Testing


Testing

Three advanced systems for the measurement of the DC and AC electrical response of up to five sensors to gas mixtures at variable humidity and controlled temperature, a MS spectrometer monitors the outlet of the test chambers. Each of the systems is equipped with one special module designed for ozone characterization, kelvin probe measurement and photoactivated characterization

An experimental set-up for optical characterisation made by a gas chamber equipped with a quartz window and placed on an active optical bench. On the bench a Multiline Ar laser, a quartz Tungsten Halogen lamp, a single monochromator and a CCD camera can detect the resistance phoactivated response, the photoluminescence and reflectance spectra in the 1eV-4eV range. A kelvin probe head placed inside the chamber measures the Surface Photo Voltage

Two Electronic Noses with static- from vials with a programmable autosampler – and dynamic – stainsteel canisters – sampling

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Electrical gas sensors testing

  • Advanced system for the measurement of the dc electrical response of 10 sensors to six different gases in presence of relative humidity, the outlet of the test chamber is connected to a MS spectrometer. This system is controlled by a Personal Computer.
  • Advanced system for the ac and dc electrical response of thin film sensors ; two gases can be simultaneously measured in presence of relative humidity. The system is equipped with an ozone generator based on a thermo-stated UV lamp discharge (ANSYCO). An ozone detector based on the wet chemical Brewer-Milford principle measures the ozone content at the outlet of the test chamber. This system is controlled by a Personal Computer.
  • Stations for long term measurements.
  • Structural and morphological characterization are carried out using the facilities present in our Faculty or in collaboration with other groups present in the Faculty.

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Optical gas sensors testing

We have realized an experimental setup for measuring optical (photoluminescence, reflectivity) and electrical (conductivity, Contact Potential Drop and Surface Photo Voltage) properties as a function of the composition of the surrounding gaseous environment at atmospheric pressure.

The test chamber is made by stainless steel and can house one device; its volume is 500 cm3. Special features are a large quartz window granting easy access for optical measurements and a microfurnace to heat up the sample in the range RT-400°C. The test chamber is kept at constant temperature (20°C) in a climatic chamber. The system used to reproduce in a controlled and repeatable way environmental conditions in the test chamber is a dynamic one based on volumetric mixing through mass flow controllers and certified bottles. Since our interest is to monitor pollutant gases in environmental condition, we used synthetic air as a gas carrier at atmospheric pressure. All measurements are performed at constant relative humidity.

Light source are a compact Ar laser (55 mW on the lines at 488nm and 514 nm and 10 mW on the line at 457nm), a Xe-Hg Lamp in the UV range coupled with a bandpass filters, a Quartz Tungsten Halogen (QTH) Lamp with power of 20 W. A single monochromator-spectrograph (Acton SP300i) is used for selection of the wavelength. At the spectrograph exit is positioned a Peltier cooled CCD camera, 1024 x 128 pixel to detect the optical signal. The CCD camera is less sensitive but much faster than a phototube, allowing fast tracking of PL variations.

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Electronic Nose

The “Electronic Nose” (EN) is a monitoring instrument that detects a wide range of organic and inorganic molecules down to the parts-per-billion level. Since gases and gas mixtures are identified by the electrical response pattern of the entire array, the EN has an unique ability to monitor and identify a wide variety of compounds.


Figure 1. The Electronic Nose EOS835 developed at SENSOR in collaboration with SACMI Company
(Imola, IT).

Beside the development of sensors, an effective ENs requires: (a) the ability to obtain reproducible gas sampling, (b) a systematic and through experimentation, (c) the development of flexible and user friendly instrumentation control, and (d) sophisticated data analysis techniques. The collaboration with the SACMI company resulted (in 2003) in the commercial olfactory system EOS835 (Figure 1). The Sensor Lab has then continued working on different EN design aspects, focusing on sensor devices, sampling systems, and data analysis.
Concerning the sampling systems, EOS835 is now equipped with two autosamplers, with the possibility to work in a static (Figure 2)  or dynamic way (Figure 3).


Figure 2. The autosampler HT200 for static headspace has been developed for EOS835 in collaboration with the company HT Brescia. It is equipped with a carousel loading 40 samples and an oven/shaker which allows the headspace generation. Sample headspace is then injected into the sensor chamber. HT200 can be equipped with SPME fiber.


Figure 3. The autosampler for dynamic headspace ACS012 has been developed by SACMI: each position is termostated for the sample headspace generation.