An instrumentation system measures the concentrations of three principal contaminants (nonvolatile residue, hydrocarbon vapor, and particle fallout) in real time. The system includes a computer running special-purpose application software that makes it possible to connect the system into a network (which can, in turn, be connected to the Internet) to enable both local and remote display and analysis of its readings. The system was developed for use in a Kennedy Space Center facility that was required to be maintained at a specified high degree of cleanliness for processing a spacecraft payload that was highly sensitive to contamination. The system is also adaptable to monitoring contamination in other facilities and is an example of an emerging generation of sophisticated instrumentation systems that communicate data with other equipment.

A Typical Display of sensor readings includes textual and graphical information on the recent history of concentrations of selected contaminants.
The system includes a total of six sensors attached to a purged cart. There are two sensors of each type, for measuring the three principal contaminants at two different locations. The sensors for determining the concentrations of hydro- carbon vapors are Fourier-transform infrared (FTIR) spectrometers that measure the absorbance spectra of gases in internal gas cells in the wavelength range of 2.5 to 25 μm. The sensors for determining the concentrations of nonvolatile residues are surface-acoustic-wave devices, the resonance frequencies of which depend upon the amounts of material deposited on them. The sensors for monitoring particle fallout are small scatterometers.

The sensor readings (see figure) are digitized and time-stamped and the resulting data made available over a serial link from the cart to a computer workstation located elsewhere in the facility. The sensor readings are also displayed on a screen on the cart. The data can also be made available over the network to any computer equipped with special-purpose client software and with a Transmission Control Protocol/Internet Protocol (TCP/IP) connection; the computer can be located anywhere in the world. The data are packetized according to a special application- level protocol. Access to the data can be limited to authorized IP addresses, and, in any event, is limited by the need for the special-purpose client software to implement the application- level protocol.

The control of the system and the designation of IP addresses authorized to receive data are effected at the aforementioned computer workstation. From this location, control personnel can turn the nonvolatile-residue and particle-fallout sensors on and off, and re-zero and diagnose the FTIR spectrometers. They can monitor individual infrared spectra and can download them for off-line analysis. Other individuals monitoring the data via the network can provide typed comments to each other and to the control personnel via an the Internet-like chat utility.

To facilitate the development of the special-purpose software to effect the functions described above, there was first developed a set of software elements that enables the easy and rapid development and deployment of data-presentation application programs, not only for this system, but for a wide variety of systems that utilize a variety of data-communication mechanisms. The set includes a series of forms (objects), written in Microsoft Visual Basic, that follows a defined protocol. The set also includes similar objects written in Visual C++. The C objects are suitable for use in code developed on embedded software systems, while the Visual Basic objects are better suited for use in software based on graphical user interfaces.

All of these objects utilize the same application-layer protocol, making it possible for messages to go back and forth within an application program, between different application programs on the same computer, and between application programs on separate computers, which can be connected via either a serial link or a network. The special-purpose software of the present instrumentation system includes a set of such objects that perform the communication functions.

The set of objects comprises the following three subsets:

  • For assembly and transport of packets, including mediation of access by users, there are a serial-communication object, a network User Datagram Protocol (UDP) communication object, and a network TCP communication object.
  • For routing of packets of data within an application program, there is a dispatcher object.
  • For taking actions specified by messages, there is a do-action interface, which can be built into any object to make it aware of messages.

The communication objects, as well as any message-generating objects, notify the dispatcher objects of their messages. The dispatcher objects route messages to designated recipient objects, for action by the recipient objects. Because the protocol is consistent, intercommunication is simplified and uniform, making the application programs more scalable and flexible than they otherwise would be. The disposition of messages can even be dynamically modified to adapt to changing requirements.

This work was done by Paul A. Mogan of Kennedy Space Center and Christian J. Schwindt, Steven J. Klinko, Timothy R. Hodge, Carl B. Mattson, Paul Yocom, and K. Robert McLaughlin of Dynacs Engineering Co.


NASA Tech Briefs Magazine

This article first appeared in the July, 2002 issue of NASA Tech Briefs Magazine.

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