Uma Gandhi

This article introduces a digitizer circuit for interfacing a four-wire configured resistive sensor (RX) with lead resistance compensation (RL) feature. The proposed circuit is minimalistic, utilizing only three core components: (i) an inverting amplifier, (ii) an integrator, and (iii) a comparator. The RX is integrated in the feedback path of the inverting amplifier which generates the required negative potentials for the dual-slope integrator to operate efficiently; highlighting circuit’s first novelty. The circuit operates in two distinct modes: a charging mode and a discharging mode using a couple of switches. These modes produce two separate equations involving RX and RL. By solving these equations, RX is determined independent of RL. This advancement, coupled with the circuit’s compact, and cost-effective design, underscores its second novelty. The circuit is fabricated on PCB, and has been experimentally tested for a Pt100 RTD (Resistance Temperature Detector) sensor, where the temperature changes from 0 °C to 200 °C, causing RX to vary from 100 Ω to 175.84 Ω (full span). The circuit operates on a single input supply and completes the measurement within a single charge-discharge cycle, highlighting its additional features. The sensor current (IXRMS) ranges from 5.87 mA to 6.86 mA, resulting in power dissipation between 3.44 mW and 8.27 mW across the full span. The measurement time varies from 86.21 ms to 62.39 ms, with an average error of ±0.32 %.

This paper addresses the problem of estimation of hydrogen gas concentration using current output from a sensor chip, integrated with a thin film of ZnO as a sensing layer and inbuilt microheater to obtain desired operating temperature by proposing an appropriate algorithm. The proposed algorithm minimizes the estimation delay while maximizing the estimation accuracy. The proposed algorithm also accounts for the variation in sensor performance with relative humidity. The key features of the proposed algorithm are low computational complexity, low memory requirements, compatibility with any metal-oxides-based hydrogen sensors with independent calibration or turning points, and minimal requirements to the calibration time. As proof of concept, a demonstration of the algorithm efficiency is evaluated by estimating hydrogen concentration using ZnO thin film-based gas sensor device and comparing its performance with available state-of-the-art hydrogen sensor algorithm outputs.

A novel dual-slope resistance to digital converter (RDC) for compensating lead resistance is presented. The RDC uses a dual-slope ADC structure along with three switches and a diode. It completes measurement in one charging-discharging cycle only, hence provides an improvement to existing RDCs based on direct microcontroller interfaces (DMI) where 2 or 3 charging-discharging cycles are required. Moreover, it incorporate the feature of lead resistance compensation in dual-slope RDCs. The scheme works by connecting the resistive sensor to the input terminal of the integrator of the dual-slope ADC. In the charging path (or mode), sensor resistance is present along with lead resistance; and in discharging path, sensor resistance is bypassed, and only lead resistance is there. The difference between the RC time constant during these two modes is used to find the sensor resistance. The diode is used to turn on a switch for bypassing the resistive sensor. The diode voltage drop is not there in the charging and discharging path, which is another novelty. A detailed error analysis is also carried to evaluate the performance of the scheme considering switch resistance, diode voltage drop, voltage mismatch and opamp noises. The scheme works with low-value resistive sensors (≈ 100 Ω), a feature not found in existing dual-slope RDCs. The hardware prototype of the proposed scheme on the breadboard shows a measurement time of 2.09 ms with an average error of ±0.04 % at 100 Ω when lead resistance varied from 20 Ω to 100 Ω. The scheme takes 23.44 % less time for measurement.