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The Electronic Nose and The Quadrupole Mass Spectrometer ArrayBy: Dan Karmon, Ph.D
Project Manager - QMSA
SSET Avionics/ATTI Avionics Lead Avionics Equipment Section 344
Jet Propulsion Laboratory
The Electronic Nose (E-Nose) was developed jointly by Jet Propulsion Laboratory (JPL) and the California Institute of Technology (CalTech). In many ways it mimics the human nose and is designed to monitor changes in an atmosphere to which it is exposed. It is based on the multi-sensing principle in which the distributed response of an array is used to identify the constituents of a gaseous environment. Individual sensor films are not specific to any one gas. It is in the use of an array of different sensor films that gases and gas mixtures can be uniquely identified by the pattern of measured electrical response.
The E-Nose was successfully flown on STS-95 space shuttle mission
(October 1998). It monitored the middeck air continually for over six days
and took data samples every 3 seconds. Following analysis and comparison
with other independent data, the experiment was judged to be very successful.
It was clear from the beginning that we would need a small computer
to run and control the E-Nose experiment. We chose the HP 200LX palmtop
as an available and inexpensive solution. The HP 200LX was used "as is"
secured to the cover of the E-Nose box (See picture). We only needed one
modification. We had to make the Palmtop start up without any batteries.
This made it easier to pass the stringent shuttle safety requirements.
(The experiment was operated by the Shuttle 28Vdc.) A 2 MB HP 200LX was
used along with a 6 MB flash card for safe data storage. The operational
software, programmed in Quick Basic 45 with additional C Libraries, was
also stored on the flash memory and "moved" to RAM upon power-up. This
memory configuration would have been sufficient for a 15-day Space Shuttle
mission. The 200LX controlled the experiment (pneumatic system, miniature
pump, solenoid valve, and sensor heaters) and executed the normal health
checks and safety monitoring. Additionally, since the E-Nose requires highly
accurate measurement of resistance changes, it was placed in the measurement
and error nulling loop of the sensor measurement electronics. The 200LX
controlled the interrogation of the sensors at a known time interval, registered
critical measurements, nulled outputs as needed, calibrated as needed,
registered results, registered the time, did some of the calculations,
and stored a series of parameters. The final data analysis was done after
the flight, in the lab.
Preliminary design indicated that we can leverage the experience gained on the E-Nose (See above) and apply the HP 200LX to the QMSA. In this case, however, using the 200LX "as is" was not an option. Only the 200LX circuit board will be utilized (See pictures). As in the E-Nose, the 200LX Palmtop batteries are not used. Additionally, the 200LX display signals were re-routed to a space qualified display system as required for astronaut use in space. Memory configuration was the same as the E-Nose. The 200LX was programmed in MS C 5.1 with some Lab Window libraries.
Quadrupole Mass Spectrometer Array (QMSA) Exploded View showing HP 200LX motherboard
This instrument is more complex that the E-Nose. The TGA requires an operator interface (switches, display, indicators, etc.), tool control, sensor control, and real time display of data. The 200LX handles all the TGA operations including safety interlocks, power-up, and calibration. Based on operator's selection of menu driven mode of operation the 200LX controls the sensor sequences, the data collection, the calculations, and data handling. The 200LX will store the data and send appropriate information to the new display.
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