JPH0387619A - Detector for fourier-transformation infrared spectral photometer - Google Patents

Abstract

PURPOSE:To improve the S/N of detecting signal of a pyroelectric detector by constituting the device so that in a temperature control mechanism, the power supply to an electronic thermal element is started or cut off in a period in which a data collection of the detecting signal from the pyroelectric detector is not executed. CONSTITUTION:Signals A, B from a comparator 26 obtained by comparing a detection output of a temperature sensor 14 and a reference voltage Vr are inputted to a control unit 28. In an (EOC) signal of A/D conversion, the A/D conversion is started at its rise, and ended at its fall. When the signal A is in a low level at the time point of a fall of the (EOC) signal, a signal for turning on a driving transistor 30 for a Peltier element for heating is outputted from the control unit 28, and if the signal B is in a low level at the time of falling the (eoc) signal, a signal for turning on a driving transistor 32 for a Peltier element for cooling is outputted from the control unit 28. In the case of a temperature is set to 60 deg.C in order to execute the detection in a state that the S/N is large as a detector 8, a PID control is executed, but from the viewpoint of recognizing an error temperature, the shorter the time extending the start of the power supply to the Peltier elements 10, 12 to its cut-off is, the better it is.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a detection device for a Fourier transform infrared spectrophotometer (FTIR), and particularly to a detection device using a pyroelectric detector as a detector.

(Prior art) As a pyroelectric detector, there is a TGS (triglycine sulfide) pyroelectric detector, a DTGS pyroelectric detector in which the hydrogen atoms of TGS are replaced with deuterium atoms, or a DTGS pyroelectric detector doped with L-alanine. 211 detector DLATGS
Is the pyroelectric detector #? It is equipped and used on a standard basis.

These pyroelectric detectors have low Curie temperatures. For example, T
The Curie temperature of GS is 49 degrees.

The Curie temperature of DTGS and DLATGS is 62°C. Therefore, the figure of merit of a pyroelectric detector has strong temperature dependence.

FIG. 11 shows an example of the temperature dependence of the figure of merit of a pyroelectric detector. This data was collected from the DLATGS pyroelectric detector R
This is about PY104 (product of Philips, UK). In the figure, Rv is sensitivity, NEP is No1s
e Equivalent Power, D * is R
It is a figure of merit obtained comprehensively from v and NEP,
It represents the S/N ratio. Both figures of merit are 25
It is standardized based on the value of °C. This DLATG
When using an S pyroelectric detector and prioritizing the stability of the vertical axis of the spectrum, the sensitivity Rv is constant3
It is appropriate to use it at 0-35℃, and if the highest S/N
When measuring by ratio, it is appropriate to use the temperature at 60°C.

Pyroelectric detectors have a strong temperature dependence in their figure of merit, so whether you use them at room temperature or higher temperatures,
It is necessary to provide a temperature control mechanism to keep the pyroelectric detector temperature constant. In the temperature control mechanism, an electronic cooling element such as a Peltier element is arranged close to the pyroelectric detector.

Temperature adjustment operations in conventional pyroelectric detector temperature control mechanisms are performed without synchronization with data collection of the pyroelectric detector.

(Problems to be Solved by the Invention) The input impedance of a pyroelectric detector is extremely high, about 1010Ω. Therefore, the radiation noise of electromagnetic waves affects the pyroelectric detector at the moment when the power supply to the electronic cooling element placed close to the pyroelectric detector is started or cut off, and the appearance of the detection signal is /N ratio is worsened.

The present invention provides a detection device equipped with a pyroelectric detector and a temperature control mechanism that keeps the temperature of the pyroelectric detector constant. It is an object of the present invention to provide a detection device that does not deteriorate the S/N ratio of a detection signal of a device.

(Means for Solving the Problems) In the present invention, the operation of the temperature control mechanism is controlled so that data collection from the pyroelectric detector is not performed at the time when the supply of power to the electronic cooling element in the temperature control mechanism is started or cut off. Control. Therefore, a control unit is installed in the temperature adjustment section that controls the power supply to the temperature control mechanism, and the control unit starts and cuts off the power supply to the electronic cooling element during the period when data is not collected from the pyroelectric detector. Control what you do.

For this reason, 1. For example, the start and cutoff of power to the electronic cooling element may be synchronized with the conversion end signal of the A/D converter that converts the detection signal of the pyroelectric detector into a digital signal, or the interference signal of the control interferometer. or synchronize with the return of the moving mirror after a series of interferograms have been collected.

(Function) If the power supply to the electronic cooling element is started or cut off in synchronization with the conversion end signal of A/D conversion, noise will be generated at the time of starting or cutting off and will be superimposed on the detector signal. However, since no data is being collected at that point, the S/N ratio of the captured data does not deteriorate.

An interference signal from a laser beam interferometer, which is a control interferometer, is also used as a trigger signal for A/D conversion. Therefore, by synchronizing with the interference signal of this laser beam interferometer,
It is also possible to start or cut off power supply to the electronic cooling element at a time when A/D conversion is not being performed. In this case, the time point at which power supply is started or cut off does not necessarily have to coincide with the end time of A/D conversion, but the closer it is to the end time of A/D conversion, the more it will affect the next A/D conversion operation. The possibility of this happening becomes smaller.

By the time the transfer mirror is turned back, collection of a series of interferograms has been completed. Therefore, even if noise is superimposed on the detector signal by starting or cutting off the power supply to the electronic cooling element at the time when the movable mirror is turned back, the S/N ratio will not be affected because no data is collected.

The operation of A/D converting the detection signal of the pyroelectric detector is 100~
This is done in a short cycle of 200 microseconds.

On the other hand, the turning period of the movable mirror is a long period of 0.5 to 2 seconds. If the power supply to the electronic cooling element is started or cut off in synchronization with the A/D conversion end signal or the interference signal of the laser light interferometer, it can be repeated in a short cycle of 100 to 200 μs, so pyroelectric The temperature of the detector can be controlled more precisely.

(Embodiment) FIG. 1 is a side view showing one embodiment, and FIG. 2 is a front view of the same embodiment.

2 is a shield case, which is assembled with several setscrews. A preamplifier 4 for amplifying the detection signal of the pyroelectric detector is built in the shield case 2.

A cooling base material 6 made of @ is attached to the front surface of the shield case 2, and the space between the shield case 2 and the cooling base material 6 is thermally isolated by a heat insulating material. A DLATGS pyroelectric detector 8 is attached to the cooling base material 6 as a pyroelectric detector, a heating Peltier element 10 and a cooling Peltier element 12 are attached to the cooling base material 6, and the pyroelectric detector 8 and the Vertier element 10.12 are thermally coupled. It is desirable that the Peltier elements 10 and 12 be placed near the pyroelectric detector 8 in order to reduce the amount of heat generated.

Also for the cooling base material 6. A temperature sensor 14 is attached to detect the temperature of the cooling base material 6. Each Vertier element 10
．． A heat sink 16 is provided in close contact with each of the heat sinks 12 . The cooling base material 6, the Vertier elements 10 and 12, the temperature sensor 14, and the heat sink 16 constitute a temperature control mechanism.

Reference numeral 8 is a temperature control board equipped with a temperature control unit that controls the power supply to the Peltier elements 10 and 12.
．． 12 and is attached to the front of the shield case 2.

The front of the shield case 2 also supplies power,
Several connectors 20 are provided for taking out signals.

The shield case 2 is screwed to a Bakelite plate 22, which is an insulating member, in order to electrically insulate it from the base of the FTIR, and is attached to the base via the Bakelite plate 22.

FIG. 3 shows a part of the temperature control section mounted on the temperature control board 18 in this embodiment.

24 is an amplifier that amplifies the detection signal of the temperature sensor 14;
6 inputs the amplified detected temperature signal.

This is a comparator that compares with a reference voltage Vr set according to the set temperature, and depending on the magnitude of the comparison voltage Vr, a signal A for the heating Peltier element 10 and a signal A for the cooling Peltier element 12 are generated.
It outputs signal B for.

When the detected temperature is lower than the set temperature, signal A is output, and when the detected temperature is higher than the set temperature, signal No. 78 B is output.

28 is a control unit and a signal A;

At the same time as inputting B, the detection signal of the pyroelectric detector 8 is input to A/
A conversion end signal eoc from an A/D converter that performs D conversion is input, and a signal for starting or cutting off power supply to the Peltier elements 10 and 12 is output in synchronization with the sac signal. 3
0 is a drive transistor that drives the heating Vertier element O, and 32 is a drive transistor that drives the cooling Peltier element 12. Each drive transistor 10.12
A signal for driving the Peltier element is supplied to the base from the control unit 28 via a resistor.

The operation of the control unit 28 shown in FIG. 3 will be explained in FIG. 4.

It is assumed that the Vertier element to, 12 is controlled to be turned on and off. Signal A from the comparator 26 by comparing the detection output of the temperature sensor 14 and the reference voltage Vr.

B is input to the control unit 28. A/D conversion eo
In the signal C, A/D conversion starts at the rising edge and ends at the falling edge. If the signal A is at a low level at the time of the fall of the eoc signal, a signal to turn on the drive transistor 30 for the heating Peltier element is output from the control unit 28, and if the signal B is at the low level at the time of the fall of the eoc signal. If the level is low, the control unit 28 outputs a signal that turns on the opening transistor 32 for the cooling Peltier element.

When a DLATGS, for example, is used as the detector 8 and the temperature is set to, for example, 60° C. in order to perform detection with a large S/N ratio, it is necessary to finely control the temperature. In such a case, for example, PID control is performed,
From the viewpoint of recognizing the error temperature, the shorter the time from the start to the cutoff of power supply to the Peltier elements 10 and 12, the better.

In that case, it is desirable to use an A/D converted eoc signal as in the embodiment, or to use an interference signal from a laser beam interferometer.

In the Vertier element, the direction of heat transfer differs depending on the polarity of the applied voltage. Therefore, it is possible to adjust the temperature to a constant temperature near room temperature using a single Vertier element.

5 and 6 show an embodiment in which a single Vertier element is used for both heating and cooling purposes.

A preamplifier 4 for amplifying the detection signal of the pyroelectric detector is built into the shield case 2, and a pyroelectric detector 8 such as a DLATGS system is attached to the front of the shield case 2. It is thermally coupled to one Vertier element.

A temperature sensor 4 for detecting the temperature of the cooling base material 6 is installed near the Beltier element 1.

Reference numeral 13 denotes a metal fitting, which also serves as a heat dissipation member of the Peltier device 1. 18 is a temperature control board equipped with a temperature control section for controlling the power supply to the Beltier element 1, 22 is Bakelite which is an insulating member, and 20 is a connector.

In this embodiment, the circuit shown in FIG. 7 is mounted on the temperature control board 18 as a temperature MA node for using one Bertier element 11 for both heating and cooling purposes.

In FIG. 7, 36A is a comparator that makes the Bertier element 11 work on the heating side, 36B is a comparator that makes the Bertier element 11 work on the cooling side, and the signal from the temperature sensor 14 is input to the comparator 36A, and
The constant voltage breakdown is reduced and input to comparator 36B.

A reference voltage Vr from a Zener diode is applied to the comparators 36A and 36B, forming a window comparator 34. The signal from temperature sensor 14 provides a voltage as a function of environmental temperature.

two comparators 36A of the window comparators;
The output of 36B is input to the control unit 28a, and the power supply to the Vertier element 11 is started or cut off in synchronization with the conversion end signal 80Q of the A/D converter, as explained in FIG.

Two S systems are used to apply power to one Beltier element.
E P P (Single ended push
A pull) amplifier circuit is composed of transistors Q1 to Q4.

Next, the operation of the temperature control section shown in FIG. 7 will be explained.

As shown in FIG. 8, the window comparator 34 has two threshold values: a high pressure side threshold and a constant pressure side threshold a. When the voltage detected by the temperature sensor 14 is between the two threshold values a and b, both comparators 36
The outputs of A and 36B both become low level, none of the transistors Q1 to Q4 turn on, and no current flows through the Bertier element 11.

When the detection voltage of the temperature sensor 14 exceeds b, the transistors Q3 and Q2 turn on at the timing of the fall of the conversion end signal eoc of the A/D converter, and the Bertier element 1
1, a current flows in the direction from A to B, and the Bertier element 11
Cooling is performed by

When the detection voltage of the temperature sensor falls below a, transistors Q1 and Q4 turn on at the timing of the fall of the conversion end signal eOC of the A/D converter, and the Bertier element 11
A current flows in the direction from A to A, and heating is performed by the Beltier element 11.

Generally, a window comparator is usually set with hysteresis as shown in FIG.

However, due to an offset between the comparators 36A and 36B, the outputs of both the comparators 36A and 36B rarely become high level. At this time, the seventh
In the circuit shown in the figure, all of the transistors Q1 to Q4 are turned on, and the transistor Q
1 to Q2. A short circuit current flows from transistor Q3 to Q4.

FIG. 10 shows a protection circuit 38 to prevent this short-circuit condition.
This shows an example in which .

In FIG. 10, a protection circuit 38 consisting of an EX-OR circuit and an AND circuit is provided between the window comparator 34 and the control unit 28a. In the EX-OR circuit, when the outputs of both comparators 36A and 36B go high, the output of the EX-OR circuit goes low, and the AND circuit prevents transistors Q1 to Q4 from turning on. . As a result, transistor Q1
~Destruction of Q4 can be prevented.

FIG. 7 is an example of simple comparison control.
It is also possible to perform optimal adaptive control based on temperature information.

(Effects of the Invention) In the present invention, in the temperature control mechanism that keeps the temperature of the pyroelectric detector constant, the power supply to the electronic cooling element is started and Since the pyroelectric detector is cut off, the S/N ratio of data from the pyroelectric detector is improved.

[Brief explanation of drawings]

Fig. 1 is a side view showing one embodiment, Fig. 2 is a front view of the same embodiment, Fig. 3 is a circuit diagram showing the temperature control section in the same embodiment, and Fig. 4 is a timing diagram showing the operation of the control unit. figure,
Fig. 5 is a side view showing another embodiment, Fig. 6 is a front view of the same embodiment, Fig. 7 is a circuit diagram showing the temperature control section in the same embodiment, and Fig. 8 is a circuit diagram of the circuit in Fig. 7. Figure 9 is a diagram showing the operation of the window comparator, Figure 9 is a diagram showing hysteresis in the window comparator, Figure 10 is a circuit diagram showing the temperature control unit equipped with a protection circuit, Figure 11 is the temperature of the figure of merit of the pyroelectric detector. It is a diagram showing dependence. 8...DLATGS pyroelectric detector, 10...
...Peltier element for heating, 11...Bertier element for heating and cooling, 2...Peltier element for cooling, 14...Temperature sensor, 16... Heat sink, 18...Temperature control board, 28...Control unit.

Claims (1)

[Claims] (1) A temperature control mechanism including a pyroelectric detector, an electronic cooling element and a temperature sensor for keeping the temperature of the pyroelectric detector constant, and a detection signal of the temperature sensor inputted to the electronic cooling element. In the detection device, the temperature adjustment section starts and cuts off the supply of power to the electronic cooling element during a period when data is not collected from the pyroelectric detector. A detection device characterized by comprising a control unit that performs.