Breaking contact

Figure 19.4 Rear view of a bulk oil circuit breaker assembly showing single-break contacts, self aligning cluster Isolating contacts, terminal bushing and arc control pots (Courtesy ...

Dry bulb sensors may be bi-metal strips, thermistors or refrigerant-filled phials or bellows responding to pressure differences caused by temperature change. These, in turn, provide an electrical or mechanical signal. The mechanical items are used to alter the value of potentiometers or make-or-break contacts. The signals are transmitted to amplifiers, which respond to the degree of error. An important feature is the proportional band of temperature over which the controls call for up to full plant capacity. 

Qnantized adhesion was observed by Hoh et al. [53] for a SisN4 tip breaking contact with a glass snrface in water, which had been NaOH adjusted to pH 8.5. As described at the beginning of Section IILA, a more accurate description of the measurement would be quantized displacement, which can be evaluated as quantized adhesion by multiplying the observed displacement by the lever stiffness. The authors speculate that their observations conld be explained either by the breaking of discrete numbers of hydrogen bonds between the tip and surface or by the breakdown of the continuum properties of water in close proximity to a solid surface. 

Charging by contact electrification is an active mechanism whenever dissimilar particles make and break contact with each other, or whenever they slide over a chute or an electrode. This charging mechanism is most frequently used to charge selectively and obtain an electrostatic separation of two species of dielectric materials as realized in a free fall electrostatic separator. 

Bimetallic Thermometers. These use two metals of different coefficients of thermal expansion that are bonded together their heating bends the device, and an electrical contact can then be made or broken. Thermometer coils that expand/contract with temperature and make or break contact with a mercury electrode are used in household thermostats and industrial control apparatus. 

Fuse, Liquid-Metal, Self-Healing. When mercury replaces the filament of an exploding-wire fuse, it. will break contact by vaporizing upon application of an overvoltage, then make contact by condensing when (he overload disappears. This happens within a heavy-walled capillary tube connecting two reservoirs (see sketch). Evaporation forces mercury from the capillary to break the. circuit Experimental quartz glass and pyrex tubes exhibit da-... 

Windblown particles have been observed to build up quite a hefty charge by contact electrification on insulated bare wire fences, and in general, on any conducting surface that is isolated from ground. Static electricity is also formed by make and break contact as you exit a vehicle or can be observed as static cling with various types of fabric. A harmless discharge to the door... 

After the electrochemical experiments were completed, M3 was raised to break contact with the electrolyte, the cell was... 

Why is our only child breaking contact with us a few years after leaving home ... 

Friction loss from sudden contraction of cross section. When the cross section of the conduit is suddenly reduced, the fluid stream cannot follow around the sharp corner and the stream breaks contact with the wall of the conduit. A jet is formed, which flows into the stagnant fluid in the smaller section. The jet first contracts and then expands to fill the smaller cross section, and downstream from the point of contraction the normal velocity distribution eventually is reestablished. The cross section of minimum area at which the jet changes from a contraction to an expansion is called the vena contracta. The flow pattern of a sndden contraction is shown in Fig. 5.14. Section CC is drawn at the vena contracta. Vortices appear as shown in the figure. 

Emersion of the electrode in transfer systems has relied on either the use of a completely volatile electrolyte (normally aqueous HF [17, 19]) whose residue adhering to the electrode can be pumped off, or a washing procedure in which the electrolyte is replaced by the (volatile) solvent [14]. In either case, it is necessary to consider what processes can occur as potential control is lost when the electrode breaks contact with the solution. The resistance measurements mentioned above suggest that no substantial changes occur provided that no faradaic processes are possible. Traces of oxygen in the ambient gas above the electrolyte can also cause oxidation of surface species and great care is essential to use purified gas when the surface species are susceptible. For example, sub-monolayer deposits of non-noble metallic atoms are readily oxidized and so are observable ex-situ with difficulty [42],... 

After 1444 cycles of making contact - breaking contact operations an inner atomic structure of the Co-Ge contact has altered. We suppose that a material (both Co and Ge) in a junction region has degenerated because of many mechanical and thermal processes. Thermal processes are induced by the electrical current during measurements. The main conductance plateau is shifted from 2G0 to 1.5G0. One can see conductance traces before and after the... 

The 225 kV was off-line and the loss of voltage led to the two diesels LHPE and LHPF starting without coupling diesel LHPE due to incorrect operation of the voltage regulator (fuse break contacts) and despite changeover to the standby regulator... 

It is evident from these results that two of the adhesion proeesses (making contact and breaking contact) can be observed in the atomie force microscope. The size of the contact spot can also be deteeted if some additional technique for sensing contact spot size is used, for example, eleetrieal contact or thermal contact. Thus the three stages of adhesion can be found in the AFM. It has become clear from sueh measurements that all materials adhere in this test, verifying the first law of adhesion. These results will be considered in more detail in Chapter 4. 

Figure 14.4. (a) Peeling Ihe ideal adhesion test, (b) Results for making and breaking contact. 

Small stick (to break contact between funnel and flask)... 

There was no spark when you made initial contact, only when you broke the contact. However, you might have caused the two pieces of metal to "bounce" (make and then break contact very fast) before settling down, while you were trying to push them together. In that case there would be a visible... 

A "fuse," as most readers know, protects against too much current flow by melting and thus breaking contact to the power source. It must be replaced after doing its protective job, while a "circuit breaker" (see index) can be reset after it has been "tripped" (operated to break contact), without replacing it. Sometimes a circuit breaker is an electromagnetic relay, and sometimes an SCR or Triac. 

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