Electrical interference

Over the period of service the P-scan unit has proved to be a reliable system, operating in a stable manner under the conditions of strong electrical interference, natural atmospheric precipitation. The mechanical scanner of the system adapts quite... 

The most important appHcation of fiber-optic laser-based communication is in long-distance telecommunications (92,93). Fiber-optic systems offer very high capacity, low cost-per-channel, light weight, small size, and immunity to crosstalk and electrical interference. 

In general, low level detection is masked by the noise level inherent in any measuring device. Electrochemical methods are susceptible to electrical interference from external sources, variations in reference electrode parameters resulting from aging or contamination, and interference from redox... 

Protect against electromagnetic interference (EMI), electrical interference and radio frequency interference (REI)... 

Minimize the effect of electrical interference by the design, installation and selection of instrumented systems... 

Other than the system harmonics, electrical interferences are also caused by line disturbances, which may be caused by lightning, switching, sparking or a fault. As discussed in Chapter 17, line disturbances occur at very high frequencies but some may coincide with the audio frequency of telephone lines, and cause disturbance in the audio quality of the telephone system. All these disturbances are referred to as inductive interferences. 

We provide more details on inductive interferences in the box below, to make the subject of electrical interference more informative. We also provide a passing reference to communication systems being adopted worldwide. 

The basic instrumentation required for controlled-potential experiments is relatively inexpensive and readily available commercially. The basic necessities include a cell (with a three-electrode system), a voltammetric analyzer (consisting of a potentiostatic circuitry and a voltage ramp generator), and an X-Y-t recorder (or plotter). Modem voltammetric analyzers are versatile enough to perform many modes of operation. Depending upon the specific experiment, other components may be required. For example, a faradaic cage is desired for work with ultramicroelectrodes. The system should be located in a room free from major electrical interferences, vibrations, and drastic fluctuations in temperature. 

Electrochemical sensors have several disadvantages with respect to optical sensors (i) they are based on electrodes and require a reference electrode (ii) the liquid-liquid junction is easily perturbed by external factors (iii) they are sensitive to electrical interferences (iv) miniaturization is not easy and their cost is relatively high. However, optical sensors also have some disadvantages (i) ambient light can interfere (ii) the range over which the concentration of an analyte can be accurately measured is often limited (iii) they have generally limited long-term stability. 

Electrical interference. When low-level electrical signals are measured, it is very likely that substantial error may be introduced in the measurement by extraneous... 

Because optical fibers are nonconducting, fiber optic systems provide excellent electrical isolation and immunity from electrical interference. Signal losses are much lower in fibers (as low as 0.20 dB/km) compared to other guided transmission media, such as twisted copper pairs, coaxial cable, and metallic waveguides. In addition, the bandwidth or information carrying capacity of fibers is far greater. When one or more optical fibers are packaged into cables, the cables are smaller and more flexible than their metallic counterparts. 

Figure 27.16B shows the method known as pulsed coulometric detection (PCD). In this case, the current is integrated over a longer period and the time period is an integral number of 16.7-ms segments with typical total integration times of greater than 200 ms. The use of this type of waveform eliminates the most common electrical interference (60 Hz sinusoidal) encountered in pulsed electrochemical detection, and thereby increases the detection limits for most compounds. 

Modifications to a Bendix TOF mass spectrometer that resulted in a tenfold reduction in the statistical fluctuations of peak heights of the mass spectrum have been reported [11]. The modified apparatus was used to investigate the flash photodecomposition of lead tetramethyl [12] and the vacuum ultraviolet flash photolysis of vinyl bromide [5]. Further changes were made to reduce electrical interference from the flashlamp discharge,... 

The spectrophotometer should be located in a clean environment away from direct sunlight and drafts, at a reasonably even temperature, and free from electrical interference. 

Optical sensors display several advantages over electronic sensors. Since photons rather than electrons carry the information, they are almost immune to electrical interference. Usually the optical components are made from glass chips or fibre-optic cable fibres, giving them excellent mechanical and thermal stability and often, moreover, a high chemical resistivity. Finally the use of glass, especially fibre-optic, fibres helps to minimise the size and weight of these sensors. Optical sensors, especially fibre-optic sensors have been the subject of several recent reviews [116-120]. 

For detection of DNA fragments, Fe(phen)32+ was used as the electrochemi-cally active intercalation reagent. The constant background current from free Fe(phen)32+ decreased in the presence of the DNA-Fe(phen)32+ complexes. Therefore, this is an indirect amperometric detection method. It was found that a distance of 300 pm, instead of 600 pm, between the working electrode and reference electrode has produced less electrical interference (in the form of a sloping baseline), allowing the use of a separation voltage up to 1200 V (240 V/cm) [745]. 

Check to make sure that no air bubbles are in the pressure transducers. Add filters to remove electrical interference. 

Electrometer amplifier— An electronic amplifier with an extremely high -> input impedance (Rln > 1014 Q). The device allows measurements of electrical voltages (potentials) at practically zero current. Early devices employed specially designed and selected vacuum tubes (electrometer tubes) operated in a mode with very low grid current. The development of field effect transistors of various types allowed the application of solid-state devices. Electrometer amplifiers are employed in - pH meters (and generally in so-called pi meters, where I stands for ion), all types of instruments for po-tentiometric measurements and in the reference electrode input of -> potentiostats. Because of the high input impedance electrometer amplifiers are sensitive towards electric interferences, consequently some potentiostats have their -> reference electrode input circuitry (essentially an electrometer amplifier) mounted in a separate housing to be attached as close as possible to the reference electrode in order to minimize external interference. 

Care must be taken when designing cathodic protection systems in built-up areas as electrical interference from transmission lines or electrical rail systems may cause stray current corrosion at points in the structure close to the tramway or transmissions line [41]. 

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