JPH05264369A - Method and device for detecting temperature - Google Patents

Abstract

PURPOSE:To detect the temperature of an object by applying an AC voltage across a thermister, the resistance of which changes in accordance with its ambient temperature, and detecting a voltage change caused by the resistance change of the thermister. CONSTITUTION:A thermister RT, the resistance of which largely changes in accordance with the variation of its ambient temperature, is connected between the common contacts of change-over switches 1 and 2. The switches 1 and 2 are respectively connected to their (+) and (-) side contacts by means of output Q1 and Q2 from a transmitter 4 and an electric current flows in the direction shown by the solid line from a DC power source E through the (+) side contact of the switch 1, thermister RT, an< (-) side contact of the switch 2. When the outputs Q1 and Q2 of the transmitter change, the connecting directions of the switches 1 and 2 change and the electric current flows in the direction shown by the broken line. Then the output of an A/D converter 3 is inputted to a voltage-temperature conversion circuit 5 and the circuit 5 outputs the output after converting the output into temperature data. Therefore, the flowing direction of the electric current flowing through the thermister RT is changed and migration caused by the generation and reduction of metallic ions in an electrode section can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting device for detecting an ambient environmental temperature used in an air conditioner or the like.

[0002]

2. Description of the Related Art As a conventional temperature detecting device, as shown in FIG. 9, a fixed resistance RL and a thermistor RT are connected in series to a DC power source E, and a voltage is output from an intermediate connection point between the fixed resistance RL and the thermistor RT. The output voltage is measured and the
It is generally used to detect the temperature based on the relationship between the resistance value of the thermistor RT measured by the characteristics of the mister RT and the ambient environmental temperature.

Further, in such a temperature detecting thermistor RT, as shown in FIGS. 10 and 11, electrodes 51 made of a highly conductive material such as silver are provided on both end surfaces of a thin columnar semiconductor 50. The wiring 51 is soldered 53 to the electrode 51. Then, from the semiconductor 50 to the wiring 52
The resin coating 55 is applied to the entire element from the covered portion 54.

[0004]

However, a voltage is constantly applied in one direction to the electrode 51 portion of such a thermistor RT, and when moisture is present in this portion,
The positive electrode metal, such as silver, is ionized and begins to melt,
Metal ions move from the + side electrode to the-side electrode,
At the side electrode, reduction occurs and a gradually growing migration occurs.

When this migration grows, both electrodes 51, 51 begin to conduct, and in the initial state, the thermistor R
The resistance value of T becomes unstable, and finally both electrodes 5
There has been a problem that short circuits 1 and 51 cause a failure.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems, to suppress the generation of migration in the electrodes of the thermistor, and to provide a highly reliable temperature detecting device.

[0007]

In order to solve the above-mentioned object, in the invention of claim 1, an alternating current is applied to a thermistor whose resistance value changes according to the ambient environment temperature, and the resistance change of the thermistor. The temperature is detected by detecting the voltage change based on

According to the second aspect of the present invention, the DC power source, the thermistor whose resistance value changes according to the ambient environment temperature, and one end of the thermistor are connected to one end of the thermistor, and the thermistor is connected in the first period.
First means for connecting one end of the mister to one end of the direct current power supply and connecting one end of the thermistor to the other end of the direct current power supply in the second period, and one end to which the other end of the thermistor is connected. Second means for connecting the other end of the thermistor to the other end of the DC power supply during the second period, and connecting the other end of the thermistor to one end for the DC power supply during the second period, the first period and the second period. The control means for alternately generating the periods of approximately the same time length is provided.

Further, according to the invention of claim 3, the output pulse of the pulse generator comprises a pair of switching elements connected in series to the DC power source and connected in series so that when one of the switching elements is on, the other is off. A first switch circuit that is on / off controlled in synchronism with the above, and a pair of series-connected switching elements that are connected in parallel to the first switch circuit. When one of the switching elements is on, the other is off, Also, between the corresponding switching elements of the first switch circuit, a second switching circuit that is on / off controlled so that when one is on, the other is off, and an intermediate between each of the first and second switch circuits A thermistor connected between the connection points, the resistance value of which changes according to the ambient temperature, is provided.

[0010]

In such a structure, since an alternating current is applied to the thermistor whose resistance value changes according to the ambient environment temperature, the metal ions generated in the other electrode reach one electrode,
It is no longer reduced at one electrode,
The occurrence of an option is prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a temperature detecting device according to an embodiment of the present invention. In this device, the + terminal of the DC power source E is connected to one end of a fixed resistor RL whose resistance value hardly changes with temperature change, and the other end of the fixed resistor RL has an input voltage value corresponding to that value as a digital value. A / to convert to data
It is connected to the D converter 3. The other end of the fixed resistor RL is further connected to one of the + side contacts of the first changeover switch 1 and one of the + side contacts of the second changeover switch 2. A common contact of both the changeover switches 1 and 2 is connected in the middle with a thermistor RT whose resistance value greatly changes according to the change of ambient temperature. The negative contacts of the first and second changeover switches 1 and 2 are both connected to the negative terminal of the DC power source E.

The oscillator 4 outputs the switching outputs Q1 and Q2 of the contacts of the first and second changeover switches 1 and 2. These switching outputs Q1 and Q2 are transmission outputs with an on / off ratio of about 1,
, Q2 outputs are interlocked and logically contradictory. Therefore, when the output Q1 is logic "H", the output Q2 is logic "L", the common contact of the first changeover switch 1 is connected to the + side contact, and the common contact of the second changeover switch 2 is-side. Connected to the contacts. Conversely, when the output Q1 is logic "L", the output Q2 is logic "H", the common contact of the first changeover switch 1 is connected to the-side contact, and the common contact of the second changeover switch 2 is + side. Connected to the contacts.

The output of the A / D converter 3 is voltage /
The voltage / temperature conversion circuit 5 is input to the temperature conversion circuit 5, and has voltage / temperature conversion data based on the relationship between the voltage change caused by the resistance value of the thermistor RT and the ambient temperature of the thermistor RT. Then, the input output of the A / D converter 3 is converted into temperature data and output.

The operation of this embodiment will be described below. When the common contact of the first changeover switch 1 is connected to the + side contact and the common contact of the second changeover switch 2 is connected to the-side contact by the outputs Q1 and Q2 of the oscillator 4, the resistance RL from the DC power source E. , The + side contact of the first changeover switch 1, the common contact of the first changeover switch 1, the thermistor RT, the common contact of the second changeover switch 2 and the + side contact of the second changeover switch 2 in series A current flows in the direction of the solid line in FIG. When the outputs Q1 and Q2 of the oscillator 4 change, the connection directions of the first and second changeover switches 1 and 2 change, and the common contact of the first changeover switch 1 is connected to the-side contact, The common contact of the changeover switch 2 of 2 is connected to the + side contact. At this time, from the DC power source E to the resistor RL, the + side contact of the second changeover switch 2, the common contact of the second changeover switch 2, and the contact.
A current flows in the direction of the broken line in FIG. 1 through the mister RT, the common contact of the first changeover switch 1 and the + side contact of the first changeover switch 1 in series.

Thus, each time the output of the oscillator 4 changes, the first and second changeover switches 1 and 2 are changed over, and the direction of the current flowing through the thermistor RT is changed. In short, a rectangular wave AC is applied to the thermistor RT.
Since the outputs Q1 and Q2 of the oscillator 4 operate at an on / off ratio of about 1, the current direction is changed at about the same time. As a result, even if a metal ion is generated at the electrode of the thermistor RT due to the participation of water, the metal ion does not reach the other electrode and the metal ion is not reduced at the electrode portion, resulting in migration. Can be prevented. Next, a second embodiment of the present invention will be described based on FIG.

In this second embodiment, an AC voltage is applied to the thermistor RT by an electronic circuit. First, the output of the rectangular wave generator 11 composed of a multivibrator or the like is connected to the output of the preceding stage inverter. A rear 12 and a rear inverter 13. The front-stage inverter 12 constitutes the first switch circuit according to the present invention, and similarly, the rear-stage inverter 13 is the second switch circuit.
The switch circuit of.

The rectangular wave generator 11 is, as shown in FIG.
A rectangular wave pulse train having an ON time T1 and an OFF time T2 that are substantially equal to each other is output. The inverters 12 and 13 are composed of CMOS FETs 21, 22 to 31, 32, respectively, as shown in FIG. Between the output point and the input point of the inverter 13, a series circuit of a thermistor RT and a fixed resistance RL whose resistance value changes according to the ambient environment temperature is formed.

A temperature detection signal (voltage) is taken out from the connection point between the thermistor RT and the resistor RL. Then, as shown in FIG. 1, the temperature detection signal is guided to the negative input terminal of the comparator 16, and the positive input terminal of the comparator 16 is an intermediate portion of the temperature setter 17 including the fixed resistor 18 and the variable resistor 19. It is connected to the set output point defined in the connection point. The temperature setter 17 is connected between the 0 volt terminal O and the power supply terminal VDD terminal. The output of the comparator 16 controls the compressor of the air conditioner via a one-shot multivibrator 40 having an on-time slightly longer than the on-time or off-time of the output pulse of the rectangular wave generator 11. ..

In the circuits of FIGS. 2 and 4, when the output of the rectangular wave generator 11 is "1", the FET 21 is off and the FET 21 is off.
22 is turned on, FET 31 is turned on, and FET 32 is turned off. At this time, a current flows from the FET 31 through the thermistor RT and the resistor RL to the FET 22, and the resistor RL
The output voltage VOH obtained as the voltage across both ends of the thermistor R
Resistance value of T is R4, resistance value of resistance RL is R5, power supply VDD
Assuming that the voltage of VDD is VDD, VOH = VDD × R5 / (R4 + R5).

When the output of the rectangular wave generator 11 is "0", the FET 21 is turned on, the FET 22 is turned off, the FET 31 is turned off, and the FET 32 is turned on contrary to the above, and the resistor RL and the resistor are turned on from the FET 21. A current flows to the FET 32 through the mister RT, and the output voltage V at this time
The OL becomes VOL = VDD × R4 / (R4 + R5).

The output voltage VOH or VOL thus obtained is input to the negative input terminal of the comparator 16,
Assuming that the voltage Vs corresponding to the set temperature from the temperature setter 17 that is input to the positive input terminal, that is, the resistance value R18 of the fixed resistor 18 and the resistance value R19 of the variable resistor 19, is Vs = VDD × R9 / ( R8 + R9) (see FIG. 5). The comparator 6 outputs "H" level when VOH or VOL is larger than VS, and outputs "L" level otherwise (see FIG. 6).

When the temperature is high, the resistance value R4 of the thermistor RT
Becomes smaller, the value of VOL becomes smaller, and the value of VOH becomes larger. At this time, VOH> VS and VOL> VS, and the output of the comparator 16 is always at "L" level, and the operation of the compressor of the air conditioner is continued.

When the temperature decreases due to the cooling operation,
The resistance value R4 of the mister RT increases, the value of VOL increases and the value of VOH decreases. At this time, VOL> VS and VOH <VS, and the output of the comparator 16 repeats "H" level and "L" level as illustrated in FIGS. However, the operation of the one-shot multivibrator 40 outputs a continuous "H" level signal, and the operation of the compressor is stopped. In addition,
By properly adjusting the variable resistor 19 of the temperature setting device 17, the voltage VS can be changed to change the temperature setting value.

As described above, also in the second embodiment, the rectangular wave alternating current is applied to the thermistor RT, and as shown in FIG. Since it flows, migration can be prevented from occurring. Further, in this second embodiment, FETs 21, 22, 3
Since the semiconductor device for direct current such as 1, 32 can be used, the cost can be reduced.

Further, a third embodiment is shown in FIG. In this embodiment, the internal logic circuits 12a and 13a of the output terminal of the micro computer 50 are used, the output terminals are alternately turned on and off, and the output of the thermistor RT is supplied to the internal A / A of the micro computer 50. It is configured to be input to the D conversion input 5a. In this circuit, the external circuit other than the microcomputer 50 has only the resistor RL and the thermistor RT, and the circuit configuration is extremely simple, so that a highly practical temperature detecting device can be obtained.

[0027]

According to the present invention, by applying an alternating current to the temperature detecting thermistor, the direction of the current flowing through the thermistor is changed, and even if metal ions are generated at the electrodes of the thermistor, The metal ion does not reach the other electrode, and the metal ion is not reduced at the electrode part.
It is possible to obtain a highly reliable temperature detection method and temperature detection device that can prevent the occurrence of thermal distortion.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a temperature detection device according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a temperature detecting device according to a second embodiment of the present invention.

FIG. 3 is an operation waveform chart for explaining the operation of the temperature detection device in the embodiment.

FIG. 4 is a circuit diagram showing in detail a part of the temperature detecting device according to the embodiment.

FIG. 5 is an operation waveform chart for explaining the operation of the temperature detection device in the embodiment.

FIG. 6 is an operation waveform diagram for explaining the operation of the temperature detection device in the embodiment.

FIG. 7 is an operation waveform diagram for explaining the operation of the temperature detecting device in the embodiment.

FIG. 8 is a circuit block diagram of a temperature detecting device according to a third embodiment of the present invention.

FIG. 9 is a circuit diagram showing a conventional temperature detecting device.

FIG. 10 is a perspective view showing the configuration of a general thermistor.

FIG. 11 is a sectional view of the thermistor.

[Explanation of symbols]

E ... DC power supply, RT ... Thermistor, 1 ... First changeover switch, 2 ... Second changeover switch, 3 ... A / D converter
, 4 ... Oscillator, 5 ... Voltage / temperature conversion circuit, 12 ... Pre-stage inverter, 13 ... Post-stage inverter, 21, 22, 3
1,32 ... FET

Claims (3)

[Claims] 1. A temperature detecting method for detecting a temperature by applying an alternating current to a thermistor whose resistance value changes according to an ambient environment temperature and detecting a voltage change based on a resistance change of the thermistor. 2. A direct current power source, a thermistor whose resistance value changes according to the ambient environment temperature, one end of the thermistor is connected to one end, and one end of the thermistor is connected to the one end in a first period. First means for connecting to one end of a DC power supply and connecting one end of the thermistor to the other end of the DC power supply in a second period; and one end to which the other end of the thermistor is connected, Second means for connecting the other end of the thermistor to the other end of the DC power supply during the second period, and connecting the other end of the thermistor to one end for the DC power supply during the second period. A temperature detecting device, comprising: a control means for alternately generating the first period and the second period at substantially the same time length. 3. A pair of switching elements connected in series to a DC power source, the ON / OFF control being synchronized with an output pulse of the pulse generator so that when one of the switching elements is ON, the other is OFF. And a pair of series-connected switching elements connected in parallel to the first switch circuit, wherein one of the switching elements is turned on while the other is turned off, and the first switch circuit is provided. Between the switching elements corresponding to each other, between the second switching circuit which is on / off controlled so that when one is on, the other is off, and each intermediate connection point of the first and second switch circuits. A temperature detecting device, comprising: a thermistor whose resistance value changes in accordance with the connected ambient temperature.