JP2005128033A - Radiation thermometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation thermometer for enhancing measurement accuracy and measurement reliability by removing error factors depending on element performance of electronic circuit components or circuitry, and the effect of environmental temperature. <P>SOLUTION: This radiation thermometer is equipped with an infrared sensor for outputting a sensor output signal corresponding to the amount of infrared rays radiated from a measuring object, a temperature sensor for outputting a sensor temperature signal corresponding to the temperature of the infrared sensor itself, an amplifier including an inverting input terminal and a non-inverting input terminal for amplifying the output signal, an input switch part for connecting the output signal to either the inverting input terminal or the non-inverting input terminal, and a control part for calculating the temperature of the measuring object based on the output signal amplified by the amplifier and the temperature signal. The control part calculates the temperature of the measuring object based on a difference signal between an output signal inputted into the inverting input terminal for amplification and an output signal inputted into the non-inverting input terminal for amplification. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiation thermometer that measures the temperature of a measurement object using infrared rays emitted from the measurement object.

As this type of radiation thermometer, for example, an infrared thermometer for measuring by the method disclosed in Japanese Patent Laid-Open No. 8-145800 is known. This infrared thermometer is an infrared sensor, a probe that captures infrared rays from the ear canal, a temperature sensor that detects the temperature of the infrared sensor itself, a preamplifier (amplifier) that amplifies the output of the infrared sensor and the output of the temperature sensor, and is amplified by the preamplifier. A / D converter that A / D converts the output of the infrared sensor and the output of the temperature sensor, and a CPU that calculates the temperature of the measurement target from the output of the infrared sensor and the temperature sensor that have been A / D converted ing.

In such an infrared thermometer, the temperature of the measurement object is calculated based on a predetermined calculation formula (for example, see Patent Document 1) from the output of the infrared sensor and the output of the temperature sensor taken in as digital data by the CPU.
JP 61-117422 A

  However, in the case of the prior art as described above, it is difficult to improve the measurement accuracy or measurement reliability due to the element performance of the electronic circuit components constituting the infrared thermometer, the error factor depending on the circuit configuration, and the influence of the environmental temperature. It has become.

  That is, it is known that an offset voltage (or offset current) of an input circuit is generally present in an amplifier, and this greatly shifts the output voltage level. Here, the offset voltage is a voltage obtained by converting the output voltage appearing at the output terminal in the state where the amplifier has no input signal into the voltage on the input side. As a method of eliminating this offset voltage, a method of applying a voltage in the opposite direction to the offset voltage to the input terminal and a method of adjusting the bias of the transistor inside the amplifier are known (Okamura Ikuo, published by CQ Publishing, "OP amplifier circuit design"). However, such a method is not necessarily stable with respect to a temperature change, and there is a problem that an increase in the number of components and circuit complexity are caused.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to eliminate the element characteristics of the circuit components constituting the radiation thermometer and the error factor due to the circuit configuration, and to perform highly accurate measurement. It is to provide a radiation thermometer.

  In order to achieve the above object, the present invention adopts the following configuration. That is, the present invention provides an infrared sensor that outputs a sensor output signal corresponding to the amount of infrared rays emitted from a measurement target, and a temperature sensor that outputs a sensor temperature signal corresponding to the temperature of the infrared sensor itself. It is a thermometer and further includes the following configuration.

  The present invention provides an amplifier including an inverting input terminal and a non-inverting input terminal for amplifying the sensor output signal, and for connecting the sensor output signal to either the inverting input terminal or the non-inverting input terminal. An input switch unit; and a control unit that calculates the temperature of the measurement target based on the sensor output signal amplified by the amplifier and the sensor temperature signal.

  The control unit calculates a temperature to be measured based on a difference signal between the sensor output signal amplified from the inverting input terminal and the sensor output signal amplified from the non-inverting input terminal.

  According to the present invention, since the offset voltage of the amplifier can be eliminated easily and stably in the radiation thermometer, the measurement accuracy can be improved.

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

(Basic form)
Prior to the description of the embodiment that best represents the features of the present invention, a basic radiation thermometer will be described with reference to FIGS. 1 and 2, and will be referred to as appropriate in the description of the embodiment of the present invention described later.

  FIG. 1 is a block diagram of a radiation thermometer according to the basic form of the present invention, and FIG. 2 is a flowchart showing its operation.

<Configuration of radiation thermometer>
A block diagram showing the configuration of this radiation thermometer is shown in FIG. The radiation thermometer includes an infrared sensor 1 that detects infrared rays radiated from a measurement target (for example, an eardrum in an ear canal), a temperature sensor 2 that measures the temperature of the infrared sensor 1 itself, and an output (sensor) of the infrared sensor 1 Output signal) and the output of the temperature sensor 2 (sensor temperature signal), an amplifier 3 for amplifying them, a reference voltage generator 11 for generating a reference voltage as a reference input voltage, and a sensor amplified by the amplifier 3 A / D that converts output signal, sensor temperature signal and reference input voltage into digital data
A converter 4 and a signal selection circuit 10 for connecting any one of a sensor output signal, a sensor temperature signal, and a reference input voltage amplified by the amplifier 3 in accordance with an input switching signal to an input circuit of the A / D converter 4; The CPU 5 (corresponding to the control unit) that calculates the temperature of the measurement object based on the sensor output signal and the sensor temperature signal converted into digital data by the A / D converter 4 by executing the control program, and the measurement calculated by the CPU 5 An LCD 6 (liquid crystal display) for displaying the target temperature and a memory 7 for storing a control program and data are provided.

  The infrared sensor 1 is composed of a thermopile, and generates a sensor output signal (electromotive force) in response to infrared rays from a measurement target.

  The temperature sensor 2 is composed of a thermistor, and detects a change in temperature of the infrared sensor 1 itself as a change in resistance value by contacting the infrared sensor 1. The change in voltage across the thermistor due to this change in resistance corresponds to the sensor temperature signal.

The amplifier 3 receives the output of the infrared sensor 1 (sensor output signal) and the output of the temperature sensor 2 (sensor temperature signal) and amplifies them to a signal level that can be converted by the A / D converter 4.

  The voltage generated from the reference voltage generator 11 is used as a reference input voltage when the CPU 5 measures the conversion linearity of the A / D converter 4.

The signal selection circuit 10 performs A / D on any one of the sensor output signal amplified by the amplifier 3 according to the switching signal input from the CPU 5, the sensor temperature signal, and the reference input voltage generated by the reference voltage generator 11. Connect to the input terminal of the converter 4.

  The processing of the A / D converter 4 and the CPU 5 will be described in detail below.

<Conversion method of A / D converter>
The A / D converter 4 converts the sensor output signal and the sensor temperature signal amplified by the amplifier 3 into digital data. In this embodiment, a double integration type A / D converter composed of an integration circuit (corresponding to an integrator), a comparator and a counter is adopted as the A / D converter 4 (for example, published by Japan Science and Technology Publishing Co., Ltd. by Noriyuki Ito). (Refer to section 16.3 Double Integrating AD Converter in "Digital Circuits"). FIG. 8 shows the configuration of a double integration type A / D converter.

  This type of A / D converter integrates the input signal V1 to be converted by a T1 (hereinafter referred to as charging time) integrating circuit for a certain period, and discharges it with a known discharge reference voltage V2. The digital data of the input signal V1 is obtained from the time T2 (actually, the number of clocks measured by the counter), the charging time T1 and the discharge reference voltage V2. This relationship is expressed by the following (Formula 1).

T2 = -T1 × (V1-V3) / (V2-V3) ..... (Formula 1)
Here, V1 is the voltage of the input signal.
V2: Reference voltage for discharge.
V3: A reference potential of the A / D converter 4.
T1: The charging time of the integration circuit by the input signal.
T2: discharge time.

The input signal voltage (V1-V3) based on the reference potential V3 is proportional to the discharge time T2, so that the gate signal that is on during the discharge time T2 passes the reference clock pulse and counts it with the counter. The digital data after A / D conversion can be obtained from the counter value.

<CPU processing>
The CPU 5 executes the control program stored in the memory 7 and calculates the temperature of the measurement object from the sensor output signal and sensor temperature signal converted into digital data. At that time, the CPU 5
By inputting a switching signal to the signal selection circuit 10, a reference input voltage is applied from the signal selection circuit 10 to the A / D converter 4, and the conversion linearity of the A / D converter 4 is measured in advance. Based on the above, the temperature of the measurement object is corrected. Hereinafter, the processing of the CPU 5 will be described in detail.

Now, in the above double integral type A / D converter, A / D conversion output (digital data) obtained when A / D conversion is performed on the same reference input voltage with two kinds of charging time T1a and T1b is ADa, Assuming ADb, if the above (Equation 1) holds,
T1a / T1b = ADa / ADb ..... (Formula 2)
Is established. That is, even when the same input signal is A / D converted, the A / D conversion output is proportional to the charging time of the integration circuit. This equivalently represents the same result as when A / D conversion is performed on various input signal voltages (V1-V3) with the same charging time T1 in (Equation 1).

However, in an actual double integration type A / D converter, (Equation 2) does not necessarily hold due to the influence of the leakage current of the capacitor of the integration circuit. This is equivalent to the fact that A / D conversion output (digital data) proportional to the input signal voltage cannot always be obtained when various input signal voltages are A / D converted with the same charging time. It represents the error in the conversion linearity of the integral type A / D converter. there
X = T1a / T1b-ADa / ADb ..... (Formula 3)
If the error is calculated in advance by changing the charging time, the actual A / D conversion output (digital data) can be corrected.

FIG. 3 plots a plurality of measured values 101 with the charging time as the horizontal axis and the output (digital data) measured by A / D converting the same reference input voltage at various charging times as the vertical axis. It is a graph which shows an example with the theoretical value 100 illustrated with the continuous line. In FIG. 3, a plurality of actually measured values 101 correspond to conversion linearity, and a theoretical value 100 corresponds to ideal conversion linearity.

Further, FIG. 4 shows the measured value 101 of the A / D conversion output (digital data) shown in FIG. 3 as the horizontal axis and the error from the theoretical value (ideal conversion linearity) at that time as the vertical axis. It is a graph which shows the error curve 102 obtained as a result of plotting. If the actual A / D conversion output (digital data) is corrected with the value obtained from the empirical formula (error curve) of FIG. 4, the error from the theoretical value 100 of the conversion linearity shown in FIG. 3 is eliminated. Can do. Such an empirical formula can be generally obtained by the method of least squares.

In the present embodiment, the CPU 5 holds the coefficient of the error curve 102 (empirical formula) as shown in FIG. 4 in the memory 7 from the conversion linearity data measured in advance, and uses this error curve 102 to / D conversion output (digital data) is corrected, and the measurement target (based on the corrected digital data)
The temperature of the eardrum is calculated.

<Operation example>
Next, an example of the overall operation of the radiation thermometer shown in FIG. 1 will be described according to the flowchart of FIG.

  First, when a power switch (not shown) is turned on (step 101 (hereinafter abbreviated as S101)), the CPU 5 executes a control program stored in the memory 7 and executes the following operation.

First, the CPU 5 controls the signal selection circuit 10, connects the reference input voltage from the reference voltage generator 11 to the input terminal of the A / D converter 4, and then sets a plurality of charging times for charging the integration circuit. The A / D converter 4 is set to execute A / D conversion a plurality of times, and the conversion linearity error curve 102 shown in FIG. 4 is obtained (S102). Thereafter, the CPU 5 enters a standby state (S103).

When a measurement start switch (not shown) is pressed, the CPU 5 detects that the measurement start switch has been pressed, and starts measurement using the detection as a trigger (S104).

First, the sensor temperature signal of the temperature sensor 2 is A / D converted to obtain digital data (S
105).

Next, the sensor output signal of the infrared sensor 1 is A / D converted to obtain the digital data (S
106).

Next, the CPU 5 obtains A / D conversion correction values of the sensor temperature signal and the sensor output signal from the conversion linearity error curve 102 obtained in the process of S102 (S107).

After that, the A / D conversion correction value is used to correct the digital data of the sensor temperature signal and the sensor output signal obtained in the processes of S105 and S106. (S108).

In this way, each time the power switch is turned on, the CPU 5 calculates the conversion linearity of the A / D converter 4 and corrects the error due to the deviation from the theoretical value. Even if a temperature change occurs, the temperature of the object to be measured is obtained using the A / D conversion output in which the error due to the deviation from the theoretical value of the conversion linearity is corrected according to the change. Therefore, the accuracy of temperature measurement by the radiation thermometer can be increased.

<Modification>
In the configuration shown in FIG. 1, the output (reference input voltage) of the reference voltage generator 11 is directly connected to the A / D converter 4 through the signal selection circuit 10. The reference input voltage may be input to the signal selection circuit 10 through the amplifier 3. By doing so, it is possible to measure and correct the conversion linearity of the amplifier 3 and the A / D converter 4 combined.

If the output signal of the infrared sensor 1 or the temperature sensor 2 is sufficiently large and can be converted by the A / D converter 4, these signals should be directly A / D converted by the A / D converter 4. The amplifier 3 can be omitted.

In this embodiment, the conversion linearity of the A / D converter 4 is generally measured to correct the digital data. However, the error generation factor illustrated in FIG. 3 or FIG. 4
The digital data may be corrected by assuming the leakage current of the capacitor in the integration circuit in FIG.

If the resistance of the integrating circuit is R, the capacitance is C, and the output voltage of the integrated signal is V0, the output voltage of the integrating circuit is as follows when the input signal voltage is the reference input voltage Vi (constant): 4).
V0 = ViT1 / CR ..... (Formula 4)
Here, T1 is the charging time of the integrating circuit.

However, if there is a leakage current in the capacitor of the integrating circuit and this is Δi1 (the equivalent leakage resistance value at that time is r1), the output voltage is as shown in the following (Equation 5).
V0 = (T1 / C) (Vi / R-Δi1)
= ViT1 / CR ・ (1- R / r1) ..... (Formula 5)

On the other hand, when the capacitor of the integration circuit charged to V0 is discharged with the reference reference voltage Vr
V0 = VrT2 / CR ..... (Formula 6)
Here, T2 is the discharge time of the integrating circuit.

However, if there is a leakage current in the capacitor of the integrating circuit and this is Δi2 (the equivalent leakage resistance value at that time is r2), the output voltage is as shown in (Equation 7) below.
V0 = (T2 / C) (Vr / R-Δi2)
= VrT2 / CR ・ (1- R / r2) ..... (Formula 7)

Therefore, when the known reference input voltage Vi is input to the integrating circuit of the A / D converter 4 and integrated at a predetermined charging time T1, the measured value of the integrating circuit output V0 and the value calculated by the theoretical formula (Formula 4) The leakage resistance r1 is obtained from the difference in accordance with the above (Equation 5), and the difference between the measured value of the discharge time T2 when the charged voltage V0 is discharged with the discharge reference voltage Vr and the theoretical equation (Equation 6) ( The leakage resistance r2 can be calculated according to Equation 7).

Therefore, these R, r1, and r2 are held in the memory, and the CPU 5 corrects the output of the A / D converter 4 according to (Equation 5) and (Equation 7). Can be obtained. This expresses the interpretation of the deviation of the conversion linearity from the theoretical value as the leakage resistance of the integration circuit of the A / D converter 4, and is included in one aspect of the basic form.

In this basic form, a double integration type A / D converter is used as the A / D converter 4, but the present invention is not limited to this. In short, the conversion linearity as the A / D converter 4 is measured in advance from the relationship between the reference input signal (analog signal) and the A / D conversion output (digital data) at that time, and the actual measurement is performed from the conversion linearity. It is only necessary to correct the A / D conversion output. That is, the present invention provides a reference voltage generator 11 that generates a plurality of voltages as a reference input signal even if the radiation thermometer includes an A / D converter without means for changing the charging time of the integration circuit. If applicable. Therefore, the infrared sensor 1, the temperature sensor 2, and the A / D, regardless of the A / D conversion method, such as an A / D converter with a sample-and-hold circuit, a counter clamp type A / D converter, and a successive approximation A / D converter. The present invention can also be applied to a radiation thermometer having a converter 4.

In this basic form, the radiation thermometer that corrects the error of the conversion linearity of the A / D conversion output is shown.
If the measured conversion linearity deviates greatly from the theoretical value, the correction may be stopped and a display to that effect may be displayed. FIG. 5 shows a flowchart of a program for performing such display. 5 is obtained by adding the processes of S120 to S122 to the process of FIG. 2 and omitting the processes after S104 of FIG.

  In this process, after measuring the conversion linearity as in FIG. 2 (S102), it is determined whether or not the deviation from the theoretical value of the actually measured conversion linearity is within a predetermined range (S120). If there is, it shifts to the standby state as in FIG. 2 (S103), but if it is not within the predetermined range, it indicates that the conversion linearity has deteriorated (S121) and turns off the power (S122). .

  In this way, measurement is performed in a situation where the leakage current of the integration circuit temporarily increases and the measurement reliability becomes low due to high humidity or an environment where condensation due to sudden temperature changes occurs. It is possible to stop and prevent display of measurement results with large errors.

In this basic mode, an example of measuring the conversion linearity of A / D conversion each time the power switch is turned on has been shown. Instead, an explicit instruction (for example, an instruction by a dedicated push button) is given in advance. May be detected and measured, and an error curve based on the measurement result may be held until the next instruction. In addition, a control program executed by the CPU 5 may be interrupted by a timer to periodically measure the conversion linearity of A / D conversion. Or you may make it obtain | require conversion linearity for every measurement of the temperature (body temperature) of a measuring object.

(Embodiment)
Embodiments that best represent the features of the present invention will be described below.
The radiation thermometer which concerns on embodiment of this invention is demonstrated using FIG.6 and FIG.7. FIG. 6 is a block diagram showing the configuration of the radiation thermometer according to the third embodiment, and FIG. 7 is a diagram showing a change in the amplified signal by the amplifier 3 shown in FIG.

The radiation thermometer according to the present embodiment eliminates the offset voltage of the amplifier 3. As shown in FIG. 6, the voltage at both ends of the infrared sensor 1 can be inverted to the inverting input terminal 3a and the non-inverting input terminal 3b of the amplifier 3 via switches 15 to 18 (corresponding to the input switch unit). It is connected. Connections of the switches 15 to 18 can be switched by a switching signal from the CPU 5. Since other configurations and operations are the same as those of the basic mode, the same components are denoted by the same reference numerals and description thereof is omitted.

In such a configuration, the output Vout1 of the amplifier 3 when the switches 15 and 17 are turned on and the output Vout2 of the amplifier 3 when the switches 16 and 18 are turned on are respectively the outputs (starts) of the infrared sensor 1. Power) is a result obtained by amplifying each of the inverting input terminal 3a and the non-inverting input terminal 3b of the amplifier 3 by being replaced with each other. .

  This relationship can be shown in the following equation.

Vout1 = G ・ (E + Vos + Vr) ..... (Formula 6)
Vout2 = G ・ (-E + Vos-Vr) ..... (Formula 7)
Where E is the output (electromotive force) of the infrared sensor 1.
Vos: the offset voltage of the amplifier 3.
Vr: Reference voltage.
G: The gain of the amplifier 3

Taking the difference between (Equation 6) and (Equation 7)
Vout1− Vout2 = 2G ・ (E + Vr) ..... (Formula 8)
Thus, the offset voltage of the amplifier 3 is canceled. Therefore, by latching either Vout1 or Vout2, taking the differential signal of both, and performing A / D conversion, the influence of the offset voltage of the amplifier 3 can be eliminated during temperature measurement. As a result, it is possible to suppress the influence of the fluctuation of the offset voltage due to the temperature characteristics of the amplifier 3 and the change over time in the temperature measurement, and the temperature measurement accuracy can be improved.

Each of Vout1 and Vout2 may be A / D converted, and the difference may be obtained from the digital data after each conversion.

The block diagram which shows the structure of the radiation thermometer which concerns on the basic form of this invention Flow chart showing the operation of the radiation thermometer according to the basic form Graph showing A / D conversion output against charging time of integration circuit Graph showing error from conversion linearity for A / D conversion output Flow chart showing the operation of the radiation thermometer of the modification of the basic form The block diagram which shows the structure of the radiation thermometer which concerns on embodiment of this invention. The figure which shows the amplifier output signal which concerns on embodiment of this invention Diagram showing double integral A / D converter according to basic configuration

Explanation of symbols

1 Infrared sensor 2 Temperature sensor 3 Amplifier 4 A / D converter 5 CPU
10 Signal selection circuit 11 Reference voltage

Claims (1)

An infrared sensor that outputs a sensor output signal corresponding to the amount of infrared rays emitted from the measurement object, a temperature sensor that outputs a sensor temperature signal corresponding to the temperature of the infrared sensor itself, and amplifying the sensor output signal An amplifier including an inverting input terminal and a non-inverting input terminal, an input switch unit for connecting the sensor output signal to either the inverting input terminal or the non-inverting input terminal, and a sensor output amplified by the amplifier A controller that calculates the temperature of the measurement object based on the signal and the sensor temperature signal,
The control unit is a radiation thermometer that calculates a temperature to be measured based on a difference signal between the sensor output signal amplified from the inverting input terminal and the sensor output signal amplified from the non-inverting input terminal.

Images