JPS6039788Y2 - radiation thermometer - Google Patents

Description

[Detailed description of the invention] This invention uses an optical chopper to time-divide the incident light emitted from the object to be measured and the comparison light emitted from the comparison light source, and make them alternately enter the photodetector. The present invention relates to a radiation thermometer that automatically controls the brightness of a comparison light source so as to minimize the difference in light so as to balance the two and measure the temperature of the object to be measured.

As shown in FIG. 1, in the radiation thermometer, incident light emitted from a measurement object 11 is given to a chopper 13 via a lens 12, and is time-divided and alternately transmitted by the chopper 13 and comparison light emitted from a comparison light source 14. The light is incident on the photodetector 15.

From the photodetector 15, an AC voltage signal 1 is obtained according to the energy difference between the incident light and the comparison light.

The AC signal (1) is amplified by the AC amplifier 16.

The amplified output ■2 is synchronously rectified by a synchronous rectifier 17 in synchronization with the chopper operation of the chopper 13, and divided into a DC voltage corresponding to the intensity of the incident light and a DC voltage corresponding to the intensity of the comparison light. , the difference between the two is amplified by the amplifier 18.

The amplified output V3 is converted into a current I by the voltage-current conversion circuit 19, and the current is supplied to the lamp of the comparison light source 14.

As a result, the lamp current is automatically controlled to a value that balances the incident light and the comparison light.

Therefore, the temperature of the object to be measured 11 can be measured from the value of this lamp current.

In the AC amplifier 16, for example, the output side of the operational amplifier 21 is connected to a common potential point through a voltage dividing circuit of resistive elements 22.23, and the connection point of the resistive elements 22.23 is connected to the operational amplifier 21.
It is configured by being connected as a feedback to the input side of the circuit.

The chopper 13 includes a rotary plate 24 in which reflective portions and transmitting portions are provided at equiangular intervals, and a motor 2 that rotates the rotary plate 24.
5, and the rotation timing of the rotary plate 24 and the synchronous timing generating means 26 detect the synchronous rectifier 1.
7.

In the voltage-current conversion circuit 19, the output of the amplifier 18 is npn.
Supplied to the base of transistor 27, transistor 2
The emitter of transistor 7 is connected to a common potential point through a resistor 28, the collector is connected to the base of a pnp transistor 29, and is also connected to a power supply terminal 32 through a resistor 31, and the emitter of the transistor 29 is connected to a power supply terminal 32 through a resistor 33. and the collector is connected to the lamp 14
are connected to a common potential point through a filament of

In this conventional radiation thermometer, the loop gain of the measurement circuit changes greatly depending on the measurement temperature and the ambient temperature, so when the ambient temperature is relatively high at the lower limit of the measurement temperature range, the loop gain is insufficient and temperature fluctuation errors occur. Also, when the ambient temperature is relatively low at the upper end of the measurement temperature range, the loop gain is too large and the circuit is likely to oscillate.
Tends to become unstable.

For these reasons, there was a drawback that a wide temperature range could not be measured.

To further explain these points, in the radiation thermometer shown in FIG.
The relationship between the energy W of the comparison light from one lamp 14 is expressed in a gain block diagram as shown in FIG.

That is, when a slight change ΔT occurs in the temperature of the object 11, the energy of the incident light changes ΔW, and the difference between this and the energy change ΔWr of the comparison light of the feedback gain β is detected by the photodetector 15 with sensitivity S. , the AC signal output (2) outputs a minute change ΔI in the lamp current through a circuit 34 with a gain A from the AC amplifier 16 to the voltage-current conversion circuit 19.

SA (1) Δ””I+SAβΔW It is expressed as

(a) The relationship between the measured temperature T (K) and the incident energy W is shown in FIG. 3, where W is proportional to To.

Here, n is a constant determined by the wavelength spectrum of the sensitivity S of the photodetector 15, etc.

For example, n=9 to 11.

(b) As shown in Fig. 4, the sensitivity S changes depending on the incident energy W and decreases as W increases, and the sensitivity S changes with the incident energy W.
When S is small, it also changes depending on the ambient temperature t, and the higher the ambient temperature t, the greater the sensitivity S becomes.

(c) The gain A is determined by the constant of the electric circuit, and in FIG. 1, it is constant regardless of the AC voltage V1, and 9=□1 also becomes 1 0μ@0 R2R2R6.

Here, R19R2=R3=R4, R5=R6 are the resistance values of the resistance elements 22, 23, 28, 31, and 33, respectively, and μ is the amplification factor of the amplifier 18.

) Lamp current I and radiant energy W from the lamp 14,
As shown in FIG. 5, W' is proportional to Im.

Here, m varies depending on the lamp 14, but for example, n=7
~4.

From now on β key, ■ β=aI frame W’rz l =I m becomes.

When m=7 to 4, 1≧0.9 to 0.7. β and Wf
The relationship with is shown in FIG.

From (a) to (a) above, the relationship between the loop gain G=SAβ of the feedback circuit in FIG. 2 and the measured temperature T is as shown in FIG.

In other words, as mentioned earlier, when the measured temperature T is low, the loop gain G becomes too small and errors tend to occur in the measured temperature, and when the measured temperature T is high and the ambient temperature t is relatively low, the loop gain G becomes high. It becomes too unstable.

The purpose of this invention is to provide a radiation thermometer that can accurately measure even when the measured temperature is low and operates stably even when the measured temperature is high and the ambient temperature is low.

According to this invention, one of the resistive elements that determines the amplification factor from the AC amplifier circuit to the voltage-current converter circuit is one whose resistance value changes depending on the ambient temperature. The decrease in the sensitivity of the photodetector element when the amplification factor is high is compensated for by increasing the amplification factor.

In addition, an element whose resistance value changes nonlinearly depending on the current is used as the resistance element that determines the conversion rate of the voltage-current conversion circuit, and the increase in loop gain at the upper limit of the measurement range means that the conversion rate of the voltage-current conversion circuit is Suppress by increasing by decreasing.

In this way, the range of change in loop gain is narrowed.

An example of a radiation thermometer according to this invention is shown in FIG. 8, in which parts corresponding to those in FIG. 1 are given the same reference numerals.

In this embodiment, a negative temperature coefficient AC resistance element 36 is used in place of the resistance element 23 that defines the amplification factor of the AC amplifier 16.

Further, instead of the feedback resistance element 33 of the voltage-current conversion circuit 19, a nonlinear resistance element 37, such as a nichrome wire or a tungsten wire, whose resistance value increases as the current increases, is used.

The loop gain G of the radiation thermometer shown in FIG. 8 is expressed as G=SAβ, as in the conventional case, and S, A.

Of β, S and β are the same as before, but A is.

=1 Zheng (6), ,, also, IR2(t) R4
It becomes R6(I).

R2(t) is the resistance value of the resistance element 36, and the ambient temperature t
R6(I) is the resistance value of the resistance element 37, and changes depending on the lamp current I.

The relationship between the resistance value R2(t) of the resistance element 36 and the temperature t decreases as t increases, as shown in FIG. 9, for example.

The resistance value R6 (I) of the nonlinear resistance element 37 and the lamp current (
Regarding the relationship with I), for example, as shown in FIG. 10, as I increases, the resistance value increases nonlinearly.

Therefore, as shown in FIG. 11, the gain A decreases as the current 2 increases, and increases as the temperature t increases.

S-W in Fig. 4, A-I in Fig. 11, β-Wr in Fig. 6
The relationship between the loop gain G...SAβ and the measured temperature T is determined from the relationships of Wr I in FIG. 5 and WT in FIG. 3B, as shown in FIG. 12.

As can be seen from FIG. 12, the change in the loop gain G becomes smaller with respect to a change in the measured temperature T, and even when the temperature T is low, the gain G does not change with a change in the ambient temperature t.

Therefore, temperature measurement over a wide range is possible.

Furthermore, the temperature drift at the lower limit of the measurement temperature range is small.

Furthermore, the drawback of changes in physical characteristics of the photodetector 15 due to temperature can be easily corrected using an electric circuit.

Note that in the AC amplifier 16, a temperature-sensitive resistance element with a positive temperature coefficient whose resistance value changes depending on the ambient temperature may be used instead of the resistance element 24.

Furthermore, a temperature-sensitive resistance element with a negative temperature coefficient may be used as the resistance element 28 of the voltage-current conversion circuit, so that the amplification factor A changes according to changes in the ambient temperature.

The temperature-sensitive resistance element should be placed near the photodetector 15, and if the voltage-current conversion circuit 19 is provided away from the photodetector 15 or if sufficient gain is obtained with the AC amplifier 16, it should be placed near the AC amplifier 16. It is better to connect a temperature-sensitive resistance element and change its amplification factor according to the temperature t.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram showing a conventional radiation thermometer, Fig. 2 is an equivalent circuit diagram for its minute temperature change T, Fig. 3 is an incident light energy W-measured temperature T characteristic diagram, and Fig. 4 is photodetection. Figure 5 shows the comparison light energy W characteristic diagram, Figure 6 shows the feedback gain β vs comparative light energy W characteristic diagram, and Figure 7 shows the loop gain G measurement. Temperature T characteristic diagram, Figure 8 is a connection diagram showing an example of a radiation thermometer according to this invention, and Figure 9 is the resistance value R2 (t) of the temperature-sensitive resistance element.
-Characteristic diagram of ambient temperature, Figure 10 is resistance value R6(t) of nonlinear resistance element, lamp current characteristic diagram, Figure 11 is amplification factor A-
The lamp current characteristic diagram, FIG. 12, is a loop gain G-measured temperature characteristic diagram of the thermometer of this invention. 11: Measurement object, 13: Chopper, 14: Comparison light source, 15: Photodetector, 16: AC amplifier, 17: Synchronous rectifier circuit, 18: Amplifier, 19: [Positive current conversion circuit, 36:
Negative temperature coefficient resistance element, 37: Nonlinear resistance element.

Claims (1)

[Scope of utility model registration request] The incident light emitted from the object to be measured and the comparison light emitted from the comparison light source lamp are alternately irradiated onto the photodetector by a chopper, and the peak value is determined according to the intensity difference between the incident light and the comparison light. The AC signal is amplified by an AC amplifier, and the amplified output is synchronously rectified and separated into a DC voltage corresponding to the intensity of the above-mentioned incident light and a DC voltage corresponding to the intensity of the above-mentioned comparison light. Then, the difference between these two is amplified and the amplified output is converted into a current by a voltage-current converter, and the current of the comparison light source lamp is controlled by the current to balance the incident light and the comparison light, and then the comparison is made. In the radiation thermometer that measures the temperature of the object to be measured based on the value of the light source lamp current, at least one of the resistance elements that determines the amplification factor between the AC amplifier and the voltage-current converter has a resistance value that changes depending on the ambient temperature. at least one of the resistive elements determining the conversion factor of the voltage-to-current converter increases the current according to the magnitude of the lamp current; A radiation thermometer that uses a nonlinear resistance element whose resistance value changes so that the conversion rate decreases, and the loop gain of the measurement circuit is kept almost constant regardless of changes in the measurement temperature and ambient temperature.