JPS6018733A - Temperature measuring device - Google Patents

Abstract

PURPOSE:To simplify the constitution of a temperature measuring device, by counting clock pulses during the period, in which the afterglow output of a temperature dependent fluorescent body exceeds a specified level. CONSTITUTION:A temperature dependent afterglow signal from a fluorescent body 2 is converted into an electric signal by a light receiving device 4 through an optical fiber 1, a half mirror 11, and the like. When the level of the signal exceeds a specified value, the output of a comparator 6 forming a level discriminator becomes a high level, an AND gate 7, through which clock pulses from an oscillator 8 passes, is opened, the clock pulses are counted by a counter (a) of a CPU 10, and a temperature is measured. Therefore, an A/D converter and the like are not required, signal processing becomes easy, and the constitution of the temperature measuring device utilizing the afterglow characteristics is simplified.

Description

[Detailed Description of the Invention] Background of the Invention The present invention is characterized in that it is not affected by electromagnetic fields because it does not use an optical wetness measurement signal using a fluorescent material, and is one of the best among optical fibers. Optical humidity measurement using a phosphor has the advantage that the input light and output light of the measurement system can be easily distinguished because the wavelength of the light is converted during the excitation-emission process of the phosphor. Therefore, input and output light can be transmitted using a single optical fiber, making the transmission system compact.

Temperature measurement techniques using fluorescent materials can be roughly divided into two types: those that utilize temperature changes caused by the fluorescence phenomenon during excitation, and those that utilize humidity changes that occur after the excitation stops. Applications of the afterglow phenomenon include those based on changes in afterglow brightness and those based on changes in afterglow time.

FIG. 1 shows the principle of a conventional temperature measuring device that utilizes temperature changes during afterglow time. When the phosphor is excited with excitation light (A), the phosphor emits fluorescent light and afterglow). The light after the excitation stop time to is afterglow. This afterglow time changes depending on the humidity. In Figure 1, T I < T 2
<T 3, and generally the higher the temperature, the shorter the afterglow time.

The afterglow time τd is defined as the time until the afterglow luminance reaches 0.11p from the peak luminance Ip at the time of stopping the excitation to. The afterglow signal converted into an electrical signal by the optical receiver is sampled by a sampling pulse (C),
A/D conversion is performed.

This A/D converted sampling data is shown enlarged in analog form (b) for convenience. Between the first data, which is the peak value Ip, and the n-th data, which can be considered to have a luminance of O, up to the X-th data, which has the value closest to the luminance of 0.11p, is the data within the afterglow time τd. be. The period of sampling pulse C) is t
s, the afterglow time can be expressed as τd≠x*ts.

The method of measuring afterglow described above has been modified to redefine the afterglow time in a practical manner, and the method of measuring the afterglow time based on this new definition is based on USP 4.22 Fluorescence and afterglow measurement using a receiver. Light is received. This afterglow light reception signal is sampled and held for a period of time th from the excitation stop time to,
Based on this hold value, the output regulating system normalizes the waveform of the afterglow signal as shown in (g). That is, the degree of amplification of the received light signal is automatically adjusted so that the peak levels of all afterglows become a constant value LO. The afterglow signal is discriminated based on these levels and converted into a pulse signal. The pulse width wt of this pulse signal is defined as the afterglow time, and this pulse width wt
t is detected.

In measuring afterglow time based on the definition shown in FIG. 1, data is collected for all points tO to tn in the measurement time period, and then 0. Determine which data indicates the value of IIp, and then determine the afterglow time τd
The problem is that the processing is complex and time consuming. Furthermore, the resolution of time measurement is determined by the speed of A/D conversion, and it is not always possible to obtain sufficiently high precision resolution. That is, temperature changes in afterglow time are generally smaller than temperature changes in brightness. therefore,
Residual resolution due to temperature changes requires considerably high time resolution. This high value means that extremely expensive ultra-high speed A/D converters are required to make accurate temperature measurements.
Another drawback is that it cannot be applied to short afterglow phosphors whose afterglow time is on the order of milliseconds or less.

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

I (t)= A −I p(I') * exp (
--) ... (1) Here, T is the temperature, t is the time measured from the excitation stop point (to), time (t) is the afterglow brightness at time (1), and I
P(1) is the afterglow brightness at the time of stopping excitation (1=0),
τ(1) 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 Ip■ and τ■, and a change in τ(1) due to humidity appears as a change in afterglow time due to humidity.

Since the afterglow time τd is the time required for the afterglow brightness to attenuate to 10 degrees from the time when excitation is stopped as described above, this afterglow time τd is given by the following equation.

From equation (2), it can be seen that even if the temperature change in l11(T) shows a large value, if the temperature change in τ(g) is small, the temperature change in the afterglow time τd is also small. That is, the afterglow time τd is dominated only by τ.

The measurement method shown in Figure 2 normalizes the waveform, which complicates signal processing, and the measured value does not include data immediately after excitation stops, where the rate of change in afterglow brightness is greatest. There are drawbacks. Since normalization is simply achieved by automatic adjustment of the magnification, it does nothing to improve accuracy. The method shown in FIG. 2 is, in principle, between the predetermined levels Ll and L2 with respect to the normalized peak brightness (level LO), that is, the peak brightness /
L OX 100% and L2/L.

This is because only the time in the interval between 1 x 100% is measured.

SUMMARY OF THE INVENTION The present invention provides a temperature measuring device that uses a new measurement quantity, rather than the conventional afterglow time measurement, to obtain higher resolution, thus providing high precision and easy signal processing. The purpose is to

The temperature measuring device according to the present invention includes a phosphor whose afterglow characteristic is temperature dependent, a light receiving means that detects the afterglow of the excitation that excites the phosphor and converts it into an electrical signal, and a light receiving means that detects the afterglow of the excitation that excites the phosphor and converts it into an electric signal. a level discrimination circuit that discriminates at a predetermined level, a clock pulse generation means that generates a clock pulse of a constant frequency, a gate circuit that is controlled by the output of the level discrimination circuit and allows the input clock pulse to pass; means for counting clock pulses output from the gate circuit, and calculation means for calculating the temperature by comparing the obtained count value with the temperature characteristic of the count value set in advance according to the phosphor. It is characterized by becoming. Clock pulse counting start time 3 Preferably, this is the time when dream excitation stops.

As mentioned above, in conventional temperature measurement, the afterglow varies from the peak brightness Ip at the time of stopping excitation to its predetermined or peak brightness Ip.
Since the time required for the afterglow brightness to decay from a certain percentage of p to another certain percentage is measured as the afterglow time, the factor of the peak brightness Ip is eliminated and only the amount that depends on τ■ is measured. . On the other hand, in this invention,
The time required for the afterglow to decay from the peak luminance Ip(T) to a certain luminance level Is (hereinafter referred to as decay time) is measured.

Therefore, the decay time td measured in this invention is expressed as follows using equation (1).

As is clear from comparing equation (3) with equation (2),
On the other hand, in equation (3), the decay time 2 is equal to τ and Ip
(1). This is a factor that affects the temperature T. For example, fluorophore YFa:yb
, the amount of change in the afterglow time τd of Er is within the temperature range 0 to 300.
The decay time t takes into account the two temperature factors τ(1) and Ip(I'), whereas
The amount of change in d is about 7 times. As a result, the decay time t
It will be understood that the rate of change of d with respect to humidity changes can be increased, resulting in higher resolution. Furthermore, a wide range of fluorescent materials can be selected that can be used as temperature measurement sensors.

In addition, this invention uses a simple level discrimination circuit and a clock
Since the above decay time td can be measured by the combination of the pulse generation circuit, gate circuit, and counter,
This eliminates the need for conventional operations such as A/D conversion using an A/D converter and storing sample data in RAM, making signal processing easy and the configuration simple. It is also possible to adjust the measurement resolution by the frequency of the clock pulse.

In the present invention, a variety of phosphors can be used without any limitation as long as the afterglow characteristics are temperature dependent and the afterglow decay time is measurable. Preferably, a phosphor having a decay time of about 10 se6 to lQ see is used. For example, for εμ ultraviolet light excitation, rare earth metal oxysulfides such as Y2O25i:Shi, sulfide phosphors such as ZnS:Ln (Ln is a general term for rare earth elements), SrS:Ln, and C
Many types of RT phosphors can be used. In addition, in infrared light excitation, LnF3: (Yb, Er), LnOF: (
Yb, Er), Description of Examples Hereinafter, the present invention will be described in further detail with reference to the drawings.

FIG. 3 shows the configuration of the temperature measuring device, and FIG. 4 shows its operation. A predetermined fluorescent material (2) is attached to the tip of the optical fiber (1) to constitute a temperature probe. The humidity probe is placed with its tip in contact with the atmosphere or object whose temperature is to be measured. C.P.
A timing pulse signal CP) is output from the UflO). This pulse () is for driving the external light device (3), and is emitted at a constant period (Ta). This period (
Ta) is set to a time sufficient for the afterglow emitted from the phosphor (2) to completely disappear at all temperatures within the measurement range.

It is output and irradiated to the phosphor (2) through the optical fiber (1). The fluorescence and afterglow emitted from the phosphor (2) by this excitation propagate through the optical fiber (1), are extracted via the beam splitter (11), and are sent to the light receiver (4).
The light is received by the The detection signal from the photoreceiver (4) is amplified by a variable amplification amplifier (5) and then input to a comparator (6).

The comparator (6) outputs an H level signal only when the level of the afterglow signal (G) is equal to or higher than a predetermined level Is. The output of comparator (6) is AN
This becomes the first gate control signal for the D gate (7). AND
Also input to the gate (7) is a signal inverted by the N01 circuit (9) of the timing pulse (P) as a second gate control signal.

The second gate signal is pulsed separately from the CPU (10
) may be output. The variable frequency clock pulse generator circuit (8) outputs adjusted frequency clock pulses which are sent to the AN, D gate (7). The AND gate (7) is opened from the time when the timing pulse T) falls (that is, when the excitation stops) until the afterglow signal (G) becomes level 8 or less. clock·
The pulse passes through the gate (7) and enters the counter (
The pulse (6) counter may be one that utilizes registers or memory areas within the CPU (10);
(In) It may be an externally provided counter. In any case, the pulse input to the counter (
6) is counted, and this counted value represents the decay time.

The excitation of the phosphor (2) is repeated a predetermined number of times N times at each period Ta, and the count value of the counter each time is added and stored in a register.

In the memory of the CPU (10), the decay time td (counter count value, addition value of N count values) of the fluorescent material used is measured in advance at various temperatures T, and the decay time td (counter count value, addition value of the count value N times) is measured in advance, and a known function is stored. The characteristics shown in FIG. 5 are set in advance.

After the above measurements are completed N times, the CPU (10) compares the measured count value (or the N times added value) with this humidity characteristic to determine the humidity.

[Brief explanation of drawings]

Figures 1 and 2 are waveform diagrams showing the conventional method of measuring afterglow time, Figure 3 is a block diagram showing an embodiment of the present invention, Figure 4 is its waveform diagram, and Figure 5 is a diagram of the decay time. It is a graph showing temperature characteristics. Optical device, (41... Light receiver, (6)... Comparator, (7)... Gate circuit, (8)... Clock, pulse generation circuit, (10)... CPU0 and above. 4 people 1) + C eaves υ↓ri■season■gu-

Claims (2)

[Claims] (1) A phosphor whose afterglow characteristics are temperature dependent, a single stage of excitation to excite the phosphor, and a method that detects the afterglow of the light emitted from the excited phosphor and converts it into an electrical signal. A light receiving means, a level discrimination circuit that discriminates the received afterglow signal at a predetermined level, a clock pulse generation means that generates a clock pulse of a constant frequency, and a level discrimination circuit that is controlled by the output and inputted. a gate circuit that allows the passage of clock pulses, a means for counting the clock pulses, and a calculation means for calculating the temperature by comparing the obtained count value with the temperature characteristic of the count value set in advance according to the phosphor. A humidity measuring device consisting of . (2) The temperature measuring device according to claim (1), wherein the clock pulse counting start point is the excitation stop point.