Electrical potential monitoring

The measurement of the electrical potential between the piece of process equipment (or a probe of the same material) and a fixed reference electrode will provide information on the corrosion risks. The technique requires that the process fluid be conductive and the electrochemistry of the system well understood. Potential monitoring does not give a measure of the corrosion rate, but wfll indicate the 

For practical purposes, a robust and stable reference electrode must be selected. The location of the test probe and the reference electrode may be critical to the provision of reliable information and require careful consideration. High-impedance voltmeters ( 1 megohm) should be used to record potentials, in combination with a chart recorder. 

In aqueous process streams where the control of pH is critical either to the efficiency of the process 

The removal of process fluid samples to a laboratory for pH measurement is not a reliable method of determining the system pH, since the pH of the sample may alter considerably as a consequence of the sampling procedures. For many applications on-line monitoring using pH probes is the only reliable method of monitoring unit or system pH. 

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Linear polarization instruments provide an instantaneous corrosion-rate data, by utilizing polarization phenomena. These instruments are commercially available as two-electrode Corrater and three electrode Pairmeter (Figure 4-472). The instruments are portable, with probes that can be utilized at several locations in the drilling fluid circulatory systems. In both Corrater and Pairmeter, the technique involves monitoring electrical potential of one of the electrodes with respect to one of the other electrodes as a small electrical current is applied. The amount of applied current necessary to change potential (no more than 10 to 20 mV) is proportional to corrosion intensity. The electronic meter converts the amount of current to read out a number that represents the corrosion rate in mpy. Before recording the data, sufficient time should be allowed for the electrodes to reach equilibrium with the environment. The corrosion-rate reading obtained by these instruments is due to corrosion of the probe element at that instant [184]. 

To monitor the movement of surfactant ions in the octanol membrane visually, electrical potential oscillation across the octanol membrane was measured with eriochrome black T (EBT) as colored surfactant in phase w2 [20]. Migration of EBT from interface o/w2 toward bulk phase o could be seen during the induction period of oscillation. After EBT reached interface o/wl, the first pulse of oscillation started. Thus, surfactant ions at interface o/wl are indispensable for oscillation. Considerable convection in phase o and... 

Figure 22. Shown is the schematic outline of the four-terminal device in Figure 13 with its reduced logic profiles and subsequent truth table outputs where the electrostatic potential is varied through inputs V1in and V2,in. The central methylene is depicted as an electrical barrier. Monitoring of the electrostatic potential output is observed at Vout, and FI...

Monitoring electric potential during hydraulic stimulation... 

An important advantage of these techniques is that the measurements of electrical potential can be very accurate, which allows monitoring until almost complete conversion, or until equilibrium in a reversible process. In fact, potentiometry is extremely powerful for obtaining equilibrium constants [25]. However, there are also restrictions and limitations (a) the solution must be conducting (b) the response time of the electrode can be relatively long, so there is a limit to the speed of a reaction which can be monitored and (c) there can be appreciable interference from impurities, or intermediates and products. 

PLM can also be detected using a more recently developed technique, actigraphic monitoring. This technique is not identical to the standard EMG monitoring, since actigraphs record movement and not electrical potentials [82], The advantage of actigraphy is that it is much less expensive than PSG, can be conducted in any... 

A typical Mazzoni fatty acid neutralization soap plant is illustrated in Fig. 36.5.6 The operation of this plant involves the pumping of the reactants through preheaters to a turbodisperser, or high-shear mixer, where the contact of the reactants with each other initiates the formation of neat soap. The soap mass, which is partially reacted at this stage, then proceeds to the mixer where it is recirculated until the neutralization is complete. The completion of the neutralization reaction is monitored continuously by an electric potential (millivolt, mV) measurement for alkalinity. The neat soap is then dried by vacuum spray-dryers, as described earlier, to produce soap pellets ready for finishing into soap bars. 

The advantages of applying the PEVD process to deposit auxiliary phases are not only based on the mechanism of PEVD product crystal growth, but also arise from close control over the entire process achieved by adjusting the applied dc electric potential and monitoring current. Thus, the superiority of PEVD is obvious since the Na COj auxiliary phase can be deposited in a well-controlled manner at the... 

An impedance measurement can be made either by applying an electrical potential and monitoring the current response or, conversely, by passing current and monitoring the potential response. Several decades of frequencies can be scanned rapidly and accurately using a frequency response analyzer [4]. An alternative approach applies multiple frequencies simultaneously (white noise) and deconvolutes the response with a lock-in amplifier. The use of an... 

Consider, for example, a test sample of material with a well-defined geometry as shown in Fig. 2. Reversible electrodes are attached to opposite planar faces of the test article, and a sinusoidal electrical potential (V ) is applied via a waveform generator. The current response is monitored with a frequency response analyzer (FRA), which converts the signal to the frequency domain. The amplitude (A) of the input wave is adjusted to the range in which the system responds linearly, about 10 mV. Thus, the perturbation can be described by the following equation ... 

Electrochemical detection involves the induction of a change in redox state (electrolysis) by application of an electrical potential to an electrode (71). Compounds that can be readily detected by this means are termed electroactive. Under physiological conditions, these compounds tend to be in their reduced state in the nervous system because of the rich level of antioxidants (e.g., ascorbic acid) and, thus, can be oxidized by application of a positive potential to the electrode. The evolved electrons are detected at the electrode in the form of electrical current. This current is proportional to the number of electroactive molecules at the surface of the electrode, and therefore it is proportional to their concentration in the bulk solution. By implanting an electrode in the extracellular space close to the release site and detecting changes in the local (extracellular) concentration of the neurotransmitter, neurotransmitter release can be monitored. The key advantage of this approach is the high temporal resolution that can be in the millisecond domain. Neurotransmitters that can be detected this way include dopamine, norepinephrine, epinephrine, serotonin, and melatonin. 

A relatively recent development in radon gas monitoring is the electret system (Kotrappa et al, 1988). In effect this is an ionization chamber with an electret foil in the chamber, into which radon gas diffuses through a filter. The electret is a plastic foil which carries a permanent electric charge and therefore an electric potential. The decay of Rn and RnD in the chamber ionises the air, and the electric field caused by the potential on the electret attracts these ions to the electret. The electret loses its charge proportionally to the number of ions collected. The charge, or voltage on the electret is... 

Few experimental studies have been reported on the behavior of short cracks. However, in one study. Prater et al. [101] used an electrical potential drop method to monitor the growth oif surface cracks in carbon steel in oxygenated (8 ppm O2) high-temperature (288 °C) water. The cracks were semielliptical in shape and the crack... 

The use of potential-sensitive fluorescent probes to monitor the electrical potential across a cell membrane permits an accurate, noninvasive measurement of membrane potential changes in a wide variety of cells, vesicles, and organelles without the external electrical or mechanical manipulation required by micro-... 

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