US 2003/0192781 A1 · Process and device for monitoring the hydrogen concentration

Abstract

A process and a device are provided for monitoring the hydrogen concentration in a gas with at least one device, which comprises an electrochemical gas sensor and a bipotentiostat, e.g., for use in internal combustion engines with hydrogen, in fuel cells and in the petrochemical industry. The electrochemical gas sensor used has two working electrodes (3) and (4), with which the hydrogen and oxygen concentrations are determined in the gas in different steps due to the application of a voltage by a bipotentiostat (5-18). In an additional, optional step, a voltage in the range of −1,100 mV to −800 mV is applied to a working electrode (4), so that hydrogen is formed at the working electrode (4) and the functional surface of the working electrode (4) as well as the sensitivity of the working electrode (3) to hydrogen can be checked. A cyclic repetition of the process steps, preferably offset in time, with two devices makes possible the continuous monitoring of the hydrogen and oxygen concentrations with regular checking of the working electrodes (3, 4) for their readiness to function.

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Claims20

Dependent claims

A process for monitoring the hydrogen concentration in a gas mixture with at least one first device comprising an electrochemical gas sensor, the process following steps forming a measuring cycle, wherein the process begins with any one of the steps comprising:

a) applying a voltage to a first working electrode in a first potential range, bringing about the oxidation of hydrogen, via a first operational amplifier, applying a voltage to a second working electrode in a second potential range, bringing about the reduction of oxygen, via a second operational amplifier, measuring a current conduction proportional to the concentration of hydrogen at the first working electrode, measuring a current conduction proportional to the concentration of oxygen at the second working electrode, sending the measured current values as a signal to a microcontroller and comparing the measured values with a preset signal value at the microcontroller;
b) applying to the two working electrodes a voltage in the second potential range, bringing about a reduction of oxygen, via the first and second operational amplifiers, measuring a current conduction proportional to the concentration of oxygen at the first and second working electrodes, sending the measured current values as a signal to the microcontroller and comparing the measured values with preset signal values at the microcontroller;
and
c) interrupting a connection between the first operational amplifier and the first working electrode by opening a first switch to form an open circuit, determining an open circuit potential at the first working electrode, sending the open circuit potential value as a signal to the microcontroller via an instrument amplifier, comparing the open circuit signal with preset parameters at the microcontroller, applying a voltage in the second potential range to the second working electrode, bringing about the reduction of oxygen, via the second operational amplifier, measuring a current conduction proportional to the concentration of the oxygen at the second working electrode, sending a measured current conduction as a signal to the microcontroller and comparing the current conduction signal with a preset signal value at the microcontroller.

1 more element

A device comprising:

a first working electrode with a first operational amplifier for applying a voltage to the first working electrode in a first potential range, bringing about the oxidation of hydrogen;
a second working electrode with a second operational amplifier for applying a voltage to the second working electrode in a second potential range, bringing about the reduction of oxygen;
a measuring device with a microcontroller, the measuring device for determining an open circuit potential and measuring a current conduction proportional to the concentration of hydrogen at the first working electrode and measuring a current conduction proportional to the concentration of oxygen at the second working electrode and sending the measured current values as a signal to the microcontroller and comparing the measured values with a preset signal value at the microcontroller, the first and second operational amplifiers applying to the two working electrodes a voltage in the second potential range, bringing about a reduction of oxygen and the measuring device measuring a current conduction proportional to the concentration of oxygen at the first and second working electrodes and sending the measured current values as a signal to the microcontroller and comparing the measured values with preset signal values at the microcontroller and a switch interrupting a connection between the first operational amplifier and the first working electrode to form the open circuit and the measuring device determining an open circuit potential at the first working electrode and sending the open circuit potential value as a signal to the microcontroller via an instrument amplifier and comparing the open circuit signal with a preset signal value at the microcontroller and the second operational amplifier applying a voltage in the second potential range to the second working electrode, bringing about the reduction of oxygen, and the measuring device measuring a current conduction proportional to the concentration of the oxygen at the second working electrode and sending a measured current conduction as a signal to the microcontroller and comparing the current conduction signal with a preset signal value at the microcontroller, the first working electrode being part of one of a first device unit or a second device unit and covering the first potential range with 0 mV to 200 mV and the second potential range with −700 mV to −300 mV;
and the second working electrode covering the second potential range with −700 mV to −300 mV as well as the third potential range with −1,100 mV to −800 mV.

1 more element

A process for monitoring the hydrogen concentration in a gas mixture with at least one first device comprising an electrochemical gas sensor, the process comprising the steps of forming a measuring cycle, beginning with any one of the steps of:

applying a voltage to a first working electrode in a first potential range, bringing about the oxidation of hydrogen, via a first operational amplifier and applying a voltage to a second working electrode in a second potential range, bringing about the reduction of oxygen, via a second operational amplifier and measuring a current conduction proportional to the concentration of hydrogen at the first working electrode and measuring a current conduction proportional to the concentration of oxygen at the second working electrode and sending the measured current values as a signal to a microcontroller and comparing the measured values with a preset signal value at the microcontroller;
applying to the two working electrodes a voltage in the second potential range, bringing about a reduction of oxygen, via the first and second operational amplifiers, and measuring a current conduction proportional to the concentration of oxygen at the first and second working electrodes and sending the measured current values as a signal to the microcontroller and comparing the measured values with preset signal values at the microcontroller;
interrupting a connection between the first operational amplifier and the first working electrode by opening a first switch to form an open circuit, and determining an open circuit potential at the first working electrode and sending the open circuit potential value as a signal to the microcontroller via an instrument amplifier and comparing the open circuit signal with a preset signal value at the microcontroller and applying a voltage in the second potential range to the second working electrode, bringing about the reduction of oxygen, via the second operational amplifier, and measuring a current conduction proportional to the concentration of the oxygen at the second working electrode and sending a measured current conduction as a signal to the microcontroller and comparing the current conduction signal with a preset signal value at the microcontroller.

Dependencies are inferred from the claim text.

Description3,321 words

Summary2,139 words

#The present invention pertains to a process and a device for monitoring the hydrogen concentration in a gas mixture.

#An electrochemical oxygen sensor with two working electrodes called a measuring electrode and a protective electrode, a counterelectrode called an auxiliary electrode, as well as a reference electrode is described in DE 197 26 453 C2. The measuring electrode, the protective electrode and the auxiliary electrode are arranged plane-parallel to one another with mats introduced between them, which are impregnated with an electrolyte and act as separators. The sensitivity of the sensor to vibration is considerably reduced by this type of arrangement. The electrolyte with the electrodes located in it is screened from the gas to be measured via a diffusion membrane consisting of polytetrafluoroethylene. All electrodes used are made of the same material, e.g., gold, platinum or alloys thereof An electrochemical gas sensor with a diffusion membrane consisting of a polymer containing bis-2,2-trifluoromethyl-4,5-difluoro-1,3-dioxol, especially a copolymer from the monomers bis-2,2-trifluoromethyl-4,5-difluoro-1,3-dioxol and tetrafluoroethylene (trademark “Teflon® AF”) has been known from DE 200 22 508 U1. Shorter response time and improved sensitivity to gases such as oxygen and hydrogen can be observed during the measurement with such diffusion membranes.

#The object of the present invention is to provide a process and a device that make possible the monitoring of the hydrogen concentration in a gas mixture and in which the readiness to function of the device is checked at the same time. In addition, it is possible to monitor the oxygen concentration.

Brief description of the drawings2 figures

#In the drawings:

#FIG. 1 is a schematic view showing a device with an electrochemical gas sensor for monitoring the hydrogen and oxygen concentrations in a gas; and

#FIG. 2 is a graph showing the changes in the voltage over time at the two working electrodes of the device according to FIG. 1.

Detailed description1,129 words

#Referring to the drawings in particular, FIG. 1 shows a device with an electrochemical gas sensor and a bipotentiostat 5-18 for monitoring the hydrogen and oxygen concentrations in a gas mixture. The electrochemical gas sensor comprises a first working electrode 3 and a second working electrode 4, as well as a counterelectrode 2 and a reference electrode 1. A corresponding voltage is applied to the two working electrodes 3, 4 by the bipotentiostat 5-18, which is controlled by a microcontroller 14. The bipotentiostat 5-18 comprises a first precision resistor 7, a first operational amplifier 8 and a second operational amplifier 11, a second precision resistor 17 and a third operational amplifier 18. The voltage is applied to the working electrodes 3, 4 via two circuits that have, in principle, an identical design within the device. The mode of operation of the circuits is described on the basis of the circuit for the first working electrode 3. A signal, which is converted by a first digital-analog converter 13 and is amplified by the first operational amplifier 8, with which the first precision resistor 7 is connected in parallel, is preset in the microcontroller 14. Via a downstream, closed first switch 9, the signal reaches the first working electrode 3, to which a voltage is correspondingly applied. The first switch 9 is connected to the microcontroller 14 via a line, which is shown as being interrupted in FIG. 1 with the two line terminations A for reasons of clarity. The first switch 9 is actuated by the microcontroller 14 such that it is closed when a voltage is applied to the first working electrode 3 and it is opened when the course of the open circuit potential is measured on the first working electrode 3; this corresponds to the voltage measured with a high ohmic resistance between the reference electrode and the working electrode, without an external potential regulation being performed (open circuit). The first operational amplifier 8 is connected to a multiplexer 16 via a line that is likewise shown as being interrupted by two line terminations C. The signals entering the multiplexer 16 are sent to an analog-digital converter 15 and from there to the microcontroller 14. The first working electrode 3 is located on the side of the electrochemical gas sensor facing the gas to be measured. The first working electrode 3, the reference electrode 1 and the counterelectrode 2 are connected, via the intermediary of the third operational amplifier 18, to a first instrument amplifier 5, which sends the signals to the multiplexer 16 during the measurement of the course of the open circuit potential on the working electrode 3. From there, the signals reach the microcontroller 14 via the analog-digital converter 15. A circuit fully analogous to the above-described circuit for the first working electrode 3 is provided for the second working electrode 4. A second digital-analog converter 12 sends the signals from the microcontroller 14 to the second operational amplifier 11, with which the second precision resistor 17 is connected in parallel. Via a second switch 10, which is likewise shown in the closed state in FIG. 1, the signal reaches the second working electrode 4, to which a corresponding voltage is applied. The second switch 10 is connected to the microcontroller 14 via a line shown as being interrupted at the line terminations B and can be actuated in the same manner as the first switch 9 when needed. The second operational amplifier 11 is likewise connected to the multiplexer 16. The second working electrode 4 is located on the side of the electrochemical gas sensor facing the liquid electrolyte. The second working electrode 4, the reference electrode 1 as well as the counterelectrode 2 via the third operational amplifier 18 are connected to a second instrument amplifier 6, which likewise sends the incoming signals to the multiplexer 16 for an optionally performed measurement of the course of the open circuit potential on the second working electrode 4.

#FIG. 2 shows the time course of the voltage on the first working electrode 3 and on the second working electrode 4 in millivolts [mV], as voltage is applied to them corresponding to the actuation by the microcontroller 14.

#With the switches 9, 10 closed, 100 mV are present on the first working electrode 3 for determining the hydrogen concentration during the first time period B1, and −600 mV are present on the second working electrode 4 for the determination of the oxygen concentration.

Process and device for monitoring the hydrogen concentration

Life of this patent

Process and device for monitoring the hydrogen concentration

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims20

Description3,321 words

Drawings

Classification4 codes

Life of this patent

Description3,321 words