JP3117401B2 - Sensor life judgment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection circuit using a bridge circuit, and more particularly, to a method for judging the deterioration of a sensor with time.

[0002]

2. Description of the Related Art As an example of measuring the concentration of a gas contained in a gas phase, there is, for example, the measurement of the concentration of a gaseous alcohol in a gas phase. When measuring the concentration of the gaseous phase alcohol in the gas phase, it is known that an alcohol-containing liquid such as sake is injected into a heated measuring tank, and the gaseous phase alcohol concentration is detected by a contact combustion gas sensor. . This contact combustion type gas sensor is a gas sensor for detecting flammable gas, and is an element formed by burying a platinum resistance wire coil in an oxidation catalyst.

[0003] The principle of gas detection by the catalytic combustion type gas sensor having such a configuration is as follows.
When the air containing flammable gas comes into contact with this oxidation catalyst at about 300 ° C., even if the concentration of flammable gas is lower than the ignition temperature or lower than the lower limit of explosion, the combustion of the oxidation catalyst causes catalytic combustion. Occurs, and the heat of the reaction increases the temperature of the contact combustion type gas sensor to increase the electric resistance of the platinum resistance wire. The concentration of the combustible gas can be measured by extracting the increase in the electric resistance as an electric signal.

FIG. 2 shows an alcohol concentration measuring circuit using a catalytic combustion type gas sensor. As shown in FIG.
A bridge circuit 5 is constituted by a sensor 1 for detecting combustible gas, a sensor 2 for temperature compensation, and two fixed resistors 3 and 4. A variable resistor VR1 is connected to a connection point of the bridge circuit 5 with the fixed resistors 3 and 4 for adjusting an imbalance of the output of the bridge circuit caused by a difference between sensors. A power supply E1 is connected between the two input terminals of the bridge circuit 5, and the movable terminal of the variable resistor VR1 is connected to the bridge circuit 5 in order to extract the output of the bridge circuit 5.
, And is connected through a resistor 6 to an inverting input terminal of an amplifier 7. The other output terminal of the bridge circuit 5 is connected to a non-inverting input terminal of an amplifier 7 via a resistor 8.

[0005] The output of the amplifier 7 is input to an arithmetic circuit 9. The arithmetic circuit 9 calculates the gas-phase alcohol concentration detected by the sensor 1 based on the differential output of the amplifier 7 and derives it to the display means 10. Input means such as a keyboard (not shown) is connected to the display means 10.
In addition to the display of the gas-phase alcohol concentration value calculated by the arithmetic circuit 9, a shift value caused by the variation of the sensor 1 by the operation of the input means, an alcohol concentration measurement work message, and the like are displayed at 0.

In order to measure the gas-phase alcohol concentration using such an alcohol concentration meter, the bridge balance is adjusted in advance with a variable resistor VR1 so that the output of the bridge circuit is at a specified value.

In this adjusted state, liquor is poured into the heated measuring tank as described above, and the sensor 1
The sensor 1 is placed in a gas phase containing a gaseous alcohol while a current is passed through the platinum resistance wire to heat the platinum resistance wire. By bringing the oxidation catalyst of the sensor 1 into contact with the gaseous alcohol, the electric resistance of the sensor 1 changes, and the equilibrium state of the bridge circuit 5 is broken in accordance with the change. Therefore, a signal corresponding to the vapor-phase alcohol concentration appears at the differential output of the bridge circuit, and this signal is amplified by the amplifier 7 and then input to the arithmetic circuit 9, where the alcohol concentration is calculated and the display means 10 And the measurement of the gas-phase alcohol concentration is thus performed.

[0008]

In the above-described alcohol concentration meter, when the sensor 1 deteriorates with time, the output of the sensor 1 decreases, thereby decreasing the output of the bridge circuit. Therefore, the output V1 of the bridge circuit or the amplifier 7
By measuring the output V2, it is possible to determine the deterioration with time of the sensor. However, since such measurement requires a measuring instrument, there is a problem that a person having specialized knowledge about the measuring instrument must work.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a sensor life determining method capable of performing inspection and adjustment work of a sensor without requiring specialized knowledge. I do.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a bridge circuit having at least one sensor and a bridge circuit having a first variable resistor for obtaining an equilibrium state.
Further, a second variable resistor for maintaining the bridge circuit in a balanced state when the first variable resistor is set at a predetermined specified position is added, and the balanced state of the bridge circuit is set to the first variable resistance. This can be achieved by determining that the sensor has reached the end of its life when it reaches outside the adjustable range of the variable resistance.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the detailed description thereof will be omitted.

The difference from the circuit shown in FIG. 2 is that the bridge circuit 5 is further provided with a second variable resistor VR2. The second variable resistor VR2 is connected in series to the resistor 4 forming the bridge circuit 5.

The measuring circuit configured as described above is adjusted as follows. First, the first variable resistor VR1 is set to a neutral position. Next, the position of the second variable resistor VR2 is adjusted so that the bridge circuit 5 is in an equilibrium state with the first variable resistor VR1 in the neutral position. The operation for adjusting the measurement circuit is set to the detection circuit adjustment mode, and the output of the sensor 1 is displayed on the display means 10 via the amplifier 7 and the arithmetic circuit 9. Various modes of the detection circuit such as a “detection circuit adjustment mode” are selectively displayed on the display unit 10. By the above adjustment, the bridge circuit 5 constituting the measurement circuit is always in an equilibrium state when the first variable resistor VR1 is at the neutral position. Therefore, the first variable resistor VR1
Is set the same in all the detection circuits.

In the measurement circuit adjusted as described above, the sensor 1 deteriorates with the lapse of time, and the equilibrium state of the bridge circuit 5 is broken. Therefore, it is necessary to check and adjust the measuring circuit. The inspection and adjustment of the measurement circuit is performed by the first variable resistor VR1.
To maintain the bridge circuit 5 in an equilibrium state. This operation is performed by monitoring the value displayed on the display unit 10. By adjusting the first variable resistor VR1, the balanced state of the bridge circuit can be maintained.

While the balanced state of the bridge circuit 5 can be maintained by the first variable resistor VR1, the sensor 1 can be used, but even if the first variable resistor VR1 is adjusted, the bridge circuit 5 is kept in a balanced state. When the sensor 1 cannot be maintained, that is, when the balanced state of the bridge circuit cannot be achieved within the adjustment range of the first variable resistor, the sensor 1 can be determined to have reached the end of its life. Note that the resistance value of the first variable resistor VR1 is a value corresponding to the case where the sensor has deteriorated and has reached the end of its life.

As described above, according to the present invention, the bridge circuit 5 is set to be in an equilibrium state when the first variable resistor VR1 is first in the neutral position. As a result, the adjustment range of the first variable resistor VR1 is always constant, and the unbalanced state of the bridge circuit caused by the deterioration of the sensor can be adjusted by the first variable resistor VR1.

[0017]

As described above, according to the present invention, a bridge circuit having at least one sensor and having a first variable resistor for obtaining an equilibrium state and having a bridge configuration is further provided. Adding a second variable resistor for maintaining the bridge circuit in an equilibrium state when the first variable resistor is set at a predetermined specified position, wherein the equilibrium state of the bridge circuit is set to the first variable resistor; The sensor is determined to have reached the end of its service life when it has reached a point outside the adjustment range.
Inspection and adjustment can be performed without using a measuring instrument or the like as in the related art, so that a person having specialized knowledge on the measuring instrument is not required. Further, it is possible to clarify the time for replacing the sensor with reference to a time when the bridge circuit cannot maintain the equilibrium state of the bridge circuit due to the first variable resistor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing a conventional detection circuit.

[Explanation of symbols]

 1, 2 sensor 3, 4, 6, 8 fixed resistor 5 bridge circuit 7 amplifier 9 arithmetic circuit 10 display means VR1 first variable resistor VR2 second variable resistor E1 power supply

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/00-27/24 G01R 27/00-27/32

Claims (1)

(57) [Claims] 1. A bridge circuit having at least one sensor and having a first variable resistor for obtaining an equilibrium state, wherein the first variable resistor is further provided in a predetermined position. Adding a second variable resistor to maintain the bridge circuit in a balanced state when set to
A sensor life determining method for determining that the sensor has reached the end of its life when an equilibrium state of the bridge circuit is out of an adjustment range of the first variable resistor.