Instituto Nacional de
Tecnología Industrial
Centro de Investigacion y Desarrollo en
Telecomunicaciones, Electrónica e
Informática
Internet Controlled Gas-Mixing System
S. Tropea, D. Brengi, L.Malatto, L. Fraigi
UTIC, CITEI-INTI, C.C.157, (1650) San Martín, Buenos Aires, Argentina.
Email: salvador@inti.gov.ar
Presented on IBERSENSOR 2000
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Summary
In this work a gas mixing bench controlled by Internet is presented. The mixing system is controlled by a GNU/Linux server
with software developed specially for this application. The control software allows the selection of gas type, mixture
concentration, mixing times and valves configuration. Remote programming and monitoring can be done from any terminal
connected to the Internet. The server have secure and encrypted connections for each control terminal avoiding possible
external attacks.
Keywords: gas, mixing, GNU, Linux, Internet, automation
Subject category: G (sensor systems)
Introduction
The generation of stable and reproducible gas mixtures is extremely important for the characterization and the
comprehensive understanding of the conduction mechanisms of solid state gas sensors. Suitable techniques to produce low
concentration mixtures of gases involve dynamic methods.
The mixing system is constituted by:
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Gas flow unit equipped with 7 mass flow controllers (MFC), valves, solenoid valves,
pipelines and a sensors test chamber.
Remote control and measurement interface.
Server software running on a GNU/Linux operating system.
Terminal user control software.
Gas flow unit
The gas pipelines connect the gas tubes to seven MFCs. The system has manual
valves and solenoid valves to configure the different gas circuits. The gas mixing
ends in a chamber for gas sensor testing and calibration.
Remote control and measurement interface
The remote interface drives the MFCs and the solenoid valves of the gas flow unit. It is connected between the server
machine and the MFCs . This unit have:
Mode selection (local or remote mode)
Manual control for the MFCs (local mode).
Manual control for the solenoid valves.
Gas flow indication (front pannel LCD).
Computer interface for remote mode.
Independant regulated power supply for each MFC.
In remote mode, analog and digital signals from the computer (server machine) have total control over the MFCs and the
solenoid valves.
Server machine
The server is a 486DX33 with 8 Mb of RAM, digital and analog I/O (Keithley DAS1600) and
Ethernet network interface. The analog outputs of the DAS1600 are used to control the setpoint of
seven MFCs.
The analog inputs read the gas flow of each MFC using an A/D with a resolution of 12 bits. This
server is also connected to the local area network (LAN) with an Ethernet card.
A kernel module was specially designed to perform low level communication with two analog and
digital I/O boards.
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Kernel module
This part of the program works as a kernel module that can be plugged in the kernel space. The module can be inserted to or
removed from the kernel at any time.
As it runs in the kernel space the module have access to all the low level resources found in the machine, in this particular
case the module handles the I/O boards.
To communicate with the user space, where the server software is running, some special kind of files called devices are
used. The server sofware excahnges information with the kernel module using the IOCTL mechanism.
The control software (client-server)
The control software was created using a client-server model. The server software runs on
the server machine connected directly to the mixing bench. The client software establish
communication with the server for batch programming and process monitoring.
Server software
The server side uses a Debian GNU/Linux operating system and runs as a UNIX daemon started at boot time. This program
executes the control process dedicated to control the remote interface, and the communication process to receive the user
commands from the TCP/IP network and transfers them to the control process. Both processes communicate using pipes,
the interprocess communication mechanism most commonly used in UNIX. If the communication gets stalled the control
process doesn't stop and hence the programmed steps keeps working. This architecture makes the software much more
robust.
User control software (client)
The client (user software) have the following features:
Selection of gas type
Selection of mixture concentration
Selection of mixing times
Solenoid valves configuration
Colored text windows, menus and mouse facilities
Run in UNIX systems (GNU/Linux) or in DOS compatible operating systems
(Windows, OS/2, etc.).
The client can run on any authorized host from Internet including the server machine
itself.
Security
In order to increase the security of this gas mixing system a secure shell (SSH) utility was used. The SSH application
validates users and establishes connections through the network. It usually uses the RSA mechanism for validation and DES
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for encryption.
Conclusion
The GNU/Linux operating system has proven to be an effective tool for laboratory automation. The system developed was
designed to program and monitor gas mixing from any terminal connected to Internet in a secure and reliable way.
Download
Presentation of the project at the "2das Jornadas Regionales de Software Libre" event, Montevideo, Uruguay (spanish
version only):
Open Document
JPEG images: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Authors
Laura Malatto and Liliana Fraigi in a poster
session
Laura Malatto, Liliana Fraigi and Diego
Brengi
Salvador Tropea and Liliana
Fraigi
Last update: 22/06/2001
Webmaster : brengi@inti.gov.ar
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