the ATLAS system: it makes project- or company-specific data usable for the other calculation modules and at the same time documents which supporting values were used in the calculation.
Calculation workflow
- Create the table: The table receives a unique name; the data points are then entered as pairs of X value and function value Y. For families of curves, a parameter value (parameter 1, parameter 2) is additionally stored for each curve.
- Define the multipliers: Multipliers can be defined for X values, parameters and function values, for example to convert the table units to the units used in the project, or to scale a normalized characteristic curve.
- Specify the current evaluation point: For the calculation, the current X value and – for families of curves – the current parameter value are entered. Both should lie within the range covered by the data points.
- Interpolate and form the final value: The module interpolates between the data points (for families of curves, additionally between the parameter curves), applies the multipliers and delivers the final value Y, which can be taken over into downstream calculations.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Name of table Name of table | Extension) | – |
| Name of table Name of table | Extension) | – |
| Current value Current value | X1 X2 | – |
| Current value Current value | X1 X2 | – |
| Current parameter Current parameter | P1 P2 | – |
| Current parameter Current parameter | P1 P2 | – |
| Function value Y Function value Y | FY1 FY2 | – |
| Function value Y Function value Y | FY1 FY2 | – |
| X value 1 X value 2 | Xe1 Xe2 | – |
| X value 1 X value 2 | Xe1 Xe2 | – |
| Multiplier Multiplier | MXe1 MXe2 | – |
| Multiplier Multiplier | MXe1 MXe2 | – |
| 1 | Additor AXe1 Additor AXe2 | – |
| 2 | Additor AXe1 Additor AXe2 | – |
| Parameter 1 Parameter 2 | Pe1 Pe2 | – |
| Parameter 1 Parameter 2 | Pe1 Pe2 | – |
| Multiplier Multiplier | MPe1 MPe2 | – |
| Multiplier Multiplier | MPe1 MPe2 | – |
| 1 | Additor APe1 Additor APe2 | – |
| 2 | Additor APe1 Additor APe2 | – |
| 1.Funktionswert | Additor AY1 Additor AY2 | – |
| 2.Funktionswert | Additor AY1 Additor AY2 | – |
| Multiplier Multiplier | MY1 MY2 | – |
| Multiplier Multiplier | MY1 MY2 | – |
Frequently asked questions
How accurate is the interpolation between the data points?
The accuracy depends solely on the density and quality of the data points. For strongly curved characteristics, the data points should be concentrated where the curve changes rapidly; linear interpolation between points that are too far apart can otherwise produce noticeable errors. A spot check comparing individual interpolated values against the original diagram is recommended.
What must be observed for values outside the table range?
Extrapolation beyond the first or last data point is fundamentally critical, because the course of the curve is not substantiated there. Physical characteristic curves (e.g. pump curves, coefficient curves) often behave completely differently outside the measured range. The covered X and parameter range should therefore encompass the entire operating range of the plant from the outset.
What are the multipliers intended for?
Primarily for unit conversions and scaling: a table in bar can thus enter directly into a calculation in N/mm², or a characteristic curve normalized to the rated point is scaled with the actual rated value. It is important to document the multipliers so that it remains traceable later in which units the original data were given.