JPS5910491B2 - Sensor static characteristic measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring static characteristics of an oxygen concentration sensor used as an air/fuel ratio detector in a mission control system, for example.

For example, this type of sensor is detected by a static characteristic measuring device.

When measuring the static characteristics (this characteristic is an inverted S-shaped curve as shown in Fig. 1) of the oxygen concentration sensor described in Japanese Patent Application Laid-open No. 49-126392', which is a device, conventionally the mission control The sensor is attached to a predetermined part of the system, and the fluctuating output electromotive force of the oxygen concentration sensor is passed through a low-pass filter to obtain an average voltage, which is used as a means for measuring static characteristics. However, this method is not suitable for the characteristics of the sensor shown by the dotted line in FIG.
When the oxygen concentration shown in in is given, the output electromotive force of the sensor becomes an asymmetrical waveform as shown in Aout in Fig. 2, so when this output Aout is averaged, it becomes lower than the actual amplitude center position Po. Since the level at position P is obtained, the characteristic shown by the solid line in FIG. 2 is detected, which is different from the static characteristic shown by the dotted line in the same figure, and is not suitable as a static characteristic measuring device for a sensor. Alternatively, instead of using gas flowing through the engineering mission control system, gas at a constant oxygen concentration is supplied from an oxygen gas cylinder or the like, and the output electromotive force of the sensor is measured by gradually changing the oxygen concentration. It is also possible to detect static characteristics, but since the static characteristics differ depending on the temperature, there are drawbacks such as keeping the temperature at the same high temperature as the exhaust gas and difficult to accurately detect parts with steep falls. Ta.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a static characteristic measuring device for a sensor that can accurately measure the static characteristics of a sensing object using simple means, and that can easily determine the superiority or inferiority of the performance of the sensing object. .

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 1 is an exhaust pipe, and 2 is an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas flowing through the exhaust pipe 1. In FIG.

As shown in Fig. 1, this sensor 2 generates an electromotive force in its output according to the oxygen concentration in the exhaust gas.As is clear from Fig. 1, when the oxygen concentration reaches a predetermined value, the output electromotive force increases. It has the property of rapidly decreasing to a low level. It is known that the oxygen concentration in the exhaust gas has a waveform with a constant period, but in the case of a single cylinder as an example, it has a substantially sine curve as shown in FIG. When the amplitude center of this oxygen concentration is at point A in Figure 4, the output A of sensor 2 will be the time ratio of the high level H and low level L as shown in Figure 5 A, as described in Figure 2. The H level is long and the L level is short, resulting in a waveform that is not 1:1 but asymmetrical in the vertical direction. The output A of said sensor 2 is amplified by a buffer preamplifier 3 and its output B is applied to a first input of a comparator 4.
The waveform of the output B is as shown in FIG. 5B. 5 is a ramp function generator.

The output C of the ramp function generator 5 is applied to the second input of the comparator 4. The output C of the ramp function generator 5 is shown in FIG.
As shown in FIG.
The decrease is repeated alternately, and when the level of the first input of the comparator 4 exceeds the level of the second input, the output D becomes a pulse as shown in FIG. 5D. The output C of the ramp function generator 5 becomes an increasing voltage when the pulse of the output D of the comparator 4 is "1", and becomes a decreasing voltage when the pulse is "0". In this way, the zero average value of the output of the ramp function generator 5, shown as a dashed line in FIG. 5C, approaches the center of the amplitude of the output B of the amplifier 3, shown as a dashed line in FIG. 5B. The output of this ramp function generator 5 is
A low-pass filter (or average value circuit) 6 provides an output E corresponding to the average value voltage of the ramp function generator 5, which is indicated by a chain line in FIG. 5C. As shown in FIG. 5E, this output E takes a value that converges to the amplitude center of the output B of the amplifier 3 after a predetermined time. Below, the amplitude center of the change in oxygen concentration (
When the point A in FIG. 4 is moved, the output voltage of the low-pass filter 6 is also generated as a different value, and by plotting this value, a characteristic of a steep fall as shown in FIG. 1 can be obtained.

Next, a specific circuit of an embodiment of the present invention will be explained with reference to FIGS. 6 and 7.

Note that the same parts as in FIG. 3 are indicated with the same reference numerals. First, in FIG. 6, the preamplifier 3 includes operational amplifiers 3a to 3d,
It is composed of diodes 3e to 3n, a variable resistor 31, and a resistor 3j. The comparator 4 is a comparison circuit 4a consisting of an arithmetic unit.
The ramp function generator 5 includes operational amplifiers 5a and 5b1.
It consists of a variable resistor 5C1, a reset/start switch 5d, an integrating capacitor 5e, and a resistor 5f. Furthermore, the low-pass filter 6 is composed of a power amplifier 6a, a capacitor 6b, and a resistor 6c. Operational amplifier 5b, resistor 5f
An integrating circuit S is constituted by the capacitor 5e and the capacitor 5e.
In the embodiment configured as described above, the output of the sensor 2 is amplified by the operational amplifier 3at3b, and then amplified to a desired value by the operational amplifier 3d, and then provided to the operational amplifier 4a.

This amplifier 4a is controlled by the output of the amplifier 5b of the ramp function generator 5, producing a pulse at the output of the comparator 4a as described above. This pulse operates the operational amplifier 5a, switches the polarity of the integral operation of the operational amplifier 5b, and sends out the output of the ramp function described above. Set switch 5
d was set to the set side during measurement. The operational amplifier 6a of the low-pass filter 6 averages the output of the operational amplifier 5b together with the capacitor 6b and resistor 6c and outputs the average value. In this embodiment, since the polarity of the integral of the ramp function generator 5 is determined digitally, the control becomes reliable. Figure 7 shows that the polarity of the integral of the comparator 4 and the ramp function generator 5 is switched at the sixth point.
In an embodiment different from that shown in the figure, the comparator 4 is an operational amplifier 4a.
, Zener diode 4b, resistor 4d, inverter 4e
The polarity of the integral of the ramp function generator 5 is switched by analog switches 5g and 5n.

The analog switch 5g is directly controlled by the output of the operational amplifier 4a and outputs a negative voltage -E, and the switch 5n is controlled by the output of the inverter 4c and outputs a positive voltage E. By integrating these voltages -E and E in an integrating circuit S, a ramp function is obtained. That is, the ramp function is increased or decreased when the output level of the operational amplifier 4a changes. By using this analog switch, the circuit configuration can be simplified. As described above, according to the present invention, there is an advantage that the static characteristics of the oxygen concentration sensor, which is a detector, can be accurately measured with a simple circuit in a state where the oxygen concentration fluctuates periodically, such as in exhaust gas. .

Further, according to the present invention, the performance state of the sensor can be easily determined by comparing the output of the sensor whose performance characteristics are known from the measurement results. Further, according to the present invention, there are various excellent effects such as the time required for developing a sensor used in an emission control system, which is one of the exhaust countermeasures, can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a static characteristic diagram of the oxygen concentration sensor, Fig. 2 is a characteristic diagram of the sensor when measured with a conventional sensor static characteristic measuring device, and Fig. 3 is a block diagram showing an embodiment of the present invention. 4 and 5 are characteristic diagrams and waveform explanatory diagrams for explaining the embodiment of FIG. 3, and FIGS. 6 and 7 are specific circuit diagrams of FIG. 3. 1... Exhaust pipe, 2... Oxygen concentration sensor, 3... Buffer preamplifier, 4... Comparator, 5... Ramp function generator, 6...
Low pass filter (average value circuit).

Claims (1)

[Claims] 1. A buffer preamplifier that amplifies the detection signal of the exhaust gas sensor, a comparator that compares the detection signal of this buffer preamplifier with the output signal of the ramp function generator, and increases or decreases according to the comparison signal of this comparator. The present invention further includes a ramp function generator that sends out an output signal, and the output of the ramp function generator is fed back to a comparator to converge the output signal of the ramp function generator to the amplitude center level of the detection signal. Characteristic sensor static characteristic measuring device