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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]