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Telemark University College
Department of Electrical Engineering, Information Technology and Cybernetics
Faculty of Technology, Postboks 203, Kjølnes ring 56, N-3901 Porsgrunn, Norway. Tel: +47 35 57 50 00 Fax: +47 35 57 54 01
Datalogging in LabVIEW
HANS-PETTER HALVORSEN, 2011.01.04
ii
PREFACE
In this lab you will learn basic Data Acquisition (DAQ) and how to use a DAQ unit in LabVIEW. We will use the
USB-6008 DAQ device from National Instruments. NI USB-6008 is a simple and low-cost USV based
multifunction I/O device from National Instruments. The device is well suited for training and education
purpose.
The purpose of data acquisition is to measure an electrical or physical phenomenon such as voltage, current,
temperature, pressure, or sound. PC-based data acquisition uses a combination of hardware, software, and a
computer to take measurements.
The principle of Data Acquisition:
USB-6008 DAQ device from National Instruments:
iii
TABLE OF CONTENTS
Preface ..................................................................................................................................................................... ii
Table of Contents .................................................................................................................................................... iii
1 Introduction to Data Acquisition ....................................................................................................................4
2 Datalogging .....................................................................................................................................................8
3 Additional Tasks............................................................................................................................................15
4
1 INTRODUCTION TO DATA ACQUISITION
In this task we will learn basic Data Acquisition in LabVIEW. We will use the USB-6008 DAQ device.
Background information for this task is described in detailed in the Tutorial “Data Acquisition in
LabVIEW”. The Tutorial consists of pdf documents, videos, example code, additional resources and links.
http://home.hit.no/~hansha/?tutorial=daq
The purpose of data acquisition is to measure an electrical or physical phenomenon such as voltage, current,
temperature, pressure, or sound. PC-based data acquisition uses a combination of modular hardware,
application software, and a computer to take measurements. While each data acquisition system is defined by
its application requirements, every system shares a common goal of acquiring, analyzing, and presenting
information. Data acquisition systems incorporate signals, sensors, actuators, signal conditioning, data
acquisition devices, and application software.
So summing up, Data Acquisition is the process of:
Acquiring signals from real-world phenomena
Digitizing the signals
Analyzing, presenting and saving the data
5 Introduction to Data Acquisition
Lab Work: Datalogging in LabVIEW
The DAQ system has the following parts involved, see Figure:
The parts are:
Physical input/output signals
DAQ device/hardware
Driver software
Your software application (Application software)
The NI-DAQmx Driver software is the layer of software for easily communicating with the hardware. It forms
the middle layer between the application software and the hardware. Driver software also prevents a
programmer from having to do register-level programming or complicated commands in order to access the
hardware functions.
The DAQmx palette in LabVIEW:
The DAQ Assistant, included with NI-DAQmx, is a graphical, interactive guide for configuring, testing, and
acquiring measurement data. With a single click, you can even generate code based on your configuration,
making it easier and faster to develop complex operations. Because DAQ Assistant is completely menu-driven,
6 Introduction to Data Acquisition
Lab Work: Datalogging in LabVIEW
you will make fewer programming errors and drastically decrease the time from setting up your DAQ system to
taking your first measurement.
NI USB-6008 is a simple and low-cost multifunction I/O device from National Instruments.
The device has the following specifications:
8 analog inputs (12-bit, 10 kS/s)
2 analog outputs (12-bit, 150 S/s)
12 digital I/O
USB connection, No extra power-supply neeeded
Compatible with LabVIEW, LabWindows/CVI, and Measurement Studio for Visual Studio .NET
NI-DAQmx driver software
The NI USB-6008 is well suited for education purposes due to its small size and easy USB connection.
Measurement & Automation Explorer (MAX) provides access to your National Instruments devices and
systems.
With MAX, you can:
Configure your National Instruments hardware and software
Create and edit channels, tasks, interfaces, scales, and virtual instruments
Execute system diagnostics
View devices and instruments connected to your system
Update your National Instruments software
In addition to the standard tools, MAX can expose item-specific tools you can use to configure, diagnose, or
test your system, depending on which NI products you install. As you navigate through MAX, the contents of
the application menu and toolbar change to reflect these new tools.
7 Introduction to Data Acquisition
Lab Work: Datalogging in LabVIEW
8
2 DATALOGGING
In this task we will connect our DAQ device to a “real” process (small-scale model).
Below we see the Lab Equipment available for this assignment:
Level Tank Air Heater
In this Lab we can select one of these models. Which one you use is not relevant for the purpose of this lab
work.
Documents of how to use the Level Tank/Air Heater and the USB-6008 DAQ device is available from
http://home.hit.no/~hansha.
Level Tank: http://home.hit.no/~hansha/?equipment=leveltank
Air Heater: http://home.hit.no/~hansha/?equipment=airheater
USB-6008: http://home.hit.no/~hansha/?equipment=usb6008
Task 1: Test DAQ Device on Real Process
Select one of the processes above and connect you DAQ device to the system.
→ Log data (Temperature for the Air Heater system or Level for the Water Tank) for different input signals (u).
→ Show the results in a Chart.
You may want to use the “Waveform Chart” located in the Graph palette:
9 Datalogging
Lab Work: Datalogging in LabVIEW
Here is a LabVIEW example:
Scaling:
Make sure to scale the output signal from the system (Voltage signal) to Temperature (Air Heater) or Level
(Water Tank).
Air Heater output: 1-5V → 20-50 o
C.
Water Tank output: 0-5V → 0-20cm.
The following linear relationship applies:
10 Datalogging
Lab Work: Datalogging in LabVIEW
You have to find a (slope) and b (intercept). The following formulas may be used:
This gives:
where
→ It is good practice to implement the scaling using a SubVI.
[End of Task]
Task 2: Manual Control
→ Try to act like a controller: Let’s say you want the setpoint to be 15cm (Level Tank)/35 degrees C (Air
Heater) and then try to manually adjust the control signal (u) so the Temperature stays on the setpoint.
You need to extend the program from a previous task so that the control signal u is sent to the DAQ unit.
Use the “DAQmx Write.vi”:
11 Datalogging
Lab Work: Datalogging in LabVIEW
[End of Task]
Task 3: Write to Measurement File
Extend your program so the logged data can be saved to a Measurement File.
You can use the Write to Measurement File function on the File I/O palette in LabVIEW for writing data to text
files (use the LVM data file format, not the TDMS file format which give binary files).
Recommended settings for the “Write To Measurement File”:
12 Datalogging
Lab Work: Datalogging in LabVIEW
Example of LabVIEW Program:
Open the *.lvm file in, e.g., Notepad in order to see the results.
[End of Task]
13 Datalogging
Lab Work: Datalogging in LabVIEW
Task 4: Read from Measurement File:
Create another program that open the measurement file and shows the data in an array and a Graph.
Use the “Read From Measurement File” in LabVIEW.
Recommended settings for the “Read From Measurement File”:
Example of LabVIEW program:
14 Datalogging
Lab Work: Datalogging in LabVIEW
You should also open the file in Excel and plot the data in Excel.
[End of Task]
Task 5: Import Data to Excel
In this task we will open the measurement file created in a previous task in MS Excel.
→ Open the measurement file in Excel
→ Calculate the average (mean) of the logged data (use the built-in mean function in Excel)
→ Create a plot of the logged data
[End of Task]
15
3 ADDITIONAL TASKS
Task 6: Datalogging and Virtual Instruments
Create a “Virtual Instrument” with the following components:
1. Toolbar
2. Owned Label
3. Numeric Control
4. Free Label
5. Numeric Control Terminal
6. Knob Terminal
7. Numeric Constant
8. Multiply Function
9. Icon
10. Knob Control
11. Plot Legend
12. XY Graph
13. Wire Data Path
14. XY Graph Terminal
15. Bundle Function
16. SubVI
17. For Loop Structure
Below we see the front panel and the block diagram for the virtual instrument.
16 Additional Tasks
Lab Work: Datalogging in LabVIEW
→ The SubVI (number 16) shall read the temperature from the Air Heater using the USB-6008 DAQ (Data
Acquisition) device.
17 Additional Tasks
Lab Work: Datalogging in LabVIEW
Telemark University College
Faculty of Technology
Kjølnes Ring 56
N-3914 Porsgrunn, Norway
www.hit.no
Hans-Petter Halvorsen, M.Sc.
Telemark University College
Department of Electrical Engineering, Information Technology and Cybernetics
Phone: +47 3557 5158
E-mail: [email protected]
Blog: http://home.hit.no/~hansha/
Room: B-237a