SOFTWARE

Unity Systems

Custom Waveforms for Unity devices

Open

 

Introduction

Unity is the latest release of control firmware from GDS Instruments. With improvements in accuracy and stability, it has been developed with the aim of easing the system’s control from the User’s perspective while making the machines more reliable. For more information about the Unity interface in GDSLab please refer to GDS Helpsheet 195 – Unity Interface in GDSLab.

Pre-defined Waveforms

The User can access different types of waveforms through the Waveform Control Tab in Unity’s main window. All of the GDS devices capable of performing dynamic tests are pre-programmed with a sinusoidal wave with the possibility of upgrading to trapezoidal waveform (AS-AG), Haversine waveform (AASHTO) or custom User-defined waveforms. Examples of pre-defined waveforms are presented below:

Open

Creating a custom waveform file

Unity uses a standard comma-separated value file (.csv) to load a user-defined waveform. Files in this format can be created using Microsoft Excel or other open-source software.

Creating a .csv file

In the example below an Absolute Value of a Sine Function Waveform will be generated using an Excel Spreadsheet. A typical custom file consists of 256 rows of data, representing points on a time axis of a waveform The period of a wave is dependent on a user-specified frequency of the test, i.e a frequency of 0.1Hz will result in a period of a wave equal to 10 second and frequency of 5Hz will shorten the period to 0.2 seconds. The amplitude for each time-point is specified on a dimensionless scale from -1 to 1, which will be multiplied by a user-specified amplitude for the test.

In the example above column A represents values of amplitude (rounded to 9th decimal place) for each one of the 256 time-points. Column D is used as a reference for the time scale and Column C specifies the phase of the sinusoidal wave at a given point in time.

The following formulas were used to calculate the values in Column A and C:

Once the calculations were complete only the values from column A ware exported to a separate Excel file and saved in a .csv format.

Loading Custom Waveform files into Unity

New custom waveform files can be loaded from the Waveform Control Tab by selecting the required option from the drop-down list shown in the screenshot below.

A result of loading the .csv file created in Section 2.1 of this Helpsheet is shown below.

Once the file is loaded it will automatically be used for the next dynamic test in GDSLab. Choosing a Single Waveform option in the Waveform Control Tab will result in only one cycle being performed during a test in GDSLab. Please select Repeat Waveform to run continuously for a specified number of cycles.

Results in GDSLab from a test using custom waveform

The following settings have been used in the Advanced Cyclic Triaxial Testing module in GDSLab: (For more information about the stage set up windows, please refer to the GDSLab Manual)

The ABS sine wave was specified to run 5 cycles at 0.1Hz with an amplitude of 0.1kN and a datum of 0.5kN. Results of the test are shown below: