Analysis of the dynamics of an active control of the surface potential in metal oxide gas sensors

Abstract

Gas sensing is nowadays a key actor in pollution observation and detection of chemical toxic agents or explosives. All these applications require the shortest possible time response. Very recently, a control of the surface potential in gas sensors based on metal oxides has experimentally shown to dramatically improve the time response of metal-oxide gas sensors. The proposed control is inspired in sigma-delta modulators. This paper aims at studying the resulting dynamics in the sensor from a theoretical point of view. Using state space models, it is shown how the state variables, namely the concentrations of ionized species in the sensing layer, evolve with time in open and closed loop configuration. This analysis studies how it is possible to alter the dynamics of the overall system, while at the same time keeping some important characteristics of sigma-delta modulators, such as quantization noise-shaping. Numerical simulations validate the obtained results.

Open loop testing for optimizing the closed loop operation of chemical systems

“…A first analysis of the controls was presented in [1]. The objective in this paper is to extend these first results by providing a practical procedure for setting up key control parameters needed in the controls, in particular the target surface potential value.…”

“…Nowadays it is very common to optimize chemical systems and processes using closed loop controls in the operation phase. The use of these controls is quite widespread and they can be found in very different types of devices, plants or systems, [1,2,3,4,5]. In many of these areas, though, the presence of uncertainties, [6], makes particularly difficult to adjust beforehand the multiple configuration parameters involved in the controls.…”

“…Recently, controls have been proposed for operating MOX-based gas sensors under constant surface potential (SP) [8,9,1]. This is one example of system in which the manipulation of macroscopic variables allows the control of chemical variables defined in the nanoscale [10].…”

Acceleration of the Measurement Time of Thermopiles Using Sigma-Delta Control

“…Additionally, controls based on sigma-delta modulation have been also proposed for MOX gas sensors [21,25] and a first mathematical analysis has been presented in Reference [26]. This means that the proposed techniques are transversal and can be applied to a number of different sensor fields.…”