Abstract
The signal from a resistive sensor must be converted into a digital signal to be compatible with a computer through an interface circuit. Resistance-to-Period converter, used as interface, is preferred if the resistance variations are very large. This paper presents the structure of an interface circuit for resistive sensors that is highly robust to component and power supply variations. Robustness is achieved by using the ratiometric approach, thus complex circuits or highly accurate voltage references are not necessary. To validate the proposed approach, a prototype was implemented using discrete components. Measurements were carried out considering a variation of ±35% in the single supply voltage and a range from 1 k Ω to 1 M Ω .
Highlights
In recent years, the demand for sensors has increased in many areas, from medical and consumer electronics to automotive and industrial applications
Their resistance may vary from a few tens Ω such as thermistors, strain gauges, Resistance Temperature Detectors (RTD), piezo-resistive sensors, etc., to several MΩ such as various gas chemiresistive sensors, light dependent resistors (LDR), soil moisture, etc
A robust converter for obtaining a quasi-digital output directly from a resistive sensor is presented in this work
Summary
The demand for sensors has increased in many areas, from medical and consumer electronics to automotive and industrial applications. Resistive sensors are widely used in the industry for the measurement of displacement, strain, flow, force, pressure, temperature, light, weight, humidity, gas concentration and moisture, among others. Their resistance may vary from a few tens Ω such as thermistors, strain gauges, Resistance Temperature Detectors (RTD), piezo-resistive sensors, etc., to several MΩ such as various gas chemiresistive sensors, light dependent resistors (LDR), soil moisture, etc. To assess the resistive parameter, voltage may be applied across the sensor while the current is read or vice versa. This voltage or current must be converted into a digital domain to be compatible with a computer, DAQ system, microcontroller or microprocessor using an interface. According to [1], direct measurement of resistance changes can be done by two different ways: In the case of small resistance variations, circuits based on voltage dividers and Wheatstone bridges followed by precision differential or instrumentation amplifiers to reduce the offset voltage are used
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