2. Loading Files
You can use the LabVIEW System Identification Assistant to load measurement data files (.lvm). A measurement data file is a tab-delimited text file you can open with a spreadsheet or text-editing application. A measurement data file includes information about the data, such as the date and time the data was generated. You also can use the System Identification Assistant to load ASCII, SPICE, PSpice, or Multisim files.
Complete the following steps to load a measurement data file containing sample input and output signals. This data file contains signals acquired from a DC motor.
- Click the Add Step button, shown below, to open the Add Step menu.
A step is a configurable function that acquires, generates, analyzes, loads, or stores signals. Steps process input signals and produce output signals. You can configure the operation of steps by specifying values in the Configuration View, or Step Setup tab, for each step. You create projects by adding steps to the Project View.
- Select Load/Save Signals»Load from LVM to add a Load from LVM step to the Project View. The Configuration View for the Load from LVM step appears.
Tip When you move the cursor over a step in the Add Step menu, a description of that step appears in the help window at the bottom of the Add Step menu.
- In the Configuration View, click the Browse button, shown below, next to the Import file path text box. Navigate to the National Instruments\Express Workbench\System Identification Assistant\Examples\getting_started directory.
- Select dc_motor_data.lvm and click the OK button to load this file. Notice that this file contains two signals, Motor Input and Motor Output, which appear in the Signals in file table.
- Verify that the Import checkbox next to Motor Input has a checkmark. This checkbox configures the System Identification Assistant to load the Motor Input signal from this measurement data file. This signal is a square periodic function of the voltage. You will use this stimulus data to estimate and validate the dynamic model of the motor.
Notice that the signal you load appears on the Imported Signal graph in the Configuration View. Also notice that information about the data, including the date and time the data was generated, appears on the ID tab in the File and Signal Selection section. The other tabs in this section contain additional information about the data.
You can create a probe to obtain information about a signal. In the Project View, expand the dc_motor_data.lvm item, right-click the Motor Input signal, and select Probe from the shortcut menu to create the probe. Notice that the probe displays information about the signal, including which step you used to generate the signal.
- Close the probe.
- In the Project View, expand the dc_motor_data.lvm item, right-click the Motor Input signal, and select Rename from the shortcut menu to rename the signal. Change the name of this signal to Raw Stimulus Data.
Note In the Project View, a blue arrow indicates an output of a step. A red arrow indicates an input of a step. The blue and red arrows are shown below. step output step input
- In the Configuration View, place a checkmark in the Import checkbox next to Motor Output to configure the System Identification Assistant to load the Motor Output signal from this measurement data file. This signal is the speed of the motor over time and is dependent on the voltage data points in Raw Stimulus Data. You will use this data to estimate and validate the model for the motor.
Notice that this signal appears to be periodic except for sharp spikes near sample times 1.0 and 2.5. These spikes indicate bad or missing data caused by sensor failures. You will learn how to rebuild this data in the Rebuilding Missing Data exercise.
- In the Project View, rename the Motor Output signal to Raw Response Data.
- Select File»Save Project As and save this project as Sample Project.seproj to an easily accessible location. A .seproj file is a workbench project, which refers to the LabVIEW SignalExpress framework in which the System Identification Assistant resides.
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