Electric circuit meter base

Exciting developments based on electromagnetic induction raced along from that time, giving us the sophisticated products our everyday lives depend on. During most of the period productive uses for eddy current technology were few and few people believed in it as a usefiil tool eddy currents caused power loss in electrical circuits and, due to the skin effect, currents flowed only in the outer surfaces of conductors when the user had paid for all the copper in the cable. The speedometer and the familiar household power meter are examples of everyday uses that we may tend to forget about. The brakes on some models of exercise bicycle are based on the same principle. 

Several manufacturers make explosimeters or combustible gas indicators. Although they differ somewhat in design and operating features, their operation is based on the fact that a measurable amount of heat is released when a combustible gas or vapor is burned. Most meters contain a battery-operated electrical circuit known as a Wheatstone bridge, which is balanced by means of controls on the outside of the instrument. 

Figure 18-1 A pH meter gives the pH of the solution directly. When the electrode is dipped into a solution, the meter displays the pH. The pH meter is based on the glass electrode. This sensing device generates a voltage that is proportional to the pH of the solution in which the electrode is placed. The instrument has an electrical circuit to amplify the voltage from the electrode and a meter that relates the voltage to the pH of the solution. Before being used, a pH meter must be calibrated with a series of solutions of known pH.

When the current is measured in an electric circuit, the observation is the flow of charge for a period of time. The base unit of current, the ampere (A), is a combined unit defined as one coulomb per second 1 A = 1 C s . Devices called amp-meters (or ammeters) measure current. If a known current passes through a circuit for a known time, the charge can be easily calculated. 

A sensor that is especially interesting and instructive is made from a quartz crystal microbalance, or QCM. This device is based on the piezoelectric characteristics of quartz. When quartz is mechanically deformed, an electrical potential difference develops across its surface. Furthermore, when a voltage is impressed across the faces of a quartz crystal, the crystal deforms., A crystal connected in an appropriate electrical circuit oscillates at a frequency that is characteristic of the mass and shape of the crystal and that is amazingly constant as long as the mass of the crystal is constant. This property of some crystalline materials is called the piezoelectric effect and forms the basis for the QCM. Moreover, the characteristic constant frequency of the quartz crystal is the basis for modern high-precision clocks, time bases, counters, timers, and frequency meters, which in turn have led to many highly accurate and precise analyTical instrumental svsiems. 

Instruments based on the contact principle can further be divided into two classes mechanical thermometers and electrical thermometers. Mechanical thermometers are based on the thermal expansion of a gas, a liquid, or a solid material. They are simple, robust, and do not normally require power to operate. Electrical resistance thermometers utilize the connection between the electrical resistance and the sensor temperature. Thermocouples are based on the phenomenon, where a temperature-dependent voltage is created in a circuit of two different metals. Semiconductor thermometers have a diode or transistor probe, or a more advanced integrated circuit, where the voltage of the semiconductor junctions is temperature dependent. All electrical meters are easy to incorporate with modern data acquisition systems. A summary of contact thermometer properties is shown in Table 12.3. 

Nanotechnology involves the development of techniques to buUd machines from atoms and molecules. The name comes from nanometer, which is one-billionth of a meter. It involves the development of new electrical devices that depend on quantum effects that arise when the dimension of a structure is only a few atoms across. Because the techniques best suited for fabricating devices on the submicron scale originated in semiconductor processing technology for the production of integrated circuits, nanoscale devices are aU based on semiconductors. 

The largest market areas for PPS injection molding compounds are the electrical/electronic area and the mechanical area. Typical parts involved in the electrical/electronic area include coil forms, sockets, bolt yokes, motor brush holders, connectors, switches, integrated circuit and capacitor encapsulations, electronic watch bases, and relay components. In the mechanical area the following applications are important pump housings, impeller diffusers, pump vanes, end plates, valve components, heat shield, oil well valves, oil well sucker rod guides, and pH meter components. 

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