A Compact, Reliable and Efficient 16 Channel Power Supply for the Automated Screening of Semiconducting Metal Oxide Gas Sensors

Abstract

The choice of suitable semiconducting metal oxide (MOX) gas sensors for the detection of a specific gas or gas mixture is time-consuming since the sensor’s sensitivity needs to be characterized at multiple temperatures to find its optimal operating conditions. To obtain reliable measurement results, it is very important that the power for the sensor’s integrated heater is stable, regulated and error-free (or error-tolerant). Especially the error-free requirement can be only be achieved if the power supply implements failure-avoiding and failure-detection methods. The biggest challenge is deriving multiple different voltages from a common supply in an efficient way while keeping the system as small and lightweight as possible. This work presents a reliable, compact, embedded system that addresses the power supply requirements for fully automated simultaneous sensor characterization for up to 16 sensors at multiple temperatures. The system implements efficient (avg. 83.3% efficiency) voltage conversion with low ripple output (<32 mV) and supports static or temperature-cycled heating modes. Voltage and current of each channel are constantly monitored and regulated to guarantee reliable operation. To evaluate the proposed design, 16 sensors were screened. The results are shown in the experimental part of this work.

A Compact 16 Channel Embedded System with High Dynamic Range Readout and Heater Management for Semiconducting Metal Oxide Gas Sensors

“…A mirrored copy of the mainboard's shape, created with a 3D printer, is used to affix the sensor modules on the backside of the system. The core circuitry follows the same design and reliability principles as shown in our previous work [17] and is hence not described in detail. The central power line is protected against over-voltage, under-voltage, and reverse-voltage conditions by the the commercially available supply protection chip LTC4365 [18].…”

“…A built prototype with a simplified block diagram that depicts the essential components is shown in Figure 2. The heater circuit is based on a well-tested design from a previous work [17] built with the LTC3600 [22] buck down converter in conjunction with the aforementioned LTC2945 and is therefore not further elaborated here. Communication and data transfer to the master, measurement operation, and temperature management is coordinated by a central STM32L433CC [23] microcontroller.…”

“…The sensor name is the combination of the sintering temperature and respective holding time. The set includes the sintering temperatures 700, 800, 900, and 1000 • C combined with the respective holding times of 10 min, 60 min, 12 h, or 24 h. After production, all sensors were installed in a gas mixing unit (GMU) (see [17]) to which the presented system was connected.…”

Algorithms for Automatic Data Validation and Performance Assessment of MOX Gas Sensor Data Using Time Series Analysis

“…Depending on the granularity, a screening can be a very time-consuming task (i.e., several days) and should ideally be highly automatized. In our previous work, we presented hardware solutions for automated batch sintering [6] and a sensor readout system to carry out highly automated sensor screenings [7]. Since the acquired data has to be analyzed and interpreted to achieve the final goal of finding the best fitting sensor and its optimal operating temperature for a given target, an automated measurement hardware for sensor screenings is only half way to the goal.…”