Touch voltage curve

Electric shock is normally caused either by touching a conductive part that is normally live, or by touching an exposed conductive part made live by a fault. The touch voltage curve in Fig. 6.8 shows that a person in contact with 230 V must be released from this danger in 40 ms if harmful effects are to be avoided. Similarly, a person in contact with 400V must be released in 15 ms to avoid being harmed. 

Interactions between a spherical colloid and a wall can be measured by bringing probe and substrate together and monitoring the cantilever deflection as a function of the interparticle distance. The photodetector voltage versus piezo position curve can be converted into a force-distance curve. The force acting on the cantilever follows from the deflection of the cantilever and its known spring constant. The zero force is defined by the deflection of the cantilever as the colloidal probe is far from the surface of the substrate. To obtain the force-distance dependence on an absolute scale the zero distance, i.e., where the colloid touches the wall, has to be determined. Commonly, the zero distance is obtained from the force curve itself and not through an independent method [68]. 

A phase domain diagram of the nonsaturated Class C amplifier is shown in Fig. 7.55 along with a representative schematic diagram. The term nonsaturated means that the active device is not driven to the point where the collector-emitter voltage is at the lowest possible value. The curve of V 0) in Fig. 7.55(a) does not quite touch the zero line. Another way of saying this is that the transistor is always active or never conducts like a switch. It is active in the same way as Classes A and B, and because of this similarity, it may be modeled in the same way, that is, as a dependent current source. 

A good way to visualize the hazards of touch potentials is with a graph of the voltage at points near the fault measured with respect to infinite earth (as shown in Figure 27.2). As illustrated, the most hazardous conditions exist when the voltage gradient is high. It should be noted, however, that this curve is only a representative example the actual shape depends on many factors, such as, for example, the resistivity of the earth and any buried conductors in the area. 

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