JPH11281490A - Pyroelectric type radiation temperature detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy-saving and economical pyroelectric type radiation temperature detector despite of a simple structure. SOLUTION: A pyroelectric type radiation temperature detector is so constituted that a drive means 4 applying voltage such as a chopping wave, a rectangular wave, and a sine wave on a pyroelectric element 1 which receives radiation from an object to be measured is provided and a ferroelectrics polarized inversion current generated in the pyroelectric element 1 driven thereby is monitored so that an output 9 matching the temperature can be provided. This constitution can dispense with a mechanical chopper, a chopper drive part and the like added to a pyroelectric detector and necessitate no extreme high resistance which is hard to get and has high dispersion. Low-Curie-point pyroelectric materials such as DLATGS, TGS, and LATGS are preferable as pyroelectric materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric radiation temperature detector used for a radiation thermometer, an ear radiation thermometer and the like.

[0002]

2. Description of the Related Art Pyroelectric sensors are known as infrared detectors which are inexpensive and inexpensive. A general method of detecting the temperature of an object using a pyroelectric detector utilizes the fact that a pyroelectric current is generated due to a change in electric charge (spontaneous polarization) accumulated on the crystal surface when receiving infrared radiation from the object. When the pyroelectric current flows and the discharge ends, the charge on the crystal surface is neutralized,
In order to detect the temperature, a chopper is provided in front of the sensor so that a pyroelectric current is always generated in order to detect the temperature.

FIG. 6 shows an example of the configuration of a conventional pyroelectric sensor. Reference numeral 61 denotes a pyroelectric body, which emits infrared light L from an object to be measured at a predetermined period by a light beam chopper 62 driven by a drive circuit 63. The light is intermittently projected onto the pyroelectric body 61. R1 is a resistor for taking out a pyroelectric signal, and since the internal resistance of the pyroelectric body 61 is high, it is necessary to use an ultra-high resistance of about R1 = 10G-100GΩ. Reference numeral 64 denotes a field effect transistor (FET) having a large input impedance. F
The output of the ET 64 is amplified by the amplifier 65 with an input resistance R2 of about 10 kΩ, and an output as shown in a frame 66 is obtained. This is rectified by a rectifier 67 and a detection output 68
Get.

[0004]

In the pyroelectric sensor having the above structure, a mechanical chopper, a chopper driving unit, and the like must be added to the pyroelectric detector, and the structure of the detector becomes complicated. Also, the power consumption involved is large. Also,
Since the temperature of the chopper needs to be corrected depending on the outside air temperature, there are various problems such as the necessity of providing a correction circuit.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an economical pyroelectric radiation temperature detector with a simple structure and low power consumption.

[0006]

In order to achieve the above object, a pyroelectric radiation temperature detector according to the present invention comprises a pyroelectric body which receives radiation from a measurement object and has a periodic waveform such as a triangular wave, a rectangular wave, or a sine wave. A driving means for applying a voltage is provided, and an output corresponding to a temperature is obtained by monitoring a ferroelectric polarization inversion current generated in a pyroelectric body driven by the driving means.

As the pyroelectric material, it is preferable to use low curie point pyroelectric materials DLATGS, TGS and the like.

The spontaneous polarization characteristic is unique to each pyroelectric material. If the temperature characteristic of the spontaneous polarization of the material is known in advance, the temperature of the crystal can be known by measuring the spontaneous polarization value of the crystal. (Spontaneous polarization has a temperature characteristic as shown in FIG. 2). The crystal temperature rises due to radiant heat from the target, and the temperature change ΔT due to this rise is proportional to the target object temperature.

When an alternating electric field (rectangular wave, triangular wave, sine wave) or the like is externally applied to the pyroelectric body, a current (a current I expressed by the following equation (2)) flows through the pyroelectric body. In addition,
The first term in the equation (2) indicates a reversal polarization current generated when the spontaneous polarization reverses. By monitoring this inversion polarization current, it is possible to obtain an output corresponding to the temperature change ΔT. The spontaneous polarization characteristics differ depending on the pyroelectric crystal. For example, for a low-temperature monitor such as an eardrum thermometer, DLATGS having a sharp spontaneous polarization characteristic in the temperature range is most desirable. According to this method, an element such as a high resistance (10 G-100 GΩ) or an FET that is difficult to obtain and has a large variation for extracting a pyroelectric signal is not required.

[0010]

FIG. 1 shows an embodiment of a pyroelectric radiation temperature detector according to the present invention. Reference numeral 1 denotes a pyroelectric body which receives radiation (mainly infrared light) L from a temperature measuring object. Polarization P
A crystal plate of a known pyroelectric material having a temperature characteristic of s suitable for the measurement temperature range is used, and is sandwiched between a pair of electrodes 2 and 3. As a material of the pyroelectric body 1, for example, LiTaO
3 (lithium tantalate) can also be used,
It is preferable that the slope of the temperature characteristic curve of spontaneous polarization be steep in the measurement temperature range. For a temperature measurement at a relatively low temperature, a TGS-based pyroelectric material DLATG having a low Curie point is preferably used.
Preferred are S (deuterium-substituted L-alanine triglycine sulfate, Curie point Tc = 60 ° C.), TGS (triglycine sulfate, Tc = 40 ° C.), and the like. For a low-temperature monitor such as an eardrum thermometer, DLATGS (same as above), which has a spontaneous polarization characteristic in the temperature range, is optimal.

The electrodes 2 and 3 are made of NiCr as shown in the figure.
(Nickel chrome) or Au (gold) treated with gold black is used.

Reference numeral 4 denotes a pyroelectric element driving circuit for driving the pyroelectric element 1 by an alternating electric field, and generates a periodic voltage waveform such as a rectangular wave, a triangular wave, or a sine wave. In this case, the width of the rectangular wave and the repetition frequency, the frequency of the triangular wave, the sine wave, etc.
It may be determined as appropriate in consideration of the duration (peak width) of the domain-inverted current, etc., but it is desirable that these be variably configured. It is sufficient to generate any one of these waveforms, and in particular, a triangular wave is most suitable for improving the detection accuracy.However, when the type of pyroelectric body is changed, a waveform suitable for this is tested and the optimum waveform is obtained. , Each waveform can be generated, and these can be arbitrarily switched as needed.

Rm is a load resistor inserted in series with the pyroelectric body 1 in the pyroelectric body drive circuit 4, 5 is a ground, and 6 is an amplifier. The output from the amplifier 6 is expressed by the following equation (2).
, And a domain-inverted current waveform p as shown in a frame 7 is extracted from the current waveform. An integration circuit 8 integrates the polarization inversion current p, and obtains an integration result corresponding to the area of the peak of the polarization inversion current waveform in the frame 7. This integration result corresponds to the Ps value in the equation shown in FIG. 1 and is an output corresponding to the temperature rise ΔT of the pyroelectric body 1 based on the projected infrared light L. Incidentally, S corresponds to the electrode area of the pyroelectric body, and corresponds to the effective area of the strong attractant inversion.

Next, the operation of the apparatus of the present invention will be described.

A pyroelectric body generally has a temperature characteristic of spontaneous polarization Ps as shown in FIG. 2, and if the value of spontaneous polarization Ps is known, the temperature can be known. That is, the spontaneous polarization Ps is proportional to the intensity of the infrared light L contributing to the temperature rise of the pyroelectric body, while the infrared light intensity L effectively acting on the temperature change of the pyroelectric body is proportional to the value of the following equation. Eventually spontaneous polarization Ps
, The temperature of the measurement object can be measured.

A (T ⁴ n−Te ⁴ ) (1) where A is a proportional constant, T is the absolute temperature of the object to be measured, T
e is the absolute temperature of the atmosphere around the pyroelectric body.

The pyroelectric element can be represented by an equivalent circuit in which a resistance component and a capacitance component are connected in parallel as shown in FIG.
Rr is the equivalent resistance value, and Cr is the equivalent capacitance value.

In operation, the pyroelectric element drive circuit 2 drives the pyroelectric element 1 with the output voltage V. The current flowing through the pyroelectric body 1 when the infrared light L enters the pyroelectric body 1 in this state can be expressed by the following equation (2).

I = dPs / dt + Cr · dV / dt + V / Rr (2) The first term dPs / dt is a polarization reversal current accompanying a change in spontaneous polarization, and corresponds to the intensity of infrared light L and its wavelength distribution. . The second term is a capacitance current associated with a change in the drive voltage, and the third term is a resistance current proportional to the drive voltage.

The current I flowing through the pyroelectric element 1 appears as a voltage drop across a load resistor Rm inserted in series with the pyroelectric element 1, and this voltage is amplified by the amplifier 6 and other appropriate means and the polarization is inverted. Noise components other than current are removed,
A domain-inverted current waveform p as shown in a frame 7 is obtained for each half cycle of the drive voltage V. When the peak area of the current waveform p is integrated by the integrating circuit 8 to obtain the peak area, the peak area corresponds to the spontaneous polarization Ps of the pyroelectric crystal, that is, the temperature change ΔT of the pyroelectric crystal as shown in Expression (3). An output 9 is obtained.

Ps = (１ ／ S) ∫ (V / Rm) dt (3) where, S: electrode area of pyroelectric body (corresponding to effective area of strongly induced body inversion) V : Output voltage of pyroelectric body drive circuit 2 Rm: load resistance value of polarization reversal current output I This output 9 can be obtained continuously during the period when pyroelectric body 1 receives infrared light L from the object to be measured. It changes depending on the intensity of the infrared light L, and therefore the temperature of the object to be measured. As described above, according to the present invention, it is possible to continuously perform temperature detection without requiring a mechanical chopper for interrupting radiation from a measurement target.

The drive output from the drive circuit 4 to the pyroelectric element 1 can be a rectangular wave, a triangular wave, a sine wave or any other voltage waveform. When a triangular wave voltage is applied, the above equation (2) is obtained. Of these, the term Cr · dV / dt becomes a straight line, the component of Cr can be separated and removed from the current I, and the detection accuracy of the polarization inversion current related to the temperature measurement is improved.

FIGS. 4 and 5 show the above points from waveform diagrams of the driving voltage V and the pyroelectric current I. FIG. FIG. 4 shows a case in which the rectangular wave V ₁ n is driven. A spike-like waveform s having a large amplitude appears at the same time as the rise and fall of the rectangular wave, and a polarization inversion current p having a slightly smaller amplitude appears thereafter.
On the other hand, FIG. 5 is a case of driving a triangular wave V _2, spike noise generated immediately after the upper and lower vertices of the triangle wave is small, since the polarization reversal current p is considerably larger, it can improve the measurement accuracy.

Although the spontaneous polarization characteristics vary depending on the pyroelectric crystal, if a pyroelectric material DLATGS, TGS or the like having a low Curie point is used as the material of the pyroelectric body 1, the temperature of the spontaneous polarization near the measurement temperature range is increased. Since the slope of the characteristic curve is steep and the spontaneous polarization value greatly changes with a slight temperature change, the sensitivity and accuracy of temperature detection can be improved, and a pyroelectric radiation temperature detector for a radiation thermometer. It is suitable as. When a low temperature monitor such as a tympanic thermometer uses DLATGS having a spontaneous polarization characteristic in the temperature range, it is difficult to obtain a pyroelectric signal to extract a pyroelectric signal. 100GΩ) and FE
Elements such as T are not required.

[0025]

As is apparent from the above description, the pyroelectric radiation temperature detector according to the present invention can obtain the following effects.

1) An output corresponding to a temperature change ΔT can be obtained by monitoring the reversal polarization current. According to this method, an element such as a high resistance (10 G to 100 GΩ) and an FET, which are difficult to obtain and vary widely, for extracting a pyroelectric signal becomes unnecessary.

2) It is not necessary to add a mechanical chopper, a chopper driving section, and the like to the pyroelectric detector. Therefore, the structure of the detector can be simplified, the power consumption can be reduced, and there is no need to provide a correction circuit for correcting the temperature of the chopper with respect to the outside air temperature. Further, there is no need for a failure or maintenance based on the mechanical operating portion, and the detector can be configured to have a long life and be compact as a whole.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a pyroelectric radiation temperature detector according to the present invention.

FIG. 2 is a diagram showing a temperature characteristic example of spontaneous polarization of a pyroelectric body.

FIG. 3 is an equivalent circuit diagram of a pyroelectric body.

FIG. 4 is a diagram for explaining the operation of the pyroelectric radiation temperature detector according to one embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of a pyroelectric radiation temperature detector according to another embodiment of the present invention.

FIG. 6 is a configuration example diagram of a conventional pyroelectric radiation temperature detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pyroelectric body 2, 3 ... Electrode 4 ... Pyroelectric body drive circuit 5 ... Ground 6 ... Amplifier 7 ... Polarization reversal current waveform 8 ... Integration circuit 9 ... Detection output 61 ... Pyroelectric body 62 ... Light flux chopper 63 ... Chopper drive Circuit 64 ... FET 66 ... Amplification output 67 ... Rectifier circuit I ... Pyroelectric current p ... Polarization reversal current waveform Ps ... Spontaneous polarization R1 ... Super high resistance R2 ... Load resistance Rm ... Load resistance T ... Temperature V ... Pyroelectric drive Voltage

Claims (2)

[Claims] A pyroelectric body receiving radiation from a measurement object is provided with a driving means for applying a periodic waveform voltage such as a triangular wave, a rectangular wave, and a sine wave, and a ferroelectric polarization generated in the pyroelectric body driven by the driving means is provided. A pyroelectric radiation temperature detector configured to obtain an output corresponding to a temperature by monitoring a reversal current. 2. A low curie point pyroelectric material DLATGS,
The pyroelectric radiation temperature detector for a radiation thermometer according to claim 1, wherein TGS or the like is used.