Variable-inductance transducers

Such variable inductance transducers are available with strokes of 0.0025 to 0.5 m. The non-linearity of the element can range from 0.02 to 1 per cent with a sensitivity... 

An essential feature of the I.D.T. apparatus is the measurement of pressure at each end of the capillary system. The pressure at the outlet end is held constant, as it is connected to a reservoir of effectively constant hydrostatic head. The pressure measurements are made by all stainless steel variable inductance transducers (EMI model SE 1150/WG) energized by oscillator/demodulator units. The pressure transducer outputs are fed to a twin channel flat bed potentiometric recorder. The pressure measurements have a sensitivity better than 1 Nm" (0.1 mm H2O). 

Allard E M 1962 Sound and pressure signals obtained from a single intracardiac transducer IRE Trans. Bio-Med. Electron. BME-9 74-7 van Citters R L 1966 Mutual inductance transducers Methods in Medical Research vol XI, ed R F Rushmer (Chicago Year Book), pp 26-30 Reddy N P and Kesavan S K 1988 Linear variable differential transformers Encyclopedia of Medical Devices and Instrumentation ed J G Webster (New York Wiley) pp 1800-6... 

The electronic circuits used with variable capacitance transducers, are essentially the same as any other circuit used to measure capacitance. As with the inductance transducers, these circuits can take the form of a bridge circuit or specific circuits that measure capacitive reactance. One concern with capacitive sensors is that the sensor should be electrically shielded if there are electrically conductive objects in the vicinity of the sensor. Otherwise stray capacitances may affect the measurement. 

The third type transducer is very similar to the first type except the slug of a linear differentieJ. transformer or variable Inductance Is mounted on one diaphragm eind the coils of a differential transformer or inductance coil of a variable inductance is mounted on the other diaphragm. Differential pressure is then sensed by the relative movement between the coil and slug. 

Besides the strain gauge type transducer, other pressure transducers may employ variable capacitance, variable inductance, or piezoelectric crystal sensors to detect pressure changes. The low level output pressure transducer can be used in systems controlling flammable and other hazardous gases if the system has been designed such that the electronic power levels being used to excite the transducer remain very low. They can even be used in Class I, Division II areas if the proper intrinsic safety barriers are used in conjunction. Like the pressure gauge, the transducer may have a... 

Electrical Variables. Included here are those variables which are measured as the product of a process, as in the case of measuring die current and voltage of a generator, and also as part of an instrumentation system. Numerous transducers, of course, yield electrical signals that represent by inference some other variable quantity, such as a temperature or pressure. Variables in this class include electromotive force, electric current, resistance, conductance, inductance, capacitance, and impedance. 

The operation of proximity sensors can be based on a wide range of principles, including capacitance, induction, Hall and magnetic effects variable reluctance, linear variable differential transformer (LVDT), variable resistor mechanical and electromechanical limit switches optical, photoelectric, or fiber-optic sensors laser-based distance, dimension, or thickness sensors air gap sensors ultrasonic and displacement transducers. Their detection ranges vary from micrometers to meters, and their applications include the measurement of position, displacement, proximity, or operational limits in controlling moving components of valves and dampers. Either linear or angular position can be measured ... 

Another type of electrical pressure transducer is a variable-reluctance device. The deflections of a diaphragm of magnetic stainless steel are sensed by two inductance pickup coils. With ac-bridge circuitry, this transducer delivers a full-scale output of 40 mV per volt for a variety of ranges from 0 4 Torr (0- 0.08 PSIA) to 0- 3200 PSIA. 

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