JPH065221B2 - Zirconia oxygen analyzer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zirconia-type oximeter in which wiring required for temperature control and signal transmission is significantly reduced.

<Prior Art> Conventionally, in an oximeter using a zirconia oxygen sensor, two lines for extracting an output signal from the sensor, two lines for supplying power to a heater for heating the sensor,
Moreover, in order to adjust the temperature of the heater, a total of six compensating wires such as two thermocouples for detecting the temperature of the sensor portion are required.

Further, conventionally, a plurality of zirconia-type oxygen sensors may be collectively handled by one converter. In such a case, however, the number of wires between the converter and the sensor becomes too large. , The temperature controllers TC1, T are provided for each of the zirconia oxygen sensors S1, S2 ,.
C2 ... is provided and four wires for temperature control are individually reduced to reduce the number of wires to the converter CV1.

Thus, in the conventional device, the number of wires is large, the terminal box is inevitably large, and the cost is high.
In addition, it was a cause of incorrect wiring. Furthermore, when handling multiple zirconia oxygen sensors with one converter,
It was necessary to provide a temperature controller for each sensor.

<Problems to be Solved by the Invention> A technical problem to be solved by the present invention is to drastically reduce wiring required for temperature control and signal transmission in the zirconia oximeter.

<Means for Solving Problems> In order to achieve such an object, the present invention applies a voltage from a power supply to a zirconia oxygen sensor and measures a current flowing between electrodes of the zirconia oxygen sensor. In a zirconia-type oxygen sensor densitometer for measuring the oxygen concentration, a first diode connected in series between the power supply and the zirconia-type oxygen sensor, and provided in proximity to the zirconia-type oxygen sensor, , A heater-temperature sensor that heats the zirconia-type oxygen sensor and measures the temperature of the zirconia-type oxygen sensor based on a current flowing through itself, and is connected in series between the heater-temperature sensor and the power source, A second diode provided with a polarity opposite to that of the first diode; and a positive polarity and a negative polarity of the power source are alternately switched, A switch means for applying a forward bias voltage alternately diode and the second diode, upon application of a forward bias voltage to the second diode, to measure the current flowing through the heater and temperature sensor,
A current detection element for obtaining the temperature of the heater / temperature sensor, and a switch for switching the switching means when the temperature obtained by the current detection element reaches a set temperature to apply a forward bias voltage to the first diode for measurement. It is characterized in that a drive circuit for switching to the mode is provided.

<Operation> The above-mentioned technical means operates as follows. That is, the measurement by the zirconia oxygen sensor and the temperature adjustment by the heater / temperature sensor resistor are performed using the same wiring between the sensor and the converter, or at least a part of the wiring is shared, Since the time division is performed, the number of wires required for temperature control and signal transmission can be significantly reduced as compared with the conventional device.

<Example> An example of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an apparatus according to an embodiment of the present invention. In the figure, S is a zirconia-type oxygen sensor as shown in, for example, Japanese Patent Publication No. 59-26895, and this portion will be described with reference to an enlarged view of FIG. S01 is a solid electrolyte using stabilized zirconia, S02 is an adapter forming a chamber, and zirconia S
01 is attached to one surface. A diffusion hole S03 is provided at the top of this adapter. S04 is a porous inner electrode provided on the surface on the chamber side, and S05 is a porous outer electrode provided on the outer surface of the zirconia S01.

Stabilized zirconia becomes a good oxygen ion conductor at high temperature, and therefore when a DC voltage is applied between the electrodes in a heated state, this causes a difference between oxygen in the outdoor gas environment and oxygen in the internal gas environment. A pressure gradient is formed, and a current proportional to the oxygen diffused into the internal chamber flows through the diffusion hole S03 between these electrodes.

Returning to FIG. 1, D1 is a first diode connected in series to the zirconia oxygen sensor S, and R1 is a heater / temperature sensor resistor. As the resistor, a platinum wire or a tungsten wire having a large temperature coefficient of resistance is used. Further, the one in which the relationship between the temperature and the resistance is obtained in advance is used. D2 is a second diode having a polarity opposite to that of the first diode D1 and connected in series to the heater / temperature sensor resistor R1.

The two series circuits formed by these are connected to the wiring L1.
And L2 are connected in parallel. The portion A surrounded by the alternate long and short dash line is a portion that is heated to a high temperature, and in an actual configuration, it must be installed separately from the first and second diodes D1 and D2.

A portion B surrounded by an alternate long and short dash line is a converter, in which a power source Vo, changeover switches SW1, SW2 and SW3 for inverting the polarity of the power source and connecting to the two series circuits, a resistor R2 and a zener diode ZD1 A constant voltage circuit, a detection resistor Ro that detects the current i1 flowing in the series circuit to generate the output voltage Eo, and a current detection element M1 that detects the current i2 flowing in the heater / temperature sensor resistor R1.

COM is an arithmetic unit that generates a temperature control signal based on the signal Ei from the current detection element M1, and DR1 is a drive circuit that generates pulses for driving the changeover switches SW1 to SW3 based on the output of this arithmetic unit.

The operation of the apparatus according to the embodiment of the present invention thus configured will be described with reference to the waveform chart of FIG. In FIG. 3, the figure (a) shows the state of temperature control, and the figure (b) shows the state of measurement. When the changeover switches SW1 to SW3 are changed to the states shown in FIG. 1, the changeover switches SW1 to SW3 are in the measurement state, and the first diode D1 is forward biased,
A measurement current i1 flows between the electrodes of the zirconia oxygen sensor S.

As shown in FIG. 3 (b), immediately after the start of the measurement period, a large amount of oxygen exists in the chamber of the zirconia oxygen sensor S, so a large current flows, but the diffusion hole S
Since the diffusion rate of oxygen performed through 03 is slower than the rate at which oxygen becomes oxygen ions and moves through the zirconia S01 portion, the amount of oxygen existing in the chamber decreases with the passage of time, and the measured current i1 is shown in the figure. It gradually decreases as shown.

The oxygen amount is measured by integrating the current i1 over the measurement period to '(in the present embodiment, the output voltage Eo detected by the detection resistor Ro is integrated and obtained).

Next, the temperature is adjusted by switching the changeover switches SW1 to SW3 to the state opposite to that shown in FIG. As a result, the second diode D2 is forward biased, and the current i2 flows through the heater / temperature sensor resistor R1.

The resistance value Rh of the heater / temperature sensor resistor R1 is calculated as follows: Rh = Vo / i2 (1) Since the relationship between the temperature and the resistance value of the resistor R1 is previously calculated, the temperature is calculated from the resistance value Rh. You can know

The arithmetic unit COM (1) is calculated, and an output based on the difference between the temperature signal and the set temperature is given to the drive circuit DR1.

The drive circuit DR1 generates a drive pulse composed of, for example, three states of positive, zero, and negative. The changeover switches SW1 to SW3 are changed over by this state pulse, and the period to
The temperature control and the measurement in the period to 'are alternately performed in a time division manner. In the temperature adjustment period to, the power source Vo is further connected to the heater / temperature sensor S to perform heating, and
It consists of the remaining period. The period t1 is determined based on the error signal between the temperature signal and the set temperature, and the temperature is controlled so that the resistance value of the heater / temperature sensor resistor R1 becomes constant based on this.

FIG. 4 is a circuit diagram showing an apparatus according to another embodiment of the present invention.
In the figure, the same elements as the elements in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the device of the present embodiment, as the zirconia oxygen sensor S,
A Nernst type sensor is used in which porous electrodes are provided on both sides of zirconia, and a reference gas and a measurement gas are directly contacted from both sides to generate an electromotive force according to a partial pressure difference of oxygen in these environmental gases. This sensor acts as a battery, and in the case of the device of this embodiment, the wiring L3 is newly provided and the measurement voltage is detected between the wiring L2 and L3.

The measurement by the zirconia oxygen sensor S and the temperature adjustment by the heater / temperature sensor resistor R1 are performed in a time-division manner, which is the same as the embodiment apparatus shown in FIG.

<Advantages of the Invention> According to the present invention, the measurement by the zirconia oxygen sensor and the temperature adjustment by the heater / temperature sensor resistor are performed by using the same wiring between the sensor and the converter, or Since at least part of the wiring is shared and the wiring is performed in a time-division manner, the number of wirings required for temperature control and signal transmission can be significantly reduced as compared with the conventional device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a partially enlarged view of the apparatus of the embodiment of the present invention shown in FIG.
FIG. 4 is a waveform diagram for explaining the operation of the device of the present invention shown in the figure, FIG. 4 is a circuit diagram showing another device of the present invention, and FIG. 5 is a configuration diagram of a conventional device. S ... Zirconia oxygen sensor, D1 ... First diode, R1 ... Heater / temperature sensor resistor, D2 ... Second diode, B ... Converter, Vo ... Power supply, SW1-SW
3 ... Changeover switch, COM ... Arithmetic device, DR1 ... Driving circuit, L1 to L3 ... Wiring

Claims (1)

[Claims] 1. A zirconia oxygen sensor densitometer for measuring oxygen concentration by applying a voltage from a power source to a zirconia oxygen sensor and measuring a current flowing between electrodes of the zirconia oxygen sensor, comprising: A first diode connected in series between the zirconia oxygen sensor and the zirconia oxygen sensor, which is provided in proximity to the zirconia oxygen sensor, heats the zirconia oxygen sensor, and based on the current flowing through itself, A heater / temperature sensor for measuring the temperature of a zirconia-type oxygen sensor, a second diode connected in series between the heater / temperature sensor and the power source, and having a polarity opposite to that of the first diode, and the power source. Is alternately switched between positive and negative polarities, and a forward bias voltage is alternately applied to the first diode and the second diode. And a value of a current flowing through the heater / temperature sensor when a forward bias voltage is applied to the second diode,
A current detecting element for obtaining the temperature of the heater / temperature sensor, and a switch for switching the switch means when the temperature obtained by the current detecting element reaches a set temperature to apply a forward bias voltage to the first diode for measurement. A zirconia-type oxygen sensor densitometer characterized by having a drive circuit for switching to a mode.