Design and fabrication of an amperometric CO gas sensor and a readout circuit using a low-noise transimpedance amplifier to achieve standard analog outputs

Abstract

This article presents a sensor design method that utilizes two electrodes made of gold and tin oxide, along with a gas concentration detection circuit. The use of an n-type semiconductor with a rutile structure contributes to improved sensitivity, and a sol-gel coating with SnO2 is applied. The sensor includes 20 finger electrodes printed on a ceramic substrate, along with a heater placed on the bottom layer to enable interaction with the external environment. The gas concentration is detected through the use of an amperometric method and an ultra-low noise amplifier. The proposed system incorporates a microcontroller and a low-noise analog interface, delivering standard analog outputs ranging from 0 ∼ 10 V and 4 ∼ 20 mA, proportional to the gas concentration. The experimental results demonstrate a sensitivity of 6nA/ppm within the range of 0 ∼ 470 ppm, with a detection limit of 1 ppm. Key advantages of the proposed circuit include linear response within the specified range, resistance to thermal changes, and cost-effectiveness. Moreover, the sensor exhibits reliable repeatability, with a response time of 27.5 s and a recovery time of 39 s. The front-end circuit's adjustable bandwidth and gain enable precise fine-tuning of the measured CO concentration range.