JP2000241258A - Temperature measuring device and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost and high-precision measuring device in a temperature measuring device using a three-wire resistance temperature sensor. SOLUTION: A plurality of reference resistors 31, 32, 33 and 34 are prepared, and in addition to wires 3a and 3b of a resistance temperature sensor 1, these reference resistors are connected to a constant current power supply 14 in order. The temperature is determined by measuring the generated voltages and comparing these voltages. The temperature can be measured with one constant current power supply, and the draft of the constant current power supply can be canceled by comparing the temperature with the voltage generated in the reference resistor. Therefore, since accuracy and stability are not so required except for the resistor, a highly accurate temperature measuring device 10 can be provided using an inexpensive circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature measuring device and a measuring method for measuring a temperature using a three-wire type resistance temperature detector.

[0002]

2. Description of the Related Art Since the electrical resistance of a metal changes in proportion to the temperature, the temperature can be determined by measuring the resistance. A platinum resistor which has appropriate conditions as a resistor for temperature measurement is a platinum resistor, which is also specified and standardized in JIS. This sensor has a large change in resistance value, and when viewed as a voltage change, the change is about one digit larger than that of a thermocouple.
It has high stability, long-term stability of 0.1 ° C. or more, and high measurement accuracy. There is also an advantage that the temperature can be immediately determined from the reading of the resistance value. On the other hand, as compared with a thermistor which is a general temperature sensor, the resistance value of the resistance temperature detector and the resistance change due to the temperature are small. Therefore, the temperature measuring resistor cannot be handled by a simple circuit such as simply measuring a resistance value and performing A / D conversion on the resistance value, or connecting the resistance value to an oscillation circuit to convert the temperature.

FIG. 7 shows an example of a conventional temperature measuring device using a resistance temperature detector. The three-wire type resistance temperature sensor 1 is configured such that a platinum resistance element as a resistance temperature element 2 is connected by a cable 3. The cable 3 is a resistance thermometer 2
A first wiring 3a and a second wiring 3b for connecting both ends of the wiring to a measuring device to measure the resistance value, and a ground wiring 3c used for canceling the wiring resistance. Wiring 3c is connected in parallel with the second wiring 3b. The conventional measuring device 90 prepares two constant current power supplies 91a and 91b, and connects them to the first and second wirings 3a and 3b, respectively.
Then, a voltage difference Vt generated between the first and second wirings 3a and 3b is obtained by a differential amplifier 92, and is converted into digital data using an A / D conversion function 93. Under this condition, the first, second and third wiring resistances R1, R2 and R3 are equal and the output current I
If 1 and I2 are equal, the wiring resistances (R1 + R3) and (R2 + R3) are cancelled, and the following voltage difference Vt is obtained.

Vt = I1 × Rt (1) Here, Rt is a resistance value of the resistance bulb.

Therefore, if the output current I1 of the two constant current power supplies 91 is known, the resistance value Rt of the resistance temperature detector 2 can be immediately known, and the resistance value Rt is converted by the conversion function 97 of the processor 95 to be displayed on the LCD 12 by the temperature conversion. can do.

[0006]

However, such a temperature measuring device requires two constant current power supply devices or constant current circuits, and consumes a large amount of power. further,
It is necessary that the same current flows from each constant current power supply to each wiring, and that the output current must be stable. As shown in FIG. 8, the characteristic that the output current fluctuates due to the load resistance generally appears in the constant current circuit. Therefore, if the resistance value of the RTD changes with the temperature, the current value also fluctuates minutely, which causes a measurement error. It may be. Therefore, in order to accurately measure the temperature with the measuring device shown in FIG. 7, a constant current power supply circuit with high accuracy and high stability is required, and the cost of the measuring device increases.

Further, as shown in FIG. 9, the A / D conversion circuit also has a conversion characteristic, and is not converted into a digital value that is linear with respect to the measured voltage in all regions. For this reason, the processor 95 is provided with a linear correction function 96 as shown in FIG. 7, but in order to increase the measurement accuracy, a differential amplifier and an A / D conversion circuit also need to have high accuracy and stability. . Therefore, also in this respect, the cost of the measuring device increases.

Further, as shown in FIG. 10, the resistance value Rt of the resistance bulb changes almost in proportion to the temperature, but is not completely linear and has some tolerance. Therefore, in order to accurately determine the temperature, correction using a look-up table or the like is necessary.

As described above, the conventional temperature measuring device using a resistance temperature detector has high versatility because the resistance temperature detector is standardized, and can cover a wide temperature range. Measuring devices with high measurement accuracy were large and expensive.

In view of the above, an object of the present invention is to provide a temperature measuring device using a resistance temperature detector, which is compact, has high measuring accuracy, and can be supplied at low cost. I have. It is another object of the present invention to provide a measuring device that is compact in size, can be easily moved and installed, and can measure even a battery for a long time.

[0011]

For this reason, in the present invention, a plurality of reference resistors are prepared, and these reference resistors are defined along with the first and second wirings connected to the temperature measuring resistor. The temperature is obtained by comparing the voltage generated by the reference resistor and the voltage generated by the resistance temperature detector by connecting to a current power supply. That is, the first and second wirings connected to both ends of the resistance temperature detector of the present invention;
A temperature measuring device capable of measuring a temperature by connecting a three-wire type resistance temperature sensor provided with a third wiring for grounding connected in parallel to the second wiring comprises: a constant current power supply; A plurality of reference resistors each having a resistance value in or near a range in which the resistance value of the temperature measuring resistor changes depending on the temperature; and a constant current power supply in order of each of the first and second wirings and the plurality of reference resistors. And voltage measuring means for measuring the voltage generated at each of them, and means for comparing the voltage generated by the resistance temperature detector and the voltage generated by the plurality of reference resistors by linear interpolation or the like to convert the voltage into a temperature. Also, a three-wire system including first and second wires connected to both ends of the resistance temperature detector of the present invention, and a third wire for grounding connected in parallel to the second wire. A method of measuring a temperature using a resistance temperature sensor includes a plurality of reference resistances having a resistance value in a range in which the resistance value of the resistance temperature element changes with temperature or in the vicinity thereof in addition to the first and second wirings. Connect each of the bodies in turn to a constant current power supply, measure the voltage generated at each, and compare the voltage generated by the resistance temperature detector and the voltage generated by the plurality of reference resistors, and convert to temperature And

By sequentially connecting a constant current power supply to the first and second wirings connected to the resistance temperature detector, a voltage difference generated in the resistance temperature detector can be measured with one constant current power supply. . Further, a plurality of reference resistors are prepared in a range where the resistance value of the temperature measuring resistor changes with temperature or in the vicinity thereof, and they are sequentially connected to the same constant current power supply, and the voltage generated in them is measured. Thus, the voltage corresponding to the resistance value that the resistance thermometer will show can be known by a method such as linear interpolation. Therefore, by comparing the voltage generated in the reference resistor with the voltage difference generated in the resistance bulb, the environment to be measured by the resistance bulb can be measured without knowing the current supplied from the constant current power supply. Alternatively, the temperature of an object or the like can be known. Therefore, if the resistance value of the reference resistor is stable with high accuracy, even if the output current of the constant current power supply drifts due to various causes, the influence can be canceled. Therefore, accurate temperature measurement is possible even with a constant current power supply that is not so high in accuracy and stability.

In particular, since the temperature can be determined by the voltage generated in the reference resistor having a resistance value close to the resistance value indicated by the temperature measuring resistor, sufficient accuracy can be obtained even with a constant current power supply in which the current characteristics drift due to the load resistance. High temperatures are obtained. Further, even if the A / D conversion characteristic with respect to the voltage is not linear over the entire voltage range, when measuring the voltage of the reference resistor,
The D conversion characteristics are reflected. Therefore, even without performing the linear correction processing of the A / D converter, it is possible to obtain a highly accurate temperature by comparing the voltage generated at the temperature measuring resistor with the voltage generated at the reference resistor. Furthermore, reflect the temperature tolerance of platinum in the temperature indicated by the voltage generated in the reference resistor, or reflect the temperature tolerance of platinum when linearly interpolating them and comparing with the voltage generated in the resistance thermometer. It is also possible to measure the temperature with higher accuracy.

A measuring apparatus and a measuring method for individually connecting a first and a second wiring connected to a resistance temperature detector and a reference resistance to a constant current power supply and measuring a voltage generated at each of them are described below. Even if the number of pairs (sets or channels) of the first and second wirings is increased, the circuit is not so complicated, and there is no need to increase the constant current power supply and the reference resistor. Therefore, even if the number of channels is increased, the power consumption does not increase so much, and the circuit configuration can be simplified. Therefore, it is possible to provide a measuring device that easily connects to a large number of resistance temperature sensors and measures a plurality of temperatures by using multiple channels at the same time.

When measuring the voltage of the second wiring, it is difficult to measure the voltage because the wiring resistance of the second wiring connected to the grounded third wiring is very small. For this reason, by connecting a grounding resistor having an appropriate resistance value to the third wiring, it is possible to more accurately and easily measure the voltage generated in the resistance temperature detector.

On the other hand, a plurality of reference resistors are connected in series to the second wiring, respectively, and the resistance thermometer and the first and third resistances are connected.
It is also possible to obtain a temperature by comparing a voltage generated by the resistance value including the wiring of the reference resistor with a voltage generated by the resistance value including the reference resistor and the second and third wirings. In this method, a large number of reference resistors are required when multi-channeling is performed, but a voltage based only on the wiring resistance is not measured. Therefore, highly accurate measurement can be performed without providing a ground resistance.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below with reference to the drawings. FIG. 1 shows an outline of a temperature measuring device according to the present invention and a system for acquiring data using the temperature measuring device. FIG. 7 shows a temperature measuring apparatus 10 according to this embodiment.
Is a measuring device to which the three-wire type resistance temperature sensor 1 shown in FIG. 1 is connected to measure the temperature of the measurement object such as the environment or the object where the resistance temperature detector 2 is located. Then, the measured temperature is temporarily stored in the measuring device, transmitted to the personal computer 6 via the communication cable 5 at an appropriate timing, and can be analyzed. As described above, by using the measuring apparatus 10 of the present embodiment, it is possible to construct a temperature data logger system capable of performing processing such as displaying and analyzing measured temperature data on a personal computer.

The measuring device 10 of the present embodiment is provided with two connectors 11 to which the resistance temperature sensor 1 can be connected. The data obtained from each of the sensors 1 is also used independently in the measurement and recording functions described later. Can be processed. Therefore, the temperature measurement device 10 of this example can measure and record two channels with one device, and can measure, monitor, or record the temperature of different measurement objects with one device.

In the measuring apparatus 10 of this embodiment, an LCD panel 12 for monitoring measurement data, measurement conditions and the like is provided at the center. It also has a built-in battery, and the entire device is handy. For this reason, it is also possible for the user to carry the vehicle for patrol inspection and the like to monitor the temperature at an appropriate place. Then, the measured data can be collectively transferred to a personal computer via a communication cable or the like, and the data can be analyzed. On the other hand, it is also possible to set the sensor 1 at a predetermined place and monitor the temperature over a long period of time. Can also. Also, instead of a communication cable,
It is of course possible to transmit the measurement data by other transmission means such as a telephone line or wireless.

FIG. 2 is a block diagram showing a schematic function of the temperature measuring device 1 of the present embodiment. The measuring device 1 of the present example
Two connectors 1 for connecting the resistance temperature sensor 1
1 and the wires (first and second wires 3a and 3b) of the resistance temperature sensor 1 connected to these connectors 11.
Are sequentially connected to the constant current power supply 14 and a voltage measuring unit 20 for measuring a voltage generated in each of the power supplies is provided. further,
The measuring device 1 of the present example has four reference resistors 31, 32, 3
3 and 34, and the voltage measuring unit 20 includes the sensor 1
, And these reference resistors 31, 32, 33
And 34 are also connected to the constant current power supply 14 in order to measure the voltage generated thereby.

Further, the measuring device 10 includes a voltage measuring unit 20.
Function 5 that compares the voltage measured by the method and converts it into temperature
And a control unit 50 for storing the calculated temperature.
A communication unit 56 that communicates with the AM 55 and a host device such as a personal computer and that can transmit data stored in the RAM 55 is provided. The converted temperature and the like can be further displayed on the monitor 12 from the control unit 50. Further, in each connector 11, a ground line (third wiring) 3c of the sensor 1 is connected to a ground circuit 60, and a ground resistor 61 having an appropriate resistance value is connected to the ground line 3c. Connected in series.

The voltage measuring section 20 of this embodiment will be described in more detail. The voltage measurement unit 20 includes first and second wires 3a, 3a, 3a, and 3b of each of the sensors 1 and 1 'connected to the connector 11.
b, 3a 'and 3b' and reference resistors 31, 3
2, 33, and 34 in order, respectively.
4 and a voltage V1, which is generated on each of the wirings 3a, 3b, 3a 'and 3b',
V2, V3 and V4, and the respective reference resistors 31, 3
, Vc2, Vc2, Vc1
a second switch 22 for measuring c3 and Vc4 in sequence
And The first and second switches 21 and 22 are synchronously controlled by the control unit 50, and when the first wiring 3 a is connected to the constant current power supply 14 by the first switch 21, the second switch 22 The switch connected to the wiring 3a is closed so that the voltage generated on the first wiring 3a can be measured. The voltage can be similarly measured for other wirings and reference resistors.

Each of the voltages sampled in order by the second switch 22 in this way is guided to an A / D converter 24 through an amplifier 23 and converted into digital data. Then, the digitized voltage value is sent to the control unit 50 realized by a processor such as a CPU, and can be converted into a temperature by comparing the voltage value generated by each wiring and the reference resistor.

FIG. 3 is a flowchart showing a processing procedure in the measuring apparatus 10 of this embodiment. Hereinafter, further description will be made with reference to this flowchart. First, after a predetermined sampling interval has elapsed in step 71, the measuring apparatus 10 of the present example switches the first and second switches 21 and 22 of the voltage measuring unit 20 in order in step 72, and in step 73 Measure the value. When all the voltage values V1 to V4 and Vc1 to Vc4 are obtained in step 74, in step 75, the temperature conversion function 51 performs a process of converting the measured voltages into temperatures.

In the measuring device 10 of the present embodiment, each of the reference resistors 31, 3 housed as the reference resistor group 30.
Of the resistance values Rc1, Rc2, Rc3 and Rc4 of 2, 33 and 34, the resistance values Rc2, Rc3 and Rc4
Is selected in a range where the resistance value Rt of the platinum resistance thermometer 2 will vary depending on the temperature to be measured normally. For example, as shown in FIG. 4, the respective resistance values are set to the resistance values shown when the platinum temperature measuring resistor 2 is at 100 ° C., 300 ° C., and 500 ° C. On the other hand, the resistance value Rc1 is set to 0Ω in order to cancel the offset of the amplifier 23 using the ground resistance 61.

Therefore, the voltages Vc1, Vc2, Vc3 obtained by connecting the respective resistors to the constant current power supply 14 are obtained.
By subtracting the voltage Vc1 from Vc4 and Vc4, 0V
And the resistance values Rc2, Rc of the reference resistors 32, 33 and 34
The voltages Vc2 ′, Vc3 ′ and Vc4 ′ can be obtained from c3 and Rc4. For this reason, as shown in FIG. 5, the voltages Vc2 ′, Vc3 ′ and Vc4 ′ obtained by connecting the respective resistors to the constant current power supply 14 indicate that the temperature-measuring resistor 2 has 100 ° C., 300 ° C. and 500 ° C. It is a voltage generated when connected to the constant current power supply 14 in a state of being set in an environment of ° C. Further, the voltage 0V can be virtually used as a value when the temperature measuring resistor 2 is 0V, for example, -273 ° C.

As described above, the reference resistance 31 is set to 0Ω and the ground resistance 6 common to the reference resistances 32, 33 and 34 is set.
By measuring the voltage of 1, the voltage fluctuation due to the offset of the amplifier 23 can be eliminated. Therefore, a highly accurate temperature can be measured without being affected by the environmental conditions such as the accuracy of the amplifier and the ambient temperature.

On the other hand, in the sensor, a voltage difference Vr1 obtained by subtracting the voltage V2 of the wiring 3b from the voltage V1 of the wiring 3a of the sensor 1 is the voltage generated by the resistance temperature detector 2. Accordingly, of the voltages Vc2 ′, Vc3 ′ and Vc4 ′ generated by the resistors, the voltages Vc2 ′ and Vc2 ′ of the reference resistors (the resistors 32 and 33 in the example of FIG. 5) indicating the voltages before and after the voltage difference Vr1 are shown. By selecting Vc3 ', performing linear interpolation, and comparing, the temperature T1 of the measurement target of the resistance temperature detector 2 can be obtained from the voltage difference Vr1.

The temperature T2 of the measuring object of the temperature measuring resistor 2 'of the other sensor 1' can be obtained in the same manner, and the voltage difference Vr2 between the voltages V3 and V4 is determined by the voltage indicated by the reference resistors before and after the temperature. Vc1 ', that is, 0V, and the voltage Vc2'
By comparing with, the temperature T2 can be obtained.
Of course, the setting of each resistance value of the reference resistance group 30 can be appropriately selected. By selecting the resistance value of the reference resistor so that the voltage generated by the resistance temperature detector 2 is close to or between the voltage generated by the reference resistor, more accurate temperature measurement can be performed.

The temperature thus obtained is recorded in the RAM 55 for each channel in step 76. In the measuring apparatus 10 of the present embodiment, temperatures measured at sampling intervals set in advance for each channel are recorded in order. Then, at a preset timing or a request from the host side,
The data in the RAM 55 is transmitted to the personal computer 4 as a host via the communication cable 3. The measuring device 10 of the present embodiment sequentially stores the converted temperature measurement values in the RAM 5.
5, and the measurement time is not recorded. Of course, the measurement time may be recorded, but the temperature is measured at each preset sampling time interval and the value is stored, so that the analysis can be performed by a personal computer or the like without recording the measurement time. It is possible to individually determine the measurement time when performing the measurement. Therefore, by recording only the measured temperature data, the capacity of the RAM 55 is sufficiently utilized, and a long-time temperature measurement can be performed.

Although the measuring apparatus 10 of this embodiment has a sufficient memory capacity for normal measurement, the memory capacity may be insufficient depending on the measurement situation. Therefore, the measuring device 1
0 has two measurement modes, two one-time and endless. In the one-time mode, when the memory capacity becomes full, recording of the measured temperature is stopped at that time and the contents of the memory are held. On the other hand, in the endless mode, when the memory capacity becomes full, recording is performed while overwriting the measured temperature by returning to the beginning of the memory address. The user can select which mode to measure.

As described above, the temperature measuring device 10 of the present embodiment
The constant current power supply 14 is connected to the first and second wirings 3 a and 3 b connected to the resistance temperature detector 2 and the reference resistances 31, 32, 33 and 34 by the switch 21 of the voltage measurement unit 20.
Are connected in order. Therefore, the voltage difference generated in the resistance bulb 2 can be measured by one constant current power supply 14, so that the power consumption during the measurement can be reduced.

Further, a constant current, at which the constant current power supply 14 is stable, can be applied to the temperature measuring resistor 2 and each of the reference resistors 31, 32, 33 and 34.
The temperature of the measurement target of the resistance temperature detector 2 is obtained by comparing the voltages generated in the resistance temperature detector 2 and the reference resistances 31, 32, 33 and 34. Therefore, it is not necessary to know the current value itself flowing from the constant current power supply 14 to the temperature measuring resistor 2 and each reference resistor. Further, the constant current power supply 14
The current supplied from is sampled during each voltage
That is, it is only necessary that the operation be stable while the switch is being changed. Therefore, even if the current value itself fluctuates at a time interval longer than the sampling period, it does not affect the accuracy of the measured temperature. For this reason, in the temperature measuring device 10 of this example, the temperature can be measured with a simple measuring circuit, and further,
A constant current power supply circuit does not require much accuracy and stability. Therefore, highly accurate temperature measurement can be performed with a constant current power supply having a simple configuration using an operational amplifier and a resistor.

As shown in FIG. 8, even if a constant current power supply has a characteristic in which a current value that can be supplied by a load such as a connected resistor fluctuates slightly, the reference resistors 31 and 3
2, Vc1 obtained by connecting 2, 33 and 34,
The characteristics are reflected on Vc2, Vc3 and Vc4.
For this reason, even if the current supplied from the constant current power supply 14 slightly changes according to the resistance value indicated by the resistance temperature detector 2, the current is generated by the reference resistor having a resistance value close to the resistance value indicated by the resistance temperature detector 2. By comparing with the voltage, the load characteristic of the constant current power supply 14 is canceled. Therefore, even if a constant current power supply having the characteristics shown in FIG. 8 is adopted, the temperature can be measured with high accuracy.

As shown in FIG. 9, some A / D converters 24 exhibit non-linear characteristics when converting an input voltage value into a digital value. However, in the measuring device 10 of the present embodiment, the reference resistors 31, 32, 33
When measuring the voltages generated at the steps 34 and 34, a voltage value including such A / D characteristics is obtained as a digital value. Therefore, in the temperature conversion function 51, A /
By comparing the D-converted voltage value of the resistance temperature detector 2 with the A / D-converted voltage values of the reference resistors 31, 32, 33, and 34, the A / D conversion characteristics are also canceled. You. Further, the offset of the amplifier 23 can be canceled by setting the resistance Rc1 to 0Ω and measuring the voltage of the ground resistance 61 as described above. Therefore, the A / D converter 24 and the amplifier 23 associated therewith are not so high in accuracy and stability, and a highly accurate temperature can be obtained.

As described above, in the temperature measuring device 10 of the present embodiment, the reference resistor group 30 needs to have a high resistance value, but other constant current power supplies, amplifiers, and A / A
The D converter does not require much accuracy and stability.
On the other hand, since the current drift of the constant current power supply and the non-linear characteristics of the A / D converter are all canceled, a highly accurate temperature can be obtained. Therefore, it is possible to provide a highly reliable temperature measuring device that is low in cost, has high measurement accuracy, and is not affected by environmental temperature and the like.

Further, as shown in FIG. 10, the relationship between the temperature and the resistance value of the platinum resistance temperature detector 2 is almost proportional but not perfect. In this example, the voltage values Vc2 ′, Vc3 ′ and Vc obtained by the reference resistors 31, 32, 33 and 34
By including the tolerance of the platinum resistance temperature detector in the temperature setting corresponding to 4 ', the temperature can be converted to a more accurate temperature and recorded or displayed. Also, when interpolating between the voltage values Vc2 ', Vc3' and Vc4 'obtained by the reference resistor, interpolation should be performed using a function or a look-up table taking into account the tolerance of the platinum resistance thermometer instead of performing linear interpolation. It is possible to obtain a more accurate temperature.

In this embodiment, the ground resistance 61 is connected to the third wiring 3c of the resistance temperature sensor 1. Therefore, when the voltage V2 is measured by connecting the second wiring 3b to the constant current power supply 14, the voltage due to the ground resistance 61 can be measured in addition to the wiring resistance. When there is no ground resistance 61, only the wiring resistance is required, so that a voltage close to 0V needs to be measured. For this reason, it is required that the amplifier 23 and the A / D converter 24 have a wide operating range and are stable. Further, even when a high-precision amplifier and A / D converter are employed, it is difficult to improve the measurement accuracy near 0 V. On the other hand, since the voltage near 0 V does not need to be measured by connecting the ground resistor 61, the amplifier 23 and the A / D converter 24 do not have a very wide measurement range and a low-precision one is sufficient. Therefore, also in this respect, the cost of the measuring device 10 can be reduced. Further, even when an A / D converter with low accuracy is employed, the measurement accuracy of the voltage can be increased because there is no measurement near 0 V, and as a result, a highly accurate temperature can be obtained.

The temperature measuring device 19 shown in FIG. 6 is a different example of the temperature measuring device according to the present invention. The temperature measuring device 19 of the present example is a measuring device provided with one connector 11, in which the three-wire type resistance temperature sensor 1 is attached as a single unit so that the temperature of one channel can be measured. It is. In the temperature measuring device 19 of the present example, each of the reference resistors 31, 32, 33 and 3 of the reference resistor group 30 is used.
4 are connected in series to the second wiring 3b of the sensor 1, respectively. Then, the first switch 21 and the second switch 22 of the voltage measuring unit 20 are sequentially and synchronously switched so that the voltage of the first wiring 3a of the sensor 1 and the second wiring 3b are connected in series. The voltage generated by each of the reference resistors 31, 32, 33 and 34 can be measured.

Each voltage measured in this way is:
The data is converted into a digital signal via the amplifier 23 and the A / D converter 24, and the temperature of the measurement object of the resistance temperature detector 2 is obtained by the same method as that of the measuring device 10 described above. However, in the measuring apparatus 10 of the present example, the voltage V1 generated by the temperature measuring resistor 2 including the first wiring 3a (including the third wiring 3c) and the second wiring 3b are included. (Although the third wiring 3c is included), each of the reference resistors 31, 32,
The voltages Vc1, Vc2, V generated by 33 and 34
c3 and Vc4 are compared and converted to temperature. Even in such a case, the wiring resistance R1 of the first wiring 3a and the second resistance
Since the wiring resistance R2 of the wiring 3b is the same and canceled, the temperature can be accurately obtained by the same method as described above. Since the temperature is obtained by comparing the voltage generated when the temperature measuring resistor and the reference resistor are connected to the same constant current power supply 14, high accuracy except for the reference resistor is performed as described above. Is unnecessary, and a low-cost, high-precision temperature measuring device can be realized.

Further, in the temperature measuring device 19 of this embodiment, since the reference resistors 31, 32, 33 and 34 are respectively connected to the second wiring 3b, it is necessary to measure the voltage drop due to only the wiring resistance. Absent. In particular, the reference resistor 3
1 is, for example, 60.3Ω corresponding to -100 ° C.
, The voltage of the reference resistor 31 can also be used as a reference when converting the temperature. On the other hand, in order to obtain the offset of the amplifier 23 in the same manner as described above, an appropriate resistor may be connected to the common wiring of the reference resistor group 30, and the resistance value of the reference resistor 31 may be set to 0Ω. As a result, similarly to the above, the influence of the amplifier 23 can be eliminated.

As described above, in the temperature measuring device 19 of the present embodiment, a voltage value near 0 V cannot be measured without connecting the grounding resistor to the grounding line 3c, and the measurement accuracy is high with a simple circuit. Temperature measurement can be performed. Further, the second wiring 3b
Since there is no need to measure the voltage value generated in the circuit, the circuit can be simplified and the measurement time can be shortened in this respect as well.

As described above, the temperature measuring device 19 shown in FIG.
As a temperature measuring device for measuring the temperature of one channel, the circuit can be simplified and provided at a lower cost than the temperature measuring device 10 shown in FIG. However, since each reference resistor is connected to the second wiring 3b, it is difficult to increase the number of channels. On the other hand, in the temperature measuring device 10 shown in FIG.
The voltage generated on the first and second wirings 3a and 3b of each sensor when a plurality of sensors are connected may be measured in order. Therefore, it is extremely easy to increase the number of channels. The number of channels is not limited to two, but may be three or more. And
Even if the number of channels is increased, the number of reference resistors does not need to be increased, and the circuit is not enlarged and the measurement time is not significantly increased. Further, since the power consumption does not increase so much, it is possible to realize a measuring device which can measure the temperature at many measurement points with low power consumption.

In the above description, an example is described in which four reference resistors are provided. However, the number of reference resistors may be three or less, or may be five or more. Increasing the number of reference resistors improves the measurement accuracy, but takes time to switch the resistors and measure the voltage. In the above description, the voltage generated by the reference resistor is measured every time the temperature is measured.However, when the temperature change of the object to be measured is small, or when the drift of the constant current power supply is not so large, the temperature is measured. When the measurement is performed a plurality of times, the reference resistor may be periodically connected to a constant current power supply to measure the voltage, and the value may be stored. By reducing the frequency of measuring the voltage generated by the reference resistor, one measurement interval can be shortened and the power consumption can be reduced. Therefore, it is very effective in a case where temperature measurement is performed for a long time using a battery.

In addition, an inexpensive switch such as an analog switch is sufficient as a switch for switching the connection between the wiring and the reference resistor, and the switch may be switched synchronously under the control of the CPU serving as the control unit 50. Of course, the accuracy of synchronization is not so high, and it is only necessary to control the timing at which the voltage of the wiring or the reference resistor can be measured while connected to the constant current power supply.

Further, in the measuring device of this embodiment, the reference resistor must have high stability and high accuracy. For this reason, a resistor having a value that matches the resistance value at the desired temperature may be selected. Conversely, a resistor having an appropriate resistance value is adopted, and the temperature corresponding to the resistance value of the resistor is determined by the CPU. It is also possible to increase the measurement accuracy of the temperature which is stored and converted into the temperature.

[0047]

As described above, in the temperature measuring device of the present invention, the wires of the resistance temperature sensor are sequentially connected to the constant current power supply, and a plurality of reference resistance elements are prepared. The temperature is determined by comparing the voltages generated by sequentially connecting to the same constant current power supply. Therefore, only one constant current power supply is required, and its accuracy and stability are not so required. Further, accuracy and stability of an A / D converter for digitizing a voltage and an amplifier associated therewith are not so required. That is, the measuring device of the present invention can accurately obtain the temperature to be measured by the resistance temperature detector without using a high-precision electric element or electric circuit other than the reference resistance. Therefore, a temperature measuring device with high measurement accuracy and high reliability can be supplied at low cost. The constant current power supply is 1
Therefore, power consumption for measurement can be reduced, and a temperature measurement device suitable for driving with a battery can be provided.

For this reason, the temperature measuring device of the present invention can measure the temperature with high accuracy at low cost by using a highly versatile three-wire type resistance temperature sensor.
It is suitable as a temperature data collection tool in a wide range of fields such as agriculture and R & D.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a temperature measuring device according to the present invention and a system for measuring temperature using the same.

FIG. 2 is a block diagram showing a schematic configuration of the temperature measuring device shown in FIG.

FIG. 3 is a flowchart showing a process of measuring in the temperature measuring device shown in FIG.

FIG. 4 is a diagram showing an example of a resistance value of a reference resistor employed in the temperature measuring device.

FIG. 5 is a graph showing a process of converting a temperature from an obtained voltage value in a temperature measuring device.

FIG. 6 is a block diagram showing another example of the temperature measuring device according to the present invention.

FIG. 7 is a block diagram showing an example of a conventional temperature measuring device.

FIG. 8 is a graph showing an example of characteristics of a constant current power supply.

FIG. 9 is a graph showing an example of characteristics of an A / D converter.

FIG. 10 is a graph showing an example of characteristics of a platinum temperature sensor.

[Description of Signs] 1 RTD sensor 2 RTD 3 Wiring 10 Temperature measurement device 11 Connector 12 Display unit (LCD panel) 14 Constant current power supply 20 Voltage measurement unit 21, 22 Switching switch 24 A / D converter REFERENCE SIGNS LIST 30 reference resistor group 31, 32, 33, 34 reference resistor 50 control unit 51 temperature conversion function 55 RAM 56 communication unit 60 ground circuit 61 ground resistance

Claims (5)

[Claims] 1. A three-wire system comprising first and second wires connected to both ends of a resistance temperature detector and a third wire for grounding connected in parallel to the second wire. What is claimed is: 1. A temperature measuring device capable of measuring a temperature by connecting a resistance temperature sensor, comprising: a constant current power supply; A voltage measuring means for sequentially connecting each of the first and second wirings and the plurality of reference resistors to the constant current power supply and measuring a voltage generated at each of the reference resistors; A temperature measuring device comprising: means for comparing a voltage generated by the temperature resistor with a voltage generated by a plurality of reference resistors and converting the voltage into a temperature. 2. The temperature measuring device according to claim 1, wherein the temperature measuring device has a ground resistance connected to the third wiring. 3. The device according to claim 1, wherein the plurality of reference resistors are connected in series to the second wire, and the voltage measuring means measures a voltage generated by the second wire and the reference resistor. Temperature measuring device characterized by being performed. 4. A three-wire system comprising: first and second wirings connected to both ends of a resistance temperature detector; and a third wiring for grounding connected in parallel to the second wirings. A method for measuring a temperature using a resistance temperature sensor, comprising a resistance value of the resistance temperature element in a range or a vicinity thereof in which the resistance value of the resistance temperature element changes with temperature, in addition to the first and second wirings. A voltage measuring step of sequentially connecting each of the plurality of reference resistors to a constant current power supply and measuring a voltage generated in each of the plurality of reference resistors, and comparing a voltage generated by the temperature measuring resistor and a voltage generated by the plurality of reference resistors. And converting the temperature into a temperature. 5. The method according to claim 4, wherein the plurality of reference resistors are respectively connected in series to the second wiring, and in the voltage measuring step, a voltage generated by the second wiring and the reference resistance is measured. Temperature measurement method characterized by being performed.