JPH02157648A - Instrument for measuring concentration of oxygen - Google Patents

Abstract

PURPOSE:To prevent rush current and to make rapid and exact measurement by gently increasing a bias voltage within timer set time after completion of warming up. CONSTITUTION:An oxygen sensor 6 and a power source section 10 for biasing at the time of starting are connected via a switch 13 to turn on a heater control section 9 and to supply the power source to a heater 5 and a sensor 6 as well as to simultaneously operate a timer 12 at the time of measurement. A stabilized zirconia disk 2 attains the operatable state after the completion of this warming-up. The power source section 10 gently increases the bias voltage. The sensor 6 is interrupted from the power source section 10 by the switch 13 when a set up signal is outputted from the timer 12. The sensor 6 is then connected to a power source section 11 for stationary biasing. The specified bias voltage is then impressed between platinum electrodes 3a and 3b. The excess oxygen molecules which do not receive the limitation of diffusion by a vent hole 4b in the gap 4a of a cap 4 are gently discharged through the disk 2 by this the rush current is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to an oxygen concentration measuring device equipped with a heating type oxygen sensor.

"Prior Art" As an oxygen sensor included in an oxygen concentration measuring device, the one shown in FIG. 5 is conventionally known.

In the figure, numeral 1 is an oxygen sensor. This oxygen sensor l includes a stabilized zirconia disk 2 and two platinum electrodes 3a.
, 3b, a cap 4, and a heater 5. The stabilized zirconia disk 2 is made by processing stabilized zirconia into a disk shape. The above stabilized zirconia is a mixture of pure zirconium oxide (ZrO,), yttrium oxide (Y to S), and calcium oxide (Cab).
) etc., and due to the oxygen ion vacancies introduced inside during the solid solution, at high temperatures,
It exhibits properties as a solid electrolyte, that is, oxygen ion conductivity. The platinum electrode 3a is formed on the upper surface of the stabilized zirconia disk 2 in the drawing, and the platinum electrode 3b is formed on the lower surface of the stabilized zirconia disk 2 in the drawing.

The cap 4 covers the platinum electrode 3a with a predetermined gap 4a in between, and is adhesively fixed to the upper peripheral edge of the stabilized zirconia disk 2. A small ventilation hole 4b is bored in the center of the head plate of the cap 4.

Air can enter and diffuse into the gap 4a in the cap 4 from the outside through the ventilation hole 4b. Further, the heater 5 includes a film-shaped heating resistor that generates Joule heat when energized. This heating resistor, that is, the heater 5 is connected to the head plate portion 4c of the cap 4.
is formed in close contact with the outer surface of the

The oxygen sensor 1 having the above configuration is placed in a measurement gas and operates as follows. First, the heater 5 is energized to heat the stabilized zirconia disk 2, and the platinum electrode 3a
A bias voltage is applied between both surfaces of the stabilized zirconia disk 2 using the electrode 3b as a negative electrode and the platinum electrode 3b as a positive electrode. The stabilized Zirmania disk 2 to which a bias voltage has been applied does not exhibit oxygen ion conductivity at an initial low temperature, but when it is eventually heated to around a predetermined temperature (approximately 400°C), oxygen ion conductivity occurs. It becomes conductive and performs the oxygen pumping action described below.

That is, the stabilized zirconia disk 2 takes into itself the oxygen molecules shown by the arrows in the void 4a via the platinum electrode 3a (negative electrode). Then, after ionizing the captured oxygen molecules and transporting them to the opposite surface, the platinum electrode 3
b (positive electrode), and is again discharged to the outside (in the direction of arrow B) as oxygen molecules. Due to this movement of oxygen, a current using oxygen ions as carriers (hereinafter referred to as oxygen ion current) flows through the stabilized zirconia disk 2.
As shown in Figure 6, this oxygen ion current is due to the oxygen in the measurement gas! Increases in increments of 1 degree. The reason for this is
This is because the higher the oxygen concentration, the more oxygen molecules are taken in. On the other hand, regarding the bias voltage, the oxygen ion current does not necessarily increase as the bias voltage increases; as shown in the figure, the bias voltage region where the oxygen ion current is constant is ,f,・
... exists. The oxygen ion current that exhibits a constant value in the bias voltage regions f, r, . . . is hereinafter referred to as a limiting current. Such a limiting current can be obtained by
This is because one surface of the stabilized zirconia disk 2 is covered with a cap 4 having a ventilation hole 4b. That is, when the bias voltage is increased, the amount of oxygen molecules taken into the stabilized zirconia disk 2 increases, so that the rate of decrease of oxygen molecules in the void 4a also becomes faster. on the other hand. External replenishment that corresponds to the decrease in oxygen molecules in the void 4a is limited to a certain extent by the small ventilation holes 4b, so in a stable state, regardless of the magnitude of the bias voltage, the internal supply of oxygen molecules in the stabilized zirconia disk 2 ends up being limited. The amount of oxygen ion movement is constant,
This becomes the limiting current. FIG. 7 is a characteristic diagram showing the relationship between oxygen concentration and limiting current value. It can be seen from this figure that the oxygen concentration and the limiting current value have a linear relationship. Therefore, in an oxygen concentration measuring device equipped with an oxygen sensor 1, a bias voltage of Vw (sixth
(see figure) and detects the limiting current value at that time. It is designed to detect once.

"Problem to be Solved by the Invention" By the way, in the above-mentioned conventional oxygen concentration measuring device using the oxygen sensor 1, as shown in FIG. Therefore, a constant bias voltage was already applied between the platinum electrodes 3a and 3b before warm-up. For this reason,
The following inconvenience occurred. That is, immediately after the warm-up ends (after about 30 seconds), the concentration of oxygen molecules inside the gap 4a is the same as the concentration of oxygen molecules outside the cap 4,
Therefore, oxygen molecules are in a state where they can move in large quantities within the stabilized zirconia disk 2 without being supplied from the outside via the vent hole 4b. In addition to this, a large bias voltage is applied immediately after the warm-up is completed, so that after the warm-up is completed, as shown by the broken line C in FIG. A large inrush current was occurring. For this reason,
The problem has been that it takes a lot of time to obtain a stable output current (limit current).

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oxygen concentration measuring device that can perform quick and accurate measurements by preventing rush current.

"Means for Solving the Problems" This invention provides a solid electrolyte layer exhibiting oxygen ion conductivity,
The oxygen sensor includes bias electrodes formed on both sides of the solid electrolyte layer, a gas diffusion chamber, and a heating element that heats the solid electrolyte layer. The above problem is solved by providing a means for doing so.

"Effect" After warm-up is completed, the bias voltage increases gradually within the timer set time, so excess oxygen molecules that exist in the internal space of the cap part and are not restricted by the ventilation holes are stabilized. It is slowly discharged through the zirconia disk. Therefore, no inrush current occurs and the system stabilizes quickly.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the electrical configuration of an oxygen concentration measuring device according to an embodiment of the present invention. In this diagram,
6 is an oxygen sensor having the same configuration as the oxygen sensor 1 shown in FIG. The resistor 7 and the current source 8 represent the electrical configuration of the oxygen sensor 6 as an equinodal circuit. That is,
The resistor 7 represents the heater 5 in FIG. 4, and the current source 8 represents the stabilized zirconia disk 2 and the two platinum electrodes 3a and 3b formed on both sides of the stabilized zirconia disk 2 in the same figure. It is something.

9 is a heater control section that controls the temperature of the heater 5.

Further, IO is a starting bias power supply section having an integral circuit configuration, and as shown in FIG. 2, it is composed of a voltage source 100, an operational amplifier IO, a feedback capacitor 120, and a resistor . As a result, when the voltage source lOO is turned on, it outputs a voltage (solid line Ba in FIG. 3) that gradually increases over time. Note that this voltage increase characteristic can be arbitrarily set by appropriately selecting the feedback capacitor 120 and the resistor 130 and changing the time constant. Reference numeral 11 denotes a constant bias power supply section that outputs a constant voltage (solid line Ba in Figure 3), which is a well-known constant voltage '
2t[ is used. 12 is a timer, and when the bias power supply is turned on (that is, the voltage source 100 is
(When the timer enters the N state), time measurement is started, and a timer is set when 90 seconds have elapsed from the start of time measurement. Also,
Reference numeral 13 denotes a changeover switch for switching the connection state between the oxygen sensor 6 and the starting bias power supply unit 10 or the steady bias power supply unit 11 to either one. 14 is an l/v converter that converts the output current signal into a voltage signal.

In the above configuration, to measure oxygen concentration, first,
The oxygen sensor 6 and the starting bias power supply unit 10 are connected via the switch 13. and,
The heater control section 9 is turned on, power is applied to the heater 5, and at the same time, bias power is applied to the oxygen sensor 6 at the time of starting. At the same time, the timer 12 also starts timing. Thirty seconds after the heater power is turned on, warm-up is completed and the stabilized zirconia disk 2 is ready to perform the oxygen pumping action. However, at this point, the bias voltage Ba (Figure m3) applied between the platinum electrodes 3a and 3b from the bias power supply unit 10 during startup is still low (
Therefore, as shown in FIG. 4, the output current of the oxygen sensor 6 is weak. After the warm-up is completed, the starting bias power supply unit IO gradually increases the bias voltage Ba along the curve shown in FIG. 3, and almost reaches the steady-state value Vs just before the timer set time elapses. Do it like this. During this time, the output current A of the oxygen sensor 6 also gradually increases in accordance with the increase in the bias voltage Ba, as shown in FIG. When 90 seconds have passed after the heater is turned on, the timer 12 outputs a set-up signal to the changeover switch 13. When receiving the set-up signal, the changeover switch 13 disconnects the oxygen sensor 6 and the starting bias power supply 10 and connects the oxygen sensor 6 and the steady bias power supply 11. As a result, a constant bias voltage Bb is applied between the platinum electrodes 3a and 3b.
(Fig. 3) is applied. The level of this bias voltage Bb is approximately the same as the level Vs of the output voltage (bias voltage) of the starting bias power supply unit 10 immediately before the timer set time elapses.

According to the above configuration, excess oxygen molecules existing in the gap 4a in the cap 4 whose diffusion is not restricted by the vent hole 4b are slowly discharged through the stabilized zirconia disk 2, so that an inrush current can be prevented from occurring. Therefore, stabilization time can be shortened, and rapid and accurate measurements can be made.

In the above-described embodiment, a case was described in which the timer 12 and the changeover switch 13 were used to switch from the starting bias power supply section 10 to the steady-state bias power supply section 11.
2 and changeover switch 13 are not essential.

For example, by using only a bias power supply with the same configuration as shown in Figure 2, if the time constant is set appropriately, almost the same effect as described above can be obtained (the curve shown by the solid line in Figure 3).
can be obtained.

Furthermore, in the above embodiment, the case was described in which the bias voltage at startup was increased along a gentle curve, but instead of this, the bias voltage at startup may be increased gradually in stages. You can also do it.

"Effects of the Invention" As is clear from the above explanation, the oxygen F4 degree measuring device of the present invention is equipped with a means for gradually raising the bias voltage at startup and then keeping it constant, so that warm-up is completed. Even immediately after, excess oxygen molecules present in the gas diffusion chamber can be slowly discharged through the solid electrolyte layer. Therefore, generation of rush current can be prevented. Therefore, stabilization time can be shortened,
This enables quick and accurate measurements.

Therefore, to prevent oxygen deficiency, oxygen fi[2
It is suitable for application in cases where promptness is required, such as measurement of

[Brief explanation of the drawing]

Fig. 1 is a professional diagram showing the electrical configuration of an oxygen concentration measuring device that is an embodiment of the present invention, Fig. 2 is a circuit diagram showing the electrical configuration of the starting bias power supply section, and Fig. 3 is the same. FIG. 4 is a diagram showing temporal fluctuations in the output current in the embodiment and the conventional device; FIG. 5 is applied to the embodiment. FIG. 6 is a side sectional view showing the configuration of the oxygen sensor, FIG. 6 is a diagram showing the output current characteristics of the oxygen sensor, and FIG. 7 is a diagram showing the limiting current characteristics of the oxygen sensor. 1.6...Oxygen sensor, 2...Stabilized zirconia disk (solid electrolyte WI), aa, ab
...Platinum electrode (bias electrode), 4...
・Cap (gas diffusion chamber), 4a...Gap (gas diffusion chamber), 4b...Vent hole, 4C...
・Headboard part, 5... Heater (heating element), 7...
... Resistance (heating means), 8 ... Current source (solid electrolyte layer, bias electrode), 9 ... Heater control section, 10 ... Bias power supply section at startup , 11...
... Steady bias power supply section, 12 ... Timer, 13 ... Switch 1. Figure 1 Figure 2

Claims (1)

[Scope of Claims] An oxygen device comprising a solid electrolyte layer exhibiting oxygen ion conductivity, bias electrodes formed on both sides of the solid electrolyte layer, a gas diffusion chamber, and a heating element that heats the solid electrolyte layer. An oxygen concentration measuring device comprising: a sensor; and means for gradually raising a bias voltage and then keeping it constant at the time of starting.