Quasi-digital Sensor Research Articles

Design and Development of Quasi Digital Sensor Based Spirometer

The lack of cost-effective diagnostic devices like spirometer is becoming a prevalent challenge to the diagnosis and effective management of life-threatening respiratory diseases. This paper presents the design, development, and implementation of differential pressure sensing quasi digital sensor and instrument for spirometer application. A system which fulfills the medical standard specifications has been designed and developed by exploiting the venturi tube (Bernoulli’s principle) and quasi digital sensor principles. A low power microcontroller (PIC24F) based embedded system, venturi tube based quasi digital sensor, data acquisition software, and user interface were developed. A lab made prototype device has been constructed, tested, and subsequently analyzed the recorded data from the computer. This cost effective ($150) spirometer model can be used for detection of pulmonary diseases rural area and it is going to add a new dimension to the diagnosis of many lung diseases.

Deployment of the inductance-based quasi digital sensor and instrument to monitor the metallic liquid level

Deployment of the inductance-based quasi digital sensor and instrument to monitor the metallic liquid level

Design and development of a quasi-digital sensor and instrument for water turbidity measurement

In this paper, the design, realization, fabrication and assembly of a prototype water turbidity monitoring instrument based on an opto-resistive quasi-digital sensor has been proposed. The turbidity sensor has been constructed with LED (590 nm) as the light source, a light-dependent resistor, fixed capacitor and logic gate inverter. The primary output signal from the sensor is in the form of a transistor–transistor-logic pulse stream with 50% duty cycle. This form of the output signal can be directly interfaced with the microcontroller. To process pulse stream from the sensor, to convert into turbidity value in NTU and to display on an LCD, a microcontroller (PIC18f4550)-based embedded system has been developed. The turbidity monitoring instrument has been constructed, calibrated and experimentally tested by measuring the turbidity of the water in the range of 0–1000 NTU. The turbidity of 0–1000 NTU corresponded to the output frequency of 40.6–18.8 kHz with sensitivity of 22 Hz/NTU. This is a high-precision, low-power, portable instrument with low manufacturing costs compared to commercial turbidity monitoring instruments.

Design and Development of Opto-Resistive Type Quasi-Digital Sensor and Instrument for Online Assessment of the Quality of Lubricant Oil

In rotating machinery, the color of lubricant oil changes due to oxidation, degradation, and contamination. It is a crucial parameter to cognize the healthiness of the lubricant oil. This paper presents the design and development of a low-cost, high-precision quasi-digital sensor with an opto-resistive technique to detect the color of the lubricant oil with a microcontroller (PIC18F4550)-based instrument. The developed instrument reads the sensor output, displays the condition of the lubricant oil on LCD, announces the alarm to alert the operator, and communicates the healthiness of the lubricant oil to the computer. As per the ASTM D1500 standard, the color scale of the lubricant oil varies from 0.5 to 8.0. In the studies conducted at the laboratory, this color scale corresponds to the sensor output frequency in the range of 76.87–61.63 kHz. The sensitivity of the color sensor is 1905 Hz/color code. Apart from this, an additional sensor is provided to measure the turbidity of the lubricant oil, which helps in compensating the error in color scale due to turbidity. In addition to revealing of lube oil color, it can also detect the size of the particles in the lubricant oil. To perform these tasks, an algorithm and an application software have been developed and loaded into the flash memory of the microcontroller.

A 0.35-μm CMOS-MEMS Oscillator for High-Resolution Distributed Mass Detection.

This paper presents the design, fabrication, and electrical characterization of an electrostatically actuated and capacitive sensed 2-MHz plate resonator structure that exhibits a predicted mass sensitivity of ~250 pg·cm−2·Hz−1. The resonator is embedded in a fully on-chip Pierce oscillator scheme, thus obtaining a quasi-digital output sensor with a short-term frequency stability of 1.2 Hz (0.63 ppm) in air conditions, corresponding to an equivalent mass noise floor as low as 300 pg·cm−2. The monolithic CMOS-MEMS sensor device is fabricated using a commercial 0.35-μm 2-poly-4-metal complementary metal-oxide-semiconductor (CMOS) process, thus featuring low cost, batch production, fast turnaround time, and an easy platform for prototyping distributed mass sensors with unprecedented mass resolution for this kind of devices.

Deployment of an inductance-based quasi-digital sensor to detect metallic wear debris in lubricant oil of rotating machinery

In rotating machinery due to continuous rotational induced wear and tear, metallic debris will be produced and mixes with the in-service lubricant oil over the course of time. This debris gives the sign of potential machine failure due to the aging of critical parts like gears and bearings. The size and type of wear debris has a direct relationship with the degree of wear in the machine and gives information about the healthiness of equipment. This article presents an inductive quasi-digital sensor to detect the metallic debris, its type; size in the lubrication oil of rotating machinery. A microcontroller based low cost, low power, high resolution and high precise instrument with alarm indication and LCD is developed to detect ferrous debris of sizes from 30 µm and non-ferrous debris of 50 µm. It is thoroughly tested and calibrated with ferrous, non-ferrous debris of different sizes in the air environment. Finally, an experiment is conducted to check the performance of the instrument by circulating lubricant oil containing ferrous, non-ferrous debris through the sensor.

Deployment of quasi-digital sensor for high temperature molten salt level measurement in pyroprocessing plants.

Development of a liquid molten salt level sensor device that can detect the level of liquid molten salt in the process vessels of pyrochemical reprocessing of spent metallic fuels is detailed. It is proposed to apply a resistive-type pulsating sensor-based level measurement approach. There are no commercially available sensors due to limitations of high temperature, radiation, and physical dimensions. A compact, simple, rugged, low power, and high precise pulsating sensor-based level probe and simple instrumentation for the molten salt liquid level sensor to work in the extreme conditions has been indigenously developed, with high precision and accuracy. The working principle, design concept, and results have been discussed. This level probe is mainly composed of the variable resistor made up of ceramic rods. This resistor constitutes the part of resistance-capacitance-type Logic Gate Oscillator (LGO). A change in the molten salt level inside the tank causes a small change in the resistance which in turn changes the pulse frequency of the LGO. Thus the frequency, the output of the instrument that is displayed on the LCD of an embedded system, is a function of molten salt level. In the present design, the range of level measurement is about 10 mm. The sensitivity in position measurement up to 10 mm is ∼2.5 kHz/mm.

Self-Oscillating Fluxgate-Based Quasi-Digital Sensor for DC High-Current Measurement

A quasi-digital dc current sensor with rated current of ±600 A while overload current of about ±750 A is proposed in this paper. The new sensor is based on the open-loop self-oscillating fluxgate technology, but its originality is using a microcontroller unit to detect the duty cycle of the exciting voltage of the fluxgate. Compared with the published similar method, the whole signal chain of the new sensor is quasi-digital and without low-pass filter and analog-to-digital converter required when connected to digital systems. A precisely theoretical equation with respect to the linear dependence between the duty cycle and the current to be measured is established. Based on the equation, factors affecting the sensor sensitivity, accuracy, and resolution are determined, which constitutes the theoretical basis on the optimization design of the new sensor. The sensor linearity is improved using the least-squares polynomial fitting method. Some key specifications including the linearity, repeatability, and power supply effect of the sensor are characterized. The measurement results show that the linearity of the new sensor with the theoretical equation is better than 1.7% in the full scale of ±600 A, and can be improved to 0.3% when the fifth-order polynomial fitting method is used.

CMOS quasi‐digital temperature sensor for battery operated systems

A high performance 1.2 V–0.18 µm CMOS quasi-digital temperature sensor is presented with frequency output suitable to be used in battery operated systems. It is based on a multivibrator current-to-frequency converter and works properly over a temperature range of –40 to + 120°C, exhibiting a linear sensitivity of 442 Hz/°C with accuracy better than 1.0°C and a power consumption of 1.8 µW.

Design and Theoretical Analysis of a Resonant Sensor for Liquid Density Measurement

In order to increase the accuracy of on-line liquid density measurements, a sensor equipped with a tuning fork as the resonant sensitive component is designed in this paper. It is a quasi-digital sensor with simple structure and high precision. The sensor is based on resonance theory and composed of a sensitive unit and a closed-loop control unit, where the sensitive unit consists of the actuator, the resonant tuning fork and the detector and the closed-loop control unit comprises precondition circuit, digital signal processing and control unit, analog-to-digital converter and digital-to-analog converter. An approximate parameters model of the tuning fork is established and the impact of liquid density, position of the tuning fork, temperature and structural parameters on the natural frequency of the tuning fork are also analyzed. On this basis, a tuning fork liquid density measurement sensor is developed. In addition, experimental testing on the sensor has been carried out on standard calibration facilities under constant 20 °C, and the sensor coefficients are calibrated. The experimental results show that the repeatability error is about 0.03% and the accuracy is about 0.4 kg/m3. The results also confirm that the method to increase the accuracy of liquid density measurement is feasible.

Experimental analysis of power supply interference rejection in commercial quasi-digital sensors

The power supply interference rejection of four commercial quasi-digital sensors (ADXL202, SMT160-30, TMP04, MAX6676) has been experimentally analyzed by using a test method that allows us to easily select the amplitude and frequency of the interfering signal. Slow and fast changes of the sensor supply voltage yield bias errors and increase the uncertainty of the output signal parameter (time interval, mark-space ratio) that carries the information about the measured physical quantity. The effects of the interference on the output information are unique when the interfering frequency equals a multiple of the output signal frequency. For the sensors analyzed, a 100 mV sine-wave interference increased the uncertainty from 14 to 140 times that obtained when the supply voltage was clean. These experimental results cannot be directly predicted from the power supply rejection ratio value and the performance figures in manufacturer's data sheets.

Analysis of power supply interference effects on quasi-digital sensors

Quasi-digital sensors are very common and attractive for new designs because their time-based output signal can be directly connected to a digital system with time measurement capability. However, the same as modulating sensors, quasi-digital sensors are susceptible to power supply interference. Their data sheets specify a power supply rejection ratio (PSRR) value, but it often refers only to the effects on the bias error produced by a slow power supply voltage change. This paper provides a theoretical analysis of the effects of power supply interference on the output information of quasi-digital sensors. According to the developed models, the uncertainty in the output information depends on the frequency and the amplitude of the interference superimposed on the supply voltage. Furthermore, the sensor sensitivity to power supply interference also depends on the measurand. The proposed models are qualitatively validated with experimental data from commercial sensors based on pulse-frequency modulation (PFM).

Trigger uncertainty in period-to-code converters based on counters embedded in microcontrollers

Abstract Microcontrollers with embedded counters offer a simple, compact interface for quasi-digital sensors whose output period depends on the measurand. However, as opposed to bench-top universal counters, manufacturers of microcontrollers do not specify the uncertainty inherent to measurements performed with embedded time-counters. This paper analyses the effects of input signal slew rate, signal-to-noise ratio and power supply noise on the uncertainty of periods measured with a PIC16F873 microcontroller. That uncertainty is evaluated by the standard deviation and histogram of the measured time periods. Two noise parameters have been considered: bandwidth (for Gaussian noise) or frequency (for sinusoidal interference), and intensity (rms amplitude). Trigger uncertainty increases for slow signal slew rate, and it is slightly larger when Gaussian noise or sine wave interference are added to the input signal than when they are added to the power supply. Interference whose frequency is close (but not equal) to that of the input signal yields larger trigger uncertainty than interference whose frequency is apart from that of the input signal. Trigger uncertainty resulting from Gaussian noise of a given rms power increases for reduced noise bandwidth.

Sealed-cavity resonant microbeam pressure sensor

A quasi-digital pressure sensor based on polysilicon resonant microbeams has been demonstrated. Pressure sensitivities of nearly 4000 counts per second per psi have been attained on a 10 psi device with a base frequency of 233 000 Hz. Short-term stability as low as 0.01 ppm of the base frequency is typical. The microbeams are fabricated with their own integral vacuum cavities, allowing high-Q operation in the differential pressure mode or in contact with liquids such as silicone oil. Design considerations include the effects of internal strain and lead to a push-pull layout configuration independent of microbeam strain or diaphragm thickness. Fabrication technology incorporates fine-grained polysilicon, surface micromachining, bulk micromachining, and reactive sealing. Packaging into precision avionics headers is being used for preliminary testing. Testing results indicate suitability for precision avionics, industrial, and commercial applications. Optical methods have been used to test resonant microbeam pressure sensors and verify the push-pull design methodology. Testing methods developed under this effort include electrostatic drive/piezoresistive sensing, optical drive/optical sensing, substrate piezoelectric drive/optical sensing, and electrostatic drive/laser vibrometer sensing. Wafer-level testing of 200 μm×46 μm×1.9 μm microbeams shows an average fundamental frequency of 553 150 and first overtone of 1 332 550 Hz. The standard deviations across the wafer are 0.15 and 0.10%, respectively. The internal strain and effective thickness can be determined with high resolution. Laser vibrometer measurements through the microbeam shell verify the fundamental frequency and reveal at least ten overtones up to 25 MHz.

A Sensor System with Pulse-Number Output

As part of an examination of the problems of instrumentation compatible with on-line computers, a design has been produced for a simple quasi-digital sensor system. In this, the information about the sensed variable is carried by the number of pulses in a pulse train transmitted by the sensor upon interrogation. This form of sensor system has a number of attractive features. The characteristics of the system are analysed and possibilities of further development proposed.