RU2396554C1 - Method of determining gas sensor working capacity - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: in order to determine working capacity of a semiconductor gas sensor, the detecting element of the sensor is heated in the temperature interval for adsorption of a gas in whose atmosphere the sensor lies. When the detecting element is heated, the amplitude of the signal at the output of the sensor is simultaneously measured on at least two fixed frequencies. The amplitude of the signal is compared and working capacity of the sensor is determined from the difference value.

EFFECT: design of a simple and reliable method of determining working capacity of a gas sensor with a semiconductor gas element in the presence of a multi-component gas mixture which is the atmosphere.

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Description

The invention relates to the field of gas research and analysis using semiconductor gas sensors and is aimed at solving the problem of determining their health.

When conducting measurements using a semiconductor gas analyzer, the question of the reliability of the signal at the output of the device is of paramount importance, since the simple presence of a signal is ambiguous to determine the fact of its operability.

A known method for testing the reliability of an electrochemical sensor in the absence of an external gas source, which consists in the fact that the signal at the output of the sensor is measured after briefly turning on the voltage of reverse polarity between the working and comparative electrode of the sensor (see US patent 6404205 from 05/08/2000 MKI G01N 27 / 62).

The disadvantage of this method is the difficulty of implementation and the possibility of application for a limited type of sensors and only when measuring carbon monoxide, as well as the dependence on environmental conditions.

There is also a method of determining the operability of a gas sensor, which is the closest in technical essence to the proposed one, which consists in measuring the amplitude of the signal at the output of the sensor element of the sensor, enclosed in a shell with a limited opening, during short-term heating of the sensor (see E.E. Karpov , EF Karpov et al. “Ways to improve thermocatalytic methanometers”, J. “Sensor” 2002, No. 4, p. 2).

The limited application is a significant drawback of the known method, since it can be used only for thermocatalytic sensors and single-component gas mixtures.

The technical result of the proposed method is to solve the problem of creating a simple and reliable method for determining the health of a gas sensor with a semiconductor gas element in the presence of a multicomponent gas mixture, which is the atmosphere.

This technical result is achieved by the fact that in the method for determining the operability of a gas sensor, the signal amplitudes are measured at the sensor output when the sensor is heated in the temperature range of gas adsorption on its surface at the same time at least at two fixed frequencies determined by the type of gas being measured, signal amplitudes are compared and the magnitude of the difference is judged on the performance of the sensor.

The essence of the proposed method is illustrated by drawings.

Figure 1 shows a diagram of the signal on the load resistance for a workable and inoperative sensor.

Figure 2 shows an example of the Fourier spectrum of the output signal of a workable sensor in the atmosphere with the addition of CO.

Figure 3 presents an example block diagram of a device that implements this method.

Figure 1 presents the result of measuring the noise of the output signal of the sensor 2, taken from the load resistance 1 (figure 3) in an atmosphere of air with a gas additive CO. For a working sensor, the output signal (curve 2) is characterized by periodic voltage fluctuations, determined by the oscillation of the resistance of the gas-sensitive element of the sensor.

In the case of an inoperative sensor, no voltage fluctuations are observed in the sensor output signal (curve 1).

Figure 2 shows the Fourier spectrum of the output signal of a working sensor in an atmosphere of air with the addition of CO. The spectrum is characterized by individual high-amplitude peaks corresponding to voltage fluctuations at oscillation frequencies of 0.55 Hz and 1.11 Hz.

The proposed method for determining the operability of a sensor, for example, for a CO gas, consists in distinguishing two frequency regions, where one of the regions contains the oscillation frequency, and the second region certainly does not contain any of the frequencies. Further, the two selected signals are mutually subtracted and compared with the threshold. For a working sensor, the resulting signal (containing a high-amplitude oscillation frequency) must be guaranteed to exceed a threshold, which indicates the sensor's working ability or, in the case of a working senor, the presence of CO gas in the atmosphere. In the case of work with other gases, there may be more such frequencies.

The proposed method can be implemented using the device shown in figure 3, where 3, 4 - notch filters based on operational amplifiers; 1 - load resistor from which the output signal is removed; 5 - device for mutual subtraction of signals from 3 and 4 and comparison with a threshold, 2 - sensor.

The value of the load resistor 1 is determined from the criterion for removing the maximum signal power from the resistor. The values of capacities and resistors in the notch filters 3 and 4 are determined by the value of the oscillation frequency of the sensor resistance for the CO gas. These values are calculated at the stage of preliminary investigation of the sensor in the atmosphere with a guaranteed CO gas content with a known concentration.

The determination of the oscillation frequencies is carried out according to the following algorithm: a measurement is made of the noise of the sensor in an atmosphere of air with CO gas; the Fourier transform of the measured noise is carried out and the oscillation frequencies are determined from the obtained spectrum. Block 3 together with the load resistor 1 form a notch filter configured to pass the frequency region near the peak with a maximum amplitude of the oscillation of the sensor resistance. Block 4 together with the load resistor 1 form a notch filter tuned to the frequency range of the signal, for which, according to preliminary measurements, there is no resistance oscillation. Block 5 performs the function of mutual subtraction of signals and comparison with a threshold. If the threshold is exceeded by 2–3 times, a nonzero signal appears at the output of block 5.

All units are based on operational amplifiers, resistors, and capacitors.

The proposed method allows you to quite simply, quickly and reliably determine the fact of the gas sensor working in the atmosphere and can be used for a wide range of gas analyzers with a heated sensing element.

Claims (1)

A method for determining the operability of a gas sensor, which consists in measuring the signal amplitudes at the sensor output when the sensor is heated, characterized in that the signal amplitudes at the sensor output are measured when it is heated in the temperature range of gas adsorption on the surface of the sensor at least at least at two fixed frequencies, determined by the type of the measured gas, the magnitudes of the amplitudes of the signals are compared and the efficiency of the sensor is judged by the difference.

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