JPH0452661Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a radiation thermometer that can measure temperatures in a wide range from low to high temperatures.

<Prior Art> FIG. 3 shows an example of a conventional radiation thermometer. In the figure, 1 is a lens, 2 is an optical filter, 3 is a photodetector, 400 is a first stage amplifier having a feedback resistor 401, 11 is an analog/digital conversion circuit, and 12 is a temperature calculation circuit. In such a configuration, the synchrotron radiation emitted from the object to be measured is converged by the lens 1, passed through the optical filter 2, and converted into an electrical signal by the photodetector 3. This converted electric signal is amplified by a first stage amplifier 400 constituting a signal processing circuit, converted to a digital signal via an analog/digital conversion circuit 11, and inputted to a temperature calculation circuit. This temperature calculation circuit is composed of a microprocessor, etc., and performs calculations to convert an input digital signal into temperature and outputs the result.

By the way, using a radiation thermometer for example 400 ~
In order to measure a wide range of temperatures over 3000℃, it is necessary to measure light in a very wide range from the weak light of about pW to about mW. However, the conventional circuit shown in Figure 3 cannot measure light over such a wide range, and for this reason, conventionally the first stage amplifier 400
400 to 3000℃ with some models by changing the feedback resistor 401
It was common to cover a temperature range of about

<Problems to be solved by the invention> As described above, the reason why conventional radiation thermometers cannot measure the radiation from the object to be measured in a wide range from pW to mW is that the first stage amplifier 4
00 automatic gain switching is difficult. This means that in order to automatically switch the gain of the first-stage amplifier, the level of the input signal must be determined at the stage of the input signal (output signal of photodetector 3) before it enters the first-stage amplifier. This is because it is usually difficult to know the level of the input signal until it has passed through the first stage amplifier.

<Means for Solving the Problems> The present invention has been made to solve these problems, and is designed to enable automatic gain switching in the first stage amplifier. That is, in order to achieve automatic gain switching, a first-stage amplifier for amplifying the output of the photodetector and a sample-and-hold circuit for holding the output of the first-stage amplifier;
A second amplifier for further amplifying the output of the sample and hold circuit, a logarithmic conversion circuit for logarithmically converting the output of the sample and hold circuit, and a logarithmically converted value of the first stage amplifier and the second amplifier. A signal processing circuit was constructed by a gain switching signal generation circuit for a first stage amplifier and a second amplifier for determining the gain.

The present invention will be described below with reference to examples.

<Example> FIG. 1 is a connection diagram showing an example of the radiation thermometer according to the present invention. In the figure, 1 is a lens, 2
3 is an optical filter, 3 is a photodetector, and 4 is a first stage amplifier having gain switching means. In the first stage amplifier 4, reference numeral 41 indicates that the photodetector 3 is connected between its input terminals.
is connected to an operational amplifier, C1 to C3 are capacitors whose capacitances are selected as C1>C2>C3, and SW
1 to SW3 are changeover switches each having changeover contacts a and b. The capacitors C1 to C3 and the switches SW1 to SW3 are connected in series, respectively, and these series circuits are connected in parallel to the feedback circuit of the operational amplifier 41. The first stage amplifier 4 having such a configuration integrates the output of the photodetector 3, but in order to realize a wide range, the integration time is changed depending on the capacitor selected as described later. 5 is a sample and hold circuit that samples and holds the output of the first stage amplifier 4.
It consists of SW4, capacitor C4, and voltage follower 51. 6 is a logarithmic conversion circuit,
It consists of an amplifier 61, a diode D connected to its feedback circuit, a resistor R2 connected to the inverting input terminal, and a DC voltage source E, and logarithmically converts the output Vs _H of the sample-and-hold circuit 5 inputted via the resistor R1. do. 7 is a signal generation circuit that generates switching signals P1 to P3 that change the gain of the first stage amplifier 4 and a signal P4 that controls the sample switch SW4 of the sample and hold circuit 5, and has a reference value different from that of the operational amplifiers 71 to 73, respectively. voltage source
It consists of a comparator consisting of Vr1 to Vr3 and a switch control signal generation circuit 74, and is connected to the output terminal of the logarithmic conversion circuit 6.

10 is a second amplifier provided to increase resolution. The second amplifier 10 consists of an operational amplifier 101, resistors R3 to R6, and switches SW5 to SW7.The non-inverting input terminal of the amplifier 101 is connected to the output terminal of the sample & hold circuit 5, and the inverting input terminal is connected to the resistor R3. common potential point through
COM, and resistors R4 to R6 and switch SW5 are connected between the inverting input terminal and output terminal, respectively.
A series circuit consisting of SW7 is connected in parallel. 8 is a gain switching generation circuit that generates switching signals P5 to P7 for switching the gain of the second amplifier; operational amplifiers 81 to 83; a comparator and switch control signal generation circuit 84 consisting of reference voltages Vr4 to Vr6 having different values, respectively; configured,
It is connected to the output terminal of the logarithmic conversion circuit 6. 11
12 is an analog/digital converter that converts the output of the second amplifier into a digital signal, and 12 is a temperature calculation circuit. The temperature calculation circuit 12 is composed of a microprocessor, etc., and performs calculations to convert an input digital signal into temperature and outputs the result. 13
1 is a reference pulse generation circuit, which is used to generate a gain switching signal in the first stage amplifier gain switching signal generation circuit 7 and the second amplifier gain switching signal generation circuit 8. The circuit including the first stage amplifier 4, sample hold circuit 5, second amplifier 10, analog/digital conversion circuit 11, temperature calculation circuit 12, etc. described above processes the electrical signal output from the photodetector 3, and detects the value of the object to be measured. Configure a signal processing circuit to determine temperature.

The operation of the radiation thermometer according to the present invention having such a configuration will be explained as follows using the timing chart shown in FIG. As explained in Figure 3,
The synchrotron radiation emitted from the object to be measured is converged by a lens 1 and then passed through an optical filter 2 to a photodetector 3.
is converted into an electrical signal. On the other hand, the reference pulse generation circuit 13 configuring the signal processing circuit outputs a low signal for a certain period T1, and then a high signal for a period T2, as shown in FIG. 2a. Output. On the other hand, the switch control signal generation circuit 74 in the first stage amplifier gain switching signal generation circuit 7 generates a switch pulse P1 with a time width t1 and a switch pulse P1 with a time width t2, as shown in FIGS.
2 (and a switch pulse P3 with a time width t3). First stage amplifier 4 by pulses P1 to P3
The switches SW1 to SW3 are driven, and the time widths t1, t2, and t3 are, for example, 0.5 msec for t1 and 0.5 msec for t2.
5msec, t3 is 25msec, and the capacitances of capacitors C1, C2, and C3 are 1μF for C1 and 25msec for t3.
2 is selected to be 0.01μF, and C3 is selected to be 50pF. Therefore, the ratio of the gains of the first stage amplifier 4 when pulses P1, P2, and P3 are selected is 1:10 ³ :10 ⁶ , making it possible to measure a wide range. Therefore, first, in period T1, in order to minimize the gain of the first stage amplifier, the switch SW1 connected to the capacitor C1 having the largest capacity among the capacitors C1, C2, and C3 is switched from the B contact side to the A contact side. As a result, the capacitor C1 begins to be charged by the output current of the detector 3. At this time, the other switches SW2 and SW3 remain as b contacts. The operations of these switches SW1, SW2, and SW3 are performed by switch pulses P1 to P3, as described above. On the other hand, sample & hold circuit 5
The switch SW4 is a switch pulse P with a time width t1.
4 (FIG. 2e) from off to on. The capacitor C1 is charged during the time width t1 of the switch pulse P1, and then the switch
SW1 is returned to the b contact side again, and just before that, switch SW4 of the sample & hold circuit 5 is turned off, and the output voltage Vs of the first stage amplifier 4 is held by the capacitor C4. Figure 3f shows the output Vs of the first stage amplifier 4, and Figure 3g shows the sample &amp;
The output Vs _H of the hold circuit 5 is shown. Thereafter, the output of the sample and hold circuit 5 is logarithmically converted by a logarithmic conversion circuit 6, and the logarithmically converted voltage is applied to comparators 71, 72, 73 that constitute the first stage amplifier gain switching signal generation circuit 7. The signal is compared with reference voltages Vr1, Vr2, and Vr3 and determined. This determination result is the switch control signal generation circuit 7.
4, and the gain of the first stage amplifier 4 in the next period T2 of this circuit 74 is determined. This state is stored until the next period T1 begins.

Now, in period T2, the switch is activated according to the result of the determination of the gain of the first stage amplifier 4 in the previous period T1.
One of SW1, SW2, and SW3 is switched from the B contact side to the A contact side. In Figure 2, the period T
2, the switch SW2 is switched from the B contact side to the A contact side by the switch pulse P2, and the capacitor C is changed by the output current of the detector 3.
2 begins to be charged. Further, the switch SW4 of the sample and hold circuit 5 is switched from off to on by a switch pulse P4 having a time width t2. Charging to capacitor C2 is done by switch pulse P.
2 pulse width t2, and then the switch SW
2 is again returned to the b contact side by the switch pulse P2, and just before that, the switch SW4 of the sample & hold circuit 5 is turned off and the output of the first stage amplifier 4 is held. Thereafter, the output of the sample and hold circuit 5 is logarithmically converted by a logarithm conversion circuit 6, and the level of the logarithmically converted voltage is then applied to comparators 81, 82, 83, and its level is determined using reference voltages Vr4, Vr5, and Vr6. This determination result is sent to the switch control signal generation circuit 84, and the gain of the second amplifier 10 is determined. Switches SW5, SW6, SW that constitute the second amplifier
7 are driven by switch pulses P5, P6 and P7 shown in FIG. 2h, i and j, respectively. Here, we will consider a case where switch pulse P7 is selected as a result of determination of the gain of the output of logarithmic conversion circuit 6, and switch SW7 is thereby turned on. As shown in FIG. 2, a switch SW7 is turned on by a switch pulse P7 generated after a predetermined period of time has passed since the output of the first stage amplifier 4 is held in the sample and hold circuit 5. As a result, the gain of the second amplifier 10 becomes (R3+R6)/R3. While switch SW7 is on,
As shown in FIG. 2, the output of the second amplifier 10 is converted into a digital signal by the analog/digital conversion circuit 11, and the digital signal is passed to the temperature calculation circuit 12, where the temperature is determined.

This completes the measurement at one point, but the reference pulse P0
The above measurement sequence is repeated in response to the occurrence of.

<Effects of the invention> As explained above, according to the invention, since the first stage amplifier automatically switches the gain, it is possible to create a radiation thermometer that covers the temperature range that was conventionally covered by multiple models with a single model. Can be configured. Furthermore, since the first stage amplifier is an integrating amplifier, and the integration time changes depending on the gain, a long integration time is used when measuring weak light with a small S/N of the signal to be measured, and a strong signal with a large S/N is used. In the case of light, the integration time can be shortened, so it is rational because there is no need to unnecessarily slow down the measurement time (and therefore the response time of the measuring instrument) by adjusting the measurement of the entire range to the lowest intensity light as in the past. It is true.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an embodiment of the radiation thermometer according to the present invention, FIG. 2 is a timing diagram explaining the operation of the circuit shown in FIG. 1, and FIG. 3 is a conventional example. 1... Lens, 2... Optical filter, 3... Photodetector, 4... First stage amplifier, 5... Sample & hold circuit, 6... Logarithmic amplifier, 7... First stage amplifier gain switching signal generation circuit, 8 ...Second amplifier gain switching signal generation circuit, 10...Second amplifier, 1
1...Analog/digital conversion circuit, 12...
Temperature calculation circuit, 13...Reference pulse generation circuit.

Claims (1)

[Scope of utility model registration request] A radiation thermometer in which the temperature of the object to be measured is determined by applying emitted light from the object to be measured to a photodetector via an optical filter and processing the electrical signal output from the photodetector by a signal processing circuit. In the above, the signal processing circuit includes a first stage amplifier which has an integration function whose gain is switched and whose integration time is changed according to the gain and is supplied with the output signal of the photodetector, and a sample amplifier which holds the output of this first stage amplifier. a hold circuit, a logarithmic conversion circuit that logarithmically converts the held output thereof, and a circuit that generates a gain switching signal for the first stage amplifier using a comparator from the output of the logarithmic conversion circuit to determine the gain of the first stage amplifier; a second with gain switching for amplifying the output of the sample and hold circuit;
an amplifier, a circuit that uses a comparator to generate a gain switching signal for a second amplifier from the output of the logarithmic amplifier, an analog/digital conversion circuit that converts the output of the second amplifier into a digital signal, and the analog/digital conversion circuit. A radiation thermometer characterized by comprising an arithmetic circuit that performs arithmetic operations to convert an output signal into temperature.