Sensor testing techniques

The usefulness of the LSER approach hinges on the similarity of the partitioning coefficients obtained from the sensing experiments (Ks) and the gas chromatographic experiments (Kqc)- In other words, it is assumed that the relationship Ks Kgc holds. This is how LSER is used for evaluation of a new sensing material. First, the coefficient Kqc is obtained from the tabulated database or experimentally. Second, the multiple linear regression technique (see Chapter 10) is used to obtain the best fit for the sensor test data, and the individual coefficients in (2.3) are evaluated. This approach has been used successfully in evaluation of multiple materials for gas sensors (Abraham et al., 1995 Grate et al., 1996). 

In previous chapters, we have already discussed the mass-sensitive detection of both small molecules and microorganisms and thus have covered the analyte size range below 1 nm and above 10 nm. The gap in between is bridged by macromolecules and some colloidal particles. Special analytical interest is devoted to biomacromolecules, such as proteins and enzymes and nucleic acids, which are also of chnical interest. For these classes of compounds, a wide variety of rapid testing techniques exist, which can also be seen by the mun-ber of excellent and recent reviews both on protein [59] and DNA [60-62] detection. Due to the broad range of techniques already available in chemistry and clinical science, MIP sensor applications for these analytes are still somewhat rare. For entire DNA strands, no imprinting strategy related to... 

This paper will describe a complete operational system, by components, that is currently providing performance data of sufficient accuracy to facilitate development testing at the Pratt. Whitney Research and Development Center. Sensor calibration techniques and equipment will be reviewed as well as complete system operation. 

Electrochemical sensors and techniques recently have been developed to test the corrosivity of the environment as well... 

Modular components of future chemical sensor systems are introduced briefly Their development involves, in particular, new or fine-tuned (well-known) sensor-active materials and transducers A molecular understanding of the sensing mechanisms is shown to be a prerequisite for the development of a new generation of sensor systems with particular emphasis on their miniaturization and integration This understanding requires comparative microscopic, spectroscopic and sensor test studies on prototype materials to be performed, which requires to use experimental setups that combine the usual techniques of interface analysis with sensor preparation and sensor test chambers A few selected case studies on prototype materials are chosen to illustrate recent trends in the development of new materials and transducers for integrated chemical and biochemical sensor systems... 

Diagnostics can be applied as self-testing techniques for sensors and valves in addition to functional testing or proof testing which is carried out periodically as part of the overall maintenance of the SIS. 

For testing of other sensors the techniques are not always so simple or elTective. Here are a few suggestions. The workshop attendees may have their own ideas to add here. With the aid of the flip chart we will sketch out and discuss methods for typical sensors. These will include ... 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

Since it was proposed in the early 1980s [6, 7], spin-relaxation has been extensively used to determine the surface-to-volume ratio of porous materials [8-10]. Pore structure has been probed by the effect on the diffusion coefficient [11, 12] and the diffusion propagator [13,14], Self-diffusion coefficient measurements as a function of diffusion time provide surface-to-volume ratio information for the early times, and tortuosity for the long times. Recent techniques of two-dimensional NMR of relaxation and diffusion [15-21] have proven particularly interesting for several applications. The development of portable NMR sensors (e.g., NMR logging devices [22] and NMR-MOUSE [23]) and novel concepts for ex situ NMR [24, 25] demonstrate the potential to extend the NMR technology to a broad application of field material testing. 

Center for Healthcare Technologies at Lawrence Livermore National Laboratory in Livermore, potentially capable to measure pH at or near the stroke site29. The probe is the distal end of a 125 pm fibre tapered up to a diameter of 50 pm. A fluorescent pH-indicator, seminaphthorhodamine-1-carboxylate, is embedded inside a silica sol-gel matrix which is fixed to the fibre tip. Excitation of the dye takes place at 533 nm and the emission in correspondence of the acid (580 nm) and basic (640 nm) bands are separately detected. The use of this ratiometric technique obviates worrying about source fluctuations, which have the same effects on the two detected signals. The pH sensor developed was first characterised in the laboratory, where it showed fast response time (of the order of tens of seconds) and an accuracy of 0.05 pH units, well below the limit of detection necessary for this clinical application (0.1 pH units). The pH sensor was also tested in vivo on rats, by placing the pH sensor in the brain of a Spraque-Dawley rat at a depth of approximately 5 mm30. 

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