Ferry N. Toth

A low-cost, smart capacitive position sensor

A high-performance, low-cost, capacitive position-measuring system is described. By using a highly linear oscillator, shielding and a three-signal approach, most of the errors are eliminated. The accuracy amounts to 1 mu m over a 1 mm range. Since the output of the oscillator can directly be connected to a microcontroller, an A/D converter is not needed. >

Ultra-linear, low-cost measurement system for multi-electrode pF-range capacitors

An extremely accurate capacitance-measurement system has been developed. The system consists of a discrete capacitance-dependent oscillator and a microcontroller. It is suited to measure multi-electrode capacitors, with capacitances up to 2 pF. These can be measured with 100 ppm accuracy with respect to a reference capacitor. The resolution amounts to 50 aF with a 300 ms total measurement time

A very accurate measurement system for multielectrode capacitive sensors

A very accurate capacitance-measurement system consisting of a discrete capacitance-dependent oscillator and a microcontroller has been developed. It can measure multielectrode capacitors with capacitances up to 2 pF, with an accuracy of 100 ppm with respect to a reference capacitor. The resolution amounts to 50 aF with a total measurement time of 300 ms.

Low-cost CMOS interface for capacitive sensors and its application in a capacitive angular encoder

A low-cost CMOS integrated interface for capacitivesensors is presented. The interface is composed of two separatechips: a capacitance-controlled oscillator and a selector, whichresult in a structure that is able to measure several capacitancesaccurately and has a microcontroller-compatible output. In thisinterface, even large parasitic capacitances of up to 3 nF betweenthe terminals of the capacitor to be measured and ground areallowed. Prototypes of the interface chips have been fabricatedin a 0.7-µm CMOS process. The frequency of theoscillator amounts to 90 kHz. For the capacitance measurement,the interface has a resolution of 11.3 ppm and a nonlinearityof 300 ppm over a measurement range of 2 pF. In this paper, alsothe application of the interface in an accurate capacitive angularencoder is discussed.

Non-invasive detection of micro-organisms using smart temperature sensors

Abstract This paper describes a new non-destructive way of testing for the presence of micro-organisms in sterilized packaged milk products by measuring their heat production. With a properly designed calorimeter and smart signal processing, the small heat production of the micro-organisms can be reliably detected. A prototype capable of handling 100 cartons of milk, implemented with the novel smart temperature sensors, has been fabricated and tested. These tests show that a relatively small heat production of micro-organisms creating a temperature rise of 5 mK can be detected simply and reliably.

A low-cost capacitive personnel detector with fuzzy logic position estimation

Two low-cost capacitive personal detectors have been realized. One is suitable to be used as an entrance counter since it can count passing persons as well as their direction. The other can determine up to 3 persons as well as estimating their position using fuzzy logic.

A low-cost, accurate and fast capacitive displacement sensor with microcontroller interfacing

A high-performance, capacitive displacement measuring system is described. Using a very linear oscillator, shielding and a three-signal approach, most of the errors are eliminated. The accuracy amounts to 1 mu m over a 1-mm range. Since the output of the oscillator can be directly connected to a microcontroller, an analog-to-digital (A/D) converter is not needed. The system was tested in a fully automated setup, using an electrical XY table, the described sensor and a personal computer. Nonlinearity, long-term stability, and repeatability were verified.<<ETX>>

Integrated interfaces for low-cost multiple-sensor systems

The paper reviews the architecture and design of low-cost high-performance sensor systems. These systems consist of a number of multiplexed sensor elements, sensor-specific front-ends, modifiers and microcontroller or digital signal processors (DSPs). Important properties that act as focus points for the system design are: adaptability, accuracy, dynamic range, speed, power consumption, reliability and costs. To enable low-cost design and implementation, a universal set-up, using universal components, is used. Universal sensor interfaces with front-ends for resistive, capacitive, resistive-bridge sensing elements, as well as voltage-, current-and charge-generating sensing elements are discussed. The analog sensor signals are converted to analog signals in the time domain using period-modulated oscillators. The A/D conversion of the time-domain signal can be implemented in the microcontroller or DSP. It is shown that, also in this case, the principles of the sigma-delta converters can be applied. The paper shows that in a systematic overall design approach it is even possible to reduce many of the physical nonidealities of the sensor elements. As an example, the paper deals with the design problems of reliable, high-performance low-cost capacitive sensors. The problems and their solutions of both the physical and the electrical-signal processing are discussed. The examples consider the application of capacitive sensors in position detectors, liquid-level detectors and personnel detectors.

A low-cost, stable reference capacitor for capacitive sensor systems

A low-cost reference capacitor has been developed for capacitive sensor systems. The capacitance has been constructed using low-cost material. Over a temperature range from -25 to +75/spl deg/C the temperature coefficient is less than 18 ppm//spl deg/C.

A low-cost, highly stable reference capacitor for capacitive sensor systems

A low-cost reference capacitor has been developed for capacitive sensor systems. The capacitance has been constructed using low-cost material. Over a temperature range from -25...+75°C the temperature coefficient is less than 18 ppm/°C