Inductors, variable

Variable a.c. voltage and frequency IGBT or thyristor converter (7) Inductor... 

Let us examine how one determines the values of the inductor and capacitor. Several assumptions have to be made at the beginning of the design process since several of the tank circuit s characteristics are variable within the application. The first is to assume a value for the Q of the tank circuit. In the application, the Q varies greatly with the amount of load placed on the output of the supply. So, a good value to start with is... 

In the pot-cores used in inductors (see Section 9.5.1) for LC filter circuits, the fields are low enough for /T and tan i)m to vary only gradually with the field and the ratio (tan <5m)//T is sensibly constant. These cores are designed with small gaps of variable width so that their effective permeability can be adjusted in accordance with Eq. (9.12). If /tr 3> 1 Eq. (9.12) can be expressed in complex form to take account of losses and rearranged to give... 

The probe uses a single-coil for 20 mm spinning samples at room temperature. There are no tuning elements in the probe -- rather the tuning is by a variable inductor at the end of a A./4 cable as described in the discussion of quarter wave cables in V.C.8. The transformer at the end of the second quarter wave cable matches the impedance between the tank circuit and the broadband preamplifier. The output... 

With variable inductors or capacitors of sufficient range, it is possible to make a multinuclear probe which can be converted from one frequency to another merely by changing coils wound on inserts. For single coil probes such inserts can be changed conveniently by modifying commercial rf connectors, for example, BNC, and attaching them to the ends of the inserts. 

We see that such a A./4 network is easier to implement at the lower frequencies where we already noted that such networks would be more useful. At the higher frequencies we get out of range of the traditional (multiturn) variable inductors, especially for small characteristic impedance Z. 

You can make a A/4 network from scratch with commercially available variable inductors and capacitors from sources... 

Smaller variable inductors can be made by modifying commercial multi-turn variable resistors. Instead of using resistive wires, copper or silver wires can be used in the resistor shell. Although we have never tried the modification ourselves, we have used inductors made this way commercially to special order. 

In order to simplify the physical construction, we have made a A/4 network as described in this section by modifying a commercial antenna tuner. Use the type containing a high voltage variable inductor and modify the capacitors so that you end up with two equal sections on the same shaft. (Some manufacturers will sell you the capacitor plates and spacers so that you can make up any size capacitor you wish, limited only by the shaft length and breakdown voltage.)... 

The inductance switch is an innovation that provides a control of the circuit inductances. In essence, it is a two-level, variable inductor that can be switched from one value to the other by means of a control current. 

Let the inductor current ii = fe be the first state variable xi and the current across the capacitor uc = e the second state variable X2- As there is a direct causal path from the capacitor C C to the inductor I L... 

In that case, the node with the potential Va is not connected to the voltage +E supply. As its capacitance Ca to ground is neglected, there is no current ia in phase-line a and Va = E. That is, Va does not switch between values +E and -E but retains the value +E. For the RL-load, phase line current ia = 0 entails = iLa which means that two of the three inductors become dependent. That is, the number of state variables is mode-dependent and decreases to two when both switches in a leg are off. In the fourth case, the two switches in leg a operate in a complementary fashion but phase line a is interrupted so that the two load currents iiLa are permanently equal. 

The association of an inductor with a capacitor allows the two snbvarieties of electrodynamical energy, inductive (electromagnetic) and capacitive (electric or electrostatic), to be stored in the same system. The two system constitutive properties, inductance and capacitance, are the supports for the storage of energy and they link the state variables according to the following relations ... 

Methods commonly used to increase the operating bandwidth of the cavity include minimizing added tuning capacitance. The ideal case would be to resonate the plate capacitance alone with a perfect inductor. Practical cavities, however, require either the addition of a variable capacitor or a variable inductor using... 

Variable impedance A capacitor, inductor, or resistor that is adjustable in value. 

A variable capacitor is constructed to allow a user to adjust its capacitance mechanically. For example, in a radio application, using a variable capacitor coupled with an inductor allows the capacitance to be manipulated to resonate... 

Ripe grapes contain an orthophenol oxygen oxidoreductase, also known as cresolase, catechol oxidase and tyrosinase. Its activity is extremely variable, depending on the grape variety and degree of ripeness. (Dubemet, 1974). Tyrosinase consists of a group of isoenzymes differing in inductor nature and catalyzed activities (Mayer and Harel, 1979). 

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