JP4208486B2 - Temperature measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a temperature measuring device using a resistance temperature detector as a sensor, and more specifically, a temperature at which a connection circuit of a resistance temperature detector is detected and a measurement circuit is switched to either a three-wire type or a four-wire type. The present invention relates to a measuring device.
[0002]
[Prior art]
In many cases, one of the three-wire type and the four-wire type is adopted as a method of connecting the resistance temperature detector when measuring the temperature of the object to be measured using a resistance temperature detector (for example, a platinum resistance element). ing. FIG. 2 shows a three-wire measuring circuit, and FIG. 3 shows a four-wire measuring circuit.
[0003]
In the case of the three-wire measurement circuit of FIG. 2, the first and second constant current sources 11 and 12 and the voltmeter 21 are used. The first constant current source 11 is connected to one end R1a side and the other end R1b side of the resistance temperature detector R1 via the first wiring 11a and the second wiring 11b.
[0004]
The voltmeter 21 measures the voltage generated in the resistance temperature detector R1. Therefore, in the three-wire measurement circuit, one input terminal of the voltmeter 21 is connected to one end R1a side of the resistance temperature detector R1 using the first wiring 11a, and the other input terminal is the third wiring. It is connected to the other end R1b side of the resistance temperature detector R1 through 21a.
[0005]
The second constant current source 12 is, so to speak, a resistance source for wiring resistance, and is connected between the second wiring 11b and the third wiring 21a, and the same current I as the first constant current source 11 is applied to the resistance temperature detector. Supply toward the other end R1b side of R1. Thereby, an equal current I flows through each of the first wiring 11a, the third wiring 21a, and the resistance temperature detector R1.
[0006]
In the four-wire measurement circuit of FIG. 3, the first constant current source 11 and the voltmeter 21 are used, and the second constant current source 12 is not used. The principle is a four-terminal measurement method, in which a constant current I is passed from the first constant current source 11 through the first wiring 11a and the second wiring 11b to the resistance temperature detector R1, and the third wiring 21a and the fourth wiring 21b are connected. The voltage between both ends of the resistance temperature detector R1 is measured by the voltmeter 21. In either method, the voltage measured by the voltmeter 21 is finally converted into a temperature measurement value.
[0007]
[Problems to be solved by the invention]
Whether to adopt the 3-wire type or the 4-wire type depends on the user's choice, but may be determined by the specifications of the resistance temperature detector. For example, if the temperature measuring device on hand is a three-wire type, only a three-wire temperature measuring resistor can be used, and the selection range of the temperature measuring resistor is narrowed.
[0008]
Accordingly, an object of the present invention is to select either a 3-wire type or a 4-wire type measurement circuit with a single temperature measuring device, and automatically according to the connection of the resistance temperature detector. The measurement circuit is to be switched.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention uses a resistance temperature detector (R1) as a sensor, and is either a three-wire type or a four-wire type depending on how the wiring is connected to the resistance temperature detector (R1) . of Te temperature measuring device odor measurement circuit is automatically selected, 3-wire, a first wiring connected to one end of said measuring resistor either case of 4-wire (R1) (R1a) ( 11a) and a first constant current source (11) having a second wiring (11b) connected to the other end side (R1b) of the resistance temperature detector (R1) , and any of a 3-wire type and a 4-wire type even if the other end of the resistance temperature detector (R1) to one end of the third wiring is connected to the (R1b) the RTD only if (21a) and 4-wire (R1) (R1a) the fourth wiring and the voltage measuring means having (21b) (21), said first wiring connected (11a Through the above-described fourth wiring and the first switch connected between (21b) (SW1), a second switch (SW2) between said second wiring (11b) and the third wiring (21a) A second constant current source (12) for wiring resistance compensation that outputs the same current as that of the first constant current source (11) connected to each other, and a third switch provided in the fourth wiring (21b) (SW3) and a voltage detection resistor (R2) connected between the fourth wiring (21b) and the ground at a wiring portion closer to the resistance temperature detector (R1 ) than the third switch (SW3 ). The first to third switches (SW1 to SW3) are compared by comparing the voltage (VR2) detected by the voltage detection resistor (R2) including the comparator (31) with a preset reference voltage (V). and a switch control means for on-off control When the detection voltage (VR2) is lower than the reference voltage (V), the switch control means turns on both the first switch (SW1) and the second switch (SW2), and the third switch (SW3 ) Is turned off, and the first constant current source (11) and the second constant current source (12) are operated to configure the three-wire measurement circuit, and the detection voltage (VR2) is the reference voltage. When higher than (V), both the first switch (SW1) and the second switch (SW2) are turned off, the third switch (SW3) is turned on, and the first constant current source (11) And the above-described four-wire measuring circuit is configured .
[0010]
When the resistance temperature detector is connected as a three-wire type to the temperature measuring device of the present invention via the first, second, and third wirings, the fourth wiring is not used. Does not occur. Thereby, the switch control means turns on the first and second switches, turns off the third switch, and makes the internal measurement circuit correspond to the three-wire system.
[0011]
On the other hand, when the resistance temperature detector is connected as a four-wire type via the first, second, third and fourth wirings, a part of the constant current from the first constant current source flows to the voltage detection resistor. A voltage is generated in the voltage detection resistor. When this voltage is higher than the reference voltage, the switch control means turns off the first and second switches and turns on the third switch to make the internal measurement circuit compatible with the four-wire system.
[0012]
According to a preferred aspect of the present invention, the resistance value of the voltage detection resistor is set to a large resistance value that does not affect the measured value (resistance value) of the resistance temperature detector. The reference voltage is also set to a voltage value lower than the voltage generated in the resistance temperature detector.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIG. In this embodiment, the same reference numerals are used for the components that may be regarded as the same as or the same as those in the conventional example described in FIGS.
[0014]
This temperature measuring device also includes first and second constant current sources 11 and 12 and one voltmeter (voltage measuring means) 21 as a basic configuration, as in the conventional example described above. .
[0015]
The first constant current source 11 includes a first wiring 11a connected to one end R1a side of the resistance temperature detector R1, and a second wiring 11b connected to the other end R1b side of the resistance temperature detector R1. Yes. The first wiring 11a and the second wiring 11b are connected to the resistance temperature detector R1 in either of the three-wire system and the four-wire system.
[0016]
The voltmeter 21 also has two wires, a third wire 21a connected to the other end R1b side of the resistance temperature detector R1 and a fourth wire 21b connected to the one end R1a side of the temperature measurement resistor R1. However, the third wiring 21a is connected to the other end R1b of the resistance temperature detector R1 regardless of whether the third wiring 21a is a three-wire type or a four-wire type, whereas the fourth wiring 21b is a four-wire type. Only to one end R1a side of the resistance temperature detector R1.
[0017]
In the present invention, the first switch SW1 is connected between the first wiring 11a and the fourth wiring 21b. The second constant current source 12 is connected between the second wiring 11b and the third wiring 21a. The second switch SW2 is inserted in this connection circuit. As described with reference to FIG. 2, the second constant current source 12 allows the same current as the first constant current source 11 to flow toward the other end R1b of the resistance temperature detector R1.
[0018]
A third switch SW3 is provided in the fourth wiring 21b. Further, a voltage detection resistor R2 is connected between the fourth wiring 21b and the ground. The connecting portion of the voltage detection resistor R2 is closer to the temperature measuring resistor R1 than the third switch SW3.
[0019]
The present invention includes switch control means for controlling the switches SW1 to SW3. FIG. 1 shows a comparator 31 included in the switch control means. A reference voltage V is input to one input terminal of the comparator 31, and the other input terminal is connected to a voltage detection resistor R2. .
[0020]
Next, the operation of the comparator 31 will be described. The user adopts a three-wire system, one end R1a side of the resistance temperature detector R1 is connected to the first wiring 11a, the second wiring 11b and the third wiring 21a are connected to the other end R1b side, Assume that the current sources 11 and 12 are operated.
[0021]
In this case, since the fourth wiring 21b is disconnected from the resistance temperature detector R1, no current flows through the voltage detection resistor R2. Therefore, since the potential VR2 of the connection portion of the voltage detection resistor R2 is the ground potential (0V) and VR2 <V, the first and second switches SW1 and SW2 are turned on by the output of the comparator 31, and the third switch SW3 is turned off. Thereby, the three-wire measuring circuit described in FIG. 2 is configured.
[0022]
On the other hand, the user adopts a four-wire system, and connects the first wiring 11a and the fourth wiring 21b to one end R1a side of the resistance temperature detector R1, and the second wiring 11b and the second wiring to the other end R1b side. It is assumed that the first and second constant current sources 11 and 12 are operated by connecting the three wirings 21a.
[0023]
In this case, since a part of the current from the first constant current source 11 flows to the ground through the voltage detection resistor R2, the potential VR2 of the connection portion of the voltage detection resistor R2 rises. In this example, the resistance value of the voltage detection resistor R2 is set so that the potential VR2 at this time is higher than the reference voltage V.
[0024]
As a result, VR2> V is established, the output of the comparator 31 is inverted, the first and second switches SW1 and SW2 are turned off, and the third switch SW3 is turned on, and the four-wire measurement circuit described in FIG. 3 is configured. Is done.
[0025]
The resistance value of the voltage detection resistor R2 is relatively determined from the relationship between the current flowing from the first constant current source 11 and the reference voltage V, etc., but with respect to the measured value (resistance value) of the resistance temperature detector R1. It is preferable that the resistance value is large enough not to be affected.
[0026]
As an example, assuming that the resistance temperature detector R1 is a platinum resistance element having a resistance value of 100Ω at 0 ° C., a maximum measurement temperature of 300 ° C., and a resolution of 0.1 ° C., the resistance value of the voltage detection resistor R2 is about 2 MΩ. It is preferable.
[0027]
When the maximum measurement temperature is higher than this or when the resolution is made finer, the resistance value of the voltage detection resistor R2 needs to be a larger value. The reference voltage V is preferably set to a voltage value lower than the voltage generated in the resistance temperature detector R1.
[0028]
【The invention's effect】
As described above, according to the present invention, not only can the resistance temperature detector be in either the 3-wire specification or the 4-wire specification, but depending on the connection method adopted by the user, Since a 3-wire measurement circuit or a 4-wire measurement circuit is automatically configured, a temperature measurement device that can be used with confidence for the user is provided.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing an embodiment of a temperature measuring device according to the present invention.
FIG. 2 is a circuit configuration diagram showing a three-wire measuring circuit as a first conventional example.
FIG. 3 is a circuit configuration diagram showing a four-wire measuring circuit as a second conventional example.
[Explanation of symbols]
11 1st constant current source 11a 1st wiring 11b 2nd wiring 12 2nd constant current source 21 Voltmeter 21a 3rd wiring 21b 4th wiring 31 Comparator R1 Resistance thermometer R2 Voltage detection resistance SW1-SW3 switch

Claims (3)

A temperature measuring resistor (R1) is used as a sensor, and either a 3-wire or 4-wire measuring circuit is automatically selected depending on how the wiring is connected to the temperature measuring resistor (R1). measuring device smell Te,
3-wire, the other end of the one end side of the RTD any case of 4-wire (R1) the first wiring is connected to the (R1a) (11a) and the resistance temperature detector (R1) ( A first constant current source (11) having a second wiring (11b) connected to R1b) ;
In either case of the 3-wire type or the 4-wire type, the temperature measuring resistor is used only in the case of the third wiring (21a) connected to the other end side (R1b) of the temperature measuring resistor (R1 ) and the 4-wire type. Voltage measuring means (21) having a fourth wiring (21b) connected to one end side (R1a ) of (R1) ;
A first switch (SW1) connected between the first wiring (11a) and the fourth wiring (21b) ;
Wiring resistance compensation for outputting the same current as the first constant current source (11) connected via the second switch (SW2) between the second wiring (11b) and the third wiring (21a) A second constant current source (12) for
The fourth wiring and the third switch provided in (21b) (SW3), the third the RTD than switch (SW3) (R1) side near the wiring portion in the fourth wiring (21b) A voltage detection resistor (R2) connected between the ground and the ground;
On / off control of the first to third switches (SW1 to SW3) is performed by comparing a voltage (VR2) detected by the voltage detection resistor (R2) including a comparator (31) with a preset reference voltage (V). and a switch control means for,
When the detection voltage (VR2) is lower than the reference voltage (V), the switch control means turns on both the first switch (SW1) and the second switch (SW2), and the third switch (SW3 ) Is turned off and the first constant current source (11) and the second constant current source (12) are operated to configure the three-wire measurement circuit,
When the detection voltage (VR2) is higher than the reference voltage (V), both the first switch (SW1) and the second switch (SW2) are turned off, and the third switch (SW3) is turned on. The temperature measuring device is characterized in that the first constant current source (11) is operated to constitute the four-wire measuring circuit . The temperature measuring device according to claim 1, wherein the resistance value of the voltage detection resistor (R2) is a large resistance value that does not affect the measured value of the resistance temperature detector (R1) . The temperature measuring device according to claim 1 or 2, wherein the reference voltage (V) is set to a voltage value lower than a voltage generated in the resistance temperature detector (R1) .

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