Catalytic bead sensor

Pellistor or catalytic bead sensors have a fairly long lifetime, and a wide temperature range. They require 5% to 10% of oxygen to operate. 

Solid-state, electrochemical, infrared, photoionization, and catalytic bead sensors... 

Catalytic bead sensors (combustible gases), electrochemical sensors (toxic gases oxygen), etc. 

Combustible gas detectors are required whenever there is a possibility of a hazard to life or property caused by the accumulation of combustible gases. There are mainly two types of combustible/flammable gas detectors that are often used in most industries. These are the low-cost catalytic bead sensor and infrared sensor [26,27]. 

Catalytic bead flame detector. (A) Catalytic bead sensor details, (B) catalytic bead sensing... 

Infrared sensors Although these are costlier with respect to catalytic bead sensors they offer a number of advantages such as faster response ( 10 s), low maintenance, self-checking with the help of microprocessor circuitry, and measurement does not depend on O2 to detect the gas. It may be designed in... 

Metal Oxide and Catalytic Bead Hydrogen Sensors.511... 

While much of the surveyed research exhibits promising vapor-phase sensing performance, many of the technologies remain experimental and bound to a laboratory setting. Most of the commercial gas sensors available today utilize older, more mature technologies such as electrochemical cells, catalytic beads, photoionization detectors (PID), SAW, metal oxide semiconductors (MOS), and QCM. The dearth of viable organic solid-state vapor-phase chemosensors indicates that there is much work still to be done (in terms of material stability, selectivity, etc.) before commercialization becomes commonplace for organic sensors. 

Catalytic bead combustible gas infrared sensors electrochemical sensors for oxygen, and toxic gas... 

Catalytic bead-type detector This is a low-cost detection system used to detect combustible gases. The system uses a catalytic bead to oxidize combustible gases. On account of combustion there will be a change in temperature, which is detected by resistance with the help of a Wheatstone bridge. Typical sensor and measuring principles are shown in Fig. X/3.4.2-1. 

Fig. 11.1 (a, b) Configurations of pellistor (catalytic bead) gas sensors and (c) temperature-dependent heat generation of a catalytic combustion of combustible gases in air... 

Catalytic Reaction. A bead or wire is coated with a catalytic material so that it reacts with atarget gas. As the reaction on the catalyzed surface takes place, the bead or wire heats up, and changes its resistance. This resistance change can be proportionally related to the target gas concentration. An example of a catalytic bead detector is a sensor that consists oftwo beads placed in a wheatstone bridge circuit. One of the beads acts as a... 

Catalytic gas detection is based on the principal that oxidation of a combustible gas in air is promoted at the surface of a heated catalyst such as a precious metal. The oxidation reaction results in the generation of heat that provides a direct measure of the concentration of the gas that has been reacted. The sensing element embodying the catalyst is a small bead that is supported with the sensor. 

Catalytic (Pellistor) Flammable gases Air Measures the heat output due to the catalytic oxidation of flammable gas molecules. A stream of the sample is passed over the sensor which is usually a ceramic bead impregnated with Pt or Pd. The temperature variations in the sensor due to reaction are monitored. Dependent on individual design. Flammable gas detector. Usually portable... 

The components involved are streptavidin-coated donor beads and anti-GST acceptor beads (Perkin Elmer LAS, Boston, USA) and - as the biological system -the PKA subunits as cAMP sensors. Upon binding of cAMP to each regulatory (R) subunit, the PKA holoenzyme dissociates releasing the catalytic (C) subunits. 

RNA aptamer specifically binding and inhibiting the activity of the catalytic ricin A-chain (RTA) has been selected [57]. Initially 80 nucleotides long, it has been shortened to 31-nucleotide aptamer that contained all sequences and structures necessary for interacting with RTA. Inhibition properties of this aptamer exceeded known ricin inhibitors. This aptamer along with others was used to develop a multispecific sensor. Aptamers were immobilized on beads, introduced into micromachined chips on the electronic tongue sensor array, and used for the detection and quantification of proteins. The lowest detected ricin concentration using this sensor was 1 pM (320 ng/mL) [58]. 

The rapid growth in demand for catalytic flammable gas sensors to operate in hostile atmospheres (leaded petrol atmospheres, gas compressor stations, etc.) and areas where routine calibration and maintenance are difficult and costly (North Sea gas and oil platforms) has stimulated the search for sensing elements which are resistant to poisons. These devices generally take the form of a platinum wire coil embedded in a porous bead comprising active catalyst either dispersed throughout a porous substrate (5-7) or as discrete layers within the substrate (8). 

---