Transmitters, electric transducer

Among the various techniques of measurement one may be indicated as the most versatile the immersion technique (see Hartmann and Jarzynski, 1974 Hartmann, 1980). In this method acoustic waves are generated and received by two piezo-electric transducers, one acting as transmitter, the other as receiver the transducer material is... 

Figure 7-16 indicates several key control loops (a) The pressure of the core system is controlled from sensed pressure by the proportioning of power to the pressurizer electric heaters the blanket pressure is similarly controlled by a core-to-blanket differential-pressure signal. (b) The liquid levels in the pressurizers are controlled from sensed levels by pneumatic control of the letdown valves. Pneumatic control actions are derived from transducers which receive signals from electric transmitters. Electric interlock control of the pneumatic signals to final control elements is achieved by the use of solenoid-actuated pilot valves. 

Selective ion receptors represent basic units for ionic transmitters or detectors selective ion carriers correspond to ionic transducers. These units may be fitted with triggers and switches sensitive to external physical (light, electricity, heat, pressure) or chemical (other binding species, regulating sites) stimuli for connection and activation. 

Transducers in the device being tested convert the variable being measured into an electrical signal that subsequently is used to modulate the carrier of an RF transmitter. The signal is received, amplified, and demodulated on the ground, and recorded on magnetic type or on an oscillograph for subsequent analysis... 

A differential pressure (D/P) transmitter which consists of a diaphragm with the high pressure (H/P) and low pressure (L/P) inputs on opposite sides. As the differential pressure changes, the diaphragm will move. The transducer changes this mechanical motion into an electrical signal. 

Most transducers converting chemical concentration into an electrical signal have a nonlinear response for example, electrode potential and optical transmission are not directly proportional to concentration. In general, this nonlinearity is easily and simply corrected in equilibrium analytical measurements. However, it is considerably more difficult to instrumentally correct the response-versus-concentration function in reaction-rate methods, and often the correction itself can introduce significant errors in the analytical results. For example, the simple nonlinear feedback elements employed in log-response operational-amplifier circuits are not sufficiently accurate in transforming transmittance into absorbance to be used for many analytical purposes. 

Several terms for pressure measuring devices are used interchangeably including transmitters, transducers, gauges, sensors, and manometers. More precisely, a gauge is a self-contained device that converts a force from the process to a mechanical motion of needle or other type of pointer. A manometer is a term reserved for an instrument that measures the hydrostatic head of a liquid and generally operates near atmospheric pressure. A transducer or transmitter combines the sensor with a power supply and a converter— generally mechanical-to-electrical or mechanical-to-pneumatic. The sensor... 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

In this method, acoustic waves are generated by a piezoelectric transducer, which converts an oscillating electric field to a mechanical oscillation. Detection of acoustic waves that have traveled through a polymer specimen is done with the same type of transducer. Depending on its use, a transducer is called a transmitting transducer (transmitter) or receiving transducer (receiver). Common transducer materials are quartz and various polycrystalline ceramics, such as lead zirconate titanate (PZT), polarized in a strong electrostatic field. 

Final control elements are typically automated valves however, motors or other electrical devices can be used. The final control element is the last link in the modern control loop and is the device that actually makes the change in the process. Automatic valves open or close to regulate the process. Control loops usually have (1) a sensing device, (2) a transmitter, (3) a controller, (4) a transducer, and (5) an automatic valve. Automatic valves can be controlled from remote locations, making them invaluable in modern processing. 

A Figure 5 Box diagram of an absorbance-transmittance spectrophotometer (top) and an emission spectrometer (bottom). Shared components are monochromators (typically gradrtgs) and detectors (transducers) that convert photons into electrons and electrical signals. 

Adjacent to the above-cited control valves and primary sensors, and at other strategic points, there may be installed in a cabinet or on a chassis, such items as transducers, transmitters, controllers, indicators, push buttons, switches, isolating valves, cable terminal blocks, and so forth, with their associated interconnections, incoming electric and pneumatic power supplies, and connections back to the control room. These need close supervision during installation and a programme of inspection and tests to be defined, implemented and recorded. 

FIGURE 7 Sketch of an electrostatic transducer. The two electrical terminals are connected to a polarizing voltage and also to either a source of modulation (case of a transmitter) or to a high impedance amplifier (case of a microphone). 

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