Author: Carmen Bujoreanu
Faculty of Mechanics - Iasi
Year of publication: 2015
What is virtual instrumentation?
Virtual instrumentation is what was a decade ago the measuring chain, which replaced the part of physical instruments with virtual instruments. A virtual tool is composed of a hardware part (mainly a digital to analog converter) and a software part which allows the configuration of the instrument according to the user's wishes.
Not long ago, the user configured his physical instrument with the help of buttons and potentiometers, made the connections between the instrument and the paper or electronic recording devices and had to have them all in the same place to monitor and maneuver them.
Now, the user inserts a data acquisition card in the computer and with the help of the graphic programming software he configures his measuring instrument and in addition he can create as many graphic recorders as he wants.
The physical part of the measuring chain
The entire physical part of the measuring chain is on a board controlled by the computer microprocessor, all the user has to do is connect to the transducers specific to the size to be measured and know how to operate a mouse..
The representation of the physical instruments is done on the computer monitor with the help of the existing graphic elements in the library of the graphic programming language.
There are two possibilities to work with virtual instrumentation:
- you want to create the necessary tools yourself and then you need to know the language of graphic programming and have it (minimum learning time required would be 30 hours);
- you only want to be a user of virtual instrumentation, and then you have to buy from an application developer an executable program that will do only what you want.
The advantages of virtual instrumentation are also deduced from the above:
- occupies a small space (basically a computer and a monitor);
- can be with distributed elements (can measure in several places at once);
- the data can be transmitted via the internet (the measurement laboratory can be in a certain place and the analysis of the results can be done in a completely different place);
- the instruments no longer occupy a physical space (a warehouse) but are stored in the computer's memory;
- maximum flexibility regarding the configuration of the instruments (whenever an instrument can be deleted from the memory and another can be made, control elements or indicators, channels or memory can be added);
- the problems related to the dirtying of the switches or the imperfection of the connections practically disappear;
- the offset or calibration errors disappear or are greatly reduced;
- the costs regarding the purchase of devices and their maintenance are greatly reduced, taking into account that a single multifunctional data acquisition board together with the related software can replace a lot of other dedicated physical tools;
- very user friendly graphical interface;
- the relatively short learning time of the graphic programming language;
- the set of virtual instruments ready built to measure, analyze the signal, process it and transmit it wherever the user wants.
Data acquisition system
A data acquisition system (or measurement) consists mainly of transducers, signal conditioners, data acquisition boards, software and computer.
The laboratory aims to present the concept of virtual instrumentation, the characteristics of the LabVIEW environment and the structure of a virtual instrument.
After making the front panel of the VI, the functionality of the program must be implemented; the block diagram is built, which represents the source code of the instrument (it shows "HOW? 2 the problem is solved).
To make the block diagram, the graphic language G is used. The basic elements that must be known for the students to make and use virtual tools are presented.
Course structure
CHAPTER 1. Introduction
1.1. Presentation of menu options displayed at LabVIEW launch
1.2. Consult the installed examples
1.3. The role and component of the toolbar in the front panel window
1.4. Presentation of the elements in the toolbar in the block diagram window
1.5. Presentation and use of context menus
1.6. Presentation of the horizontal bar with menus
1.7. Presentation of the box with general tools
1.8. Methods of assistance in LabVIEW
CHAPTER 2. Controls and indicators
2.1. Theoretical considerations
2.2. Types of controls and indicators
2.3. Numerical type controls and indicators
2.4. Boolean controls and indicators
2.5. Controls and string type indicators
2.6. Table type and data grouping controls and indicators
2.7. Controls and indicators for graphical representations. Examples
2.8. Personal applications
CHAPTER 3. Own menus
3.1. Own menus specific to numeric elements. Exercises
3.2. Own menus specific to scale elements. Exercises
3.3. Own menus specific to Boolean elements. Exercises
3.4. Cluster own menu. Exercises
3.5. Ordering components. Exercises
3.6. Menus for ListBox, Table and Ring items. Exercises
3.7. Local variable. Exercises
3.8. Property nodes. Exercises. Theme
CHAPTER 4. Functions
4.1. Theoretical considerations. Examples
4.2. Functions for numerical values. Exercises
4.3. Functions for Boolean values. Exercises
4.4. Functions for alphanumeric values (string). Exercises
4.5. Inserting function symbols in the diagram. Exercises
4.6. Making the connections in the diagram. Exercises
4.7. Data flow. Exercises
4.8. Saving an application. Exercises
4.9. Functions for scalar values. Exercises. Theme
4.10. Functions for vector values (Array). Exercises. Theme
4.11 Functions for Cluster elements. Exercises
4.12. Picture elements and functions. Exercises. Theme
CHAPTER 5. Programming structures
5.1. Inserting structures in the diagram. Exercises
5.2. Sequence structure. Exercises
5.3. Causal structure (Houses). Exercises
5.4. Repetitive structure with fixed number of iterations (For loop). Exercises
5.5. Repetitive structure with completion condition (While loop). Exercises
5.6. Transfer registers in repetitive structures. Exercises. Theme
CHAPTER 6. Waveform Chart element. Exercise
CHAPTER 7. Waveform Graph element. Exercise
CHAPTER 8. Element XY Graph. Exercise. Theme
LabView applications
- Simulation of a control subsystem of an industrial manipulator
- Simulation of the automation system of a heat treatment furnace
- Acquisition and recording of data for measuring friction and braking moments in bearings tested for gripping
- Experimental determination of the elastic constant of a spring. The method of balance
