JPS58180922A - Temperature measuring device - Google Patents

Abstract

PURPOSE:To measure temperature accurately without adverse effects by electromagnetic fields and excited light, by integrating the afterglow signal of a fluorescent body, whose afterglow characteristic depends on temperature, for a specified time zone, and computing temperature. CONSTITUTION:A pulse P1 is outputted from a timing circuit 4 in response to an output command from a CPU10. A fluorescent body 2, whose afterglow characteristic depends on temperature, is excited by light, which is transmitted in an optical fiber 1 from a light emitting device 3. A sampling pulse P2 is generated by the sampling circuit 4 during the time period, which corresponds to an integrated time zone, from the fall of the pulse P1. By the pulse P2, the afterglow output received and detected by a light receiving device 5 and the fluorescent body 2 is written in an RAM11 through a sample and hold circuit 7, an A/D converter 12, and the like. This is repeated by a specified number of times. Then the integrated value at every sampling point for a specified time zone based on the contents of the RAM11 and the final integrated value based on the mean value are determined. The temperature is computed from an integrated value vs. temperature curve based on the afterglow characteristic. In this constitution, the temperature is measured without adverse effects by electric noises and excited light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical temperature measuring device using a fluorescent material.

Since optical temperature measurement does not use electrical signals, it has the characteristic that it is completely unaffected by noise caused by electromagnetic fields, and various devices using optical fiber technology have been developed. Among these, optical temperature measurement using light emitted from a phosphor is difficult because the wavelength of the light is converted during the excitation-emission process of the phosphor.
There is an advantage that the input light and output light of the measurement system, that is, the excitation light, and the fluorescence and afterglow from the phosphor can be separated. Therefore, input and output light can be transmitted using a single optical fiber, making the optical transmission system compact.

Fluorescent-applied temperature measurement techniques can be roughly divided into two types: those that utilize temperature changes in the emission intensity of fluorescent light, and those that utilize temperature changes in the afterglow time after excitation. In temperature measurement using temperature changes in the emission intensity of fluorescent light, excitation light with high intensity and fluorescent light with low intensity exist simultaneously, so these must be wavelength separated using spectroscopy or other methods. This method requires an optical system for this purpose, and has the disadvantage that measurement with a high S/N ratio is difficult. On the other hand, in temperature measurement that uses temperature changes in afterglow, the afterglow, which is the light after the excitation stops, is detected, so in principle, the excitation light does not affect the afterglow measurement and the optical This has the advantage that it is easy to perform measurements. However, afterglow time is measured by measuring the time from the time when excitation stops or when the brightness reaches 90% of the peak brightness at the time when excitation stops until the time when brightness reaches 10%. Since the point on the afterglow curve at which each measurement point falls is known at the end of the measurement, all signal components that form the afterglow curve are to be measured, so noise etc. The disadvantage is that measurement accuracy is easily affected by sudden or partial signal changes during the measurement process.Also, measurement of afterglow time is a measurement of afterglow intensity during the decay process of afterglow, so There is a problem in that it is difficult to measure the light intensity, and errors tend to occur in determining when the afterglow intensity becomes zero, making it impossible to accurately measure the afterglow time.

That is, the afterglow curve decreases exponentially or hyperbolically, and the curve changes very gradually in areas where the afterglow brightness is extremely small.

Therefore, it is inevitable that the error will become large in the measurement at the time when the afterglow luminance reaches 10% of the peak.

This invention makes it possible to eliminate the negative effects of excitation light by making use of temperature changes in afterglow, and to accurately measure temperature by using a new measurement quantity instead of measuring the conventional afterglow time. The purpose of the present invention is to provide a fluorescent-applied optical temperature measurement device that can perform the following steps.

A temperature measuring device according to the present invention is arranged in an atmosphere or an object whose temperature is to be measured, and includes a phosphor whose afterglow characteristic is temperature dependent, an excitation means for exciting the phosphor, and a phosphor that emits light from the excited phosphor. a light-receiving means for detecting afterglow of the light emitted by the phosphor; It is characterized by comprising a calculation means for calculating the temperature by comparing it with the temperature characteristic of the integral value of the amount of afterglow light set in advance according to the temperature characteristic. The integrating means includes an integrating circuit that directly integrates the afterglow signal in an analog manner, and data obtained by sampling the afterglow signal at appropriate time intervals is stored in a memory, and the stored sampling data is stored in a memory. For example, the central processing unit (
Both microprocessors (hereinafter referred to as CPU) and preferably microprocessors can be used. Any time period during which afterglow is output can be adopted as the integration time period.
As will be described in detail later, this time period may be fixedly determined in advance, or may be determined based on the value of the afterglow signal.

In the temperature measuring device of the present invention, the temperature is measured using the integral value of the afterglow signal in a predetermined time period.

Therefore, like traditional devices that measure afterglow time,
It is less affected by sudden or partial signal changes due to noise, etc., and since level discrimination is not performed at low brightness signal levels, the accuracy of temperature measurement can be improved. Therefore, there is no need to separate it from the excitation light, and it is possible to measure with a high S/N ratio without being adversely affected by the excitation light, and there is no need for a spectroscopic device.

In general, the temperature change in brightness at a specific point in the afterglow process has a larger rate of change than the temperature change in the afterglow time, and changes monotonically.1 The selection range of the phosphor as a temperature measurement sensor In this respect as well, the device according to the present invention has superior effects compared to conventional devices that measure afterglow time. This can be explained quantitatively as follows.

Assuming that the afterglow signal decreases exponentially, the afterglow characteristic is expressed by the following general formula.

j 1 [t) -A @ 1. O(1'l * eτ(T
) @@11 ill Here, T is the temperature, the time measured from the time when the excitation stopped, and I (I is the afterglow brightness at time (1), ■0■ is the time measured from the time when the excitation stopped (t = 0) The afterglow brightness, τ■ is the average lifetime of the excited state in the phosphor, and A is the proportionality constant.Among these parameters, those that change depending on the temperature T are 0■ and τ(1), and τ The change due to temperature in (2) appears as a change in afterglow time due to temperature.

If the afterglow time td is the time required for the afterglow brightness to decay to 10% from the time when excitation is stopped, then this time t
d is given by the following equation.

Even if the temperature change of t d = −r(Q * in −L a lU kube* as (21A lo(1), from equation (2), 0tT) shows a large value, the temperature of τ■ It can be seen that if the change is small, the temperature change in the afterglow time ta is also small.

On the other hand, the integral value l1nt(T) of the afterglow brightness used in this invention is given by the following equation, where ta,
tb is the time of the start point and end point of the integration time period, respectively.

It will be understood from the jJ+31 equation that even if the temperature change in τ■ is small, the integral value 1 int■ changes greatly in accordance with the temperature change in IO. For this reason, the present invention allows extremely accurate temperature measurements. In addition, since temperature change with a peak brightness of 0, that is, temperature quenching property is the most common property of phosphors, the range of selection of phosphor materials that can be applied to this invention is expanded, and phosphor materials that exhibit the desired temperature change can be used in this invention. The adjustment of the light body becomes objective.

In the present invention, a variety of phosphors can be used without any limitation as long as the phosphor has temperature-dependent afterglow characteristics and has a measurable afterglow time. Preferably, a phosphor with an afterglow time of about lQ-61LLS (1 to IQ'-3sec) is preferable. For example, in ultraviolet light excitation, Y20
2 S i : Rare earth metal oxysulfides such as Eu, Z n S : L n (Ln is a general term for rare earth elements), sulfide phosphors such as SrS:Ln,
Many types of CRT phosphors can be used. In addition, in infrared light excitation, LnFs; (Yb, Er)
, 1. nOF: (Yb, ET), L i Na
P4012: Yb etc. are used.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

Figure 1 shows pulsed or square wave excitation light and the waveform of light emitted from a phosphor excited by this excitation light. It is expressed differently depending on the person. The light emitted during excitation is fluorescent light, and the point at which excitation stops (t
Afterglow is the light that is emitted after (indicated by l) and attenuates over time. Among the waveforms of fluorescence and afterglow, those shown by broken lines are the waveforms at temperature Tl, and those shown by solid lines are the waveforms at temperature T2. Here, the relationship is TI<72. Generally, afterglow brightness tends to increase as the temperature decreases.

FIG. 2 shows the temperature characteristics of the integral value of the amount of afterglow light.

The integral values of the fluorescent material used are measured in advance at various temperatures T, and the characteristics shown in FIG. 2 are set in advance as known relationships. The temperature is determined by comparing the measured integrated amount of afterglow light with this temperature characteristic. The integration time period when the characteristic shown in FIG. 2 is created in advance coincides with the integration time period of the temperature measuring device in which this characteristic is used.

FIG. 3 shows the configuration of the temperature measuring device, and FIG. 5 shows its operation. A predetermined fluorescent material (2) is attached to the other four ends of the optical fiber (1) to constitute a temperature probe. The temperature probe is placed with its tip in contact with the atmosphere or object whose temperature is to be measured. Two types of timing 0 pulse signals P are generated from the timing generation circuit (4) controlled by CPUQI.
1%P2 is output. The pulse pl drives the light emitter (3) (see FIG. 1). This period Ta is set to a time sufficient for all temperatures within the measurement range (and for the afterglow emitted from the phosphor (2) to completely disappear.When the pulse P1 is input, Excitation light is output from the light emitter (3) and passes through the optical fiber (1) to the phosphor (2).
is irradiated. The fluorescence and afterglow emitted from the phosphor (2) by this excitation propagate through the optical fiber (1), are extracted via the beam splitter (9), and are taken out by the light receiver (5).
) is amplified by a preamplifier (6) and then input to a sample and hold circuit (7).

The timing output from the timing generation circuit (4)
Pulse (sampling pulse) P 2 C, as shown in FIG. 5, the falling time tl (ta) of the pulse P1
n pieces are output until time tb after an appropriate period of time has elapsed.

Each pa? The time point at which response P2 is output is LOs '1, '2
,...tn.

Further, the period of the pulse P2 is assumed to be Δ. This period Δ is also set to be slightly longer than the AD conversion operation time of the analog-to-digital (AD) converter α2.

The period from time ta to tb is the integration time period. This integration time period can be set arbitrarily, but in this embodiment, the starting point ta of the integration time period is set at the time t1 when excitation is stopped. The end point tb of the integration time period is constrained by the afterglow level at the upper limit temperature of the measurement temperature range where the afterglow has the lowest brightness. For example, the end point tb may be defined as the point in time when the afterglow level at this upper limit temperature becomes about 30% of the peak brightness (brightness at the time of stopping excitation). AD converter (1
If the operation time is fast, set the integration time period to a relatively short time, for example, set the start point t & to the excitation stop time t1, and set the end point tb to the time when the afterglow level reaches 90% of the peak brightness. , and sufficient measurement accuracy can be obtained in this case as well. By shortening the integration time period, temperature measurement can be made faster. Even when a phosphor with a relatively long afterglow time is used, the proportion of the integration time period in the afterglow time can be made small.

However, this invention does not measure afterglow time (
Since it measures the integrated afterglow light amount, it has the characteristic that accurate measurement is possible even if the number of samples n is relatively small.

Therefore, the sampling period Δt is relatively long (very good), and there is no need to use a high-speed AD converter.

Timing pulse P2 is generated by one sample hold circuit (
7) and sent to AD converter α2. Of the light detected by the receiver (5), only the afterglow signal is sampled.
A hold circuit (7) holds the level for each pulse P2. The output of this circuit (7) is the amplification circuit (8)
After being amplified, the signal is sent to the AD converter α, converted into a digital signal during a time Δt, and stored in the RAM (Ill).

RAM (111 includes an area for storing AD-converted sampling data as shown in FIG. 4, an area for storing the number of repetitions m of pulse Pl, and an integral value of the amount of afterglow light as shown in FIG. 2). An area is provided for storing the humidity characteristics of the phosphor (2).
The excitation is repeated m times, and the integrated amount of afterglow light is determined based on the integrated average of the sampling data. The sampling data area contains each sampling point tO~
For each tn, a place is provided to store sampling data from the first excitation to the m-th excitation, their m-time integrated value and average value, and the final integrated value.

The temperature measuring device shown in FIG. 3 is controlled by the CPU [lQl. The control and temperature calculation processing procedure of this CPUQ[) is shown in FIG. First, a pulse P1 output command is output from the CPUQQI to the timing generation circuit (4), and a timer in the CPUQQI starts measuring a period Ta (step C1). As a result, the pulse P1 is outputted from the circuit (4), and the pulse P2 is outputted from the falling edge of the pulse P1. CPUαO
Now, wait until time Ta has elapsed (step (22)
).

During this time, as described above, the phosphor (2) is excited, and the afterglow emitted from the phosphor (2) is then sampled into the pulse P2, etc., and after AD conversion, this data is Each sampling time point is stored in a memory location in RAM +111 that corresponds to the number of times it is repeated. T
When the timer counting RA times out, RA
The number of repetitions m in Mtll is -1 (to step)
, it is checked whether this result becomes O (step (to)). If m = Q, then step 01 is performed again.
1, and the excitation of the phosphor (2) and the sampling of the afterglow signal are repeated in the same manner.

When m afterglow measurements are completed, m in RAM+111 is
The sampling data for each sampling time is integrated at each sampling time point (step (25)), and the average of the m times is calculated (step (end)).Then, the average value for each sampling time point is all The final integral value is obtained (step side).The finally calculated integral value is compared with the temperature function of the integral value of the amount of afterglow light, and the temperature T
is calculated (step @). Although the average value of each sampling point is calculated in step ①, it is also possible to omit this process and calculate the integrated value by adding the integrated values of each sampling point, and calculate the temperature from this integrated value. The result is the same.

In the above example, the end point tb of the integration time period is fixedly determined in advance, but it may be determined depending on the level of the afterglow signal. That is, as shown in FIG. 8, the brightness level IS for determining the end point tb is determined in advance, and the RA
Store it in MQII. Then, the time point when the afterglow signal becomes equal to or lower than this level I8 is defined as the end point tb. In this case, the sampling pulse P2 is continuously output until the next timing pulse P1 is output, and sampling is performed until the afterglow signal becomes zero.

Figure 7 shows the CP when the end point tb is determined using the method described above.
U (10 processing steps are shown. Steps 21i to ■
is exactly the same as the process shown in FIG. When the average value for each sampling time point is calculated, this average value is read out (step side) and sequentially compared with the level Is (step G1)).

This process continues until an average value smaller than level IS is found. If an average value smaller than level IS is found and the average value is from sampling time tk(k)n), the average values from s41 to tk are added to calculate the integral value (step ■). The calculated integral value is compared with the temperature function of the integral value of the amount of afterglow light to obtain the temperature T (step eel).

In the above example, the period T1 of excitation of the phosphor is
Although the time period is set to be sufficient for the afterglow to completely disappear, this period Ta can be shortened to output the next pulse P1 during the afterglow process as shown in Fig. 9 to eliminate the fluorescence. It is also possible to excite the body and measure temperature using the dynamic afterglow response. In this case, the first afterglow is different from the subsequent afterglows and is therefore not used for temperature measurement. According to this method, temperature measurement can be made faster.

[Brief explanation of drawings]

Fig. 1 is a waveform diagram showing excitation light, fluorescence emitted from a phosphor, and afterglow, Fig. 2 is a graph showing temperature characteristics of integrated amount of afterglow, and Fig. 3 shows an example of the present invention. 4 is a diagram showing the contents of the RAM, FIG. 5 is a time chart showing the operation of the circuit shown in FIG. 3, and FIGS. 6 and 7 are flow charts showing the operation of the CPU. , FIG. 8 is a waveform diagram showing an example in which the end point of the integration time period is determined by the afterglow level, and FIG. 9 is a time chart showing another method of excitation. (1)...Optical fiber, (2)...Fluorescent material, (3)
... Light emitter, (4) ... Timing generation circuit, (5
)...Receiver, (7)...Sample/hold circuit, (101・-+1cPUs (Ill "@@RA
M, Q3-116'A D converter. 4 people other than the above

Claims (8)

[Claims] (1) A phosphor whose afterglow characteristics are temperature-dependent, an excitation means for exciting the phosphor, a light receiving means for detecting the afterglow of the light emitted from the excited phosphor, and a light receiving means for detecting the afterglow of the light emitted from the excited phosphor. an integrating means for calculating the integrated afterglow light amount by integrating the afterglow signal over a predetermined time period; A temperature measuring device consisting of a calculation means for calculating temperature by comparison. (2) Claim No. (2) wherein the integrating means is an integrating circuit.
1) The temperature measuring device described in item 1). (3) the integrating means stores afterglow sampling data sampled at predetermined time intervals in a memory, and adds the stored sampling data;
A temperature measuring device according to claim gE+11. (4) The temperature measuring device according to claim (1), wherein the starting point of the integration time period is the point at which the excitation of the phosphor stops. (5) The temperature measuring device according to claim (1), wherein the end point of the integration time period is determined based on the afterglow peak brightness of the phosphor at the measurement upper limit temperature. (6) The temperature measuring device according to claim (1), wherein the end point of the integration time period is a point in time when the afterglow signal becomes equal to or less than a predetermined lower limit value. (7) The temperature measuring device according to claim (1), wherein the integration time period is fixedly set in advance. (8) The temperature measuring device according to claim (1), wherein the excitation of the phosphor is repeated a plurality of times, and the temperature is calculated using the average value of the integrated amount of afterglow of the plurality of times.