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

AIR HEATER

HANS-PETTER HALVORSEN, 2010.02.09

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TABLE OF CONTENTS

Table of Contents .................................................................................................................................................... 2

1 Introduction ................................................................................................................................................... 3

2 System Description ........................................................................................................................................ 4

2.1 Features ................................................................................................................................................. 4

2.2 Mathematical model ............................................................................................................................. 5

3 NI USB-6008 ................................................................................................................................................... 6

4 LabVIEW Control Design & Simulation Module ............................................................................................. 7

4.1 PID Control ........................................................................................................................................... 11

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1 INTRODUCTION

This document gives a short description of the Air Heater Lab Equipment.

The focus will be to connect the system to a PC and create a simulation and control system in LabVIEW, C#.NET,

etc.

A proper development tool would be LabVIEW with “LabVIEW Control Design & Simulation Module” and

“LabVIEW PID and Fuzzy Logic Toolkit”.

A proper DAQ device would be the NI USB-6008 DAQ device from National Instruments, the inventor of

LabVIEW. The NI USB-6008 DAQ device is simple to configure and use.

The NI USB-6008 DAQ device is described in detail in the document “NI USB-6008 DAQ Device.pdf”.

All documents are available from http://home.hit.no/~hansha/.

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2 SYSTEM DESCRIPTION

The Figure shows an air tube with heater and temperature sensor(s).

2.1 FEATURES

Fan: A fan makes air flow through the tube. The fan is operated manually with a knob. The fan position is

indicated or measured by a voltage signal which is in the range 2 - 5 V (min, max fan speed). This voltage signal

can be measured between two terminals. The normal fan speed is defined to be the maximum speed. (We do

not know the actual volumetric flow, but this information is not necessary here.)

Heater: The air is heated by an electrical heater. The supplied power is controlled by an external voltage signal

in the range 0 - 5 V (min power, max power). This heater control signal must be applied between two

terminals. This voltage is used to control a Pulse Width Modulator (PWM) which connects/disconnects the

mains voltage to the heater.) The PWM signal is indicated by a lamp. The PWM device requires 24 VDC power

supply, which is produced by an AC/DC converter.

Temperature sensors: Two Pt100 temperature elements are available. You can use any of these, but

Temperature sensor 1 may be regarded the default sensor. These two sensors have been calibrated equally.

The sensor signals are available as voltage signals at their respective terminals. The range is 1 - 5 V, and this

voltage range corresponds to the temperature range 20 - 50oC (with a linear relation). The normal sensor

position is defined to be the outermost position in the tube.

5 System Description

Lab Equipment: Air Heater

Analog I/O device: The Figure shows the NI USB-6008 device, but any I/O device supporting the above voltage

ranges can be used.

Controllers: A temperature control system can be implemented using one of the PID control functions in

LabVIEW. Alternatively, an industrial process controller can be used, for example the Fuji PYX5 PID-controller.

2.2 MATHEMATICAL MODEL

A simple mathematical model of the system could be:

where,

u [V] is the control signal to the heater.

θt [s] is time-constant.

Kh [deg C / V] is heater gain.

θd [s] is time-delay representing air transportation and sluggishness in the heater.

Tenv is the environmental (room) temperature. It is the temperature in the outlet air of the air tube

when the control signal to the heater has been set to zero for relatively long time (some minutes).

In a simulator based on this model a proper initial value of Tout should be added. This initial value is applied to

the integrator in a block diagram representation of the model.

Note! You can adjust the parameters (θt, Kh, θd, Tenv) of the model by some simple experiments where you run

the simulator in parallel with the real process.

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3 NI USB-6008

NI USB-6008 DAQ device 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.

The NI USB-6008 DAQ device is described in detail (how the NI USB-6008 DAQ device works and how to use it

in LabVIEW) in the document “NI USB-6008 DAQ Device.pdf”.

The document is available from: http://home.hit.no/~hansha/.

For more details, see http://sine.ni.com/nips/cds/view/p/lang/en/nid/14604

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4 LABVIEW CONTROL DESIGN & SIMULATION MODULE

LabVIEW (short for Laboratory Virtual Instrumentation Engineering Workbench) is a platform and development

environment for a visual programming language from National Instruments. The graphical language is named

"G". For more information about LabVIEW, go through the training kit “An Introduction to LabVIEW”. This

document and other information about LabVIEW are available from: http://home.hit.no/~hansha/.

In LabVIEW there is an additional module for design and simulation of control systems, called “LabVIEW

Control Design and Simulation Module” and a toolkit called “LabVIEW PID and Fuzzy Logic Toolkit”.

Control Design and Simulation VIs are available from the “Control Design and Simulation” palette:

In the “Simulation” Sub palette we have the “Control and Simulation Loop” which is very useful in simulations:

In the “Continuous Linear Systems” Sub palette we want to create a simulation model:

8 LabVIEW Control Design & Simulation Module

Lab Equipment: Air Heater

The most used blocks are Integrator, Transport Delay, State-Space and Transfer Function.

The “Signal Arithmetic” Sub palette is also useful when creating a simulation model:

Example: Simulation Model

Below we see an example of a simulation model created in LabVIEW.

Example: Simulation

Below we see an example of a simulation model using the Control and Simulation Loop.

9 LabVIEW Control Design & Simulation Module

Lab Equipment: Air Heater

Notice the following:

Click on the border of the simulation loop and select “Configure Simulation Parameters…”

The following window appears (Configure Simulation Parameters):

10 LabVIEW Control Design & Simulation Module

Lab Equipment: Air Heater

In this window you set some Parameters regarding the simulation, some important are:

Final Time (s) – set how long the simulation should last. For an infinite time set “Inf”.

Enable Synchronized Timing - Specifies that you want to synchronize the timing of the Control &

Simulation Loop to a timing source. To enable synchronization, place a checkmark in this checkbox and

then choose a timing source from the Source type list box.

Click the Help button for more details.

You may also set some of these Parameters in the Block Diagram:

You may use the mouse to increase the numbers of Parameters and right-click and select “Select Input”.

11 LabVIEW Control Design & Simulation Module

Lab Equipment: Air Heater

4.1 PID CONTROL

In the “PID” Sub palette we have the functions/SubVIs for PID Control.

Note! I recommend that you use the “PID Advanced.vi”.

Example: PID Control

Below we see how we can use the PID Advanvanced.vi in order to control a simulated Model.

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: hans.p.halvorsen@hit.no

Blog: http://home.hit.no/~hansha/

Room: B-237a