SOFTWARE FOR EMBEDDED CONTROLLER DESIGN

Application in Air and Water Caloric Electronystagmographic Stimulators

C. Richter, P. Mendes, M. Tavares

Biomedical Engineering Laboratory, Catholic University of Pelotas, Rua Felix da Cunha 412, Pelotas, Brazil

V. Alves

PDI, Contronic Sistemas Automaticos Ltda., Rua Rudi Bonow, 275, Pelotas, Brazil

Keywords: Controller design, digital control, control systems modelling, water caloric stimulator, air caloric stimulator,

electronystagmography.

Abstract: This paper describes the development and tests of a software which was projected to support the work of

designing and testing dedicated embedded controllers. It was developed to accomplish two main features:

helping to model the physical system to be controlled; and helping to easily implement and test a proposed

controller to be applied to the physical system. Two practical applications are presented. The first one is the

design of a temperature controller for a new version of a water caloric stimulator named E96, which has as

main requirement fast and accurate temperature response with no overshoot. The second one is also a caloric

stimulator, but the transfer media is air instead of water. Those equipments help otorhinolaryngologists in

electronystagmography exam. Details on the caloric stimulators hardware and software, the proposed

controllers and the results, are presented. The software was considered functional for the proposed applications.

1 INTRODUCTION

Digital control of a physical system, or plant, can be

accomplished using a computer with internal

software containing the algorithm that controls,

through D/A conversion, the plant input variable.

Closed-loop digital control requires the measurement

and A/D conversion of the plant output variable.

Many different kinds of digital controllers can be

used for controlling different physical plants with

the most variable range of requirements. Examples

of requirements are the percent overshoot and the

settling time for the step response of the plant (Dorf,

2001). Prior to the controller design is the modeling

of the plant, which requires a modeling technique

using, for example, the graphical analysis of the

open-loop step response of the plant (Coelho, 2004).

The main motivation for the developed software

PACD (Plataforma para Aplicação de

Controladores Digitais, Digital Controllers

Application Platform) was to create a software that,

with the aid of an already existent hardware, would

help modelling a physical system to be controlled,

and additionally help designing a suitable controller

for it, which would be validated through real tests.

Such an ensemble of software and hardware would

be helpful for designing and testing dedicated

controllers, which later can be executed from

microcontrollers or general purpose low cost DSPs,

attempting to develop embedded dedicated

controllers. The first practical application of the

software PACD was to design temperature

controllers in two electro-medical equipments.

Human corporal equilibrium comes from the

interaction of three main systems: vision,

proprioceptive system and vestibular system.

Vestibular-Ocular Reflex (VOR) is responsible for

vision focus during head movements (Castagno,

1994). Otorhinolaryngologists use several stimuli to

diagnose diseases in the equilibrium systems.

Caloric stimulus caused by the irrigation of heated

water or air in the auditory conduit cause in healthy

patient reflex ocular movements named nystagmus.

The electric register of the ocular movements is

called electronystagmography (ENG). The first

Brazilian computerized system for ENG resulted

from the joint work of Catholic University of

Pelotas, Dr. Castagno Clinic and Contronic Sistemas

Automáticos (Castagno, 1993; Costa, 1995). A

224

Richter C., Mendes P., Tavares M. and Alves V. (2008).

SOFTWARE FOR EMBEDDED CONTROLLER DESIGN - Application in Air and Water Caloric Electronystagmographic Stimulators.

In Proceedings of the First International Conference on Biomedical Electronics and Devices, pages 224-227

DOI: 10.5220/0001054502240227

 SciTePress

caloric water stimulator named E96, shown in

Figure 1 was developed for use during ENG exam,

maintaining two water containers at different

temperatures. A caloric air stimulator named E107,

shown in Figure 2, was recently developed. Two

main advantages of the air stimulator are causing

less discomfort and allowing the exam in patients

with tympanic perforation (Brookler, 2002).

Figure 1: Water caloric stimulator model E96.

Figure 2: Air caloric stimulator model E107.

2 MATHERIALS AND METHODS

2.1 PACD Software

The PACD software was created in C language,

under Borland IDE C++ Builder 6. Its initial form

presents two operating conditions: modeling or

control. Each one includes its own graphical

interface. In modeling operating condition, the plant

is modeled using a step excitation signal and

verifying its time response. Figure 3 presents the

modeling interface, which is divided in 3 regions,

enumerated in the figure as “1”, “2” and “3”. In the

first region, it is possible to choose the step response

modeling method while the second one is used to set

the amplitude of the step heating power input, and to

set the desired air flow. The third region shows the

step temperature response. The horizontal axis

shows essay time in seconds. As far as last the essay,

this axis keep adjusting to show all essay time range.

Vertical axis shows water/air temperature in Celsius

degrees (ºC). The available step response modeling

methods in PACD allow first order or second order

models with or without time delay. Modeling

method can be chosen between Ziegler-Nichols,

Hägglund and Mollenkamp methods, as presented in

Coelho (2004).

Figure 3: PACD modelling interface.

The control interface, shown in Figure 4, is also

divided in three regions. In the first one it is possible

to choose the controller type, to insert controller

parameters and to command the compilation of the

program with the chosen controller or controllers.

The second region shows all chosen controllers and

their parameters. In the third region it is possible to

set the desired water/air temperature, the desired air

flow and to start and stop controlling the plant.

During the control operation, real water/air

temperature in ºC is graphically shown against time

in seconds. Horizontal axis is auto-adjustable. Real-

time water/air temperature is shown numerically, as

well as the difference between the desired

temperature and the real one, named error. The

control signal is also showed in the same graphic

display, from 0% to 100% of the maximum possible

power, or -100% to +100% in air equipment.

Figure 4: PACD control interface.

The main feature of this interface is the possibility of

implementing and monitoring digital controllers in a

fast and easy way. As a new essay will be done,

SOFTWARE FOR EMBEDDED CONTROLLER DESIGN - Application in Air and Water Caloric

Electronystagmographic Stimulators

225

different tuning parameters can be chosen and

different cascade controllers can be appended.

PACD current available controllers include lead, lag,

lead-lag, double-lead, double-lag, PI and PID. The

internal structure of PACD uses negative unitary

feedback, and it allows to cascade up to 10

controllers of each type. This feature makes it

possible to accomplish many different

configurations to analyze in different operation

essays, so that the controller designer can choose the

configuration that gives the best results in terms of

the desired plant operation requirements.

2.2 Water Test Setup

A testing setup was assembled, whose main parts are

shown in the block diagram shown in Figure 5. The

setup is composed by a printed circuit board from

E96 equipment, a water container with a heater

resistance inside and an additional serial

communication interface. The used microcontroller

is the Intel’s N87C196KB running at 12 MHz. The

temperature sensor is LM35DZ (National),

accompanied by an amplifier and adjustment

trimmer, allowing an adjusted error of 0.2 ºC in the

whole temperature range, from 0 ºC to 50 ºC. A

special version of the E96 embedded software was

created (C language, IAR compiler), so the equipment is

commanded through serial communication by PACD

software in the external PC. The power control variable

is delivered to a heater resistance of 700 W (220 V), and

variable percent power is determined by PWM (Pulse

Width Modulation) using integral cycle technique, in

order to avoid harmonic frequencies in the mains. The

PWM period corresponds to 50 cycles of the 60 Hz

electric network, so the power driver has 2% resolution.

Figure 5: Water caloric setup block diagram.

2.3 Air Test Hardware and Software

Air stimulator E107AR was used with a modified

protocol to facilitate the tests, and its basic block

diagram is shown in Figure 6. The main parts of the

system are composed by: an ADuC841

microcontroller (Analog Devices) running at 20

MHz; a precision resistive NTC sensor used to

measure the temperature of the heated or cooled air

flow, that after being adjusted by software, provides

0.2 ºC error in the whole temperature range (12 ºC to

50 ºC); an air pump that provides air flow from 4 to

12 liters/minute; and an air heater/cooler module

formed by refrigeration sink, a Peltier effect device

and a heater/cooler sink.

The internal E107AR software was modified to

inhibit the original temperature controller and the

periodic temperature sampling. It makes possible to

PC software setting the sampling frequency as

desired, and also, letting the PC software to control

the output air flow and the amount of power to heat

or to cool the air. The air pump power interface uses

an AC current control technique that delivers AC

voltage to the pump according to the

microcontroller's D/A converter. The Peltier effect

device is driven by an H-Bridge DC power interface,

which is controlled by the ADuC841 pulse width

modulation (PWM) output. The E107AR also has a

built-in RS232 level converter to translate the

microcontroller's TTL serial signals to ± 12 V levels

on the PC serial port.

Figure 6: Air caloric setup block diagram.

3 RESULTS

Several tests were accomplished for PACD software

validation and to find the best controller for each

setup.

3.1 Results from Water Test Setup

For modeling the water temperature system to be

controlled, a 25 % power step response was applied

and three PACD available model methods where

used. Figure 7 shows setup real step response

pointed as “A”. The letters B, C and D indicate

respectively the responses from Hägglund, Ziegler-

Nichols and Mollenkamp models. Carrying out a

manual adjustment in Ziegler-Nichols obtained

model, it was possible to arrive to the time response

indicated by “E”, which is even closer to the real

plant time response. Equation 1 shows this model.

Air flow

E107AR PCB

SRL

TTL to

RS232

Adapter

Opto-

isolated

Power

Interface

Adjust

and

amplifier

PWM

ADC0

UART

ADuC841

DAC

AC Control

Power

Interface

Air

pump

Refrigeration

Temperature sensor

Peltier effect

device

SERIAL

E96 PCB

TTL to

RS232

Adapter

EPROM

memory

80C196

ADC0

PWM

Opto-

isolated

Power

interface

Water container

Adjust

and

amplifier

resistance

temperature

sensor

UART

Controllers in software

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices

226

Figure 7: Water plant and models step response.

2.592

()

600 1

−

(1)

Based on the selected model, several controllers

were projected and tested according to classical

control techniques (Dorf, 2001). The desired tem-

perature was 44 °C and the initial temperature was

25 °C. An excellent step response of a controller

using a cascade of phase-lead and PI compensators is

shown in Figure 8, achieving 0% percent overshoot, 100

seconds settling time and ± 0.1 ºC stationary error.

Figure 8: Water phase-lead + PI controller.

3.2 Results from Air Test Setup

Modeling the system from a 25 % power step input,

it was obtained the model shown in Equation 2.

1250

1528.0

)(

−

(2)

In all tests the desired temperature was 44 °C and

the initial temperature was 25 °C, with 12 l/min air

flow. After testing several developed controllers, the

best step response was obtained from a cascade of

phase-lead and PI compensators. Figure 9 shows this

result, which achieved 1.80 % overshoot (0.34ºC), 45

seconds settling time and ± 0.31 ºC stationary error.

Figure 9: Air phase-lead + PI controller.

4 CONCLUSIONS

Analysing both water and air step responses achieved

from cascade phase-lead and PI compensators, the

responses where much better than the required results,

which where set to 0.5 ºC maximum overshoot, 180

seconds of settling time and ± 0.5 ºC stationary error.

This way, the PACD software was considered

effective for the proposed applications, allowing the

model construction and testing of several controllers,

so helping to determine a better choice for the final

controller. In the future, PACD will be improved to

support other modelling methods and control

strategies, such as adaptive control.

ACKNOWLEDGEMENTS

The authors thank Brazilian Agency CNPq for scholar-

ship and financial support through grant 481638/2004-0.

REFERENCES

Dorf, R.C., Bishop, R.H., 2001. Sistemas de Controle

Modernos. LTC. Rio de Janeiro.

Coelho, A.A.R.; Coelho, L.S., 2004. Identificação de Siste-

mas Dinâmicos Lineares. Ed. da UFSC. Florianópolis.

Castagno, L.A., Tavares, M.C., Richter, C.M. et al., 1994.

Sistema Computadorizado de Eletronistagmografia e

Vectonistagmografia “UCPel/Castagno” (Versão 3.0).

Anais do IV CBIS, pp. 26-31.

Castagno, L.A, Tavares, M.C., Cava, R.A. et al., 1993.

Eletronistagmografia computadorizada: o novo

sistema de aquisicao de dados ENGc UCPel/Castagno.

Rev. Bras. Otorrinol., v. 594, pp. 263-265.

Costa, M.H., Tavares, M.C., Richter, C.M., Castagno,

L.A., 1995. Automatic analysis of electronys-

tagmographic signals. 38th Midwest Symposium on

Circuits and Systems, v.2, pp. 1349-1352.

Brookler, K.H., 2002. A case of normal ENG findings on

air caloric stimulus that were not substantiated by

water stimulus. Ear, Nose & Throat Journal, v. 81,

n.8.

SOFTWARE FOR EMBEDDED CONTROLLER DESIGN - Application in Air and Water Caloric

Electronystagmographic Stimulators

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