Probe systems

Fig. 4 Testing configurations of the pump-probe system (a) pulse-echo configuration, (b) split...

When designing a system for thrust bearing proteetion, it is neeessary to monitor small ehanges in rotor axial movement equal to oil film thiekness. Probe system aeeuraey and probe mounting must be earefully analyzed to minimize temperature drift. Drift from temperature ehanges ean be unae-eeptably high. 

The high-high probe is completely independent of the other probes and is hardwired to shut down the system completely, independent of the computer. (In the preliminary safety review, the hazards associated with HF overfeed were identified as important thus the independent high-high shutdown probe system was installed.) All systems are designed to fail into safe conditions. The HF control valves are air operated and of a design that makes it impossible for HF to contaminate the air supply. 

Probe systems, also called as the ultrasonic horn are being most frequently used for the sonochemical research at laboratory scale of operation. A typical schematic representation of the setup of probe systems has been given in Fig. 2.5. These are typically immersion type of transducers and the most important advantage of using... 

Other intravascular-probe systems have been proposed by Abbott (Mountain View, CA)18 and by Optex Biomedical (Woodlands, TX)19, where the structure of the probe is essentially similar to the CDI one previously described i.e. three different multimode fibres, each of which is associated with the specific chemistry and charged with the detection of a single measurand. 

Ozaki, K. Sekiguchi, H. Wakana, S. Goto, Y. Umehara, Y. Matsumoto, J., Novel optical probing system with submicron spatial resolution for internal diagnosis of VLSI circuits, Proc. Int. Test. Conf. 1996, 269 275... 

Most chemists working on sonochemistry in the laboratory will either use some form of ultrasonic bath or a commercial probe system. The latter instruments are often equipped with a pulse facility which was originally designed for biological cell disruption where temperature control is important. This pulse facility enables the power ultrasound to be delivered intermittently and thereby allow periods of cool-... 

The above studies were carried out at relatively low powers - typically a few W cm produced by a cup-horn. When greater acoustic power is applied through a probe system (of the order of 20 — 30 W cm ) it is possible to induce some quite specta-... 

Rehmann [90] has employed ultrasound to improve the yield of polyphenylene, thought at one time to have a future as a conducting material. Using dibromobenzene and a nickel complex catalyst he investigated both bath and probe systems and found that sonication led to improved yield when compared to the conventional synthesis (i. e. reflux) and also had the advantage of allowing the use of a lower temperature (20 °C). 

In general they found both enhanced reaction rates and polymers with lower poly-dispersities in the presence of ultrasound provided by both bath and probe systems. Higher ultrasonic intensities resulted in narrower molar mass distributions. 

The same workers [84] have also examined the copolymerisation of a-methylstyrene and 4-bromostyrene again with similiar effect using 25 kHz probe system. In the absence of an electrical potential but in the presence of ultrasound, they failed to produce any sonochemically-induced polymerisation of the monomer over a 24 h period. This is an important experiment since ultrasound is well knovm to produce radical species which could themselves influence polymerisation. 

Reduced power compared with probe system. 

For the probe system, whatever design of horn is used, a large maximum power density can be achieved at the radiating tip. This can be of the order several hundred W cm . The working frequencies are normally of the order 20 - 40 kHz. A number of probe devices are commercially available and, up to a few years ago (before the advent of sonochemistry) were referred to as cell disrupters. The majority operate at 20 kHz and utilise a wide range of different metal probes. The advantages of the probe method of energy input are threefold ... 

Laboratory Scale Reactors Involving Probe Systems... 

Although the use of a probe provides several advantages over the use of baths (vide supra), they do suffer from a common disadvantage - they are only capable of operating at single fixed frequency. There are however two additional problems peculiar to probe systems ... 

Yeh and Keeler 244) extended the method of laser-scattering spectroscopy to probe systems undergoing rapid chemical reactions. They observed the spectral line broadening in light from a singlemode He-Ne laser scattered from multicomponent solutions, as a function of time. The experiment employed a pressure-scanned Fabry-Perrot interferometer and photon counting techniques. 

Fig 2 Charge Configuration Used to Compare Pressure Probe System with the Ioniza-tion Probe System. The Barrier Introduces a Detonation Delay Time... 

A comparison of the ionization and pressure probe systems in a single test provides some insight into the initiation of a porous bed of granular expls by relatively weak shock waves. A typical exptl arrangement and the oscillograms produced are shown in Fig 5 of the report, which is reproduced here as Fig 2, without oscillograms... 

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