Method for determining the oxygen content in gases, uninfluenced by temperature variations

• US 4,394,222 A
• Filed: 11/19/1980
• Issued: 07/19/1983
• Est. Priority Date: 11/20/1979
• Status: Expired due to Term

• Current Assignee: Brown Boveri & CIE AG (ABB Limited)
• Original Assignee: Brown Boveri & CIE AG (ABB Limited)
• Inventors: Rohr, Franz-Josef
• Primary Examiner(s): Tung, T.
• Application Number:
  US06/208,432
• Time in Patent Office: 972 Days
• Field of Search: 204/1 S, 204/1 T, 204/195 S, 204/195 R
• US Class Current: 205/785
• CPC Class Codes: G01N 27/4065 Circuit arrangements specially adapted therefor
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser
• CPC Class Codes: G01N 33/0031 comprising two or more sensors, e.g. a sensor array

Abstract

Determining the oxygen content in gases, particularly combustion exhaust gases, uninfluenced by temperature variations of the gases by passing the gases into a first electrical measuring cell having a solid electrolyte and electrodes connected to a current source. A diffusion-limited electric current flow dependent on the oxygen content of the gases is obtained and measured as a first electrical signal. Passing an auxiliary gas with constant oxygen content into a second measuring cell similar to the first cell and under the same conditions and obtaining a second electrical signal. The quotient of the two electrical signals is a measure of the oxygen content of the gases uninfluenced by temperature variations of the gases.

Claims

1. Method for determining the oxygen content in gases influenced by temperature variations of the gases which comprises passing said gases in contact with a first electrochemical measuring cell connected to a voltage source, said electrochemical cell having a solid electrolyte which is heated to an operating temperature, and through which a diffusion-limited electric current flows which depends on the oxygen content of the gases and the magnitude of which is determined as a first electrical signal measuring the oxygen content of the gases, the combination therewith of deriving a second electrical signal from the oxygen content of an auxiliary gas with a constant oxygen content by passing the auxiliary gas in contact with a second electrochemical measuring cell which is approximately identical to the first measuring cell with respect to design, operation and operating conditions to obtain said second electrical signal, and forming a temperature-independent quotient from the two electrical signals and employing the quotient as a measure of the oxygen content of the gases, wherein a heater is disposed in the first measuring cell to heat the electrolyte which is an oxygen ion-containing solid electrolyte, a first electrode adjacent an inside surface of the electrolyte and a second electrode adjacent the opposite outside surface, said electrodes connected to the voltage source to form an electric circuit, with one of said electrodes acted on by said gases causing an electric current which flows as a function of the oxygen content of said gases, wherein the second measuring cell also has a solid electrolyte with electrodes on the inside and outside surfaces of the electrolyte, wherein the solid electrolytes of the first and the second measuring cells consist of one piece, wherein the outer electrode for the first cell and for the second cell each is surrounded by an interspace with openings for the introduction and discharge for the feed gases and the auxiliary gas, wherein the interspace of the first cell is connected to said gases and the interspace of the second cell is connected to the auxiliary gas with a double-throw switching device to enable switching the flow of gases from the first interspace to the second interspace and the flow of auxiliary gas from the second interspace to the first interspace and the reverse, wherein the electrodes of the second cell are connected to the voltage source to form a second electric circuit, with said auxiliary gas acting on one of said electrodes causing an electric current to flow in the second circuit as a function of the oxygen content of the auxiliary gas, wherein the two electric circuits are connected to a divider for forming the quotient of said two determined electric current signals, and wherein the temperature-independent quotient is fed to a receiving device acting as an indicating, regulating or controlling device.

2. Method according to claim 1, wherein the interior of the solid electrolyte is in communication with the ambient atmosphere, and wherein a common heater heats both cells.

3. Method for determining the oxygen content in gases influenced by temperature variations of the gases which comprises passing said gases in contact with a first electrochemical measuring cell connected to a voltage source, said electrochemical cell having a solid electrolyte which is heated to an operating temperature, and through which a diffusion-limited electric current flows which depends on the oxygen content of the gases and the magnitude of which is determined as a first electrical signal measuring the oxygen content of the gases, the combination therewith of deriving a second electrical signal from the oxygen content of an auxiliary gas with a constant oxygen content by passing the auxiliary gas in contact with a second electrochemical measuring cell which is approximately identical to the first measuring cell with respect to design, operation and operating conditions to obtain said second electrical signal, and forming a temperature-independent quotient from the two electrical signals and employing the quotient as a measure of the oxygen content of the gases, wherein a heater is disposed in the first measuring cell to heat the electrolyte which is an oxygen ion-conducting solid electrolyte, a first electrode adjacent an inside surface of the electrolyte and a second electrode adjacent the opposite outside surface, said electrodes connected to the voltage source to form an electric circuit, with one of said electrodes acted on by said gases causing an electric current which flows as a function of the oxygen content of said gases, wherein the second measuring cell also has a solid electrolyte with two electrodes on the inside and outside surfaces of the electrolyte wherein the second cell has, as compared to the first cell, in the vicinity of the electrodes, approximately, the same dimensions, the same design and the same heater, wherein the electrodes of the second cell are connected to the voltage source to form a second electric circuit with said auxiliary gas acting on one of said electrodes causing an electric current to flow in the second circuit as a function of the oxygen content of the auxiliary gas, wherein the two electric currents are connected to a divider for forming the quotient of said two determined electric signals, and wherein the temperature-independent quotient is fed to a receiving device acting as an indicating, regulating or controlling device, wherein the solid electrolyte of the first cell is tubular, wherein the heater is a heating tube surrounding the electrolyte forming a first interspace, wherein the second measuring cell is arranged in an extension of the heating tube as a mirror image of the first cell with respect to a mirror plane which extends perpendicularly to the longitudinal axis of the interspace, wherein the first interspace is separated by a partition arranged in the mirror plane from a second interspace, wherein each of the interspaces is closed off from the outside by a terminating wall, and wherein each wall has inlets for the introduction of the gases and the auxiliary gas, respectively.

4. Method according to claim 3, wherein the tubular solid electrolytes are each closed off at one end in the vicinity of the partition, and the other ends of the electrolytes are in communication with the outside space.