JPS6258121A - Electronic thermometer - Google Patents

Abstract

PURPOSE:To reduce the error due to the effect generated when the abrupt change in temp. is generated, by reducing temp. difference at the time of oscillation per time by a reference resistor and at the time of oscillation per time by a temp.-sensitive resistor by reducing time difference at the times of both oscillations. CONSTITUTION:An oscillation part 1 is constituted of a time constant circuit 15 consisting of a thermistor 11, a reference resistor 12, a change-over switch 13 and a condenser 14 and an oscillator 16. A comparing part 2 compares respective oscillation frequencies corresponding to the change-over of the resistor of the oscillator 16 to output the pulse signal corresponding to temp. and a control part 3 allows the comparing part 2 to take comparing operation due to the change-over of the resistor of the oscillator 16 over predetermined plural times. Further, an adding part 4 receives pulse signals outputted from the comparing part 2 over plural times and cumulates the same. A temp. data converting part 5 receives the output signal of the adding part 4 and converts said signal to temp. data to display the same on a display part 6. By this method, temp. difference at the time of oscillation by the reference resistor 12 and at the time of oscillation by the thermistor 11 is reduced and the error due to the temp. difference is reduced corresponding thereto.

Description

[Detailed description of the invention] (a) Industrial application field This invention includes an electronic thermometer, particularly a reference resistor and a temperature-sensitive resistor in an oscillator, and connects these resistors to the oscillator to cause oscillation. This paper relates to improvements in electronic thermometers that measure temperature by comparing oscillation frequencies.

(B) Conventional technology Conventional electronic thermometers switch between a reference resistance and the resistance of a temperature-sensitive element (temperature-sensitive resistor) to oscillate an oscillator, compare the oscillation frequencies, and generate a pulse signal corresponding to the temperature. On the other hand, there is a device in which temperature data corresponding to this pulse signal is stored in advance in a storage means, and temperature data corresponding to the temperature at the time of measurement is read out from the storage means and displayed on a display.

In this type of conventional electronic thermometer, the reference resistance and the resistance of the temperature sensing element are switched only once for each measurement.

(c) Problems to be Solved by the Invention In the above-mentioned conventional electronic thermometer, the reference resistor and oscillator have some dependence on temperature.

Therefore, the oscillation frequency of the oscillator also has dependence.

In order to correct this temperature dependence, in addition to the temperature-sensitive resistor, a reference resistor is provided and connected to the same oscillator by switching, so that the oscillation frequency when the reference resistor is connected and the oscillation frequency when the temperature-sensitive resistor is connected. Temperature is measured by comparing the oscillation frequencies of In other words, even if there is a difference in temperature during measurement, if the temperature change during measurement is gradual, the oscillation frequency will be affected in the same direction when the reference resistor is connected and when the temperature-sensitive resistor is connected.
canceled out. Furthermore, there is almost no difference in temperature between when the reference resistor is connected and when the temperature-sensitive resistor is connected. Therefore, the above correction is extremely effective for gradual temperature changes.

However, when there is a sudden change in temperature, a large difference occurs between the temperatures during oscillation by the reference resistor and oscillation by the temperature-sensitive resistor, and the condition of assuming the same temperature when comparing both oscillation frequencies breaks down, causing the measurement results to vary. There was a problem in that errors occurred.

In view of the above, the present invention provides that even when there is a sudden change in temperature,
The purpose of this invention is to provide an electronic thermometer that can perform measurements with high precision.

(d) Means and action for solving the problems In order to solve the above problems, the electronic thermometer of the present invention is capable of switching the resistance constituting the time constant circuit between a reference resistance and a temperature-sensitive resistance. an oscillation section including the constructed oscillator; a comparison means for comparing respective oscillation frequencies according to switching of the resistance of the oscillator and outputting a pulse signal corresponding to temperature; and said comparison means for switching the resistance of the oscillator. control means for performing the comparison operation a predetermined plurality of times; addition means for receiving and accumulating pulse signals output from the comparison means for a plurality of times; It consists of a temperature data converter that converts temperature data into temperature data, and a display that displays the temperature data output from the temperature data converter.

In this electronic thermometer, first, a reference resistor is connected to an oscillator to oscillate for a predetermined period of time, then a temperature-sensitive resistor is switched to the oscillator, and each oscillation frequency is compared by a comparing means to generate a pulse signal corresponding to the temperature. is output, and this pulse signal is added to the adding means. Next, the oscillation frequencies obtained by switching the connection of the reference resistor and the temperature-sensitive resistor are compared, and a pulse signal corresponding to the temperature is outputted from the comparing means and cumulatively added by the adding means. Then, repeat the above switching, comparison, and cumulative addition a predetermined number of times, 8 times,
The finally obtained cumulative output signal of the adding means is input to the temperature data converter, and this output signal is converted into temperature data and displayed on the display. If the time required for one measurement is the same as that of the conventional electronic thermometer, the switching interval between the reference resistance and the temperature-sensitive resistor of the electronic thermometer of the present invention will be 1/N of that of the conventional electronic thermometer.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a block diagram showing the circuit configuration of an electronic thermometer according to an embodiment of the present invention.

The electronic thermometer of this embodiment includes an oscillation section 1, a comparison section 2, a control section 3 for repeating the operation of the comparison section 2 N1 times, and a pulse signal that is cumulatively added according to the temperature output from the comparison section 2. It is composed of an adding means 4, a temperature data converting section 5, and a display section 6.

The oscillator 1 includes a thermistor (temperature-sensitive resistor) 11 and a reference resistor 1.
2. It is composed of a time constant circuit 15 consisting of a changeover switch 13 and a capacitor 14, and an oscillator 16. The thermistor 11 and reference resistor 12 have one end connected to a power source (battery), the other end connected to a capacitor 14 via a switch 13, and the other end of the capacitor 14 grounded. The oscillation frequency of the oscillator 16 is determined by the time constants of the thermistor 11 and the capacitor 14 or the reference resistor 12 and the capacitor 14.

Next, the configuration of the comparing section 2 will be explained. The output of the oscillator 16 is added to the counter 17, and the N of this counter 17 is
The o count output is applied to the delay circuit 18 and also to the launch circuit 19. Further, the output of the delay circuit 18 is configured so that the switch 13 is switched by "1" or "0" of the set Q output of the flip-flop 20.Furthermore, the output of the delay circuit 18 is switched by the OR circuit 2.
It is also added to counter 17 and counter 22 via 5 to clear them.

The clock signal output from the clock oscillator 21 is counted by a counter 22, and the output of this counter 22 is applied to a latch circuit 19 and a comparison circuit 23. The clock oscillator 21, counter 22, and latch circuit 19 measure the time until the counter 17 counts N0 pulses, and temporarily hold the time.

The comparison circuit 23 compares the count value of the counter 22 and the output of the launch circuit 19, and applies the matched output to the delay circuit 24, and the output of the delay circuit 24 is applied to the counter 17 and the counter 22 via the OR circuit 25. , both counters 17
．． 22 is cleared, and the flip-flop 20 is also reset by the output of the delay circuit 24.

The output of the oscillator 16 is applied to one end of the AND gate 26 of the adder 4, and the cent output end of the flip-flop 20 is connected to the other input end. Furthermore, the output of this AND gate 26 is added to a counter 27.

That is, only when the flip-flop 20 is set, the output of the oscillator 16 passes through the AND gate 26,
It is configured to be input to a counter 27.

The temperature data converter 5 is composed of a decoder 28 that receives the count output of the counter 27, a ROM 29 that stores temperature difference data corresponding to the input, and a shift register 30 that stores the output of this ROM 29. The temperature data derived from the shift register 30 is displayed on the display 32 via the driver 31 that constitutes the display section 6.

The counter 33 that constitutes the control section 3 counts +1 upon receiving the signal from the delay circuit 24, and the count amplifier signal passes through the delay circuit 34 and clears itself and the counter 27.

FIG. 2 shows a specific example of the oscillator 16.

The connection point between the common terminal of the capacitor 14 and the switch 13 is
It is connected to the inputs of inverters 4I and 42 and the conductive electrode of MOS transistor 43 via a discharge resistor 40. One inverter 41 has hysteresis characteristics, but the other inverter 42 does not have hysteresis characteristics. The outputs of the inverters 41 and 42 are applied to gate circuits 44 and 45, respectively, and the output of the gate circuit 44 is applied to the set input terminal of the flip-flop 46.
The outputs of are applied to the reset inputs of flip-flops 46, respectively. Further, the output of the flip-flop 46 is connected to the gate of the MO3I-transistor 43 and the counter 1
7 and the AND gate 26.

Next, the operation of the electronic thermometer of the above embodiment will be explained.

First, in the initial state of measurement, the counters 27 and 33 are reset.

In the oscillator 1, when the switch 13 is connected to the reference resistor 12 side, the capacitor 14 is connected to the reference resistor 12 side.
The terminal voltage gradually increases as shown in FIG. And the terminal voltage is the inverter 41
When the on-voltage 2 is reached, the flip-flop 46 is set, and the MO3I-transistor 43 is turned on accordingly.
The charging voltage of the capacitor 14 is discharged through a resistor 40 and a MOS transistor 43.

The terminal voltage of capacitor I4 drops and inverter 44
When the off-voltage (2) is reached, the flip-flop 46 is reset, the MOS transistor 43 is turned off, and the capacitor 14 is recharged.

In this case, the resistance value of the reference resistor 12 is R, the capacitor 14 is
When the capacitance of is C, the charging time tc can be expressed as -V2.

Here, if the resistance value of the resistor 40 is R, the resistance value of the thermistor 11 is Rx, and R,<<R, Rx, the discharge time can be ignored. Therefore, the oscillation frequency fo of the oscillator 16
can be expressed as .

When the switch 13 is turned on to the reference resistor 12 side, the counter 17 and the counter 22 are cleared at the same time, and the pulse signals of the oscillator 16 and the oscillator 21 are counted, respectively. When the count value of the counter 17 reaches a predetermined value NO, the count value of the counter 22 at that time is latched in the launch circuit 19 by the count up output.

By the way, since the time until the counter 17 counts NO is NO/fO, the count value of the counter 22 held in the latch circuit 19 is as follows.

Further, the count amplifier output of the counter 17 is applied to the cent terminal of the flip-flop 20 with a slight delay by the delay circuit 18, and further applied to the counter 17 and the counter 22 via the OR circuit 23. As a result, the flip-flop 20 is set and the counter 1
7 and counter 22 are cleared.

When flip-flop 20 is centered, switch 13
is switched to the thermistor 1 side. That is, the thermistor 1 is connected to the oscillator 16. In this case, the oscillation frequency fx of the oscillator 16 is -V2 when Rx is substituted for the (2) second R.

The counter 7 thereafter counts the output pulse signals of the oscillator 16 having the oscillation frequency fx. Also, flip-flop 2
Since the AND gate 26 is opened with a cent output of 0, the output pulses of the oscillator 16 are also input to the counter 27 and counted. On the other hand, the counter 22 counts the pulse signals from the clock oscillator 21 again. Here, the oscillation frequency of the clock oscillator 21 is assumed to be fc'. counter 22
When the count value reaches the count value shown in the above equation (3), the comparison circuit 23 detects a match between the two and temporarily stops counting by the counter 7. At this time, if the count of the counter 7 is Nx, the count value f c' N x/ that the counter 22 counts within the time Nx/fx for the counter 7 to count up to Nx
f x is the count value f held in the latch circuit 19
(No / f is equal to o. Therefore, fx f.

holds true.

Assuming that the frequency of the clock oscillator 21 does not change before and after switching of the switch 13, fc=fc'. Therefore, by transforming equation (5) and substituting +2) into equation (4), the following is obtained.

By the way, the resistance value Rx of the thermistor 11 can be expressed as follows.

In addition, the switch 13 is composed of a semiconductor switch, but
If the resistance value R% Rx of the reference resistor 12 and thermistor 1 is almost equal, the on-resistance and off-voltage of the switch 13 ■1
, the values of the potential voltage ■2 are considered to be equal, so k,=
It can be set to 2.

Using this and substituting the second equation (6) into the equation (7), the following holds true. If we rewrite this in terms of Tx, it becomes ■ To B NoR. In this equation (9), once Nx is determined, the temperature Tx can be determined from Nx since everything else is a constant.

As described above, the number of pulses Nx corresponding to the temperature Tx is counted by the counter 27.

On the other hand, the coincidence output signal of the comparison circuit 23 passes through the delay circuit 24 and resets the counter 7.22 and the flip-flop 20. This causes the switch 13 to change to the reference resistor 12.
It is thrown into the side. Then, the series of processing operations described above are repeated again. Further, the counter 33 is incremented by +1 by a signal from the delay circuit 24.

Until the count value of the counter 33 reaches a predetermined value N (for example, 4 times), the number of pulses NX corresponding to the temperature at that time by switching the reference resistor 12 and thermistor 11 is accumulated and counted by the counter 27 ( (added). That is, N1=4
In this case, the number of pulses Nx is calculated in four steps, and the cumulative value is counted by the counter 27.

When the count value of the counter 33 reaches N1 times, the count amplifier output passes through the delay circuit 34 to the counter 27.33.
and these counters 27.33 are cleared,
One measurement is completed. Further, the output of the delay circuit 34 is added to the register 30 as a latch signal.

Counter 27 inputs its cumulative value to decoder 28 and addresses ROM 29 before being cleared. R.O.
M29 outputs temperature data corresponding to the address designation. This output temperature data is stored in the register 30.
7 and the temperature data is applied to the display 32 via the driver 31 and displayed.

Now, for example, assuming that one measurement is performed in one second, in the above embodiment, a pulse signal corresponding to the temperature due to the oscillation of the reference resistor 12 and the oscillation of the thermistor 11 is output four times. Signal output is performed every 0.125 seconds, and switching between oscillation by the reference resistor 12 and oscillation by the thermistor 11 is performed every 0.1.25 seconds. On the other hand, with the conventional method, the oscillation of the reference resistor and the oscillation of the thermistor are switched once in one measurement, and this switching is 0.
．． This will be done every 5 seconds. Therefore, for example, if the temperature suddenly rises by 4°C per second during measurement, in the conventional system, when the reference resistance oscillates, the thermistor oscillates at 0.
While a temperature difference of 2°C occurs in 5 seconds, in this example, the temperature difference is 0.1 between oscillation with the reference resistance and oscillation with the thermistor.
The temperature difference becomes 0.5° C. in 25 seconds, and the temperature difference between the oscillation at the reference resistor 12 and the thermistor 11 becomes small, and the error due to the temperature difference decreases accordingly.

Furthermore, the resolution and accuracy of the measured temperature largely depend on the measurement time, but in this example electronic thermometer, switching between the basic resistor and thermistor is done multiple times during one measurement. , since it does not shorten the measurement time,
There is no reduction in resolution or accuracy compared to conventional methods.

(F) Effects of the Invention According to this invention, the switching between the reference resistance and the temperature-sensitive resistor is divided into multiple times in one measurement, and each time the oscillation is caused by the reference resistance and the oscillation is caused by the temperature-sensitive resistance. Since the time difference between the two oscillations is made small, the temperature difference between the two oscillations is also small, and even if there is a sudden temperature change, it is possible to reduce errors caused by the influence.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of an electronic thermometer according to an embodiment of the present invention, FIG. 2 is a connection diagram showing a specific circuit example of the oscillation part of the electronic thermometer, and FIG. FIG. 3 is a diagram showing a terminal voltage waveform of a capacitor in an oscillation section. 1: Oscillation section, 2: Comparison section, 3: Control section, 4: Addition section, 5: Temperature data conversion section, 6: Display section, 11: Temperature sensitive resistor, 12: Reference resistor, 16: Oscillator.

Claims (1)

[Claims] (1) An oscillation section including an oscillator in which the resistance constituting the time constant circuit can be switched between a reference resistance and a temperature-sensitive resistor, and the oscillation frequency of each is compared according to the switching of the resistance of this oscillator, and the temperature a comparison means for outputting a corresponding pulse signal; a control means for causing the comparison operation of the comparison means to be performed a plurality of predetermined times by switching a resistance of the oscillator; and a pulse signal output from the comparison means for a plurality of times. an adding means for receiving and accumulating; receiving an output signal of the adding means;
An electronic thermometer comprising a temperature data converter that converts this output signal into temperature data, and a display means that displays the temperature data output from the temperature data converter.