JP3082177B2 - Zirconia gas analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concentration cell type zirconia gas analyzer for measuring the concentration of O ₂ gas or the like.
The present invention relates to a zirconia gas analyzer in which the number of wires is reduced by automatically measuring a wire resistance of a signal data capturing device, a heater heating device, and a heater circuit.

[0002]

2. Description of the Related Art In a concentration cell type zirconia gas concentration meter, it is necessary to heat a zirconia sensor to a high temperature of 600 ° C. or more. FIG. 8 is a diagram illustrating the general configuration of a zirconia gas analyzer. In FIG. 1, reference numeral 1 denotes a detector including a zirconia sensor 2, a temperature sensor 3, a heater 4, and the like, and reference numeral 10 denotes a converter including a signal processing circuit 5, a temperature control circuit 6, an arithmetic control circuit 7, and the like. The electric signal detected by the zirconia sensor 2 in relation to the oxygen concentration is input to the signal processing circuit 5 via the signal wiring 12, and the processed signal is sent to the arithmetic and control circuit 7. Also, a command from the arithmetic and control circuit 7 is sent to the temperature control circuit 6, from which the heater wiring 1
Heater 4 is heated by a signal sent through 3. The heated temperature of the detector 1 is detected by the temperature sensor 3 and fed back to the temperature control circuit 6 via the signal wiring 12, the signal processing circuit 5, and the arithmetic and control circuit 7, and is maintained at a predetermined temperature.

[0003]

The heater capacity of such a zirconia analyzer is determined by the size of the zirconia sensor. Generally, a large power source is a commercial power source (100 V AC or 200 V AC). And a small one uses a low-voltage DC power supply. The heater power is always on / off for temperature control.
Off has been repeated.

On the other hand, a zirconia sensor signal (several mV to several hundred mV) or a temperature sensor (for example, a thermocouple ... several tens m)
V) In order to prevent induction noise from the heater wiring during wiring work between the converter and the converter, it is sufficient to house the signal wiring and the heater wiring in separate conduits, or use shielded cables or twisted pair wires. Since noise countermeasure work is required, there is a problem that wiring work cost becomes extremely high. In the case of a commercial power supply, the heater on / off cycle is about 20 ms (50 Hz, 60 Hz) or more.
Generally, the cutoff frequency of the low-pass filter of the amplifier of the signal processing circuit 5 needs to be set to a considerably low value because it is generally several hundred ms to several seconds. Therefore, depending on the setting, the response characteristics are adversely affected.

[0005]

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is possible to reduce the wiring work cost and to improve the reliability by making it difficult for the electric signal of the zirconia sensor or the thermocouple to receive the induction noise. It is another object of the present invention to provide a zirconia gas analyzer with improved response characteristics.

[0008]

According to one aspect of the present invention, there is provided a detector comprising a zirconia sensor, a temperature sensor, and a heater, a signal processing circuit, a temperature adjusting circuit, and an arithmetic control circuit. And a wire connecting the detector and the converter. The gas is brought into contact with the zirconia sensor heated to a predetermined temperature, and a measurement gas is obtained from an electric signal of the sensor generated in relation to a gas concentration. In a zirconia gas analyzer for determining the concentration in air, an alternating current is used as a heating means for the zirconia sensor.
A heater for outputting sufficient heating energy at an output of less than 0%, and a zero-cross detection circuit for detecting a zero-cross point of the AC current, wherein the arithmetic and control circuit captures electric signals from the zirconia sensor and the temperature sensor The timing is taken in accordance with the timing of the zero-cross signal from the zero-cross detection circuit when the AC current is not supplied to the heater.

[0009]

[0010]

[0011]

According to the first aspect, the control circuit inputs a zero-cross signal detected by the zero-cross detection circuit and converts the signal into a pulse width modulation signal having a fixed period synchronized with the signal. The ON signal of the pulse width modulation signal is output to the switch circuit of the power supply as a signal dispersed according to a predetermined algorithm. A signal from each sensor is taken in between the OFF signals of the pulse width modulation signal.

[0012]

[0013]

1 is a block diagram showing an embodiment of a zirconia gas analyzer according to the present invention. In the figure, FIG.
The same elements as those described above are denoted by the same reference numerals and redundant description is omitted, but reference numeral 20 denotes a changeover switch (for example, a solid state relay), 21 denotes an AC power supply, 22 denotes a power transformer, and 23
Is a zero cross detection circuit for detecting a zero cross point of the AC power supply 21. 25 and 25 'are input amplifiers, 27
Is a scanner circuit, 28 is a low-pass filter, 29 is A /
It is a D converter.

In the above configuration, the heater 4 is 100%
The control circuit 7 calculates a switching signal to the scanner circuit 27, an A / D conversion timing signal, and outputs a temperature
Calculate the heater temperature control signal by inputting the temperature signal from
The temperature control signal can be sent to the solid state relay 20 in synchronization with the zero cross point timing signal. In the present invention, the basic operation of the temperature control signal is performed by a pulse width modulation signal, and the A / D conversion of the signal is performed when the on / off signal is off. The duty of the pulse width modulation is consequently the same, the on / off operation is frequently performed within the pulse width modulation data update cycle, and the number of off operation states is generated intermittently. As described above, a heater having a sufficient capacity to raise the temperature even when the duty is less than 100% (for example, 80%) is used. The temperature control operation, the duty of the heater signal, and the on / off pattern are set in advance. It is decided.

Here, a time chart of the control circuit 7 in the case where zero cross detection is performed will be described with reference to FIG. In addition,
In this control circuit, the basic period of the pulse width modulation signal is 200
This shows a case where the temperature is adjusted in m seconds. In the figure, (A) is a zero cross detection signal, (B) is a basic pulse width modulation signal, (C) is a pulse width modulation signal in which an ON signal is dispersed, (D) is a heater signal in the case of an AC power supply, E)
Indicates the A / D conversion timing.

The temperature control signal is generated as a pulse width modulation signal (B) synchronized with the zero-cross detection signal (A), and the ON signal value of the signal is generated as a signal (C) dispersed by a predetermined algorithm. It is recreated and sent out to the A / C power switch circuit. In the signal of (C), A is A ₁
+ A ₂ + A ₃ , B is divided into B ₁ + B ₂ + B ₃ , C is divided into C ₁ + C ₂ and so on. Then, the A / C power supply modulated by the changeover switch becomes the heater signal (D), and this signal causes a section to be turned off every certain period. Therefore, A / D conversion of the signal is performed within this off section. In the conversion timing of (E), for example, a portion indicated by is made to correspond to a temperature sensor input, a cold junction compensation sensor input of a thermocouple, a zirconia O ₂ sensor input, and an Amp system offset gain adjustment input. Note that it is also possible to complete the A / D conversion of all inputs during each off period depending on the conversion speed of the A / D converter.

When the power supply of the heater is DC, a zero-crossing detection signal is unnecessary, so that the A / D conversion timing can be directly determined from the pulse width modulation signal (C) in FIG. According to the above configuration, since the A / D conversion timing of the zirconia sensor and the temperature sensor is programmed so as to be taken in at the timing of the zero crossing of the heater power supply, the signal processing can be performed without receiving the induction noise due to the temperature control signal of the heater. It is not necessary to use electromagnetic shields or twisted pair wires in the construction of the heater wiring and the signal wiring, so that the wiring construction including the conduit piping is simplified and the cost can be reduced. In particular, the effect is remarkable in an averaging converter used for multi-point O ₂ measurement such as connecting a plurality of zirconia O ₂ detectors and calculating the average value of the O ₂ concentration distribution mainly in the flue of a large boiler. . Since the commercial frequency may be considered as the input filter of the amplifier, the response characteristics of the device are not reduced.

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

According to the present invention, the zirconia gas analyzer with a reduced number of wirings and a reduced wiring construction cost can be realized as described in detail with the above embodiments.

[Brief description of the drawings]

FIG. 1 is a block diagram of a configuration of a zirconia gas analyzer showing an embodiment according to claim 1 of the present invention.

FIG. 2 is an explanatory diagram of a time chart of a control circuit when performing zero-cross detection.

FIG. 3 is a diagram illustrating a general configuration of a zirconia gas analyzer.

[Explanation of symbols]

1 detector 2 zirconia sensor 3 Temperature sensor 4 heater 5 the signal processing circuit 6 temperature adjusting circuit 7 arithmetic control circuit 10 converter 12 the signal wires 13 Heater wiring 20 changeover switch 23 zero-cross detection circuit

Claims (1)

(57) [Claims] 1. A detector (1) comprising a zirconia sensor (2), a temperature sensor (3) and a heater (4), a signal processing circuit (5), a temperature control circuit (6), and an arithmetic control circuit (7). And a wiring (12, 13) connecting the detector and the converter. The gas is brought into contact with the zirconia sensor heated to a predetermined temperature, and is generated in relation to the concentration of the gas. A zirconia gas analyzer for obtaining a concentration of a measurement gas from an electric signal of the sensor, a heater for outputting sufficient heating energy at an output of less than 100% by an alternating current as a heating means of the zirconia sensor; And a zero-crossing detection circuit (23) for detecting the timing.The arithmetic and control circuit determines the timing of taking in the electric signals from the zirconia sensor (2) and the temperature sensor (3) when the AC current is not supplied to the heater. zero Loss detection circuit (23)
A zirconia gas analyzer characterized in that the zirconia gas analyzer is adapted to be taken in accordance with the timing of a zero-cross signal from a rocket.