Chemical sensors inlet system

The requirements for chemical sensors suitable for use in eddy correlation direct measurements of surface fluxes are examined. The resolution of chemical sensors is examined and defined in terms of surface flux and commonly measured micrometeorological parameters. Aspects of the design and operation of sensor systems are considered. In particular, the effects of the inlet ductingy the sensing volume, and the signal processing on the ability to measure surface fluxes were analyzed. 

An example of one of TSA/TSL s R D funded MEMS based project is the Sandia National Laboratories (SNL) MicroHound project. This is based on the SNL Micro Chem Lab on a Chip , illustrated in Figure 1. The original prototype system from SNL was developed for high vapour pressure, chemical weapons (CW) detection, which utilized a MEMS GC separator, with miniature surface acoustic wave (SAW s) based sensors. The system included an inlet, coated pre-concentrators, detectors, and pumps. To make this useful for trace explosives detection, the addition of an alternate front-end sample collection/macro-preconcentrator and MEMS based coated-preconcentrator is necessary, along with the option to utilize or exclude the MEMS GC separator followed by detection by either, or both, SAW s and miniaturized IMS detectors. 

Figure 3.34 — Manifolds for implementation of a sensor containing a packed non-regenerable reagent and a regenerable fluorophore. (A) Flow-through sensor system 1 eluent vessel 2 pump 3 injection valve 4 TCPO reactor 5 CL cell 6 light-tight box with PMT 7 amplifier 8 recorder. (B) Design of the packed two-layer sensor 1 inlet capillary 2 inlet cap with frit 3 quartz tube 4 TCPO layer 5 frit 6 luminophore layer 7 outlet cap with frit 8 outlet capillary. (C) Manifold for implementation of the previous cell in biochemical applications (Reproduced from [240] and [241] with permission of the American Chemical Society and Elsevier Science Publishers, respectively).

Consider a process that consists of a reactor used for the processing of a highly unstable chemical that is sensitive to small increases in temperature. The reactor is equipped with a quench tank to protect the system against a runaway reaction and is monitored by two temperature sensors (see Fig. 17) T, and T2. Sensor T, automatically activates the quench tank outlet valve when it detects a temperature rise above the specified upper limit. Sensor T2 sounds an alarm in the control room to alert the operator to the process upset. When the alarm sounds, the operator closes the reactor inlet valve. The operator also pushes a quench tank valve button in the control room in case the quench valve fails to open. Note that A is the reactant B, the product and C, the quench. 

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