TWI418770B - Room temperature compensation method of infrared thermometer - Google Patents

Description

Room temperature compensation method for infrared thermometer

The invention relates to a compensation correction method for a thermometer, in particular to a temperature compensation method for an infrared thermometer.

A general infrared thermometer is constructed using a thermopile element. The target temperature (T _target ) is calculated by calculating the temperature difference between the target and the room temperature (ΔT _thermopile ) based on the signal generated by the thermopile element. The room temperature (T _ambient ) calculated by the thermistor is as shown in the following formula: T _target = ΔT _thermopile + T _ambient but the signal of the thermopile element is not nonlinear, that is, the temperature difference calculated from the thermopile signal is room temperature. Function: T _target (T _ambient )=ΔT _thermopile (T _ambient )+T _ambient Therefore, most of the infrared thermometers on the market that do not have room temperature compensation, if at different room temperature, the target with the same temperature When measuring, the resulting temperature value will produce a great error.

In the past, the theoretical calculation of the infrared thermometer was based on the Stefan-Boltzmann quadratic law:

V ( T _{t arg et} ⁴ - T _ambient ⁴ )

Where T _target is the target temperature and T _ambient is room temperature.

However, Stefan-Boltzmann's fourth-order law is only applicable to the full spectrum, that is, the target temperature and the room temperature n are set to 4. However, in general, an infrared thermometer is used with a filter in front of the infrared sensing element to allow only infrared rays of a specific wavelength band to pass (for example, 5 to 14 μm or 8 to 14 μm) to avoid external influence, please refer to FIG. , is the transmittance curve of 8~14μm filter.

Referring to FIG. 10, when the infrared sensing element is loaded with a filter, only infrared rays of a specific wavelength can be received, and the spectral radiant emittance affected by the filter is as shown by the solid line A, and the broken line B Represents the radiation emission when no filter is installed, and there is a significant difference between the two. However, the traditional infrared thermometer does not consider the influence of the filter, and the temperature calculation is performed by the ideal Stefan-Boltzmann quadratic law, resulting in significant errors in the calculation results.

In view of the fact that the conventional infrared thermometer does not consider the influence of the filter, and the temperature measurement produces a significant error, the main object of the present invention is to provide a room temperature compensation method for the infrared thermometer to improve the accuracy of the temperature measurement.

In order to achieve the above object, the technical means for the room temperature compensation method of the infrared thermometer of the present invention is to establish a temperature corresponding data table, and record an infrared sensing component in _a plurality of sets of fixed room temperature (T _a ) conditions. Measuring the sensing voltage (V) at different target temperatures (T _t ), thereby establishing a corresponding value table that has not been temperature compensated; calculating the relationship between the room temperature, the target temperature and the sensing voltage, Using the above corresponding numerical table to find the relationship V ( T _t ⁿ - T _a ⁿ ) the actual power value n, where n <4; calculate the temperature error value, using the difference between the theoretical value and the actual value of the radiation exit degree, calculate the different target temperature at different room temperature The corresponding temperature error value; the selected temperature compensation value is selected from the plurality of sets of temperature error values as the temperature compensation value; the compensation corresponding data table is compensated by the temperature compensation value, Wherein, in the corresponding value table, the target temperature value is subtracted from the temperature compensation value corresponding to the room temperature; and the compensated corresponding data table is stored.

By the technical means of the present invention in consideration of room temperature, the relationship between the three voltage measuring and sensing the temperature of the target Formula V ( T _t ⁿ - T _a ⁿ ), based on the uncompensated measurement result, the actual power value n<4 is calculated, and the actual power value n is used to calculate the compensation curve at different room temperature, and the compensation curve is selected from A suitable temperature compensation curve is used to compensate the original corresponding value table. When the infrared thermometer is used in practice, it is only necessary to refer to the corresponding value table after the compensation to obtain a more accurate target temperature.

The invention is a room temperature compensation method for an infrared thermometer, which can be realized by the infrared thermometer device shown in FIG. 1. The device comprises an infrared sensing component 11, a filter 12 disposed at the front end of the infrared sensing component 11, and a heat. The varistor 13, a memory 14 and a calculation circuit 15.

The infrared sensing element 11 is configured to measure the temperature (T _t ) of a target (for example, a human body), and output a corresponding sensing voltage (V) according to the measurement result. The thermistor 13 is for sensing the room temperature (T _a ). The memory 14 can be used to store the measurement results of the infrared sensing element 11 and the thermistor 13, and the related data calculated by the calculation circuit 15. The calculation circuit 15 is connected to the infrared sensing element 11, the thermistor 13 and the memory 14, receives the sensing result and calculates the target temperature value, and the target temperature value is compensated by the invention to have relatively good precision.

Please refer to FIG. 2, which is a flowchart of the method of the present invention, including the steps of: establishing a temperature corresponding value table (201), and measuring different target temperatures (T _t ) under multiple sets of fixed room temperature (T _a ) conditions and The sensing voltage (V) of the infrared sensing component is recorded, and accordingly, a corresponding value table that has not undergone temperature compensation is established. The corresponding numerical value table is stored in the memory 14 as shown in the example of the following table. The target temperature (T _t ) referred to herein is the blackbody temperature.

Calculate the relationship between the room temperature, the target temperature, and the sense voltage (202). First, define the relationship between room temperature (T _a ), target temperature (T _t ), and sense voltage (V) as V. ( T _t ⁿ - T _a ⁿ ), using the established temperature corresponding value table, the known actual value is substituted into the relational expression, and the calculation circuit 15 is used to find the actual value of the target temperature and the room temperature n-th power relationship. Value, the resulting n value will be less than the ideal value of 4, the n value obtained by different infrared thermometers slightly different, but still maintain less than 4.

The temperature error value (203) is calculated, and the calculation circuit 15 calculates the relationship between the temperature error and the room temperature and the target temperature based on the difference between the theoretical value and the actual value of the radiation exit degree. When calculating the radiative emittance, the radiation emittance of each wavelength is calculated according to Planck's law and integrated, and the different target temperatures as shown in FIG. 3 can be obtained at each room temperature. Radiation emittance (M _p ), which is the theoretical value (M _p ). On the other hand, the actual value of the radiation exit (M _f ) can be expressed as:

M _f =cσ(T _t ⁿ -T _a ⁿ )

Where c≦1, σ is the Stefan-Boltzmann's constant, σ=5.68×10 ^-12 Wm ^-2 K ^-4 , T _t and T _a respectively represent the actual values measured, and n uses the actual value calculated above. n<4; the error ΔM of the theoretical value (M _p ) of the radiation exit degree and the actual value (M _f ) can be expressed as: ΔM=M _f -M _p Temperature error ΔT can be based on the radiation emittance The error ΔM is calculated by the following formula:

Please refer to FIG. 4, for the relationship between the calculated temperature error (ΔT) and the room temperature and the target temperature, FIG. 4 shows two sets of curves, wherein the first set of curves (T ⁴ ) is based on the ideal power value n= 4 and the target temperature is calculated under the condition of 36~42 °C; the second set of curves (T ⁿ ) is calculated according to the actual power value n<4, and it can be known that the temperature error values corresponding to the two sets of curves are obvious. different.

Referring to FIG. 5, according to FIG. 4, the temperature error of n=4 has a maximum value and a minimum value at room temperature of 30 ° C and -5 ° C, respectively, and the temperature error of the remaining room temperature will be distributed between the two, so the chamber is taken. The coordinates are converted at 30 ° C and -5 ° C, and the two curves shown in Figure 5 can be established. Similarly, the temperature error of n < 4 in Figure 4 has maximum and minimum values at -10 ° C and 10 ° C respectively at room temperature. Value, so another coordinate transformation was performed on Figure 5 with a room temperature of -10 ° C and 10 ° C to establish the other two curves.

The temperature compensation value (204) is selected, and FIG. 4 shows the temperature error curve at different target temperatures. In this embodiment, the temperature of the human body is measured as an example. Therefore, a temperature error curve of 38 ° C between 36 and 42 ° C is selected as the temperature error curve. The temperature compensation value, the temperature compensation curve selected in the present invention is shown by the solid line in FIG.

The compensation corresponding value table (205), using the temperature compensation curve of FIG. 6, can compensate the target temperature according to the current room temperature, and the original corresponding value table has been established in the above step (201), so the temperature compensation curve is used to The corresponding value table is compensated, and the corresponding value table after compensation is stored in the memory 14. Wherein, the specific compensation method is to subtract the temperature compensation value corresponding to the room temperature from the target temperature value, for example, the temperature compensation curve power value n=4 at room temperature is 30 ° C and -5 ° C, corresponding The temperature compensation values are approximately 0.01 and -0.125, respectively, that is, when the temperature measurement of the target is actually performed, 0.01 or -0.125 ° C will be subtracted under the corresponding room temperature conditions. The temperature compensation curve power value n<4 at room temperature is -10 ° C and 10 ° C, the corresponding temperature compensation values are about 0.06 and -0.1, respectively, that is, when the actual temperature measurement of the target is performed, it will be in the corresponding room. Subtract 0.06 or -0.1 °C under temperature conditions.

As shown in Figures 7 and 8, the temperature error value after temperature compensation can be significantly reduced, making the temperature measurement result more accurate. The temperature error curve with the negative value n=4 and room temperature 30°C is lower than the whole curve of FIG. 5 by 0.01, the power value of n=4 and the temperature error curve of room temperature-5°C is shifted upward by 0.125. . Similarly, a temperature curve of 10 ° C and -10 ° C with a power value of n < 4 also produces an up and down offset. Comparing Fig. 5 with Fig. 7, it can be confirmed that the temperature error value of the present invention is significantly reduced, and the measurement result of the target temperature is more accurate.

When the present invention is actually applied to an infrared thermometer, since the memory 14 has a corrected corresponding value table inside, it is comparable according to the room temperature converted by the thermistor 13 and the voltage signal measured by the infrared sensing element 11. For the corresponding value table in the memory 14, the lookup table gives a more accurate target temperature.

The following provides an example to further illustrate the room temperature compensation method of the present invention. Under the condition of room temperature 25 ° C, record the original target temperature (Tt) and the corresponding measurement voltage (V) as shown in Table 1:

After calculation, the corrected value is -0.05769, and the compensated data is as shown in Table 2 below:

In summary, the present invention is considered at room temperature, the relationship between the three voltage measuring and sensing the temperature of the target Formula V ( T _t ⁿ - T _a ⁿ ), the actual sub-value n<4 is calculated based on the uncompensated measurement result, and the actual sub-value n is used to calculate the compensation curve at different room temperature, and a suitable one is selected. The temperature compensation curve is used to compensate the corresponding value table of the room temperature, the target temperature and the sensing voltage by using the temperature compensation curve, thereby reducing the temperature measurement error and making the infrared thermometer more accurate in actual application. Target temperature.

11. . . Infrared sensing component

12. . . Filter

13. . . Thermistor

14. . . Memory

15. . . Calculation circuit

Figure 1: Block diagram of an infrared thermometer circuit that can be used to implement the present invention.

Figure 2: Flow chart of the method of the present invention.

Figure 3: Radiation output at different room temperature for different target temperatures.

Figure 4: Graph of room temperature, target temperature and temperature error.

Figure 5: Temperature error curve of coordinate conversion based on the data of Figure 4.

Figure 6 is a graph of the temperature compensation curve of the present invention.

Fig. 7 is a graph showing temperature error after temperature compensation according to the present invention.

Fig. 8 is a partial enlarged view of the target temperature of 36 to 42 degrees in Fig. 7.

Figure 9: Plotting curve of a conventional 8~14μm filter.

Figure 10: Spectral radiation exit rate diagram of a conventional infrared sensing element after a filter is placed.

Claims (5)

A room temperature compensation method for an infrared thermometer includes: establishing a temperature corresponding data table, recording an infrared sensing component when measuring different target temperatures (T _t ) under _a plurality of sets of fixed room temperature (T _a ) conditions The sensing voltage (V) is used to establish a corresponding value table that has not been temperature compensated; the relationship between the room temperature, the target temperature and the sensing voltage is calculated, and the corresponding value table is used to find the relationship V. ( T _t ⁿ - T _a ⁿ ) the actual power value n, where n <4; calculate the temperature error value, using the difference between the theoretical value and the actual value of the radiation exit degree, calculate the different target temperature at different room temperature The corresponding temperature error value; the selected temperature compensation value is selected from the plurality of sets of temperature error values as the temperature compensation value; the compensation corresponding data table is compensated by the temperature compensation value, Wherein, in the corresponding value table, the target temperature value is subtracted from the temperature compensation value corresponding to the room temperature; and the compensated corresponding data table is stored. The room temperature compensation method of the infrared thermometer according to the first aspect of the patent application, in the step of calculating the temperature error value, includes: calculating the theoretical value of the radiation exit degree, and calculating the radiation emission of each wavelength according to Planck's law And integrate to obtain the radiation emission degree of different target temperature at each room temperature; calculate the actual value (M _f ) of the radiation exit degree of the radiation exit degree according to the formula M _f =cσ(T _t ⁿ -T _a ⁿ ) Calculate the actual value of the radiation exit degree, where c≦1, σ=5.68×10 ^-12 Wm ^-2 K ^-4 , T _t is the measured target temperature value, and T _a is the measured room Temperature, n is the calculated actual power value; calculate the error ΔM of the theoretical value (M _p ) of the radiation exit degree and the actual value (M _f ), where ΔM=M _f -M _p ; Calculate the temperature error. For the room temperature compensation method of the infrared thermometer according to the first or second aspect of the patent application, in the step of selecting the temperature compensation value, the temperature error value corresponding to the intermediate value of the target temperature is selected as the temperature compensation value. For the room temperature compensation method of the infrared thermometer described in claim 3, in the step of establishing the temperature corresponding data table, the corresponding value table of the target temperature of 36 to 42 degrees is established. For the room temperature compensation method of the infrared thermometer according to item 4 of the patent application scope, in the step of selecting the temperature compensation value, the temperature error value corresponding to the target temperature of 38 degrees is selected as the temperature compensation value.