GAS SENSOR CONTROL APPARATUS DESIGNED TO ENSURE ACCURACY OF MEASUREMENT IN GAS SENSOR

• US 20080197022A1
• Filed: 02/20/2008
• Published: 08/21/2008
• Est. Priority Date: 02/20/2007
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: SUZUKI, Toshiyuki, KAWASE, Tomoo, KUROKAWA, Eiichi, KAWAKI, Yohei
• Granted Patent: US 8,052,863 B2
• Time in Patent Office: Days
• US Class Current: 205/775
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser

Abstract

The gas sensor control apparatus develops a first voltage based on a first reference voltage at a negative terminal of a gas sensor device through a resistor and a second voltage based on a second reference voltage at a positive terminal of the gas sensor device. A controller samples through the resistor a sensor current, as created upon the development of the first and second voltage for measuring the concentration of gas. When the impedance of the gas sensor device is measured, the controller alternates the first voltage across the first reference voltage. The value (i.e., a zero-point) of the voltage applied to the gas sensor device when the sensor current is zero (i.e., 0 mA) depends upon the first and second reference voltages. The zero-point is corrected by regulating the second reference voltage to match an applying voltage characteristic to the gas sensor device correctly.

Claims

1. A gas sensor control apparatus designed to control an operation of a gas sensor device equipped with a solid electrolyte body and a first and a second electrode affixed to opposed surfaces of the solid electrolyte body, comprising:

a sensor current sampling resistor connected in series to a first terminal that is one of a positive and a negative terminals which leads to the first electrode of the gas sensor device;

a first voltage supply circuit works to develop a first voltage based on a first reference voltage at the first terminal leading to the gas sensor device through said sensor current sampling resistor;

a second voltage supply circuit working to develop a second voltage based on a second reference voltage at a second terminal that is other of the positive and negative terminals which leads to the second electrode of the gas sensor device; and

a controller working to sample through said sensor current sampling resistor a sensor current that is an electric current flowing through the gas sensor device upon application of voltage across the gas sensor device through the first and second terminals resulting from development of the first and second voltage at the first and second terminals and to produce a signal based on the sensor current which is a function of concentration of a given gas, when it is required to measure an impedance of the gas sensor device, said controller alternating the first voltage across the first reference voltage and sampling and outputting a resulting change in the sensor current as representing the impedance of the gas sensor device.

2. A gas sensor control apparatus as set forth in claim 1, further comprising an IC on which said first voltage supply circuit is fabricated, and wherein said second voltage supply circuit has a reference voltage circuit which works to create the second reference voltage and is located outside the IC.

3. A gas sensor control apparatus as set forth in claim 1, wherein said second voltage supply circuit includes a voltage divider which has a resistor to produce a fraction of an output of a constant voltage source to create the second reference voltage.

4. A gas sensor control apparatus as set forth in claim 1, wherein said second voltage supply circuit includes a bridge circuit made up of four resistors and a first and a second switches disposed at a high potential side and a low potential side of the bridge circuit, respectively, and wherein said controller turns on and off the first and second switches alternatively to alternate the first voltage across the first reference voltage.

5. A gas sensor control apparatus as set forth in claim 1, wherein said second voltage supply circuit works to amplify the sensor current, as sampled through said sensor current sampling resistor, to control the second voltage, as developed at the second terminal.

6. A method of controlling a voltage to be applied to a gas sensor device equipped with a solid electrolyte body and a first and a second electrode affixed to opposed surfaces of the solid electrolyte body through a gas sensor control apparatus which includes (a) a sensor current sampling resistor connected in series to a first terminal that is one of a positive and a negative terminals which leads to the first electrode of the gas sensor device, (b) a first voltage supply circuit works to develop a first voltage based on a first reference voltage at the first terminal leading to the gas sensor device through said sensor current sampling resistor, (c) a second voltage supply circuit working to develop a second voltage based on a second reference voltage at a second terminal that is other of the positive and negative terminals which leads to the second electrode of the gas sensor device, and (d) a controller working to control the second voltage to determine and apply a voltage across the gas sensor device through the first and second terminals based on a given applying voltage characteristic and to sample through said sensor current sampling resistor a sensor current that is an electric current flowing through the gas sensor device resulting from application of the voltage across the gas sensor device to produce a signal based on the sensor current which is a function of concentration of a given gas, when it is required to measure an impedance of the gas sensor device, said controller alternating the first voltage across the first reference voltage and sampling and outputting a resulting change in the sensor current as representing the impedance of the gas sensor device, said method comprising:

sampling an output characteristic of the gas sensor device; and

correcting the applying voltage characteristic based on the sampled output characteristic so as to bring the voltage applied to the gas sensor device into agreement with a desired one.