JPH04339224A - Isothermal control type calorimeter. - Google Patents

Abstract

PURPOSE:To enable the minimum isothermal control in response time by arranging a memory means to store the optimum PID constant at a light detecting section, a means for reading a PID constant by the memory within the light detecting section and a means for setting the PID constant. CONSTITUTION:A time constant of a photodetecting head A is measured beforehand and the optimum value thereof is recorded into a memory 29. As a result, in a controller 25 of the body section B, information from the memory 29 is read out when a power source is closed to be set on a programmable attenuator in a PID amplifier 23. In isothermal control type calorie meter, the measurement of a light power PL is given by a difference of heater powers PH1 and PH2 between the closing and opening of a shutter, PL=K (PH1-PH2) (K: calibration coefficient). When a range is changed, with a controller 25, a cooling current value (current value to be added to a thermal cooling element 7) as output of a constant current source 21 and a bias voltage which is applied to an amplifier 23 from the controller 25 are switched simultaneously synchronous with the changing action.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isothermally controlled calorimeter for measuring the optical power of, for example, a laser. More specifically, the present invention relates to improving the responsiveness of an isothermal control type calorimeter.

0002

2. Description of the Related Art As this type of isothermal control type calorimeter, the configuration shown in FIG. 7 is well known. In the figure, reference numeral 1 denotes a heat absorber forming a sensor section S, which is composed of a cylindrical body 3 whose inner surface is coated with a light-absorbing paint, and a heat exchanger plate 5 in which a heater 4 is embedded. 6 and 6a are temperature difference detection elements, and 7 is a thermoelectric cooling element. These elements are formed of Peltier elements having equivalent performance, and are fixed between the heat exchanger plate 5 and the temperature reference jacket 8. There is. The outer periphery of the temperature reference jacket 8 is divided into an intermediate jacket 9 and an outer jacket 10 as shown in FIG. 8 in order to stabilize the temperature.
The sensor section S is configured as a light receiving head A surrounded by a triple jacket. In addition, the cylindrical body 3
The heat capacity of the heat transfer plate 5 including the heat exchanger plate 5 and the heat capacity of the temperature reference jacket 8 are approximately 1:1000, and the temperature reference jacket 8 is larger.

Reference numeral 11 denotes a constant current source connected to the thermoelectric cooling element 7. Reference numeral 12 denotes an amplifier that amplifies the output from the temperature difference detection elements 6 and 6a.This output is input to a filter 13 and a voltmeter 16, and the output signal of the filter 13 is input to an adder 14. On the other hand, the output from the voltmeter 16 is input to the adder 14 via the arithmetic unit 17 and the programmable power supply 18, where it is added to the output from the filter 13, and the output is output to the heater 4 via the square root arithmetic unit 15. 19
is a digital voltmeter, and the voltage V applied to the heater 4
H is measured and the measured value is fed back to the arithmetic unit 17. These circuit parts constitute a main body B for the light receiving head A.

In the above configuration, when the measurement light (laser beam La) is not input, the temperature reference jacket 8 is set to room temperature, and the thermoelectric cooling element 7 consisting of a Peltier element
A current of a constant value IA is constantly applied from a constant current source 11 to the heat exchanger plate 5 side, thereby constantly cooling the heat exchanger plate 5 side. In this case, the temperature reference jacket 8 side will be heated, but since the heat capacity of the temperature reference jacket 8 is large and the amount of heating by the thermoelectric cooling element 7 is small, it will take until the temperature of the temperature reference jacket 8 is raised. is not enough. Therefore, in the device shown in FIG. 7, the thermoelectric cooling element 7 and the constant current source 11 always work to increase the temperature on the temperature reference jacket 8 side and lower the temperature on the heat absorber 1 side.

On the other hand, temperature difference detection elements 6 and 6a detect this temperature difference (nV level), and amplifier 12 amplifies the output to mV level and outputs it to filter 13 and digital voltmeter 16. After filter 13 removes noise (high frequency) components, the signal Vf is sent to adder 14.
Output to. Temperature difference △ measured by digital voltmeter 16
p is added to the calculation device 17, and after a predetermined calculation (this calculation is a known calculation for controlling the temperatures of the heat exchanger plate 5 and the reference jacket 8 to quickly match), the calculated value is obtained. is applied to programmable voltage source 18. The output Vp of the programmable voltage source 18 based on this calculated value
and the output Vf from the filter 13 are added by the adder 14 and applied to the square root calculator 15, where (Vp+Vf)
Performs the calculation of 1/2. The output of the square root calculator 15 is applied to the heater 4 to raise the temperature of the heater 4, and control the outputs of the temperature difference detection elements 6, 6a to be zero.

Therefore, in the device of FIG. 7, the thermoelectric cooling element 7
The voltage (current I) is applied from the square root calculator 15 to the heater 4 to heat the heat exchanger plate 5 which has been cooled by the action of the constant current source 11, and the temperature of the heat absorber 1 and The temperature of the temperature reference jacket 8 is controlled to match.

In such a state, the laser beam L to be measured
When the light a is incident from the upper part of the cylinder 3, the heat absorber 1 absorbs the light, and the temperature rises according to the optical power. The heat was conducted to the heat exchanger plate 5, and the heat exchanger plate 5 was in a state of temperature equilibrium.
A temperature difference occurs between the jacket 8 and the reference jacket 8. The temperature difference detection elements 6 and 6a detect this temperature difference, and the square root calculator 15 reduces the voltage value sent to the heater 4. Therefore,
The temperature of the heater 4 decreases, and the heat exchanger plate 5 and the reference jacket 8
the temperatures match again.

[0008]

By the way, the parts shown in FIG. 7 including the amplifier 12, filter 13, and square root calculator 15 can be analog-controlled by PID as shown in FIG. In this way, the number of components can be reduced and the cost of the device can be reduced. P.I.
When using D control, it is necessary to determine the constants of P (proportional), I (integral), and D (differential), but the response time constant of the photodetector (heat absorber, temperature detection element) varies depending on the individual. There is variation. For example, 10 μW ~ 10 mW
A photodetector (standard type) that measures the optical power of 0.
The response time constants of photodetectors (high power type) that measure optical powers of 1 mW to 100 mW vary greatly. Therefore, measures are taken such as adjusting the PID constant for each photodetector or selecting a PID constant that is insensitive to the time constant of the detector. However, the method of adjusting the PID constant for each photodetector eliminates the independence (compatibility) of the photodetector and the processing unit including the PID (hereinafter referred to as the main body), which limits the expandability of the system. I will do it. Furthermore, the method of adjusting a PID constant that is insensitive to the detection section time constant has the disadvantage that the measurement time becomes slow because the PID constant (critical braking condition) that minimizes the response time cannot be used.

An object of the present invention is to provide an isothermal control type calorimeter that is capable of isothermal control with the minimum response time using an optimal PID constant according to the time constant specific to each photodetector without impairing the compatibility of the photodetectors. The goal is to provide the following.

0010

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a photodetection section in which a heat absorber, a heater, a cooling means, and a temperature difference detection element are covered with a heat insulating jacket; a PID control unit that controls the temperature of the photodetector to be kept constant by driving a heater based on the temperature detection signal;
and an incident light power calculation means for calculating the incident light power from the difference in power applied to the heater depending on the presence or absence of incident light, the light detection part being connected to the main body. The main body section reads out the PID constant or information from the storage means in the photodetection section. The device is characterized in that it has a reading means and a constant setting means for setting a PID constant.

[0011]

In the present invention, the reading means of the main body reads out information from the storage means provided in the photodetecting section, and the constant setting means sets an optimum PID constant for each photodetecting section. Thereby, the light receiving heads can be exchanged and connected to a common main body, and optimal PID control can be performed in any case.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of the main parts of the isothermal control type calorimeter according to the present invention, FIG. 2 is a configuration diagram showing the configuration of the main parts shown in FIG. 1 in detail, and FIG. 3 is an explanatory diagram showing the state of measurement. FIG. 4 is a time chart showing operations during measurement.

FIG. 3 shows the operation of the entire isothermal control type calorimeter.
, will be explained with reference to FIG. In FIG. 3, it is assumed that a laser beam output from a stabilized light source D passes through an attenuator E and a shutter F and enters a light receiving head A.

In the first step of the measurement operation, the shutter F is closed and no light is incident on the light receiving head A. In this state, the power of the heater 4 is controlled so that the reference jacket 8 and the heat absorber 1 described in FIG. 7 are in a thermal equilibrium state. The power consumption of the heater 4 at this time is assumed to be PH1.

In the second step, the power of the heater 4 is controlled so that the reference jacket 8 and the heat absorber 1 are in thermal equilibrium with the shutter F open. Let the heater power consumption at this time be PH2.

[0016] As a result, the incident light power PL is replaced by the difference in heater power consumption (PH1 - PH2), and PH
By knowing 1 and PH2, the incident light power PL can be measured. The controller 25 has a function of calculating the incident light power PL through the above operation.

Next, features of this embodiment will be explained with reference to FIGS. 1 and 2. In the calorimeter of this embodiment, the time constant of the light receiving head A is measured in advance and recorded in the memory 29. The controller 25 of the main body B is configured to read information from the memory 29 when the power is turned on, and set it in the programmable attenuator 36 in the PID amplifier 23.

When the attenuation rate of the programmable attenuator 36 is D, the resistance of the integrating amplifier 35 is R, and the capacitance connected to the integrating amplifier 35 is C, the output V2 of the integrating amplifier is as follows.
It can be obtained as follows.

V1=D·Vo I=V1/R V2=−(1/C)↑Idt=−(D/CR)↑Vo dt Note that ↑ means an integral symbol. Therefore, the output V2 of the integrating amplifier is obtained by integrating Vo with the time constant CR/D.

Therefore, by setting the constant D specific to the light receiving head A, it is possible to configure the PID control for critical braking under optimal conditions. In this embodiment, PID control is used for isothermal control, but there are several ways to determine the conditions for each constant of P (proportional), I (integral), and D (differential) in PID control.

Among them, (a) critical braking condition, (b)
The results of the simulation under the digranicolus conditions are shown in FIG. 5 and below. In these figures, the vertical axis represents heater power and the horizontal axis represents time. Moreover, at the time of 10 seconds, there was light input and the heater power was lowered. Then, at the time of 40 seconds, the optical input is cut off and the heater power is increased.

Furthermore, FIG. 5 shows critical braking conditions, and FIG.
A) shows the whole, and FIGS. 5(B) and (C) show enlarged views. Figure 6 shows the digranicolus conditions, and Figure 6 (
A) shows the whole, and FIGS. 6(B) and (C) show enlarged views. In this simulation, the time constant of integration is varied in steps of 10% and 5% around the optimum value. From these figures, under critical braking conditions, when the optimum time constant is set, the error converges to within 0.1% within 10 seconds. However, if the time constant deviates by 5%, there will be an error of 0.2% even after 30 seconds.

On the other hand, under the digranichols condition, even if the time constant changes by 10%, the error converges to an error of 0.1% or less in about 20 seconds. Therefore, it can be understood that the digranicolus condition is advantageous in terms of certainty of convergence, and the optimal time constant is advantageous in terms of speed.

In this embodiment, as described above, the time constant of the light receiving head A is measured in advance, and the optimum value is recorded in the memory 29. Therefore, controller 2 of main unit B
5 reads information from the memory 29 when the power is turned on, and P
The programmable attenuator 36 in the ID amplifier 23 is set. This allows the form of a light beam in a common body,
Light receiving heads of different shapes can be connected and exchanged depending on the optical power measurement range. Furthermore, if you want to perform reliable measurements, control is performed under digranicolus conditions, and when you want to shorten the measurement time (for example, when setting the initial measurement power), control is performed under critical braking conditions, resulting in more efficient measurements. becomes possible.

In the above description, a calorimeter has been described in which temperature control is performed using a time constant suitable for the response specific to each photodetector, and isothermal control with a short response time is possible. Next, an isothermal control type calorimeter that can enter the measurement state in a short time even when the measurement range is changed will be described. The hardware configuration of such an isothermal control calorimeter is shown in Figure 1.
It is similar to the device shown in . In the isothermal control type calorimeter, the optical power PL is measured by the difference between the heater power PH1 when the shutter F is closed and the heater power PH2 when the shutter F is opened, as described above. That is, PL=K.(PH1 - PH2) K: Calibration coefficient The measurement of the heater power is given by PH=E2/R, where R is the heater resistance value and E is the voltage applied to the heater resistance.

Here, the maximum measurable power is approximately P
It is given by H1, but considering the overshoot of the system, it is set to about 70% of PH1. On the other hand, the minimum measurable power is determined by the resolution and noise of the voltage applied to the heater resistor R. For this reason, in the calorimeter, the heater power PH1 when the shutter is closed is changed depending on the optical power to be measured. Specifically, P
The control gain of the ID amplifier 23, the bias voltage (not shown) applied to the PID amplifier 23, the current value applied to the thermoelectric cooling element 7 (cooling current value), the heater power, the range of the voltmeter 16, etc. are switched. For example, in a calorimeter with a measurement range of 10μw to 20mw, 20μw, 2
There are 4 ranges: 00 μw, 2mw, and 20mw, and select the appropriate range according to the measured power. Isothermal control type calorimeters are normally controlled so that the temperatures of the heat absorber 1 and the reference jacket 8 are equal, but when changing the range, the above settings are forcibly changed, resulting in temporary control deviations. In the isothermal control type calorimeter described above, it takes time for the control to stabilize. In particular, when switching the range from a low-sensitivity range to a high-sensitivity range, the following problems occur.

FIG. 10 shows a graph when switching from a low sensitivity range to a high sensitivity range (for example, from 2 mw range to 200 μw
FIG. 3 is a diagram showing temporal changes in switching to a microwave oven), cooling power, control deviation, and heater power. Figure 11 shows when switching from high sensitivity range to low sensitivity range (for example, switching from 200 μw range to 2 mw range).
FIG. 3 is a diagram showing temporal changes in cooling power, control deviation, and heater power.

First, the case of switching from a high sensitivity range to a low sensitivity range will be explained. For example, 200μw range → 2m
When switching to w range (see Figure 11), shutter F
When closed, the value of heater power PH1 is set to 200.
Increased μw → 2mw, cooling power also 200
The controller 25 increases μw → 2mw.
Control. For example, when the range is changed at time t1, the controller synchronizes the cooling current value, which is the output of the constant current source 21, and the bias power applied to the heater 4 (actually, from the controller 25 to the PID amplifier 23).
(bias voltage applied to) are switched at the same time (Figure 11
reference). Therefore, both the cooling power and the heater power are switched synchronously from 200 μw to 2 mw.

When looking at the responses of the temperature difference detection elements 6 and 6a, the response is dominated by the power change of the cooling element 7 rather than the heater 4 power change. The reason for this is that the heat absorber 1 in which the heater 4 is embedded has a certain heat capacity, and that the cooling element 7 is closer to the temperature difference detection elements 6, 6a. Therefore, the output of the temperature difference detection elements 6, 6a is
Following the change in cooling power (Fig. 11 (1)),
As shown in FIG. 11(2), a negative control deviation is output. Therefore, the PID amplifier 23 outputs a signal that makes this control deviation zero. In other words, the heater power is controlled to be increased (see FIG. 11(3)). Since this control is within the control range of the heater power, the settling time when changing from the high sensitivity range to the low sensitivity range is short.

Next, the case of switching from the low sensitivity range to the high sensitivity range will be explained. For example, 2mw range → 200
When switching to the μw range (see Figure 10), when the shutter F is closed, the heater power PH1 is set to 2 mw.
→Reduced to 200 μw, cooling power is also 2mw
The controller 25 controls the power to decrease from →200 μw. For example, when this range change occurs at time t1, the controller synchronizes the constant current source 21.
The cooling current value, which is the output of the heater 4, and the bias power applied to the heater 4 are simultaneously switched (see FIG. 10). Therefore,
Cooling power and heater power are both 2mw → 20
Switches synchronously to 0 μw.

Here, the output changes of the temperature difference detection elements 6, 6a are controlled by the power changes of the cooling element 7, as described above. Then, the power of the cooling element 7 is 2 mw → 200
μw (see Figure 10 (1)), the cooling effect until now weakens and the temperature rises. Also, heater 4
Even if the power of the heat absorber 1 decreases from 2 mw to 200 μw, the temperature of the heat absorber 1 does not immediately decrease because the heat absorber 1 has a heat capacity. As a result of the above, the temperature difference detection elements 6 and 6a output a positive control deviation indicating that the temperature of the heat absorber 1 is higher than that of the reference jacket 8 (see FIG. 10(2)). Therefore, the PID amplifier 23 uses the heater 4 to keep the heat absorber 1 and the reference jacket 8 at the same temperature.
However, since the heater power is always greater than or equal to 0, the heat absorber 1 has to wait for natural cooling with the heater power at 0. As a result, when switching from a low-sensitivity range to a high-sensitivity range, there is a problem in that it takes time until the control becomes stable, as shown in FIG. 10(3).

The invention of claim 2 solves this problem. The apparatus according to the second aspect of the invention has the same hardware configuration as the apparatus shown in FIG. 1, as described above. The difference is that when switching from a low sensitivity range to a high sensitivity range, the bias value of the power applied to the heater 4 is decreased in synchronization with the range switching time t1, and the bias value of the power applied to the heater 4 is delayed by a certain time Δt from the range switching time t1. This point is that the value of the cooling current was controlled to be decreased from time t4 (see FIG. 12(1)). Hereinafter, the invention of claim 2 will be explained with reference to FIGS. 1 and 12. The cooling current value that the constant current source 21 outputs to the cooling element 7 and its output timing are controlled by the controller 25. Furthermore, the key input unit 28 allows the operator to select and command a measurement range by key operation, so the controller 25 can switch from which measurement range to which measurement range based on the signal from the key input unit 28. You can know whether it will happen or not. Further, the controller 25 sets the gain of the PID amplifier 23, determines the bias voltage to be applied to the PID amplifier 25, sets the measurement range of the voltmeter 17, etc. according to the commanded measurement range.

When the controller 25 receives a signal to switch from the low sensitivity range (2 mw) to the high sensitivity range (200 μw), it operates as follows. For example, when the range is switched at time t1, the bias value of the power applied to the heater 4 is decreased from 2 mw to 200 μw in synchronization with the range switching time t1 (Fig. 12 (3)
reference). On the other hand, the cooling power applied to the cooling element 7 is still controlled to maintain 2 mw (ie, a state of high cooling power) at time t1. Therefore, since the cooling power is 2 mw and the heater power is 200 μw,
Since the heat absorber 1 is forcibly cooled and its temperature is lower than that of the reference jacket 8, the temperature difference detection elements 6 and 6a output a negative control deviation indicating that the temperature of the heat absorber 1 is lower. (See Figure 12(2)).

[0034] After a certain time Δt, that is, at time t4
, the controller 25 increases the cooling power to 200 μw.
decrease to When operating in this manner, the temperature of the heat absorber 1 is lower than that of the reference jacket 8 at time t4, so by controlling the heating of the heater 4, the temperature equilibrium state of the heat absorber 1 and the reference jacket 8 is maintained. realizable. That is, as shown in FIG. 12(3), the settling time can be shortened compared to FIG. 10(3). In addition, Figure 12 (1)
The delay time Δt=t4−t1 shown in is determined by the thermal time constant of the heat absorber 1 actually manufactured. In the embodiment, it is about 5 seconds, but this value varies depending on the design of the heat absorber, so it is not limited to this value. Further, the control method for switching from the high sensitivity range to the low sensitivity range is not particularly limited. For example, the control method explained in FIG. 11 may be used. Further, in the above description, the delay time Δt was described as a constant time, but the value of the delay time Δt may be controlled by the value of the control deviation amount applied to the controller 25. For example, when the amount of control deviation exceeds a comparator level provided in the controller 25, the value of the cooling current can be decreased using this as a starting point. In this way, optimal high-speed settling becomes possible. In addition, the size of the cooling power is 20 μw
, 200 μw, 2 mw, . . . , which are digitally constant values as explained above, if these values are controlled analogously, even faster settling becomes possible.

[0035]

As described above, according to the present invention, it is possible to provide an isothermal control type calorimeter that is capable of isothermal control with a minimum response time without impairing the compatibility of the photodetector. Furthermore, even when switching from a low sensitivity range to a high sensitivity range, a thermal equilibrium state between the heat absorber and the reference jacket can be achieved in a short settling time, and measurement operations can be started in a short setup time.

[Brief explanation of drawings]

[Fig. 1] A diagram showing an example of the main part configuration of an isothermal control type calorimeter according to the present invention.

FIG. 2 is a diagram showing the configuration of the main parts of FIG. 1;

[Figure 3] Diagram showing the overall configuration of the Figure 1 device

[Figure 4] Time chart showing the measurement status of the device in Figure 1

[Fig. 5] Explanatory diagram showing the operating state of the device in Fig. 1

[Fig. 6] Explanatory diagram showing the operating state of the device in Fig. 1

[Figure 7] Diagram showing the overall configuration of a conventional example

[Figure 8] Diagram showing the detailed configuration of the light receiving head part

[Figure 9]
Explanatory diagram showing the measurement state according to the conventional example

[Figure 10] Diagram explaining the problem of responsiveness when changing the measurement range

[Figure 11] Diagram explaining the problem of responsiveness when changing the measurement range

[Figure 12] Diagram explaining the solution to the problem in Figure 10

[Explanation of symbols]

A Light receiving head B Main body 1 Heat absorber 4 Heater 6, 6a Temperature difference detection element 7 Thermoelectric cooling element 8 Standard jacket 21 Constant current source 23 PID amplifier 25 Controller 29 Memory

Claims (2)

[Claims] 1. A photodetecting section in which a heat absorber, a heater, a cooling means, and a temperature difference detection element are covered with a heat insulating jacket, and a photodetection section in which the heater is driven based on a temperature detection signal from the temperature difference detection element. An isothermal control type comprising a main body having a PID control section that controls the heater to maintain a constant temperature, and an incident light power calculation means that calculates the incident light power from the difference in power applied to the heater depending on the presence or absence of incident light. It is a calorimeter, and the photodetection section is configured to be replaceable with respect to the main body, and the PID constant or PID that is optimal for each photodetection section is set.
The main body has a storage means for storing information for calculating a constant, and the main body has a reading means for reading out a PID constant or information from the storage means in the photodetector, and a constant setting means for setting the PID constant. Isothermal control type calorimeter. Claim 2: A heat absorber that converts incident light into heat, a cooling means (7) that cools the heat absorber, a reference jacket (8) with a constant temperature, and a heater (4) that heats the heat absorber.
, a temperature difference detection element (6) that detects the temperature difference between the reference jacket and the heat absorber, and a photodetection section (
A), a constant current source (21) that supplies a cooling current to the cooling means, and a temperature difference signal outputted by the temperature difference detection element (
A PID control unit (23) that controls the heater (4) so that Δp) becomes zero, a range command means (28) that commands the measurement range, and electric power applied to the heater (4) depending on the presence or absence of incident light. An apparatus for measuring the optical power of incident light, comprising: a main body (B) comprising an incident light power calculation means (25) for calculating the incident light power from the difference between
When switching from a low sensitivity range to a high sensitivity range, the bias value of the power applied to the heater (4) is decreased in synchronization with the range switching time (t1), and the bias value of the power applied to the heater (4) is decreased for a certain time (△ t) An isothermal control type calorimeter characterized in that the value of the cooling current is controlled to decrease from a delayed time (t4).