DC voltage

Measurement of the conductivity can be carried out to high precision with specially designed cells. In practice, tiiese cells are calibrated by first measuring the conductance of an accurately known standard, and then introducing the sample under study. Conductances are usually measured at about 1 kHz AC rather than with DC voltages in order to avoid complications arismg from electrolysis at anode and cathode [8]. 

Note that in mass spectrometry/mass spectrometry (MS/MS) applications, quadrupole and magnetic sectors can be used together advantageously. It is also worth noting that the quadrapole can be operated without the DC voltages. In this RF-only mode, no mass separation occurs, and these quadrapoles are used as ion transmission guides, described in Chapter 49. 

Linked scanning techniques by which fragmentation reactions can be examined are particularly easy to apply with QqQ instmments. The ease with which RF and DC voltages can be changed rapidly means that the scanning can be done very quickly. Three common and popular types of linked scan are briefly described here and serve to illustrate its principles. 

Amplifier bandwidth. The range of signal frequencies over which an amplifier is capable of undistorted or unattenuated transmission. An operational amplifier should transmit DC voltage accurately the upper (bandwidth) limit is defined as the 3-dB point (attenuation factor of two). Because bandwidth can vary with gain, the product of gain x bandwidth can be a more useful parameter. 

Operational amplifier. A linear, high-gain DC voltage or current amplifier with high input impedance, low output impedance, and the capability of producing a bipolar output from a bipolar input. 

DC voltage to fixed frequency and voltage supply inverter... 

As described in Section 14.2.2.5, a nonsymmetric diode overvoltage arrester creates a dc voltage in operation... 

Insulating units are installed in pipelines to limit cathodic protection or to separate different materials in a mixed installation. If the pipelines are transporting electrolytes, anodic interference can occur on the pipe interior if a dc voltage, Af/, exists at the insulator of length, L. The current flowing through the insulating unit by anodic polarization of the internal wall of the pipe comes to ... 

The output filter converts the rectified rectangular ac waveform into the dc output. Forward-mode converters have a two-pole L-C filter which produces the dc average of the rectified rectangular waveform. Boost-mode converters have a single-pole, capacitive input filter which produces a dc voltage which is the peak voltage of the rectified waveform. Both are reactive impedance filters and exliibit very little loss. 

Active power factor correction circuits can take the form of nontransformer isolated switching power supply topologies, such as buck, boost, and buck/boost. The buck topology in Figure C-3 produces an output dc voltage lower than found at its input, whenever the PFC stage is operating (F > Fom). In other... 

An example of a contact mode of electromodulation would be the semiconduc-tor-insulator-metal configuration, which consists of a semiconductor, about 200 A of an insulator like AI2O3, and a semitransparent metal (about 50 A of Ni or Au). Modulating (ac) and bias (dc) voltages are applied between the front semitransparent metal and a contact on the back of the sample. To employ this mode the sample must be conducting. 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

Electrical management, or power conditioning, of fuel cell output is often essential because the fuel cell voltage is always dc and may not be at a suitable level. For stationai y applications, an inverter is needed for conversion to ac, while in cases where dc voltage is acceptable, a dc-dc converter maybe needed to adjust to the load voltage. In electric vehicles, for example, a combination of dc-dc conversion followed by inversion may be necessary to interface the fuel cell stack to a, 100 V ac motor. 

The electric voltage also has an influence on the film thickness in TFL. Shen et al. [50] used hexadecane with the addition of cholesteryl LCs in chemically pure as the lubricant to check the variation of its film thickness by applying an external DC voltage. With the technique of ROII [3,4,51], the effects of LCs polarity and concentration on film thickness and the effects of lubricant molecules on a film-forming mechanism were investigated by them. 

Fig. 27—Influence of dc voltage on thickness [50]. Load 0.174 GPa, Rolling speed 68 mm s . ...

A ceramic block such as alumina is generally used because of its chemical inertness and the orifice is bored or drilled to precise dimensions. The block is placed so that two (2) chambers result. Then if a DC voltage is applied across the electrodes, a current will flow onty through the orifice, and an effective resistance arises which depends upon the voltage applied and the size (volume of the conducting solution) of the orifice. Particles are added to one side of the two chambers created by the ceramic block, and the suspension is pumped through to the other side. There will be an electrical pulse as each particle passes through the orifice. 

Appropriate use of RF and DC voltages means that some ions can be selectively retained and product ions generated. Some of these ions can then be selected and their product ions generated. In this manner, a fragmentation chain can be established. The ion trap is a typical tandem-in-time mass spectrometer, in which precursor and product ions are created and analysed in the same physical space ionisation and ion analysis, on the other hand, take place at different times ( MS/MS in time )- The operation can be repeated several times, making it possible to perform MS11. Ion trap mass spectrometry thus consists of ... 

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