Quasi Single Point Calibration Method for High-Speed Measurements of Resistive Sensors.
TL;DR: A series of calibration methods that decrease the mean estimation time for resistive sensors, based on the TPCM and fast calibration methods I and II, are proposed.
Abstract: Direct interface circuits are a simple, inexpensive alternative for the digital conversion of a sensor reading, and in some of these circuits only passive calibration elements are required in order to carry out this conversion. In the case of resistive sensors, the most accurate methods of calibration, namely two-point calibration method (TPCM) and fast calibration methods I and II (FCMs I and II), require two calibration resistors to estimate the value of a sensor. However, although FCMs I and II considerably reduce the time necessary to estimate the value of the sensor, this may still be excessive in certain applications, such as when making repetitive readings of a sensor or readings of a large series of sensors. For these situations, this paper proposes a series of calibration methods that decrease the mean estimation time. Some of the proposed methods (quasi single-point calibration methods) are based on the TPCM, while others (fast quasi single-point calibration methods) make the most of the advantages of FCM. In general, the proposed methods significantly reduce estimation times in exchange for a small increase in errors. To validate the proposal, a circuit with a Xilinx XC3S50AN-4TQG144C FPGA has been designed and resistors in the range (267.56 Ω, 7464.5 Ω) have been measured. For 20 repetitive measurements, the proposed methods achieve time reductions of up to 61% with a relative error increase of only 0.1%.
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TL;DR: This article presents a new type of DIC with the same passive elements as a classic DIC, but which uses a high value resistor in the final instant of the resistance-to-time conversion.
Abstract: Reading resistive sensors and converting their information to digital values is a matter of great interest in practical applications. Direct Interface Circuits (DICs) perform this task efficiently through a resistance-to-time-to-digital conversion. The main benefit of this type of circuit is the simplicity of its design and the accuracy of the results. However, one of its drawbacks is that quantization errors in the measurements seriously compromise accuracy if the information is not converted using a high-frequency clock or with high capacitor values. To avoid this situation, this article presents a new type of DIC with the same passive elements as a classic DIC, but which uses a high value resistor in the final instant of the resistance-to-time conversion. The circuit has been implemented using a commercial FPGA with the capture module operating at different clock frequencies. The results show that relative errors in measuring resistors of up to $33~\Omega $ decrease to 1.56% when operating with a 12.5 MHz timer.
8 citations
Cites background or methods from "Quasi Single Point Calibration Meth..."
...There are DICs for reading different kinds of sensors: resistive [4], [9], [17] differential resistive [18], resistive arrays [12], [15], capacitive [19]–[23], inductive [24]–[26] differential inductive [11], [27], and even DICs designed to simultaneously measure any of the aforementioned sensors [5]....
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...DICs allow the use of microcontrollers [6]–[11] or a field-programmable gate array (FPGA) [12]–[15] which shows the versatility of the method....
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TL;DR: A modification of the most widely used estimation method in a resistive DIC, known as the Two-Point Calibration Method (TPCM), in which a single additional programmable digital device pin in the DIC and one extra measurement in each discharge cycle, made without slowing down the cycle, allow charge times to be reduced more than 20-fold to values around 2 µs.
Abstract: Direct Interface Circuits (DICs) carry out resistive sensor readings using a resistance-to-time-to-digital conversion without the need for analog-to-digital converters. The main advantage of this approach is the simplicity involved in designing a DIC, which only requires some additional resistors and a capacitor in order to perform the conversion. The main drawback is the time needed for this conversion, which is given by the sum of up to three capacitor charge times and their associated discharge times. This article presents a modification of the most widely used estimation method in a resistive DIC, which is known as the Two-Point Calibration Method (TPCM), in which a single additional programmable digital device pin in the DIC and one extra measurement in each discharge cycle, made without slowing down the cycle, allow charge times to be reduced more than 20-fold to values around 2 µs. The new method designed to achieve this reduction only penalizes relative errors with a small increase of between 0.2% and 0.3% for most values in the tested resistance range.
2 citations
Cites background from "Quasi Single Point Calibration Meth..."
...Although there are DICs for reading both capacitive and inductive sensors, those for resistive sensors have probably been the most widely used and analyzed in the literature, whether individually [3,7,18,19] or grouped in arrays [11,14]....
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Journal Article•
TL;DR: In this article, the calibration of pH sensor located at the OBSEA marine observatory is described, which is based on an industrial pH sensor that is connected to a CTD (Conductivity, Temperature, and Depth).
Abstract: This paper describes the calibration of pH sensor located at the OBSEA marine observatory. This instrument is based on an industrial pH sensor that is connected to a CTD (Conductivity, Temperature, and Depth). The calibration of the pH sensor has been done using a calibrated pH sensor from Institute of Marine Sciences (ICM), and in this way it has been obtained a numerical function for the pH sensor proportional to real pH.
1 citations
Dissertation•
12 May 2016
TL;DR: In this paper, the authors developed a wireless temperature and humidity autonomous system that monitored from the inside of compost, where they developed an algorithm, implementable on microcontrollers, to counteract the effects of first order step responses.
Abstract: The composting process is Nature's way of recycling organic wastes with a good quality organic fertilizer as a result. This process, though, needs of a thoroughly monitoring of temperature and humidity for a good resulting material. During this Ph.D thesis we developed a wireless temperature and humidity autonomous system that monitored from the inside of compost. The fact of measuring and transmitting from the inside implies the need of a protection for the circuit and an issue in the measure. Temperature suffers delays when measuring from the inside of a protection and, as such, we developed an algorithm, implementable on microcontrollers, to counteract the effects of first order step responses. The conditioning has been optimized in terms of components and consumption, obtaining a theoretical and experimental comparative between the classic conditioning and the use of direct interfaces. Commercial humidity sensors need to be in direct contact with the environment they are measuring, but that is not possible in compost since they can get damaged. That is why we designed a humidity sensor based on coplanar capacitive electrodes that can measure through a protection layer. Some theoretical models have been obtained for the physical optimization of both the sensor and the influence of the protective layer. Compost has never been characterised as a transmission environment, and as such, communications in compost are innovative. The heterogeneity of the material and its changes in humidity, temperature and density made the transmission complex. We found the proper frequency band to commercially work in compost and the RF transmission model in compost to estimate attenuation vs distance. El proces de compostatge es la forma que te la natura de reciclar els residus organics amb un fertilitzant organic de bona qualitat com a resultat. Aquest proces, pero, necessita d’una monitoritzacio de la temperatura i la humitat per a obtenir un bon material resultant. Durant aquesta tesi doctoral s'ha desenvolupat un sistema autonom sense fils de mesura de temperatura i humitat des de dins del compost. El fet de que la mesura i la transmissio s’hagin fet des de dins comporta la necessitat d’un material protector per l’electronica, la qual cosa esdeve un problema en la mesura. La temperatura pateix retards quan es mesura des de dins d’un material protector, i per aixo, s’ha desenvolupat un algoritme implemetanble en microcontroladors per contrarestar els efectes de respostes esglao de primer ordre. S'ha optimitzat el condicionament des del punt de vista de components i consum, obtenint una comparativa teorica i experimental entre els metodes de condicionament classic i l'us d'interficies directes. Els sensors de humitat comercials necessiten estar en contacte directe amb l’ambient a mesurar. Aixo no es possible en el compost ja que es poden malmetre. Per aixo s’ha dissenyat un sensor d’humitat basat en electrodes capacitius plans que poden mesurar a traves de capes de proteccio. S'han extret models teorics per l’optimitzacio fisica tant del sensor com de la influencia de la capa protectora El compost no ha estat mai caracteritzat com un medi de transmissio, i per tant, les comunicacions dins del compost suposen una novetat. La heterogeneitat del material i els seus canvis en temperatura, humitat i densitat fan de la transmissio un tema complex. S’ha trobat, a mes, la banda de frequencia optima per treballar comercialment i el seu model de transmissio RF estimant l’atenuacio en funcio de la distancia
1 citations
TL;DR: In this paper , a crossover randomized trial was carried out to evaluate the effect of three different hard insoles in cycling on healthy subjects, and the results showed that the maximum plantar pressure decreased significantly with the polypropylene insole containing selective aluminum in the metatarsal head and hallux areas.
Abstract: Background: Hard insoles have been proposed to decrease plantar pressure and prevent foot pain and paresthesia due to repetitive loading. The aim of this research was to analyze the effect of three different hard insoles in cycling on healthy subjects. Methods: A crossover randomized trial was carried out. The mean age of the subjects was 35 ± 3.19 years, and all of them were men. While the subjects were cycling on a stationary bicycle, their plantar pressure was recorded with nine in-shoe sensors placed in nine specific foot areas to test a standard ethylene-vinyl-acetate 52° Shore A hardness insole, a polypropylene 58° Shore D insole, and a polypropylene 580 Shore D insole with selective aluminum 60 HB Brinell hardness in the metatarsal head and hallux. Results: The maximum plantar pressure decreased significantly with the polypropylene insole containing selective aluminum in the metatarsal head and hallux areas. The maximum plantar data of the polypropylene aluminum insole in the M2 area (5.56 kgF/cm2), fifth metatarsal styloid process (6.48 kgF/cm2), M3–M4 area (4.97 kgF/cm2), and hallux (8.91 kgF/cm2) were of particular interest compared to the other insoles. Conclusions: The use of insoles made of polypropylene with aluminum in the metatarsal head and hallux areas decreases the maximum plantar pressure in cycling compared to standard EVA and polypropylene insoles.
References
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TL;DR: A novel circuit to directly connect differential resistive sensors to microcontrollers without using either a signal conditioner or an analog-to-digital converter (ADC) in the signal path is introduced.
Abstract: This paper is a continuation of a previous work with regard to the direct connection of differential sensors to microcontrollers without using intermediate electronics between them. This paper focuses on the measurement of differential capacitive sensors, whereas the previous work dealt with the resistive counterparts. The proposed circuit is analyzed, and the main limitation seems to be the fact that the magnitude of the input parasitic capacitances of the microcontroller is similar to or even higher than the sensor capacitances. Methods to overcome this limitation are proposed, particularly when measuring low-value differential capacitive sensors such as microelectromechanical system (MEMS) sensors. Experimental tests of the circuit have been carried out by measuring a commercial capacitive accelerometer working as a tilt sensor. Although such a sensor has a low value (1.5 pF) and low sensitivity (0.105 pF/g), the measurement has shown a nonlinearity error of 1% full-scale span (FSS), which is a remarkable value considering the simplicity of the circuit.
91 citations
TL;DR: In this article, the authors describe the design of a new capacitive sensor interface based on the use of a novel type of oscillator whose frequency is insensitive to low and high-frequency interfering signals by the application of a third order high-pass filter and special dither techniques.
Abstract: This paper describes the design of a new capacitive sensor interface. The interface is based on the use of a novel type of oscillator whose frequency is insensitive to low- and high-frequency interfering signals by the application of a third order high-pass filter and special dither techniques. The fully integrated 0.7 /spl mu/m CMOS circuit shows an inaccuracy of less than 100 aF with respect to a 2 pF reference capacitor over a -30/spl deg/ to +70/spl deg/C temperature range. The applied measurement concept guarantees high stability, high accuracy and a negligible influence of parasitic capacitances without the need for calibration.
89 citations
TL;DR: This paper proposes and analyses a direct interface circuit for capacitive humidity sensors that relies on directly connecting the sensor to a microcontroller without using either a signal conditioner or an analogue-to-digital converter, thus resulting in a simple, compact, low-cost and low-power interface circuit.
Abstract: This paper proposes and analyses a direct interface circuit for capacitive humidity sensors. Such a circuit relies on directly connecting the sensor to a microcontroller without using either a signal conditioner or an analogue-to-digital converter, thus resulting in a simple, compact, low-cost and low-power interface circuit. In spite of its simplicity, the interface circuit performs satisfactorily when measuring commercial capacitive humidity sensors (Philips H1 and Humirel HS1101). The non-linearity error of the interface circuit itself (0.1% full scale span (FSS)) is much smaller than that of the sensor (5.6% FSS for the H1 and 2.1% FSS for the HS1101) and, therefore, the circuit does not limit the accuracy (in terms of linearity) of the measurement, as is to be expected from a well-designed interface circuit. Furthermore, the effective resolution equals 9 bits for a measuring time of 50 ms, which are fully acceptable for humidity measurements.
69 citations
TL;DR: A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin’s internal resistance and any offset present in those pins is presented in this paper.
Abstract: Direct resistive sensor interface to a microcontroller has several advantages but has one prominent disadvantage, namely, the measurement is affected by the resistances of: 1) wires that connect the sensor to the port pins and 2) the internal resistances of the port pins of the microcontroller. A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin’s internal resistance and any offset present in those pins is presented in this paper. Since the resistances of lead wires are compensated, automatic temperature compensation (temperature effect of lead wires) is also obtained. Simulation study and results obtained from a prototype built and tested establish the efficacy of the proposed method. A maximum error of 0.06% was observed from the prototype developed, when it was tested under room temperature, after interfacing it with the sensor Pt100, with a lead wire resistance $R_{\mathrm {LD}} = 21~\Omega $ . The error increased to a maximum of 0.08%, when the $R_{\mathrm {LD}}$ varied from 0 to $100~\Omega $ . When the same prototype was tested under elevated room temperature of 30 °C to 100 °C, the maximum error observed was 0.18%.
58 citations
TL;DR: In this article, the authors proposed a direct connection of different configurations of resistive sensor bridges to a microcontroller without any intermediate active component, which relies on measuring the discharging time of a RC network that includes the resistances of the sensor bridge.
Abstract: This paper proposes the direct connection of different configurations of resistive sensor bridges to a microcontroller without any intermediate active component. Such a direct interface circuit relies on measuring the discharging time of a RC network that includes the resistances of the sensor bridge. For quarter-, half-, and full-bridge circuits, we combine the discharging times to estimate the fractional resistance change x of the bridge arms. Experimental results for half- and full-bridge circuits emulated by resistors yield a nonlinearity error below 0.3%FSR (full-scale range) for x between 0 and 0.1 and an effective resolution of 11 bit. Measurements on two commercial magnetoresistive sensors yield higher nonlinearity errors: 1.8%FSR for an AMR (Anisotropic Magnetoresistive) sensor and 5.8%FSR for a GMR (Giant Magnetoresistive) sensor, which are mainly due to the nonlinearity of the sensors themselves. Therefore, the nonlinearity of the measurement is limited by the sensors, not by the proposed interface circuit and linearisation algorithm.
54 citations