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This paper describes the design of a simple non-contact-type pressure transducer using a Bourdon tube and a Hall sensor where the effect of atmospheric temperature is compensated. In this design, a pressure sensing Hall IC is fixed with the nonmagnetic aluminum casing of a Bourdon gauge in front of a tiny disc-type permanent magnet rigidly attached with the free tip of the Bourdon tube. With the increase of pressure of the fluid inside the Bourdon tube, the free end along with the magnet moves toward the Hall sensor, and the magnetic field intensity due to the magnet on the Hall sensor increases with an increase of pressure. Due to this magnetic field, the outputs of the Hall sensor and the transducer circuit consisting of a differential amplifier and an instrumentation amplifier increase with the increase of pressure of the fluid inside the Bourdon tube. The transducer circuit consists of a unity gain differential amplifier circuit where the output of a second identical temperature sensing Hall IC is subtracted from the pressure sensing Hall IC output in order to compensate the effect of ambient temperature in the proposed transducer. The theoretical equations describing the operation of the transducer are derived in this paper. The static characteristic curves of a prototype design of the transducer are determined experimentally. The experimental results are reported in this paper. The characteristics curves are found to follow the theoretical equations with good repeatability and are free from ambient temperature effect. [ABSTRACT FROM AUTHOR]

The conventional LVDT is generally used as displacement transducer but has some limitations such as small linear range, measurement errors due to stray capacitance effect, electromagnetic interference effect, and core loss effect. In this paper, a modified LVDT type displacement transducer has been proposed in order to overcome these limitations of conventional LVDT. The proposed LVDT will consist of only two identical coils instead of three coils of conventional LVDT. This design does not require any excitation coil. In this design, two identical coils wound on a former made of ferromagnetic material act as displacement sensing inductive coils with specially designed movable core. The design has been analyzed under three cases. It has been shown that the range of the displacement transducer is about 50% of the overall length of the sensor under two cases like conventional LVDT and is about 100% of the overall length of the sensor under the third case. So in this paper, a displacement transducer has been designed and tested experimentally considering only the third case with unlimited range equal to the entire length of the sensor. The transducer consists of an op-amp-based differential inductance measuring circuit and an output instrumentation amplifier. The performance equations of this sensor under three cases and of the transducer under third case are derived in the paper. The experimental results reported in the paper are found to follow the derived equations with very good linearity and repeatability. [ABSTRACT FROM AUTHOR]

Temperature measurement and its transmission to a remote receiver are very important in any process plant, and various types of thermometer circuits are used for this purpose. In this paper, a simple temperature measurement and transmission system of an electric heater operated water bath is designed and studied experimentally without using any real thermometer. In this technique, electric heater current is taken as a temperature measuring parameter since the steady-state temperature of electric heater operated water bath depends on heater current only if we ignore a small variation of atmospheric temperature. The mathematical relations describing the operation of the proposed temperature measurement and transmission system are determined in this paper. The characteristic curves of the prototype unit of the proposed temperature transmitter are derived experimentally and are reported in this paper. The curves are found to follow the mathematical relations derived in this paper. [ABSTRACT FROM PUBLISHER]

A non-contact capacitance type liquid-level transducer for a conducting liquid consists of a short circuited non-inductive coil wound on a uniform cylinder made of insulating material, such as glass, PVC, nylon, and teflon. The cylinder is connected with a storage tank through a metallic connector and the capacitance between upper short circuited end of the coil and metallic connector varies linearly with liquid level measured from datum level. The capacitance at datum level depends on atmospheric condition and the fringe effect of other conductors. So, the transducers require frequent recalibration depending on atmospheric and environmental conditions. In the present paper, this non-contact capacitive sensor has been further modified in order to minimize this defect of non-contact capacitive sensor. Furthermore, all the conventional capacitance type-level sensors are associated with a perpendicular plate capacitance between liquid and electrode, which varies with the length of the electrode. In this paper, the effect of this perpendicular capacitor on liquid level measured has been studied and its effect is minimized. The proposed modified transducer has been designed and developed and its theory of operation has been derived. The performance of the developed transducer has been experimentally studied and the experimental results are reported in the paper. A good linear performance characteristic of the transducer with very minimum parasitic capacitance effect has been observed. [ABSTRACT FROM PUBLISHER]