Capacitive Displacement Transducer Research Articles

Disc Brake Squeal – An Experimental Approach

The phenomenon of squeal in disc brakes has been, and still is, a problem for the automotive industry. Extensive research has been done in an attempt to understand the mechanisms that cause it and in developing design procedures to reduce it to make vehicles more comfortable. Part of the research programme at Liverpool University has been the verification of finite element models of disc brakes using an experimental brake rig. Tests have been carried out on a Rover solid disc, a Mercedes solid disc and a Mercedes vented disc. The test rig houses the front knuckle in a rigid support, and the drive is to the wheel studs on the disc. There is no wheel in place. The brake calliper is mounted in the normal fashion to the knuckle. A 42 kW motor drives the disc against the action of the brake. A fixed array of 12 non-contact capacitance displacement transducers is arranged in an arc near the outer radius of the disc. These measure the axial displacement of the disc while it is rotating. During a squeal event, the measurement system records these displacements along with values of disc temperature, rotation speed, shaft torque and hydraulic pressure at a logging rate of 56 kHz. From this high definition time domain data, small time samples can be analysed using a least squares technique to determine the nature of the vibration mode at a given squeal frequency. The analysis shows that the vibration of the brake disc can take several forms. With different conditions, even on the same disc, the vibration mode can be a forward travelling wave, a backward travelling wave or a standing wave (relative to the calliper). This paper is in two parts. The first part describes the test rig and the testing procedures; the second part explains how the analysis is performed and shows some of the results from typical squeal tests.

623 Measurement of Die Deformation in Cold Forging by the Combination of Improved Capacitive Displacement Transducer and Strain Gauge

623 Measurement of Die Deformation in Cold Forging by the Combination of Improved Capacitive Displacement Transducer and Strain Gauge

The thin dielectric film capacitive displacement transducer to nanometer

The paper deals with the new capacitive transducer for small displacements (from a few micrometers to a few millimeters), denoted the Thin Dielectric Film Capacitive Displacement Transducer (TFCDT). This principle is based on the properties of a very thin dielectric film between the faced electrodes. The film may be applied by a dielectric, such as alumina. The transducers are designed in a differential form. Their electrodes have to be constructed by either photo-chemical- or laser etching. A few implementation prototypes (IPs) of the TFCDT have been designed and constructed. The first of the IPs (TO IF) has been constructed in two forms, for linear and rotary displacement by a dielectric spray varnish with thickness of about 2 /spl mu/m. The second of the IPs (II/spl deg/IP) has been designed and constructed only in the form for linear displacement, with different techniques for achieving lower thickness of the alumina dielectric film. The test results on both the I/spl deg/IP and II/spl deg/IP are critically analyzed. The sensitivity and linearity obtained, respectively, are about: 5 pF/mm, 0.6 pF//spl deg/, 25/spl times/10/sup -6/, 2 nF/mm, and 7 nm//spl mu/V, nearly in the absence of nonlinearities. A feature for improving the sensitivity and linearity, respectively, to about 40 /spl mu/V/nm and to a few/spl times/10/sup -8/ is also illustrated. A variable absolute scale of capacitance and capacitive voltage divider based on the TFCDT is also proposed.

Cardiokymograph system with a capacitance transducer and its preliminary application in the measurement of heart wall movement.

A novel cardiokymograph system is introduced. The new system features a capacitance transducer with increased sensitivity and can be used in multichannel measurements. The novelty of this technique is the injection of a current into the patient coupled with the use of a capacitive displacement transducer and the possibility of multichannel monitoring. It provides for the possibility of removing breath noise when some signal processing technique, such as adaptive filtering, is used. Further investigation is needed to demonstrate clinical significance and pathologies.

光による軸の回転精度測定法の研究 測定原理ならびに測定感度に関する考察

The measurement of errors in the axis of rotation is of growing interest, because spindle is the most important part of ultra-precision machine tool and precision measuring instrument. In most of the measuring methods for precision spindle, capacitive type displacement transducers are used to measure relative displacement between spindle and transducers. However, the electrical noise due to NC controller or spindle motor affect accuracy of these measuring methods. In an attempt to reduce electrical noise and to increase the accuracy, an optical spindle error analyzer has been developed. At first, principle of the measuring method and optical system layout are described in detail. Then, the result of the consideration on measuring sensitivity is shown.

Concepts and focus point for intelligent sensor systems

This paper discusses the state-of-the-art and current trends in the design of intelligent low-cost high-performance sensor systems. In these systems the functions of the sensors, actuators, analog interfacing circuits and microcontrollers are merged in overall designs which have been implemented, where technology allows, on common substrates. Important properties which can act as focus points for an intelligent design are: adaptability, accuracy, dynamic range, speed, power consumption, reliability and costs. The functions of A/D converters are re-evaluated and novel conversion methods presented. Some important aspects of data processing and data communication are discussed. Examples of intelligent sensor systems are given in two areas: smart temperature sensors which can detect the presence of micro-organisms in food products by sensing the temperature rise of the products with a resolution of 5 mK, and capacitive displacement transducers which can accurately sense position, speed and acceleration by measuring the (trans)capacitances in multi-electrode structures.

A capacitance displacement transducer with large dynamic range, good linearity and frequency read-out

The design of a novel capacitance displacement transducer is described. A voltage-to-frequency converter is used as a voltage supply to a resonant series LC circuit. The in-phase component of the voltage across the capacitor is detected using a phase-sensitive detector and the output is fed back to the frequency-to-voltage converter so that resonance is maintained as the capacitance varies. The capacitance is then read out in terms of frequency by a computer. The system is simple, cheap and robust. We have achieved a dynamic range of three decades from 10 pF, frequency read-out resolution of 1 ppm and linearity of 0.2%.

Microrheology of high‐polymer solutions

AbstractA new surface force apparatus is used for investigating the viscoelastic properties of high‐polymer solutions or polymer melts confined between two solid surfaces. We describe the experimental setup and discuss how to obtain the rheological behavior of the liquid from the transfer function given by two capacitance displacement transducers. In particular, we point out that for a distance between the surfaces enclosing a thin film below some thousands of Angströms, the elastic deformation of the solids is no longer negligible. Experiments conducted on a semidilute solution of polybutadiene show the applicability of the device for study of the dynamic properties of thin‐film polymers.

A new microscope for semiconductor luminescence studies

A confocal scanning optical microscope is integrated with a helium cryostat to provide submicron spatial resolution of a specimen immersed in helium. Using gaseous or superfluid liquid helium, specimen temperature can be controlled from 300 to 2 K. Monochromatic illumination is provided and luminescence is analysed by conventional means. The specimen is scanned mechanically and its position relative to the focal point of the optical system is continously monitored by a capacitance displacement transducer and an optical system that senses light reflected from the specimen surface.

Noise analysis for the triaxial capacitive displacement transducer

A computer simulation and experimental study of electric noise in the triaxial capacitance displacement transducer is presented. When combined with a measurement instrument, the simulation and study lead to an optimal design range for the value of the reference capacitor of the transducer. The range is defined in terms of the decrease in noise, relative to the increase in capacitance. A SPICE program is used to predict the noise characteristics of the triaxial displacement transducer. It is found that the signal-to-noise ratio improves as the reference capacitance of the device is increased, but also that the rate of improvement decreases with an increase in capacitance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Study of brittle fracture by acoustic emission from indentation cracks

This paper describes a novel approach for investigating the fracture of brittle solids by combining a theory of acoustic emission (AE) with the Dugdale–Barenblatt model. An example is provided with indentation-produced, half-penny-shaped cracks that were generated by pressing a Vickers indenter onto the surface of a glass plate and that produced AE signals. These were detected using four capacitive displacement transducers, one at epicenter and the other three at off-epicentral positions. Assuming that a mode I type of crack was generated and using indentation fracture mechanics, a mode I stress intensity factor KIc=7.44×105 N/m3/2 was obtained. Both dipole strength and source-time function associated with crack formation were determined from the AE theory. Assuming that an effective gauge length can be interpreted equal to a dipole linkage distance and using the Dugdale–Barenblatt model for the fracture of brittle solids, it is shown that all the other important parameters on crack formation can be determined. Included are the critical rupture stress σc=8.94 GPa, the crack tip opening displacement of 1.62 nm, the effective microstructural gauge length equal to 13.2 nm, and the time-dependent crack velocity as a function of a crack front radius.

Error computation for capacitive displacement transducers using nonlinear bridge circuits

Error computation for capacitive displacement transducers using nonlinear bridge circuits

Analysis of the performance of the capacitive displacement transducer

An output signal from the capacitive displacement transducer has been mathematically modeled. Interest is focused on the importance of the spectral content of the signal in determining transducer performance. It has been shown that the phase-error due to the space harmonics of the capacitance between the receiving and transmitting electrodes always exhibits a ripple with the spatial frequency equal to the number of the transmitting electrodes. An analysis of the mathematical model suggests general rules of mechanical and electrical design that are necessary in order to create effective and viable devices with reduced measurement errors. In particular, a variety of the staircase functions with rapidly decreasing Fourier components can be applied as the driving supply. Another alternative is to combine a specially formed driving supply with low-pass filtering in the time domain. Experimental results for three different (four-, six-, and eight-phase) transducer systems confirm the validity of the model. >

Capacitive displacement transducer

A capacitive displacement transducer for measuring relative displacement between two points or objects is disclosed as including a driven element connected to a source of input electrical signals, a receptor element connected to an electrical output signal circuit means, and two shield elements mounted between the driven and receptor elements for relative movement with respect to each other. One of the shield elements mechanically responds to one of the objects and the other shield element mechanically responds to the other object and any resulting relative movement between the shield elements changes the capacitive coupling between the driven and receptor elements to provide an electrical output signal proportional to this movement and the displacement between said objects.

Frequenzproportionaler kapazitiver Längenaufnehmer / Capacitive displacement transducer with linear frequency output

Article Frequenzproportionaler kapazitiver Längenaufnehmer / Capacitive displacement transducer with linear frequency output was published on December 1, 1986 in the journal tm - Technisches Messen (volume 53, issue JG).

The effect of intermittent forces on eruption of the rabbit incisor.

Rabbits were prepared so that a variable capacitance displacement transducer (VCDT) could be used to monitor the eruptive movements of a previously-amputated lower incisor, and a strain gauge transducer mounted on a relay-controlled plate was used to place precisely controlled intermittent forces opposing the erupting tooth. Forces of one or three g were applied under time conditions of one second on, nine seconds off (1:9); one second on, three seconds off (1:3); and one second on, one second off (1:1). The data indicate that with force present for 10% of the time (1:9), there was little or no effect on eruption rate. In contrast, 50% time (1:1) produced essentially the same intrusive effect as continuous force, and 25% time (1:3) gave an intermediate response. The data are consistent with the hypothesis that force duration is more important than force magnitude for the vertical equilibrium, as is the case for facio-lingual equilibrium.

The mobility of the lathyritic rabbit mandibular incisor in response to axially-directed extrusive loads

Axially-directed extrusive loads of 0.01-0.1N were applied to the lathyritic mandibular incisors of 12 rabbits. Tooth position was monitored continuously with a variable capacitance displacement transducer. Compared with pair-fed controls, lathyritic teeth showed markedly reduced resistance to extrusive loading, indicating that the periodontal collagen has a rôle in supporting the tooth. The pattern of tooth mobility, however, was little affected. The results may have implications for the eruptive mechanism. That eruption rates can appear unchanged by lathyrogens might not preclude an effect of the drug upon the eruptive force, assuming that there is a concomitant decrease in the resistance of the periodontal tissues to eruption. The teeth of rabbits in the pair-fed control group showed increased resistance to extrusive loading compared with animals fed ad libitum, indicating that changes in food and water intake may also influence the mechanical properties of the periodontium.

Continuous monitoring of the position of the ferret mandibular canine tooth to enable comparisons with the continuously-growing rabbit incisor

A variable capacitance displacement transducer, previously employed for continuously monitoring movements of the rabbit mandibular incisor, was modified for use with the ferret mandibular canine. Comparing this tooth of limited growth with the tooth of continuous growth, similarities were seen in the reactions to extrusive loads and the responses at death. For the tooth of limited growth, however, less creep was seen with extrusive loading and hexamethonium did not produce changes in tooth position.

The effects of continuous axially-directed intrusive loads on the erupting rabbit mandibular incisor

A cantilever beam strain-gauge transducer was used to apply continuous light intrusive loads (0.2–0.4 and 2.5 g) to unimpeded mandibular incisors. Tooth position was continuously monitored using a variable capacitance displacement transducer. After 4 days of unimpeded eruption, the animals were divided into three experimental groups: no axial loading (6 rabbits); 0.2–0.4 g of axial loading (3 rabbits); 2.5 g of axial loading (3 rabbits). During a 4-h period, light forces (0.2–0.4 g) slowed eruption to a stop, whereas a heavier force (2.5g) intruded the teeth. The data support Burn-Murdoch's (1981) ( Archs oral Biol. 26, 939–943) contention that the eruptive force of unimpeded continuously-erupting incisors is significantly less than previously thought.

Capacitive transducer for accurate displacement control

The underlying theory, design, and operation are presented for an interdigitated capacitive displacement transducer supported on an air-bearing stage. This device provides a purely electrical means of displacement measurement and offers the possibility of being closely matched to the substrate against thermal perturbations. Tests on a prototype system show the basic capacitive transducer to have a sensitivity of 2.6 mV/μm and a position uncertainty of 4 nm set by thermal noise.