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Simcenter Testlab Units

This document outlines how engineering units (i.e., measurement quantities) are handled in Simcenter Testlab. All data measured in Simcenter Testlab has specific engineering units associated with it.  

This allows data to be scaled in displays and math operations to be performed properly. Some examples are shown in Figure 1.
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Figure 1: Because Simcenter Testlab utilizes a unit system, math operations like integration (left) produce correct results, and data can be converted to another unit (right).
The Simcenter Configuration and Unit System tool is used to manage engineering units in Simcenter Testlab.  The tool enables the following:
  • Unit Conversion and Scaling: By right clicking in any display, data can be view in different units with proper scaling applied.  For example, distance could be viewed as meters, miles, kilometers, inches, etc as desired.
  • Mathematical Correctness: Because the engineering units are known, math operations are performed properly.  For example, integrating “10 g” of acceleration at 500 Hertz will result in “0.03122 m/s” of velocity.
  • Default Unit: Data of any type is displayed in the specified default.  For example, calibration factor for acceleration could be input in either “mV/m/s2” or “mV/g” but data can be displayed in a company standard of “g” by default.
  • Reference: The unit system also specifies the reference quantity for showing data in logarithmic ratio of dB. For example, the sound pressure reference is 2E-05, which allows 1 Pascal to show as 94 dB.
  • Two quantities: The quantity case feature keeps measurements of based on the same engineering unit separate.  For example, sound pressure (Pa) measured on one channel and hydraulic pressure (psi) on another channel will always displayed in their respective units.
  • Other Files: When using data files not created by Simcenter Testlab, the unit management maps the unit labels in the outside data file to known engineering units available in Simcenter Testlab.  For example, the labels “micro-strain”, “microstrain”, and “strain” all map to the Simcenter Testlab unit “uE”.

This article has the following sections:
1.    Getting Started with Simcenter Testlab Units
    1.1  Getting Started
    1.2  Unit Systems
    1.3  Saving Unit System

2.    Displays
    2.1  Scale Factor
    2.2  Log Reference
    2.3  Math

3.    Measurements
    3.1  Two Quantities of Same
    3.2  Calibration Value versus Measurement Display

4.    Invisible Units
    4.1  External Files
    4.2  CAN bus

1. Simcenter Testlab Configuration and Unit System 

The Simcenter Testlab Configuration and Unit System is a separate application, independent of Simcenter Testlab.

1.1    Getting Started

One way to start the program is to search for “unit” in Windows search as shown in Figure 2.
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Figure 2: The Simcenter Configuration and Unit System program is independent of the Simcenter Testlab application.
It is best to exit from Simcenter Testlab when making changes to the unit system. Any changes made in the Unit System will only become active after restarting Simcenter Testlab.  

If there are multiple versions of the Simcenter Configuration and Unit System, use the one with the highest revision number.

After the program is started, a list of all units available in Simcenter Testlab is shown (Figure 3):
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Figure 3: List of known/available units
Any data used in Simcenter Testlab must have units that are contained in this list.

1.2 Unit Systems

Under “File -> Select Active Unit system” there are four different selections available (Figure 4).
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Figure 4: List of available Unit Systems
The unit systems all have the same number and types of units.  The differences are the default units used when displaying data.

Some highlights of the available unit systems:
  • Technical: This is the default unit system. The default unit of acceleration is “g”.
  • SI: The default unit of acceleration is “m/s2”.
  • English: The default unit of acceleration is “in/s2”.
  • ISO 1683: Reference value for “m/s2” is 1E-06 rather than 1.
In the example shown in Figure 5, the display shows data in “m/s2”.  This is because “m/s2” is the default in the SI unit set:
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Figure 5: Display (right) shows acceleration in “m/s2” because it is the default for the SI unit set (left).

Changes can be made and saved to any of the unit systems.  For example, the default for any unit case can be edited and changed. 

Want speed to default to “furlongs per fortnight”?  No problem!

1.3 Saving Unit System

Under the “File” menu, changes to the active unit system can be saved (File -> Save then File -> Exit) as shown in Figure 6.
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Figure 6: The “File” menu of Simcenter Testlab Configuration and Unit System program
Any of the unit systems (SI, Technical, English) can be identified as the default system used by Simcenter Testlab. Because the engineering units of all data stored in a Simcenter Testlab project file are known, selecting a different unit system will scale all data properly.

2. Displays

The Simcenter Testlab Configuration and Unit System can also be used to control the selection of units that are shown in the display.  Right clicking on the axis and selecting “Unit” brings up a list of all related units based on what is marked as “Visible” in the unit system (Figure 7):
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Figure 7: Units marked “Default” or “Visible” in the Unit Configuration tool are shown when right clicking on “Unit” on the Y-axis display.
Each unit listed in the Unit Configuration list are marked with one of the following:
  • Default
  • Visible
  • Invisible

The “Default” unit is shown at the top of the list. Only one unit can be set as the default.  Invisible units are not shown at all but can be added as a display selection by changing the status to “Visible”.

2.1 Scale Factors

When the unit is changed in the display, for example meters (m) switched to kilometers (km), the data scales properly.  The scale factor used to convert meter to kilometer can be seen by double clicking on the unit in the list as shown in Figure 8.
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Figure 8: Double click on unit in Configuration tool to see the Scale Factor. In this example, “km” is related to meters by a scale factor of 0.001.
The conversion factor always relates the unit of interest to the “basis” unit for a given quantity.

In the Simcenter Testlab software, the following “basis” units are used:
  • Length: meters (m)
  • Mass: kilograms (kg)
  • Time: second (second)
  • Angle: radians
  • Temperature: degrees Kelvin (K)
  • Electric Current: amperes (amps)
  • Luminous Intensity: lumens
  • Mole

Many units are a combination of basis units. For example, acceleration is a unit of length over a unit of time squared.  The basis unit of length is “1” and time is “-2” in the unit table as shown in Figure 9.
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Figure 9: The basis unit of length is “1” and time is “-2” in the unit
All data in a Simcenter Testlab project are stored in the basis units, This ensures that performing mathematical operations between data sets have the correct results.

For example, to calculate a torque, a force (length times mass divided by time) is multiplied with a unit of length (distance).  The result is two units of length times the mass divided by time.  This is all handled behind the scenes and the proper result is obtained.

2.1 Log Reference

Another section of the unit definition defines the reference to be used when displaying data in dB as shown in Figure 10:
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Figure 10: The reference level of the unit is used when selecting “Format -> dB/Level” in a display.
For example, the reference for Pascals is 2E-05.  It is used to display Pascals of sound pressure in dB.

More information about decibels in this knowledge article: Basics: What is a decibel (dB) anyway? Why is it used?

3. Quantities

All units are grouped by Quantity case. For the same unit, there can be more than one quantity case. 

 For examples of Quantity Cases for the same unit:
  • Length, Displacement, Distance, Position
  • Pressure, AtmosphericPressure

This is illustrated in Figure 11.
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Figure 11: There are two different “Quantity Cases Names” for pressure engineering units.
Why have different quantity cases names for the same engineering unit?

This is useful when measuring the same engineering units on two different channels, but different default engineering units should be used on each channel.

For example, consider measuring sound pressure on one channel and hydraulic pressure on another as shown in Figure 12.
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Figure 12: Using different Measured Quantity cases in Simcenter Testlab Channel Setup keeps sound pressure and hydraulic pressure measured and displayed in their respective units
In this channel setup, sound pressure is defined in units of “Pa” while hydraulic pressure is defined in units of “bars”. 

Not only does this make it easier to enter the calibration values for each transducer, but all displays will default to the appropriate engineering unit as shown in Figure 13.
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Figure 13: Microphone data and hydraulic pressure are shown in their respective units
In addition to a quantity case, each unit in the list has specific settings as discussed in the next sections.

4. Invisible Units: External Files and CAN bus Units

Why have invisible units?  Even though invisible units are not shown in a display, they are used to map various spellings of a given engineering unit to the default unit. This is useful when working with non-Siemens file formats and CAN bus files.

4.1 External File

Often files acquired by other acquisition systems (Universal, SDF, RPC, etc) may contain unit labels that are not part of the Simcenter Testlab unit set. On many acquisition systems, the unit is a free text field with no enforced consistency.

The invisible units contain numerous and different spellings for a given unit. If the spelling in the external file matches any one of these spellings, the unit is correctly identified in Simcenter Testlab.

For example, different spellings for strain units (MSTRAIN, mstrain, uE, muE,…) are shown in Figure 14.
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Figure 14: The Unit configuration tool contains many different spellings for each unit, even if some are not shown in the software because they are marked invisible.
For example, a universal file might have unit labels of “mstrain”.   This will be mapped to the default unit of strain (uE) in Simcenter Testlab because it appears in the unit list.  This works even though “mstrain” is set to invisible.

If the unit label in an external file is not in the Unit Configuration Tool list, then the Y-axis will show “Unknown(label_here)” when displaying the data (Figure 15).
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Figure 15: If an engineering unit label in an external file is not listed in Simcenter Testlab, the Y-axis label shows “Unknown(label_here)” as shown on left side.  Once the unit label is added, it will map to the default unit as shown on the right.
For the “unknown” unit to be treated properly in Simcenter Testlab, it needs to be added to the list in Simcenter Testlab Unit Configuration tool.

To do so, find the unit it should be mapped to in the list (in this example, “Pascals” needs to be added, so the default unit of “Pa” is selected, and the “Add Unit…” button is pushed (Figure 16).
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Figure 16: To add a variant spelling of a unit, highlight the unit in the Simcenter Configuration tool and press “Add Unit”.  Then replace the current label with the variant spelling.  After saving, and restarting Simcenter Testlab, the new unit will map automatically.

Replace “Pa” with “Pascals” and press the OK button.  

After saving the unit system, and restarting Simcenter Testlab, the universal file will display in “Pa” rather than “Unknown(Pascals)”.

4.2 CAN Bus

Another area where the list of visible and invisible units is utilized is in decoding Controller Area Network (CAN) via a serial bus in a vehicle.

When reading digital data from CAN, a DBC (*.dbc) file is often used that contains a list of all channels on the bus, their electronic address, and the engineering unit.  There is no standard for the how to spell the engineering units in a DBC file.

Upon reading the file in the Channel Setup workbook of Simcenter Testlab, the unit labels in the DBC file are mapped to corresponding units of Simcenter Testlab (Figure 17).
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Figure 17: The Unit Labels in a CAN bus DBC file are mapped to their corresponding TestLab Unit automatically.
If the unit labels in the DBC have no corresponding Simcenter Testlab unit, they are set to “Unknown”. The unknown units can be manually set using the drop-down menu or they can be added to the unit system.

More information about using CAN-bus files in the knowledge article: CAN Bus Measurements

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Related Links: 

KB Article ID# KB000047733_EN_US



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