Methods, systems and devices are described for detecting a position-based attribute of a finger, stylus or other object with a touchpad or other sensor having a touch-sensitive region that includes a plurality of electrodes. Modulation signals for one or more electrodes are produced as a function of any number of distinct digital codes. The modulation signals are applied to an associated at least one of the plurality of electrodes to obtain a resultant signal that is electrically affected by the position of the object. The resultant signal is demodulated using the plurality of distinct digital codes to discriminate electrical effects produced by the object. The position-based attribute of the object is then determined with respect to the plurality of electrodes from the electrical effects.

Methods and systems for detecting a position-based attribute of an object using digital codes

Many types of techniques for metering the mass flow rate of bulk solids in a pneumatic pipeline have been proposed and developed during the past 20 years. This paper presents a detailed and comprehensive review of the techniques and the current state of knowledge and experience. The techniques are classified under three main categories: direct measurement of solids mass flow rates, measurement of volumetric concentrations of solids and measurement of solids velocity. Future developments and possible trends in this field are also included.

https://iopscience.iop.org/article/10.1088/0957-0233/7/12/002/pdf

Mass flow measurement of bulk solids in pneumatic pipelines

Describes a tomographic flow imaging system based on capacitance sensors. It uses eight capacitance electrodes to perform a 'body scan' of the fluid-conveying pipe, and a linear back projection algorithm is developed to reconstruct the cross-sectional image of the two-component flow from the measured capacitance values. A prototype system has been successfully assembled and reconstructed images of static distribution models are presented. Possible industrial applications and practical limitations of the system are discussed.

https://iopscience.iop.org/article/10.1088/0022-3735/22/3/009/pdf

Tomographic imaging of two-component flow using capacitance sensors

Methods, systems and devices are described for detecting a measurable capacitance using sigma-delta measurement techniques. According to various embodiments, a voltage is applied to the measurable capacitance using a first switch. The measurable capacitance is allowed to share charge with a passive network. If the charge on the passive network is past a threshold value, then the charge on the passive network is changed by a known amount for a sufficient number of repetitions until the measurable capacitance can be detected. Such a detection scheme may be readily implemented using conventional components, and can be particularly useful in sensing the position of a finger, stylus or other object with respect to a button, slider, touchpad or other input sensor.

Methods and systems for detecting a capacitance using sigma-delta measurement techniques

Purpose – The purpose of this paper is to present the sensing mechanism, design issues, performance evaluation and applications for planar capacitive sensors. In the context of characterisation and imaging of a dielectric material under test (MUT), a systematic study of sensor modelling, features and design issues is needed. In addition, the influencing factors on sensitivity distribution, and the effect of conductivity on sensor performance need to be further studied for planar capacitive sensors.Design/methodology/approach – While analytical methods can provide accurate solutions to sensors of simple geometries, numerical modelling is preferred to obtain sensor response to different design parameters and properties of MUT, and to derive the sensitivity distributions of various electrode designs. Several important parameters have been used to evaluate the response of the sensors in different sensing modes. The designs of different planar capacitive sensor arrays are presented and experimentally evaluated...

Planar capacitive sensors – designs and applications

Reviews existing instrumental techniques suitable for industrial measurement of capacitance in the range 0.1-10 pF, including resonance, oscillation, charge/discharge and AC bridge methods. It shows that in order to achieve high measurement sensitivity and good signal-to-noise ratio, the effects of stray capacitances on the measurement systems must be minimised. Several intrinsically stray-immune measuring circuits are described, including an audio-frequency transformer-ratio-arm bridge and a charge/discharge measuring circuit capable of operating at frequencies up to several MHz. The active guard method and suitable guard driving techniques for reducing the effects of strays on the measurement of grounded capacitances sensors are described. Techniques for reducing the baseline drift of the capacitance measuring circuits, such as auto-balancing and auto-calibration, etc., are also discussed.

https://iopscience.iop.org/article/10.1088/0022-3735/21/3/001/pdf

Electronic transducers for industrial measurement of low value capacitances

Electrostatic charge generated in solids/air two-component flows can cause significant errors in solids-concentration measurement systems based on capacitance techniques, and, in the worst case, can overload or even damage the measuring circuits. A transformer ratio-arm bridge capacitance transducer, incorporating synchronous demodulation and a noise attenuating input amplifier, has been developed for this type of application. The transducer has been tested on several solids-flow plants. It shows a very high immunity to charge interference and it is capable of withstanding large magnitudes of electrostatic interference without being overloaded.

A capacitance-based solids concentration transducer with high immunity to interference from the electrostatic charge generated in solids/air two-component flows

R.G. Green

Papers

Electronic transducers for industrial measurement of low value capacitances

A capacitance-based solids concentration transducer with high immunity to interference from the electrostatic charge generated in solids/air two-component flows