4tas. Jornadas de Software Libre, Montevideo, URUGUAY UYLUG
Sistema de Medicion y Control Remoto. (MyC)
Copyright (C) 2003 SaLug.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.
Sistema de Medicion y Control Remoto. (MyC)
Wiliam Pedetti, Pablo Rattin, Marcelo Zunino, Fernando Díaz, Gonzalo Frioni, Gian Zas, Mario Pereira, Miguel Pertusatti.
Integrantes de SaLug (Grupo de usuarios GNU/Linux de Salto), Salto, URUGUAY, salug@adinet.com.uy.
MyC implementa un sistema de adquisición de datos, mediante transductores específicos en función de diversos sensores, vincula dichos datos a valores preestablecidos, generando consecuentemente acciones de control sobre un conjunto de actuadores. Almacena información histórica de mediciones y actividades, genera reportes básicos y cuenta con capacidades de transmitirlos periódicamente. La mayoría de las funcionalidades del sistema son accesibles a través de una interfaz de acceso remoto.
Este proyecto es una implementación concreta de control y censado remoto. Es de carácter experimental, por el momento su uso esta limitado a fines didácticos y demostrativos. Pretende además aportar elementos de análisis, apoyar estudios de viabilidad y otros que puedan originar desarrollos que generen herramientas basadas en Software Libre.
Al momento, MyC es una herramienta capaz de resolver con autonomía ciertas condiciones ambientales. El núcleo del automatismo se concentra en un único equipo que llamaremos unidad básica de medición y control (UBMC).
UBMC es un sistema computacional montado en una caja estanca apto para funcionar sin interrupciones, en proximidad o dentro mismo del ambiente que se desea controlar. Sus funciones son recoger los valores de medición, ejecutar las acciones de control, almacenar información temporal y atender conexiones remotas. De esta manera queda conformado un dispositivo no asistido responsable del automatismo.
Si bien este proyecto esta concebido como un ejemplo de uso de Software Libre en la gestión de automatísmos con dispositivos empotrados, su diseño intenta seguir pautas que no impongan limitaciones a desarrollos de uso genérico. En general, se establece un equema modular que considre la independencia del hardware y de las herramientas de gestion e interfaces. Asi mismo se tomaron en cuenta aspectos considerados criticos como ser la confiabilidad y disponibilidad permanente.
2.1 Hardware.
El hardware necesario consta básicamente de dos sistemas computacionales compatibles con la arquitectura i386. Uno de ellos alberga la placa de adquisición de datos responsable de tomar los valores entregados por los sensores (temperatura, dirección y velocidad del viento, cantidad de agua caída), y de controlar actuadores accionando distintos dispositivos electromecánicos ( turbinas de enfriamiento, resistencias calefactoras, etc). Este equipo dotado además, de hardware para interconexión, constituye el dispositivo empotrado de gestión del automatismo. El segundo equipo puede ser cualquier computadora de escritorio convencional con capacidad de conectarse a redes.
Algunas características del hardware utilizado:
CPU i386 compatible, 166Mhz, 32Mb Ram, 4Gb HD(*)
Placa madre con ranura ISA 16 bit.
Placa para de adquisición de datos (se uso PCX-I/O, ISA):
Modems, o Placa de Red, o ambos.
Fuente de alimentación.
Gabinete estanco.
Computador estándar de escritorio.(*)
Resolución 8 bit
8 canales Multiplexados
Rango de Tensión de entrada 0 - 5 voltios
Tiempo de Conversión 27 microsegundos
Entrada/Salidas Digitales
Utiliza la unidad 8255
48 E/S Programables
Niveles Compatibles TTL
Triple Temporizador de 16 Bit
Utiliza la unidad 8253
Reloj Interno o Externo
Entrada de Interrupciones
3 Entradas enmascarables
Nivel IRQ Seleccionable
Diversos sensores han sido construídos en forma especifica para este desarrollo por integrantes del Proyecto MyC. Estos elementos han sido concebidos como prototipos para demostración.
2.2 Software
El software desarrollado establece 3 capas independientes: librería para manejo de placa de adquisición de datos LPAD, el módulo de medicion y control MMC, modulo de comunicaciones e interfaz de usuario MCI .
El Sistema Operativo para la UBMC se configura en base a 3 elementos criticos: la confiabilidad del sistema orientado a la gestión no asistida de automatismos; la optimizacion de recusos de hardware limitados y los servicios para intercambio de información.
2.2.1 LPAD Librerias para Placa de Adquisición de Datos.
Es una interfase entre las señales eléctricas adquiridas de la PAD y el MMC. Esta librería es específica del hardware empleado. El aisalmiento de esta capa, restringe desarrollos ulteriores a este único nivel. Se basa en librerias estandar de C.
2.2.2 MMC Modulo de Medicion y Control.
Se trata de un conjunto de servicios que al cargarse en memoria, disparan un set de tareas sicronizadas, generándose asi, el entorno de la aplicación del automatismo. Con una frecuencia conveniente, son ejecutadas tareas de automantenimiento, las que a su vez delimitan ciclos o jornadas de operación.
Tareas del Modulo de Control.
Base MC. Esta tarea contiene toda la lógica de MyC, es decir, las funciones de medicion y control. Maneja acceso y control de los periféricos específicos de aquicision de datos a travez de las librerias de hardware. Carga la tabla de parametrización y accede archivos para escritura de datos. Los datos de lectura recibidos son los comparados con los valores de la tabla de parametros, pudiendo determinar acciones de corrección en base a cálculos específicos. Los valores tomados en este proceso son convertidos a sus unidades físicas correspondientes con ecuaciones facilmente parametrizables en el sistema.
Generación de Reportes. El Sistema mantiene un registro histórico de todas las lecturas obtenidas.
Actualización de parámetros y configuraciones. Atendera solicitudes de modificación de los mismos.
Tarea de Registro de actividades del sistema. LOGs
Depuración de reportes en forma automática.
Servicios para la obtención de reportes y de lecturas flash y monitoreo de sensores. Estos servicios son los encargados de devolver a demanda los reportes generados por la tarea especifica, informes flash en tiempo real y sobre el estado de los sensores.
Estos servicios soportan la concurrencia de varias peticiones simultaneas. Son procesos escritos también en C como todo el Modulo de Control.
Algunas estructuras de datos y configuraciones, son actualizadas durante el proceso de automantenimiento que define el final de un ciclo de trabajo y el comienzo del siguiente. En él son transmitidos todos los datos generados en ese ciclo para su sincronización, tratamiento y almacenamiento central.
2.2.3 MDC Módulo de Comunicaciones:
Los accesos remotos se establecerán usando los estándares de protocolos TCP/IP.
Este módulo alojado tb. en el UBMC, es el encargado de resolver todas las comunicaciones del Sistema con el exterior. Se ha implementado usando un servidor http, lo cual ofrece acceso mediante un browser estandar. La interface CGI permite a este servidor procesar peticiones invocando módulos desarrollados en Perl que implementan la comunicación hacia el Módulo de Medición y Control.
2.2.3.1 IU Interface de Usuario:
Aplicativo orientado a usuario que resuelve funcionalidades de autenticación, configuracion, administración, peticiones de reportes, monitoreos, etc.
Autenticación:
La autenticación de usuario se basa en nombre de usuario y clave. Cada usuario registrado en el sistema MyC posee un perfil que define las operaciones que puede realizar.
Consulta de un dispositivo específico:
Envío de comando a dispositivo específico.
Lectura y modificación de Archivos de Configuración y de Parametros.
Una vez recibidas las respuestas el Módulo de Control las formatea con TAG html para luego ser enviadas al cliente.
Tomando como base este desarrollo se pueden implementar mediante la adición de conversores D/A Acciones de Control Proporcionales, Integrativas, o Derivativas. Ampliando de esta manera su campo de aplicación y su factibilidad económica.
Programación Profesional en C / Steve Schustack
El Entorno de Programación Unix / Brian W. Kernigham - Rob Pike
El Lenguaje de Programación C / Brian W. Kernigham - Dennis Ritchie
Sitios Web
. Documentación de Perl / http://www.perl.com/pub/q/documentation
. Documentación en linea de GNU/Linux
. El Ensamblador y Lenguaje C / http://atc.ugr.es/docencia/udigital/13.html
. El MicroProcesador 80386 / http://www.alpertron.com.ar/80386.HTM
. Manejo de Interrupciones / http://es.tldp.org/Manuales-LuCAS/DENTRO-NUCLEO-LINUX/dentro-nucleo-linux-html/dentro-nucleo-linux-2.html
GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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0. PREAMBLE
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