Rheostats

Control of wound-rotor motors, as discussed, can be effected by adjusting the external secondaiy (rotor) resistance either in steps or continuously by liquid rheostat (this method is seldom used). Commonly when secondaiy resistance is varied to adjust speed or torque or to control acceleration, multiple resistance steps are used. These steps may be switched manually (typically a drum switch) or electrically by contac tor. 

When external secondaiy resistance is used for speed adjustment, the resistors may be either infinitely adjustable (e.g., hquid rheostats) or adjustable in steps (if fine speed adjustment is not required). 

Manual rheostats can be used in series with the motor armature for the current-limiting func tion. If the rheostat has ample thermal capacity, it can also Be usedto vaiy speed. If this system is used, interlocks should be included to prevent closing of the contactor unless maximum resistance is in the circuit. 

Flcctronicdianiciil conlactois and motor starters, including rheostatic rotor starters... 

DOL in a squirrel cage or rheostat in a slip-ring motor... 

A slide-wire rheostat of 2-ampere capacity wound on a hollow enameled iron tube will carry the required current if a stream of cooling water is passed through the tube. 

Vorsatz-linse, /, lens placed in front, -papier, n. book lining paper, fiyleaf paper, vorschalten, v.t. (Elec.) introduce (into a circuit), cut in, connect, connect in series. Vorschaltwiderstand, m. (Eke.) (rheostatic) resistance, series resistance, vorschkrfen, v.t. sharpen (or strengthen) pre viously. 

Motor field rheostat.Motor field discharge resistor. . . ... 

PT, representing the actual rheostat through which nucleus modulate sensitivity/resistance to the external stimuh. Some of these proteins, such as Bax and Bak increase the conductivity ofPT (Narita et al, 1998), thereby facihtating apoptosis, whereas others (such as Bcl-2 and Bc1-Xl) inhihit cell death hy hampering the opening of PT (Shimizu et al, 1998). 

A signaling rheostat has been proposed where the relative level of SIP and ceramide determines cellular fate. This was based on the observation that ceramide, Fas and TNFa-mediated programmed cell death is suppressed by the addition of SIP (Cuvillier et al, 1996). The model assumes that ceramide is a physiological mediator of apoptosis although this is subject to controversy (Hofmann and Dixit, 1998 Kolesnick and Hannun, 1999). Indeed, sphingosine is also implicated as an apoptotic agent (see above). 

The mechanism(s) underlying this protective default are only partially understood, but it appears that this immunological rheostat is set via the activity of local dendritic cell (DC) subsets [7]. Immature DC, such as those found within the respiratory... 

Heating equipment (furnaces and drying cabinets) often contains rheostats that can be used to roughly maintain the required temperature. 

The experiment is prepared by one student and demonstrated to the class. Assemble a device for electrolysis (see Fig. 52). Include rheostat 1 for 10-20 Q and ammeter 2 for 2-3 A in the circuit. Pour a saturated sodium chloride solution coloured with a neutral litmus solution into U-tube 3. Immerse carbon electrodes 4 (by one-third) into the solution. Connect the ends of the conductors to a direct-current source (an accumulator) and pass a current of about 2 A through the solution. What is observed Explain the change in the colour of the indicator solution. Write the equations of the reactions proceeding at the electrodes. 

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