JPH0274833A - Thermometer - Google Patents

Abstract

PURPOSE:To perform accurate measurement by periodically reading the outputs of a pyroelectric element, integrating the output values, and obtaining the absolute value of temperature. CONSTITUTION:At first, temperature is measured with an auxiliary temperature measuring element 8. At the same time, accumulated electric charge in a pyroelectric element 1 is discharged. Thereafter, an insulating type FET 3 is turned ON only for one second at a 10-second period with a clock-signal generating circuit 4. The output of the pyroelectric element 1 is inputted into the gate of a FET 13 and the signal is read. The signal is discharged through an input resistor 2. The read-out value is inputted into a signal processing part 6 and transduced into temperature. The result is integrated on the initial value which is measured with the auxiliary temperature measuring element 8. The absolute value of the temperature can be accurately measured by using the pyroelectric element by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a thermometer, and more specifically, it is capable of measuring minute temperature changes with high precision, and is useful for measuring reaction heat in the chemical industry and for determining the freezing capacity of refrigerators. The present invention relates to a thermometer that can be used for measurement, temperature measurement in living organisms, etc.

Although it is easy to incorporate a conventional thermistor into a bridge circuit to achieve a temperature resolution of about 16'°C, it is very difficult to measure on the order of 10°C. The cause is not only due to various noises but also due to the element itself. That is, in the case of a thermistor, since resistance changes are measured by passing a bias current, the heat generated by the element itself causes measurement errors. In order to avoid this error as much as possible, measures have been taken to measure with zero bias current, but this does not essentially eliminate the error and therefore has its limits.

On the other hand, the pyroelectric element is an insulator and does not have such problems, so the detection accuracy of the element temperature change is 10℃/
Reach sec. In other words, this device has a temperature resolution of 10 degrees Celsius when measured as a temperature change over one second.

A detector using this pyroelectric element generally has a configuration as shown in FIG. 5, but this detector has the following problems. That is, when the pyroelectric element 1 and the input resistor 2 are connected in parallel to the impedance conversion FET 13 as shown in the figure, the electric time constant τ. Since it is expressed as the product of the capacitance CI of the element and the input resistance Rla, it ranges from several seconds to several tens of seconds.Therefore, when trying to measure the temperature change as shown by the solid line 10 in FIG. 6, the broken line in FIG. As shown in
The problem is that since the output signal 15 is discharged and attenuated by an electric time constant of 2, a temperature difference of ΔT occurs between the output signal 15 and the actual temperature. Note that since the thermal time constant is 0.1 seconds or less, a signal is output with sufficient tracking of slow temperature changes with a cycle of several minutes. In FIG. 5, 14 is an output resistor.

For this reason, pyroelectric elements are used to measure the rate of temperature change, but are not used to measure temperature.
This is the current situation.

Note that a detection element that functions as both an infrared detection element and an ambient temperature change measurement element is proposed in Japanese Patent Laid-Open No. 142427/1983.

Problems to be Solved by the Invention In view of the above circumstances, the present invention makes it possible to use a pyroelectric element having excellent temperature resolution by preventing the output of the pyroelectric element from attenuating due to the electrical time constant. In addition, since the pyroelectric element cannot measure the initial temperature at the time of starting temperature measurement and cannot obtain the absolute value of temperature measurement, it is an object of the present invention to provide a thermometer that enables absolute value measurement.

Means for Solving the Problems In order to solve the above problems, the invention according to claim 1 comprises a pyroelectric element, an input resistor, a FET, and an auxiliary temperature measuring element, and the pyroelectric element output is read out intermittently. The read output value of each time is integrated with the auxiliary temperature measurement element output value, and the temperature measurement result is obtained based on this integrated value.

The invention according to claim 2 is the invention according to claim 1,
A thermistor is used as an auxiliary temperature measuring element.

The invention according to claim 3 is the invention according to claim 1 or 2, in which the readout interval of the pyroelectric element output is set to a constant time of 1/100 or less of the time constant of the pyroelectric element circuit, and the time required for reading is set to the time constant of the pyroelectric element circuit. The distance is set to be 1/10 or less of the interval and at least 5 times the electrical time constant in the read state.

The invention according to claim 4 is the invention according to claim 3,
An isolated FET is inserted between the pyroelectric element and the input resistor,
The time constant of the pyroelectric element circuit is increasing.

The signal output of the active pyroelectric element is read out intermittently, and each time -
Once the signal is returned to zero, the signal output can be read out at a sufficiently shorter time interval than the electrical time constant τ6. It is possible to realize measurements that are almost unaffected by attenuation caused by On the other hand, if it is equipped with an auxiliary temperature measurement element,
It becomes possible to measure the absolute value of the initial temperature. Therefore, by integrating the measurement result of the temperature change by the pyroelectric element with the absolute value measurement result, the absolute value of the temperature at each measurement time can be found. The accuracy of absolute value measurement depends on the accuracy of the auxiliary temperature measurement element, but the relative temperature measurement accuracy depends on the temperature resolution of the pyroelectric element, and as mentioned above, the temperature resolution of the pyroelectric element is excellent, so According to this invention, it is possible to achieve high measurement accuracy.

Auxiliary temperature measurement elements include thermistors, platinum resistance elements,
It is convenient to use a thermocouple or the like.

The readout interval of the pyroelectric element output is a constant time of 1/100 or less of the time constant of the pyroelectric element circuit, and the time required for readout is 1/10 or less of the interval and 5 times or more of the electrical time constant in the readout state. By doing so, the effect of improving accuracy becomes greater.

When an isolated FET is inserted between the pyroelectric element and the input resistor,
When this insulated FET is OFF, the electrical time constant τ becomes a very large value. This is because at this time, a state is realized in which an insulation resistance of approximately 10,000 times the input resistance is inserted into the pyroelectric element circuit. As a result, the influence of output attenuation due to the time constant is reduced.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIG.

The thermometer according to this embodiment uses a conventional pyroelectric element 1.
, an input resistor 2, an FET 13 for impedance conversion, and an auxiliary temperature measuring element 8. The temperature measurement section 9 is composed of the pyroelectric element 1 and the auxiliary temperature measurement element 8. In this embodiment, a thermistor thermometer is used as the auxiliary temperature measuring element 8. The pyroelectric element 1 is made of lead titanate ceramics.
T+Excellent, molded to a thickness of 0.1 mm, aluminum electrodes are deposited on both surfaces to a thickness of 1 to 3 μm, and an aluminum wire is connected to the bipolar electrode film using ultrasonic bonding technology to form a metal bond. This is further reinforced with conductive adhesive. In this thermometer, an insulated FET 3 is inserted between a pyroelectric element 1 and an input resistor 2.

That is, the pyroelectric element 1 is connected to the impedance conversion FET 13 via the insulation type FET 3. Since FET3 is an insulated type, the resistance Ro between the source and drain when no voltage is applied to its gate is
tt is 1oΩ, and the capacitance Cf of the pyroelectric element 1 is 15
pF, so in this case the electrical time constant τ,. ,, = 1
It will be 500 seconds. On the other hand, the resistance value of input resistor 2 is 10
Ω, so when a voltage is applied to the gate of FET3, the electrical time constant τ,. , = o, is seconds, and F
ET3 acts as an insulation resistance approximately 10,000 times as large as input resistance 2. The output of the auxiliary temperature measuring element 8 is used only at the time of initial temperature measurement, and is processed by the signal processing section 6 as shown in the figure. The output of the pyroelectric element circuit is integrated into this.

This thermometer according to the embodiment is equipped with a clock signal generation circuit 4, as shown in the figure. FIG. 2 shows the shape of the gate trigger pulse generated by the clock signal generation circuit 4, where tt=1 second and 1t=10 seconds. In this way, the clock signal generation circuit 4 sends a trigger signal to the gate of the FET 3 for only 1 second, once every 10 seconds, and causes the pyroelectric element 1 to
I am trying to read out the output signal of. In this case, the interval of 10 seconds is the electrical time constant τ when the gate is OFF. 1. 1/ of
Since it corresponds to 150, the electrical time constant τ during this period
. . 5. The attenuation of the output signal is less than 1 inch. On the other hand, the read time of 1 second is the electrical time constant τ when the gate is turned on.

. . Since this is more than 6 times as large as 996 pixels, the output signal can be read out up to 996 channels.

A common power supply is provided to each of the above-mentioned electric circuits via the common terminal 5, but if necessary, separate DC power supplies may be provided.

FIG. 3(a) shows an example of the element temperature 10 to be measured. In the figure, 11 indicates measured temperature data. The pyroelectric element circuit outputs an electric signal corresponding to the element temperature change as shown in FIG. 3(b), and the signal processing circuit 6 sends an electric signal corresponding to the element temperature to the signal output terminal 7. It will be done. To explain in detail one example of the signal processing method in this case, as shown in the figure, it is assumed that the temperature continues to rise for the first 25 seconds, and then becomes constant. first,
In the initial setting, all signal charges of the pyroelectric element 1 are drained out, and the element is set to zero. This is the clock signal generation circuit 4
The first pulse is performed within 1 second. At the same time, the auxiliary temperature measuring element 8 performs initial temperature measurement. Then, 9 seconds later, a second pulse is used to perform the first temperature measurement using the pyroelectric element 1. As seen above, the pyroelectric element output was set to -H zero, but when FET 3 turns OFF, temperature measurement by pyroelectric element 1 starts again, so the second pulse causes the element temperature to change during that time. It is possible to obtain output that corresponds to changes. At this time, the pyroelectric element 1 is simultaneously set to zero again. The output 12 of the pyroelectric element 1 is converted into a temperature corresponding to the temperature in advance if necessary, and integrated into the initial temperature data from the auxiliary temperature measuring element 8, and this integrated value is output as a signal corresponding to the element temperature at this time. It is sent out to terminal 7. After 9 seconds have elapsed after the output of the second pulse, the second measured value is read and zeroed, the read output value is further integrated with the previous integrated value, and the second integrated value is calculated based on this second integrated value. Obtain temperature measurement results.

By repeating this process, it becomes possible to measure minute temperatures in decomposition.

Note that reading measurements once every 10 seconds is not suitable for measuring rapid temperature changes, but if the thermal time constant of the pyroelectric element is made as short as possible, it becomes possible to follow rapid temperature changes.

Therefore, in this example, τ1 = l ms,
This ensures sufficient followability and eliminates cumulative errors in temperature measurement.

FIG. 4 shows another measurement example according to the above embodiment, in which the output 12 of the pyroelectric element 1 occurs in sufficient response to the rise and fall of the element temperature 10. In other words, according to this example, it can be seen that the measurement was performed satisfactorily. In this measurement example, the time axis is scaled down to 1/2 of that in FIG. 3.

The temperature resolution in this example is 1×10° C., which approximately corresponds to the predicted value from the pyroelectric coefficient and various physical characteristics of the pyroelectric element.

That is, if the resolution of the pyroelectric detector with respect to temperature change per second is NEΔt, then the following equation is obtained. Therefore, based on this 8, lead titanate pyroelectric element (Innφx O
, 1mm7), we now have εr==177, -δ=0°006.1 = 2,5
x IQ (coulomby'aa'C), A =
(0,05)"xπ [-], d = '0.01 (punishment)
Therefore, NEΔt = 0.45 XIO(℃/S)
Since (2) is obtained, a theoretical temperature resolution of about 0.5×10° C. per second can be expected.

However, the actual measured value is 5IC11×10 as I saw earlier.
℃, which was about twice the theoretical value (calculated value).

This is thought to be due to the fact that noise greater than that predicted by theory was actually added, and the resolution increased to twice its theoretical value.

This invention is not limited to the above embodiments. For example, the auxiliary temperature measuring element may be a platinum resistance element or a thermocouple in addition to a thermistor. The means for intermittently reading out the output of the pyroelectric element, the means for setting the output value to zero, the means for increasing the electrical time constant, etc. are not limited to the means used in the above embodiments.

Effects of the Invention The inventions according to claims 1 to 4 are configured as described above, and therefore, while using a pyroelectric element, it is possible to measure temperature with almost no influence of attenuation due to the electrical time constant of the output of the pyroelectric element. ,
Moreover, it enables absolute value measurement of temperature. In this case, the accuracy of the absolute value temperature measurement is about the same as the conventional one, but the accuracy of the relative value temperature measurement is improved by about one order of magnitude than the conventional one. Claim 2
In addition, the invention described above has the advantage that temperature measurement is convenient, and the invention described in claim 3 has an additional effect that the effect of improving accuracy is extremely high. The invention according to claim 4 provides an insulated FE
The effect of output attenuation is removed by a simple means called T.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a thermometer according to the present invention, FIG. 2 is a graph showing a trigger pulse for intermittent reading, and FIG. 3 is a graph showing an example of temperature measurement in the embodiment. Figure 4 is a graph showing another example of temperature measurement;
The figure is a circuit diagram showing the configuration of a conventional detector using a pyroelectric element, and FIG. 6 is a graph showing an example of temperature measurement by the conventional pyroelectric detector. DESCRIPTION OF SYMBOLS 1... Pyroelectric element, 2... Input resistance, 3... Insulated FET, 4... Clock signal generation circuit, 6... Signal processing circuit, 7... Signal output terminal, 8... ...Auxiliary temperature measurement element, 9...Temperature measurement section, 13...Name of FE agent for impedance conversion Patent attorney Shige Takashi Awano and one other person Figure 1 + Figure 05 Prisoner Figure O /2 Gate'IJ1

Claims (4)

[Claims] (1) Equipped with a pyroelectric element, an input resistor, a FET, and an auxiliary temperature measuring element, the pyroelectric element output is read out intermittently, the read output value each time is integrated into the auxiliary temperature measuring element output value, and this integration is performed. A thermometer characterized by measuring temperature based on a value. (2) The auxiliary temperature measuring element is a thermistor, a platinum resistance element,
The thermometer according to claim 1, which is any one of thermocouples. (3) The readout interval of the pyroelectric element output is set to a constant time of 1/100 or less of the time constant of the pyroelectric element circuit, and the time required for readout is set to 1/10 or less of the interval and the electric time constant in the readout state. Claim 1 or 2 that the amount is 5 times or more
Thermometer as stated. (4) The thermometer according to claim 3, wherein an insulated FET is inserted between the pyroelectric element and the input resistor to increase the time constant of the pyroelectric element circuit.