JPH07244561A - Analog input device - Google Patents

Abstract

PURPOSE:To reduce the residual voltage of a filter and to shorten time required for abnormality detecting processing by providing this analog input device with a comparator circuit for detecting the quantity of electricity outputted from a sensor output terminal at the time of impressing test voltage. CONSTITUTION:The analog input device includes a control circuit 7 for periodically inputting a digital signal, a power supply part 8 for impressing test voltage to an output terminal of a thermocouple 1 through a resistor 9 in order to detect the abnormality of the thermocouple 1 and the comparator circuit 12 for inputting voltage outputted from the thermocouple 1 by the test voltage impressed from the power supply part 8 like a pulse, comparing the input voltage with previously set reference voltage and detecting the abnormality of a sensor. The circuit 12 consists of a resistor 121 for applying the reference voltage and a comparator 122 for executing comparison. The power supply part 8 impresses the test voltage of a waveform cut out by filtering processing to the sensor output terminal and the circuit 12 detects the abnormality of the sensor based upon the quantity of electricity outputted from the sensor output terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an analog input device for filtering and inputting a detection signal output from a sensor, for example, a thermocouple for measuring a furnace temperature in a nuclear power plant or a steam temperature of a turbine. The present invention relates to an analog input device.

[0002]

2. Description of the Related Art In an analog input device using a thermocouple for measuring the temperature of each part of a plant, the thermocouple at the measurement point and the input device are placed apart from each other and are easily affected by noise due to a strong electric field or the like. . Therefore, the detection signal output from the thermocouple is generally input to the input device via a filter having a large time constant (for example, a low-pass filter having a cutoff frequency of about 5 Hz). In addition, such thermocouples are often installed under environmentally poor conditions, and they often break or cause contact failures, so it is necessary to frequently detect abnormality in the thermocouples.

FIG. 5 is a circuit diagram showing a conventional analog input device disclosed in, for example, Japanese Patent Application Laid-Open No. 63-113622, in which 1 is a thermocouple and 2 is noise added to the wiring path of the thermocouple 1. A first filter 3 for removing the signal from the thermocouple 1 is a scan circuit composed of a transformer and a switching circuit provided to insulate the signal from the thermocouple 1 from a device in the subsequent stage, and 4 is an output of the scan circuit 3. An amplifier for amplifying, 5 is a sample hold circuit (hereinafter abbreviated as S / H circuit) for temporarily holding the output of the amplifier 4, and 6 is S / H.
An analog-to-digital converter (hereinafter abbreviated as A / D converter) for converting the output held in the H circuit 5 into a digital signal, 7 is a control circuit for periodically reading this digital signal, and 8 is a thermocouple 1 The power supply unit 10 applies a test voltage to the output terminal of the thermocouple 1 via the resistor 9 in order to detect the abnormality of the power source 10 and the semiconductor analog switch 11 during the abnormality inspection.
switched to the first filter 2 by a and 11b,
The second filter has a small time constant and is connected to the thermocouple 1 and the scan circuit 3.

Next, the operation will be described. Normally, the control circuit 7 inputs the electromotive force Vo between the output terminals of the thermocouple 1 generated according to the temperature via the first filter 2 by closing the analog switch 11a and opening the analog switch 11b. Then, the temperature is measured by this input. The output of the thermocouple 1 is noise-removed by the first filter 2 and is output to the scan circuit 3 as a DC voltage. The scan circuit 3 outputs this DC voltage output to the switches S1 and S.
Alternate 2 and 2 at high speed (eg 50 KHz)
The signal is output to the amplifier 4 by converting it into an AC signal by a transformer for insulation processing. The amplifier 4 amplifies the output signal of the scan circuit 3 and converts it into a DC analog signal for S / H.
Output to the circuit 5. This output is held in the S / H circuit 5 at a constant sampling cycle according to a command from the control circuit 7, converted into a digital signal by the A / D converter 6, and read into the control circuit 7.

Next, during the abnormality inspection of the thermocouple 1, the control circuit 7
Opens the analog switch 11a
By closing b, the first filter 2 is disconnected and the second filter 10 having a short time constant is connected instead,
A test voltage is applied from the power supply unit 8 to the output terminal of the thermocouple 1 via the resistor 9. When this test voltage is applied, the voltage signal generated between the output terminals of the thermocouple 1 is passed through the second filter 10 in the same manner as in the normal time, and the scan circuit 3, the amplifier 4, and the S
It is input to the control circuit 7 via the / H circuit 5 and the A / D converter 6.

If the thermocouple 1 is normal, the voltage e generated between the output terminals of the thermocouple 1 is divided into the internal resistance value r of the thermocouple 1 and the resistance value R of the resistor 9 with respect to the test voltage E. It is the voltage Vt = rE / (r + R) plus the electromotive force Vo of the thermocouple 1. However, since the resistance value R of the resistor 9 is set to be very large with respect to the internal resistance value r of the thermocouple 1, the divided voltage Vt becomes a value smaller than the electromotive force Vo. On the other hand, when the thermocouple 1 is in the disconnection state, the electromotive force Vo is not detected and the internal resistance value r of the thermocouple 1 becomes infinite, so that the voltage e generated between the output terminals of the thermocouple 1 becomes , Becomes equal to the test voltage E. If the test voltage E is set to be slightly larger than the normal input range, the output of the A / D converter 6 overflows, so that the disconnection of the thermocouple 1 can be detected. In the above-mentioned conventional example, since the first filter 2 having a large time constant and the second filter 10 having a small time constant are switched during the abnormality inspection, the time required for the abnormality detection processing can be shortened and the first filter can be shortened. It is possible to prevent the residual voltage of the test voltage E from remaining in the filter 2.

[0007]

Since the conventional analog input device is constructed as described above, it is necessary to provide two filters, and a plurality of analog switches are provided to switch between these filters. However, there is a problem in that the control circuit is complicated. In addition, a shift in the switching timing of the plurality of analog switches causes a whisker-like output fluctuation in the output of the filter, which may cause a measurement error. Furthermore, since a semiconductor switch having a short operating time is used as the analog switch, there is a problem that a measurement error occurs due to a minute leak current flowing through the analog switch that is in an open state during normal temperature measurement. It was

The present invention has been made in order to solve the above problems, and can detect an abnormality of a sensor without switching the filter, reduce the residual voltage of the filter due to application of a test voltage, and perform an abnormality detection process. It is an object of the present invention to obtain an analog input device that can reduce the time required for.

[0009]

According to a first aspect of the present invention, there is provided an analog input device comprising: a power supply section for applying a test voltage having a waveform cut by a filter process to an output terminal of a sensor; An abnormality detecting means for detecting the amount of electricity derived from the sensor output terminal is provided.

According to a second aspect of the present invention, in an analog input device, a power source section for applying a pulsed test voltage cut by a filter process to an output terminal of a sensor, and a sensor output terminal from the sensor output terminal when the test voltage is applied. An abnormality detecting means for detecting the derived electric quantity is provided.

According to a third aspect of the present invention, in an analog input device, a power supply unit for applying an AC test voltage having a frequency higher than a cutoff frequency for filtering to an output terminal of the sensor, and the sensor output when the test voltage is applied. An abnormality detecting means for detecting the amount of electricity derived from the terminal is provided.

According to a fourth aspect of the present invention, in an analog input device, a power supply unit for applying a test voltage to an output terminal of a sensor and a signal derived from the output terminal of the sensor are
A digital filter means for inputting a digital signal through a D / D converter and filtering the input to derive a sensor output, and an abnormality detecting means for detecting the input digital signal when the test voltage is applied. And a digital signal processor provided with, and the test voltage output from the power supply unit is a waveform cut by the filtering process.

In the analog input device according to a fifth aspect of the present invention, the abnormality detecting means is a comparator circuit for comparing an electric quantity derived from the output terminal of the sensor with a preset reference electric quantity when a test voltage is applied. It is composed.

According to a sixth aspect of the present invention, in an analog input device, a pulse-shaped test voltage cut by a filter process is applied to an output terminal of a sensor through a resistor, and when the test voltage is applied, A comparator circuit for comparing the voltage derived from the sensor output terminal with a preset reference voltage is provided.

An analog input device according to a seventh aspect of the present invention is a power supply unit for applying an AC test voltage having a frequency higher than a cutoff frequency of filtering to a sensor output terminal through a resistor, and the AC test voltage applying unit. At this time, a transformer that transforms a voltage derived from the sensor output terminal, a conversion circuit that converts an AC voltage output from the transformer into a DC voltage, and a DC voltage converted by the conversion circuit and a preset reference voltage are provided. A comparator circuit for comparison is provided.

An analog input device according to claim 8 of the present invention is a power supply section for applying a test voltage to a sensor output terminal through a resistor, and an A / D converter for a signal derived from the sensor output terminal. A digital filter means for inputting a digital signal via the input terminal and filtering the input to derive a sensor output, and an abnormality detecting means for detecting the input digital signal when the test voltage is applied. Equipped with a digital signal processor,
The test voltage output from the power supply unit is a pulse-shaped waveform cut by the filtering process.

According to a ninth aspect of the present invention, in an analog input device, a power supply section for applying a test voltage to an output terminal of a sensor via a resistor and a signal derived from the output terminal of the sensor is an A / D converter. A digital filter means for inputting a digital signal via the input terminal and filtering the input to derive a sensor output, and an abnormality detecting means for detecting the input digital signal when the test voltage is applied. Equipped with a digital signal processor,
The test voltage output from the power supply unit is an AC voltage having a frequency higher than the cutoff frequency of the filtering process.

[0018]

In the analog input device according to the first aspect of the present invention, the power supply unit applies the test voltage of the waveform cut by the filter processing to the sensor output terminal, and when the test voltage is applied, the abnormality detecting means causes the sensor output terminal to operate. An abnormality of the sensor is detected based on the amount of electricity derived from.

In the analog input device according to the second aspect of the present invention, the power supply section applies the pulse-shaped test voltage to the sensor output terminal, which is cut by the filtering process, and when the test voltage is applied, the abnormality detecting means outputs the sensor output. A sensor abnormality is detected by the amount of electricity derived from the terminal.

In the analog input device according to the third aspect of the present invention, the power supply section applies the AC test voltage having a frequency higher than the cutoff frequency of the filtering process to the sensor output terminal, and when the test voltage is applied, the abnormality detecting means. Detects an abnormality of the sensor based on the amount of electricity derived from the sensor output terminal.

In the analog input device according to a fourth aspect of the present invention, the digital signal processor inputs the amount of electricity derived from the output terminal of the sensor as a digital signal through the A / D converter, and the power supply section outputs the sensor. A test voltage having a waveform cut by the digital filter means of the digital signal processor is applied to the terminal, and at the time of applying the test voltage, the abnormality detection means of the digital signal processor uses the electric quantity derived from the sensor output terminal to detect the sensor. Detect an abnormality.

In the abnormality detecting means of the analog input device according to the fifth aspect of the present invention, when the test voltage is applied, the comparator circuit compares the electric quantity derived from the sensor output terminal with a preset reference electric quantity. , Detect the sensor abnormality.

According to a sixth aspect of the present invention, in the analog input device, the power supply section applies a pulsed test voltage to the sensor output terminal through a resistor and cut by the filter processing, and when the test voltage is applied, a comparator circuit is applied. Detects a sensor abnormality by comparing the amount of electricity derived from the sensor output terminal with a preset reference amount of electricity.

In the analog input device according to claim 7 of the present invention, the power supply section applies the AC test voltage having a frequency higher than the cutoff frequency of the filtering process to the sensor output terminal through the resistor, and when the test voltage is applied, A transformer transforms the voltage derived from the sensor output terminal, a conversion circuit converts the output of this transformer into a DC voltage, and a comparator circuit compares the converted DC voltage of this conversion circuit with a preset reference voltage. , Detect the sensor abnormality.

In the analog input device according to claim 8 of the present invention, the digital signal processor inputs the amount of electricity derived from the output terminal of the sensor as a digital signal via the A / D converter, and the power supply unit inputs the resistance. A pulse-shaped test voltage cut by the digital filter means of the digital signal processor is applied to the sensor output terminal via the sensor. When the test voltage is applied, the abnormality detection means of the digital signal processor causes the abnormality of the sensor by the digital signal. To detect.

In the analog input device according to claim 9 of the present invention, the digital signal processor inputs the electric quantity derived from the output terminal of the sensor as a digital signal through the A / D converter, and the power supply section inputs the resistance. An AC test voltage having a frequency higher than the cutoff frequency of the digital filter means of the digital signal processor is applied to the sensor output terminal through the sensor output terminal, and when the test voltage is applied, the abnormality detection means of the digital signal processor uses the digital signal to detect the sensor. To detect abnormalities.

[0027]

【Example】

Example 1. FIG. 1 is a circuit diagram showing an analog input device according to an embodiment of the present invention, and the same reference numerals as those in FIG. 5 showing a conventional analog input device indicate the same parts. In the figure, 1
Is a thermocouple, 2 is a filter with a large time constant for removing noise added to the wiring path of the thermocouple 1, and 3 is composed of a transformer and a switching circuit to insulate the signal from the thermocouple 1 from the device at the subsequent stage. Scan circuit, 4 is an amplifier for amplifying the output of the scan circuit 3, 5 is an S / H circuit for temporarily holding the output of the amplifier 4, and 6 is an S / H circuit 5
A / converts the output held at
D converter, 7 is a control circuit for periodically reading this digital signal, 8 is a power supply unit for applying a test voltage to the output terminal of the thermocouple 1 via a resistor 9 for detecting abnormality of the thermocouple 1, and 12 is When a test voltage is applied in a pulse form from the power supply unit 8, a voltage derived from the output terminal of the thermocouple 1 by this test voltage is input, and this voltage is compared with a preset reference voltage to detect a sensor abnormality. A resistor circuit 1 for providing a reference voltage for the comparator circuit 12
21 and a comparator 122 for comparison.

Next, the operation will be described. In the normal state, the control circuit 7 is similar to the conventional analog input device.
The electromotive force Vo between the output terminals of the thermocouple 1 generated according to the temperature is input via the filter 2, and the temperature is measured by this input. The output of the thermocouple 1 is input to the S / H circuit 5 via the filter 2, the scan circuit 3, and the amplifier 4, and is held in the S / H circuit 5 at a constant sampling cycle according to a command from the control circuit 7. It is converted into a digital signal by the A / D converter 6 and read by the control circuit 7.

Next, at the time of abnormality inspection, the power supply section 8 applies a pulse-shaped test voltage cut by the filter 2 to the output terminal of the thermocouple 1 via the resistor 9 according to an instruction from the control circuit 7. For example, if the filter 2 is a low-pass filter with a cutoff frequency of 5 Hz, even if the test voltage E is applied with a pulse of about 10 ms, the test voltage E
The voltage generated at the output terminal of the thermocouple 1 is attenuated by the filter 2 and does not affect the measured value of the electromotive force Vo of the thermocouple 1 input to the control circuit 7 via the filter 2.

When the thermocouple 1 is normal when the test voltage is applied, the voltage e generated between the output terminals of the thermocouple 1 is
The electromotive force Vo of the thermocouple 1 is added to the divided voltage Vt = rE / (r + R) of the internal resistance value r of the thermocouple 1 and the resistance value R of the resistor 9 with respect to the test voltage E. However, since the resistance value R of the resistor 9 is set to be very large with respect to the internal resistance value r of the thermocouple 1, the divided voltage Vt becomes a value smaller than the electromotive force Vo. On the other hand, when the thermocouple 1 is in the disconnection state, the electromotive force Vo is not detected and the internal resistance value r of the thermocouple 1 is
Becomes infinite, the voltage e generated between the output terminals of the thermocouple 1 becomes equal to the test voltage E. If the thermocouple 1 is in a poor contact state, the internal resistance value r of the thermocouple 1
Becomes large even if the divided voltage Vt does not reach the test voltage E, and the voltage e between the output terminals of the thermocouple 1 is obtained by adding the divided voltage Vt to the electromotive force Vo. Therefore, the predetermined measurement range is exceeded.

The comparator circuit 12 receives the voltage e between the output terminals of the thermocouple 1 as an input, and the comparator circuit 12
Since the comparator 122 is configured to be compared with the reference voltage set by the resistor 121, the control circuit 7 can determine the contact failure and disconnection of the thermocouple 1 by the output of the comparator circuit 12. According to the configuration of the first embodiment, as compared with the conventional analog input device, since the test voltage at the time of abnormality detection is pulsed, it is less susceptible to external noise and the pulsed test voltage is filtered. Since the residual voltage of the filter 2 is extremely small because it is cut by 2, it is not necessary to provide a second filter for abnormality detection. Further, since the abnormality detection process is performed by the comparator circuit 12, the detection can be performed at high speed and the time required for the detection process can be shortened. Further, since the control circuit 7 can be configured by separating the process of measuring the temperature by the thermocouple 1 and the process of detecting the abnormality of the thermocouple 1, the structure of the control circuit is simplified.

Example 2. FIG. 2 is a circuit diagram showing the analog input device of the second embodiment. Instead of the power supply unit 8 for applying the pulsed test voltage described in the first embodiment, an AC test voltage higher than the cutoff frequency of the filter is used. A power supply unit 8a for applying a voltage is provided, and a transformer 13 that transforms the voltage derived from the output terminal of the thermocouple 1 is provided in the preceding stage of the comparator circuit 12 described in the first embodiment, and the output of this transformer 13 is converted into a DC voltage. The conversion circuit 14 is provided.
The same reference numerals as in the first embodiment indicate the same parts.

Next, the operation will be described. The normal operation is the same as that of the first embodiment, and will be omitted. During the abnormality inspection, the power supply unit 8 causes the resistor 9 to
An AC test voltage having a frequency higher than the cutoff frequency of the filter 2 is applied to the output terminal of the thermocouple 1 via the. For example, if the filter 2 is a low-pass filter with a cutoff frequency of 5 Hz, even if an AC test voltage E of about 500 Hz is applied, the voltage generated at the output terminal of the thermocouple 1 by this test voltage E is attenuated by the filter 2. The measured value of the electromotive force Vo of the thermocouple 1 that is input to the control circuit 7 via the filter 2 is not affected.

If the thermocouple 1 is normal when the test voltage is applied, the voltage e generated between the output terminals of the thermocouple 1 is
An AC divided voltage Vt = rE / (r +) between the internal resistance value r of the thermocouple 1 and the resistance value R of the resistor 9 with respect to the AC test voltage E.
R) plus the electromotive force Vo of the thermocouple 1. However, since the resistance value R of the resistor 9 is set to be very large with respect to the internal resistance value r of the thermocouple 1, the AC divided voltage Vt becomes a value smaller than the electromotive force Vo. On the other hand, thermocouple 1
Is broken, the electromotive force Vo is not detected and the internal resistance value r of the thermocouple 1 becomes infinite.
The voltage e generated between the output terminals of the same becomes equal to the test voltage E. Further, if the thermocouple 1 is in a poor contact state, the internal resistance value r of the thermocouple 1 increases, so that the divided voltage V
Since t becomes a large value even if it does not reach the test voltage E, and the voltage e between the output terminals of the thermocouple 1 becomes a voltage obtained by superposing the AC voltage Vt on the electromotive force Vo, it exceeds the predetermined measurement range. To do.

The transformer 13 receives the voltage e between the output terminals of the thermocouple 1 as input, and transforms and outputs the divided voltage Vt of the AC test voltage, which is the AC component thereof. The conversion circuit 14 converts the output of this transformer into a DC voltage and outputs it as an input of the comparator circuit 12. Therefore, the comparator circuit 12 configures the comparator 122 to compare the DC voltage derived according to the divided voltage Vt generated at the output terminal of the thermocouple 1 with the reference voltage set by the resistor 121. The output of the circuit 12 allows the control circuit 7 to determine the contact failure and disconnection of the thermocouple 1.

According to the configuration of the second embodiment, the test voltage at the time of abnormality detection is AC, as compared with the conventional analog input device, and this AC voltage is used for the transformer 13 and the conversion circuit 1.
4, the external noise is absorbed by the transformer 13 and the conversion circuit 14, and the AC test voltage having a frequency higher than the cutoff frequency is cut by the filter 2. Therefore, the residual voltage of the filter 2 is extremely high. Since it is small, it is not necessary to provide a second filter for detecting abnormality. Also, the abnormality detection process is performed by the transformer 1.
3. Since it is performed by the conversion circuit 14 and the comparator circuit 12, the detection can be performed at high speed and the time required for the detection processing can be shortened. Further, since the control circuit 7 can be configured by separating the process of measuring the temperature by the thermocouple 1 and the process of detecting the abnormality of the thermocouple 1, the structure of the control circuit is simplified. Furthermore, since the transformer 13 insulates the wiring path of the thermocouple 1 in the second embodiment, it is possible to prevent noise from entering the comparator circuit 12. It should be noted that even if the AC test voltage is kept applied to the thermocouple 1, it does not affect the temperature measurement in the normal state, so that there is an effect that the thermocouple 1 can be constantly monitored for abnormality.

Example 3. FIG. 3 is a circuit diagram showing an analog input device of the third embodiment, in which a digital signal processor is used for the control circuit 7 of the first embodiment, and digital filter means and abnormality detecting means are provided therein. In the figure, 7a is a digital signal processor provided in place of the control circuit 7, 7a1 is digital filter means provided in the digital signal processor 7a, 7a2 is provided in the digital signal processor 7a and detects an abnormality of the thermocouple 1. Abnormality detecting means, 7a3
Is a control means provided in the digital signal processor 7a and corresponding to the control circuit 7 of the first embodiment. The same reference numerals as those in the first embodiment indicate the same parts.

Next, the operation will be described. In the normal state, similarly to the conventional analog input device, the temperature measurement by the thermocouple 1 is performed by measuring the electromotive force Vo between the output terminals of the thermocouple 1 generated according to the temperature. Thermocouple 1
Output of S / H via scan circuit 3 and amplifier 4.
The signal is input to the circuit 5, is held in the S / H circuit 5 according to a command from the digital signal processor 7a at a constant sampling period, and is converted into a digital signal by the A / D converter.
It is read by the digital signal processor 7a. Unlike the first and second embodiments, the sampling period is, for example, 0.
It is performed at a high speed of 2 ms. Digital filter means 7a
Reference numeral 1 converts the data arranged in time series of the digital signal into time series data equivalent to the output of a low-pass filter having a cutoff frequency of 5 Hz, for example, by a filter processing by software, and the thermocouple 1 of the thermocouple 1 is provided to the control means 7a3 in the subsequent stage. Output as a measured value of electromotive force Vo.

Next, during the abnormality inspection, the abnormality detecting means 7
According to the instruction of a2, the power supply unit 8 applies the pulse-shaped test voltage cut by the digital filter means 7a1 to the output terminal of the thermocouple 1 through the resistor 9. Example 1
As in the case of, if the digital filter means 7a1 corresponds to a low-pass filter with a cutoff frequency of 5 Hz, even if the test voltage E is applied with a pulse of about 10 ms, the test voltage E causes the thermocouple 1 to operate. The voltage generated at the output terminal is attenuated by the digital filter means 7a1 and does not affect the measured value of the electromotive force Vo of the thermocouple 1 input to the control means 7a3.

When the test voltage is applied, the voltage e generated between the output terminals of the thermocouple 1 is the same as that in the normal state when the scan circuit 3,
It is inputted as a digital signal to the digital signal processor 7a via the amplifier 4, the S / H circuit 5 and the A / D converter 6. If the thermocouple 1 is normal, as in the case of the first embodiment, the voltage e generated between the output terminals of the thermocouple 1 is not much affected by the test voltage E, and in the case of disconnection, e = E.
In the case of poor contact, the voltage exceeds the predetermined measurement range but does not reach the test voltage E. The abnormality detecting means 7a2 receives the voltage e generated between the output terminals of the thermocouple 1 derived by the application of the test voltage as a digital signal, performs the same abnormality detection processing as the comparator circuit of the first embodiment by software, The control means 7a3 is notified of the result.

As described above, according to the third embodiment, it is not necessary to use a filter composed of an analog circuit as in the conventional case in the analog input device. Further, since the test voltage at the time of abnormality detection is pulsed, the influence of the test voltage application on the output of the digital filter means 7a1 can be made extremely small.

Example 4. FIG. 4 is a circuit diagram showing the analog input device of the fourth embodiment. Instead of the power supply unit 8 for applying the pulsed test voltage described in the third embodiment, an AC test higher than the cutoff frequency of the digital filter means is performed. A power supply unit 8a for applying a voltage is provided. In the figure, 7b is a digital signal processor, 7b1 is a digital filter means provided in the digital signal processor 7b, 7b2 is an abnormality detection means provided in the digital signal processor 7b for detecting an abnormality of the thermocouple 1, and 7b3 is a digital signal. It is a control means provided in the processor 7b. However, the digital filter means 7b1 and the control means 7b3 are substantially the same as 7a1 and 7a3 (shown in FIG. 3) shown in the third embodiment. Moreover, the same reference numerals as those in the third embodiment denote the same components.

Next, the operation will be described. The normal operation is the same as that of the third embodiment, and will be omitted. During the abnormality inspection, the power supply unit 8a is instructed by the abnormality detecting means 7b2.
Applies an AC test voltage of a frequency higher than the cutoff frequency of the digital filter means 7b1 to the output terminal of the thermocouple 1 via the resistor 9. As in the case of the second embodiment, for example, if the digital filter means 7b1 is a low-pass filter with a cut-off frequency of 5 Hz, even if an AC test voltage E of about 500 Hz is applied, the output of the thermocouple 1 is generated by this test voltage E. The voltage generated at the terminal is attenuated by the digital filter means 7b1 and does not affect the measured value of the electromotive force Vo of the thermocouple 1 input to the control means 7b3.

When the test voltage is applied, the voltage e generated between the output terminals of the thermocouple 1 is the same as that in the normal state when the scan circuit 3,
It is input as a digital signal to the digital signal processor 7b via the amplifier 4, the S / H circuit 5 and the A / D converter 6. If the thermocouple 1 is normal, as in the case of the second embodiment, the voltage e generated between the output terminals of the thermocouple 1 is not much affected by the test voltage E, and in the case of disconnection, the AC test voltage E In the case of poor contact, the voltage does not reach the AC test voltage E but exceeds the predetermined measurement range.

The abnormality detecting means 7b2 receives, as a digital signal, the voltage e generated between the output terminals of the thermocouple 1 which is derived by the application of the test voltage, and performs an abnormality detecting process similar to that of the comparator circuit of the second embodiment by software. Then, the result is notified to the control means 7b3. As described above, according to the fourth embodiment, it is not necessary to use the conventional filter including the analog circuit in the analog input device. Moreover, since the test voltage at the time of abnormality detection is an AC voltage having a frequency higher than the cutoff frequency of the digital filter means 7b1, the influence of the application of the test voltage on the output of the digital filter means 7b1 can be made extremely small. Further, even if the AC test voltage is kept applied to the thermocouple 1, it does not affect the temperature measurement under normal conditions.
There is an effect that it can be configured to constantly monitor the abnormality.

In the first to fourth embodiments, the thermocouple is used as the sensor. However, as long as the amount of electricity derived from the output terminal of the sensor is measured by filtering, other sensors can be used. It may be a sensor.

[0047]

Since the present invention is configured as described above, it has the following effects.

In the analog input device according to the first aspect of the present invention, the test voltage output from the power supply unit is applied to the sensor output terminal as a waveform cut by the filter processing. Therefore, when the test voltage is applied, the residual voltage is applied to the filter. In addition to the filter processing, the filter for abnormality detection is provided separately from the filter processing, because the abnormality detection means for directly detecting the abnormality of the sensor from the electric quantity derived from the sensor output terminal when the test voltage is applied is provided. There is an effect that the switching process becomes unnecessary and the waiting time for the abnormality detection due to the delay time of the filter process is eliminated. Further, since the analog switch for the filter switching process is not provided, an error caused by the analog switch does not occur.

In the analog input device according to the second aspect of the present invention, the test voltage output from the power supply unit is applied to the sensor output terminal in the form of a pulse that is cut by the filter process, and therefore remains in the filter when the test voltage is applied. There is no voltage remaining.In addition to the filtering process, an abnormality detection unit is provided to detect the abnormality of the sensor directly from the quantity of electricity derived from the sensor output terminal when the test voltage is applied. No need for filter switching process of
This has the effect of eliminating the waiting time for abnormality detection due to the delay time of the filter processing. Further, since the analog switch for the filter switching process is not provided, an error caused by the analog switch does not occur.

In the analog input device according to the third aspect of the present invention, since the AC test voltage having a frequency higher than the cutoff frequency of the filtering process is applied to the sensor output terminal from the power supply section, the residual voltage is applied to the filter when the test voltage is applied. In addition to the filter processing, the filter for abnormality detection is provided separately from the filter processing, because the abnormality detection means for directly detecting the abnormality of the sensor from the electric quantity derived from the sensor output terminal when the test voltage is applied is provided. There is an effect that the switching process becomes unnecessary and the waiting time for the abnormality detection due to the delay time of the filter process is eliminated. Further, since the analog switch for the filter switching process is not provided, an error caused by the analog switch does not occur. Further, since the AC test voltage may be always applied, there is an effect that the sensor can be constantly monitored for abnormality.

In the analog input device according to the fourth aspect of the present invention, the digital filter means for filtering and deriving the sensor output and the abnormality detecting means for detecting the abnormality of the sensor when the test voltage is applied are constituted by a digital signal processor. Therefore, there is no need for a filter configured by a conventional analog circuit, and the configuration of the analog input device can be simplified. Further, the filter switching process for detecting the abnormality is not necessary and the analog switch for the filter switching process is not provided, so that the error caused by the analog switch does not occur. Furthermore, since the test voltage output from the power supply unit is applied to the sensor output terminal as a waveform cut by the filter processing, the output of the digital filter is not affected when the test voltage is applied.

In the input device of the analog detecting device according to the fifth aspect of the present invention, since the abnormality detecting means is composed of the comparator circuit having a fast response time, the time required for detecting the abnormality of the sensor can be shortened.

In the analog input device according to the sixth aspect of the present invention, the test voltage output from the power supply unit is applied to the sensor output terminal in the form of a pulse that is cut by the filter processing. There is no voltage remaining.In addition to the filtering process, an abnormality detection unit is provided to detect the abnormality of the sensor directly from the quantity of electricity derived from the sensor output terminal when the test voltage is applied. No need for filter switching process of
This has the effect of eliminating the waiting time for abnormality detection due to the delay time of the filter processing. Further, since the analog switch for the filter switching process is not provided, an error caused by the analog switch does not occur. Further, since the abnormality detecting means is composed of the comparator circuit having a fast response time, the time required for detecting the abnormality of the sensor can be shortened.

In the analog input device according to the seventh aspect of the present invention, since the AC test voltage having a frequency higher than the cutoff frequency of the filtering process is applied to the sensor output terminal from the power supply unit, the residual voltage is applied to the filter when the test voltage is applied. In addition to the filter processing, the filter for abnormality detection is provided separately from the filter processing, because the abnormality detection means for directly detecting the abnormality of the sensor from the electric quantity derived from the sensor output terminal when the test voltage is applied is provided. There is an effect that the switching process becomes unnecessary and the waiting time for the abnormality detection due to the delay time of the filter process is eliminated. Further, since the analog switch for the filter switching process is not provided, an error caused by the analog switch does not occur. Further, since the AC test voltage may be always applied, there is an effect that the sensor can be constantly monitored for abnormality. Furthermore,
Since the AC test voltage applied to the sensor output terminal is transformed by using the transformer, it is possible to insulate the sensor wiring path from the abnormality detecting means including the conversion circuit and the comparator circuit. Furthermore, since the abnormality detecting means is composed of the comparator circuit having a fast response time, the time required for detecting the abnormality of the sensor can be shortened.

In the analog input device according to the eighth aspect of the present invention, the digital filter means for deriving the sensor output by filtering and the abnormality detecting means for detecting the abnormality of the sensor when the test voltage is applied are constituted by the digital signal processor. Therefore, there is no need for a filter configured by a conventional analog circuit, and the configuration of the analog input device can be simplified. Further, the filter switching process for detecting the abnormality is not necessary and the analog switch for the filter switching process is not provided, so that the error caused by the analog switch does not occur. Furthermore, since the test voltage output from the power supply unit is applied to the sensor output terminal in the form of a pulse that is cut by the filtering process, the output of the digital filter is not affected when the test voltage is applied.

In the analog input device according to claim 9 of the present invention, the digital filter means for deriving the sensor output by filtering and the abnormality detecting means for detecting the abnormality of the sensor when the test voltage is applied are constituted by a digital signal processor. Therefore, there is no need for a filter configured by a conventional analog circuit, and the configuration of the analog input device can be simplified. Further, the filter switching process for detecting the abnormality is not necessary and the analog switch for the filter switching process is not provided, so that the error caused by the analog switch does not occur. Furthermore, since the AC test voltage having a frequency higher than the cutoff frequency of the filtering process is applied to the sensor output terminal from the power supply unit, the output of the digital filter is not affected when the test voltage is applied. Furthermore, since the AC test voltage may be always applied, there is an effect that the abnormality of the sensor can be constantly monitored.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an analog input device showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an analog input device showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram of an analog input device showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram of an analog input device showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional analog input device.

[Explanation of symbols]

 1 Thermocouple 2 Filter 7a, 7b Digital Signal Processor 8, 8a Power Supply Section 9 Resistor 12 Comparator Circuit 13 Transformer 14 Conversion Circuit

Claims (9)

[Claims] 1. An analog input device for filtering and inputting a detection signal output from a sensor, a power supply unit for applying a test voltage having a waveform cut by the filtering process to an output terminal of the sensor, and the test. An analog input device comprising an abnormality detecting means for detecting an abnormality of the sensor based on an electric quantity derived from the sensor output terminal when a voltage is applied. 2. An analog input device for filtering and inputting a detection signal output from a sensor, and a power supply section for applying a pulsed test voltage cut by the filtering process to an output terminal of the sensor, and An analog input device comprising an abnormality detecting means for detecting an abnormality of the sensor by an electric quantity derived from the sensor output terminal when a test voltage is applied. 3. An analog input device for filtering and inputting a detection signal output from a sensor, wherein a power supply unit applies an AC test voltage having a frequency higher than a cutoff frequency of the filtering process to an output terminal of the sensor. And an analog input device comprising an abnormality detecting means for detecting an abnormality of the sensor by an electric quantity derived from the sensor output terminal when the test voltage is applied. 4. An analog input device for filtering and inputting a detection signal output from a sensor, comprising: a power supply section for applying a test voltage to an output terminal of the sensor; and a signal derived from the output terminal of the sensor. Abnormality of the sensor due to the digital signal input through the A / D converter and filtering the input to derive the sensor output, and the digital signal input when the test voltage is applied. An analog input device, comprising: a digital signal processor provided with an abnormality detecting means for detecting the above, and a test voltage output from the power supply section is a waveform cut by the filter processing. 5. The abnormality detecting means comprises a comparator circuit for comparing an electric quantity derived from an output terminal of the sensor with a preset reference electric quantity when a test voltage is applied. Analog input device. 6. An analog input device for filtering and inputting a detection signal output from a sensor, wherein a pulsed test voltage cut by the filtering is applied to an output terminal of the sensor through a resistor. An analog input device comprising a power supply unit and a comparator circuit for comparing a voltage derived from the sensor output terminal with a preset reference voltage when the test voltage is applied. 7. An analog input device for filtering and inputting a detection signal output from a sensor, wherein an AC test voltage having a frequency higher than a cutoff frequency of the filtering is input to an output terminal of the sensor via a resistor. A power supply unit to be applied, a transformer that transforms a voltage derived from the sensor output terminal when the AC test voltage is applied, a conversion circuit that converts an AC voltage output from the transformer into a DC voltage, and a conversion circuit of the conversion circuit. An analog input device comprising a comparator circuit for comparing a DC voltage with a preset reference voltage. 8. An analog input device for filtering and inputting a detection signal output from a sensor, and a power supply section for applying a test voltage to the output terminal of the sensor via a resistor, and the output terminal of the sensor. Signal to be A
A digital signal is inputted via the D / D converter, and a digital filter means for filtering the input to derive a sensor output, and an abnormality of the sensor due to the digital signal inputted when the test voltage is applied. An analog input device comprising: a digital signal processor provided with an abnormality detecting means for detecting; and a test voltage output from the power supply unit, which has a pulse-like waveform cut by the filtering process. 9. An analog input device for filtering and inputting a detection signal output from a sensor, wherein a power supply unit applies a test voltage to an output terminal of the sensor via a resistor, and an output terminal of the sensor. Signal to be A
A digital signal is inputted via the D / D converter, and a digital filter means for filtering the input to derive a sensor output, and an abnormality of the sensor due to the digital signal inputted when the test voltage is applied. An analog input device, comprising: a digital signal processor provided with an abnormality detecting means for detecting; and a test voltage output from the power supply unit being an AC voltage having a frequency higher than a cutoff frequency of the filtering process.