NL2017179B1 - Temperature measuring circuit obviating calibration - Google Patents

Temperature measuring circuit obviating calibration Download PDF

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Publication number
NL2017179B1
NL2017179B1 NL2017179A NL2017179A NL2017179B1 NL 2017179 B1 NL2017179 B1 NL 2017179B1 NL 2017179 A NL2017179 A NL 2017179A NL 2017179 A NL2017179 A NL 2017179A NL 2017179 B1 NL2017179 B1 NL 2017179B1
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Netherlands
Prior art keywords
measuring
resistor
temperature
circuit
converter
Prior art date
Application number
NL2017179A
Other languages
Dutch (nl)
Inventor
Ronald Edwin Drenth Dethmer
Original Assignee
Intermodal Telematics B V
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Filing date
Publication date
Application filed by Intermodal Telematics B V filed Critical Intermodal Telematics B V
Priority to NL2017179A priority Critical patent/NL2017179B1/en
Priority to PCT/NL2017/050453 priority patent/WO2018012965A1/en
Application granted granted Critical
Publication of NL2017179B1 publication Critical patent/NL2017179B1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
    • G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
    • G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit
    • G01K7/206—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit in a potentiometer circuit

Abstract

The invention relates to a temperature measuring circuit, comprising: a measuring resistor having a temperature dependent resistance and being connected to function as a temperature sensor; a current element connected to the measuring resistor and adapted for directing a current through the measuring resistor; and an A/D-converter of which the input is connected to one side of the measuring resistor, and which is adapted to generate the digital output signal. The invention also relates to a method for measuring the temperature.

Description

Temperature measuring circuit obviating calibration
The invention relates to a temperature measuring circuit. Such circuits are widely used in process engineering and in other situations in which the temperature has to be determined.
There several principles which can be used to obtain an electrical signal representing the temperature, such as a thermocouple and semiconductors, such as PTC-resistors or NTC-resistors. However from a view point of costs and accuracy it is attractive to use metal resistors. These materials have a specific resistance dependent on the temperature. Some metals, such as platina, have a specific resistance which is closer to linear than the specific resistance of other metals over a large temperature range.
Several prior art circuits are adapted to provide wire compensation while others comprise an amplifier between the measuring resistor and the A/D-converter. Amplifiers are prone to drift and offset problems. Further prior art provides a temperature measuring circuit, comprising a measuring resistor having a temperature dependent resistance and being arranged to function as a temperature sensor, a current element connected to the measuring resistor and adapted for directing a current through the measuring resistor and an A/D-converter of which the input is connected to one side of the measuring resistor, and which is adapted to generate the digital output signal.
In this prior art circuit the current element is formed by a current source. The current source directs a current through the measuring resistor so that the voltage over the measuring resistor is a representation of the temperature under the assumption that the current through the measuring resistor is constant. An ideal current source is a theoretical element and the properties of real life current sources deviate from ideal properties. Further current sources require elaborate electronic circuitry including semiconductors, especially when the current must be as constant as possible as is required in measurement circuits. Nevertheless even carefully constructed current sources have temperature dependencies and other nonlinearities, limiting the accuracy of the measurement circuit.
The present invention aims to provide such a temperature measuring circuit, in which the disadvantages mentioned above are avoided.
This aim is reached by a temperature measuring circuit of the kind referred to above wherein the current element comprises a reference resistor, of which a first side is connected to the side of the measuring resistor which is connected to the input of the A/D-converter and that the second side of the reference resistor is connected to a reference input of the A/D-converter.
In this circuit the reference resistor takes the place of the current source. The current through the reference resistor and the measuring resistor is determined by the resistances of these resistors and by the voltage over these resistors. Hence the voltage over the measuring resistor is dependent on said voltage. As said voltage is also supplied to the A/D converter, the dependency on said voltage can be compensated assuming that the A/C converter is adapted to do so. Thus the dependency of the current from the voltage over the resistors is eliminated, allowing to use a simple resistor rather than a complicated current source circuit.
The invention also provides a method for measuring the temperature, comprising the steps of providing a measuring resistor arranged to function as a temperature sensor, directing a current through the measuring resistor and directing the voltage over the measuring resistor to the input of an A/D-converter, generating a digital output signal, wherein the current through the measuring resistor is determined by a reference resistor of which a first side is connected to the input of the A/D-converter and a second side is connected to a reference input of the A/D-converter.
The invention allows to replace the current source circuit by a resistor, but the fact that the resistance of the measurement resistor varies does not only cause a variation of the voltage supplied to the input of the A/D- converter, but it also leads to a variation in the current flowing through the two resistors. To minimize this last effect, the resistance of the reference resistor is preferably at least one order of magnitude greater than the resistance of the measurement resistor.
Further preferably the tolerance of the reference resistor is equal to or greater than the tolerance of the measuring resistor. This leads to an accuracy increase.
To simplify the circuit further, it is preferred that the second side of the reference resistor and a reference input of the A/D-converter are adapted to be connected to a power supply voltage.
As the junction between the measurement resistor and the reference resistor is connected to the input of the A/D-converter, which draws a varying input current from the junction, the currents flowing through the measurement resistor and the reference resistor respectively are not completely equal and their ratio varies. This causes a deviation from ideal situation. To make this deviation as small as possible it is preferable that the input resistance of the A/D-converter is at least one order of magnitude greater that the resistance of the measuring resistor.
Although the linearity of the temperature dependency of the resistance of the measurement resistor is high, there may a deviation from the full linearity. This deviation is known, allowing it to be compensated. Compensation may be executed in the digital section of the circuit, but a preferred embodiment provides a conditioning circuit inserted between the junction of the reference resistor and the measuring resistor and the input of the A/D-converter. This conditioning circuit may be adapted to perform the analogue compensation. Of course the conditioning circuit may be adapted to execute other functions, such as the compensation of other deviations. The conditioning circuit has preferably a high input resistance.
In many situations, such as an aggressive atmosphere, it is attractive to locate the measurement resistor only in the location in which a temperature is to be measured. Then it is preferred that the measuring resistor is located remote from the rest of the temperature measuring circuit. This has further the advantage that the temperature of the reference resistor is not subject to the temperature to be measured, eliminating a further cause for inaccuracy.
Particularly, though not exclusively in situations in which the measurement resistor is located remote from the other parts of the circuit, the wires between the measurement resistor and the reference resistor or the input of the A/D-converter, may have such a length that the current through said wire causes a significant voltage loss, adding inaccuracy to the measurement. To minimize this unfavourable effect, it is preferred that the input of the A/D-converter and the first side of the reference resistor are connected to the measuring resistor via separate wires.
The same effect may appear at the other side of the measurement resistor, and to reduce this unwanted effect as well, it is preferred that a ground input of the A/D-converter and the ground of the power supply connection are connected by separate wires to the measuring resistor.
The resistance of the measurement resistor may deviate from its original value in time. This effect is partially caused by ageing as caused by the current flowing through said resistor. To reduce the time during which the current flows, it is preferred that the temperature measurement circuit comprises a control circuit, adapted to regularly switch on and off the current flowing through the measuring resistor, wherein the duty cycle is less than 1/1000. This feature also reduces the effects of corrosion caused by electrolysis.
This embodiment also provides a method of the kind referred to above, wherein the current through the measurement resistor is regularly switched on and off with a duty cycle smaller than 1/1000.
An easy way of switching the current flowing through the measurement resistor off and on is by a switch arranged in series with the reference resistor, and being adapted to be controlled by the control circuit. Preferably this switch will be formed by a solid state switch, which maintains galvanic separation between the measurement circuit and the control circuit to avoid mutual influence. More preferably a MOSFET is used in the ground connection. However mechanical switches are not excluded.
An alternative resides in the switching on and off of the complete measurement circuit. This may be feasible depending on the design of the components thereof. This would require that the control circuit is adapted to switch on and off the A/D-converter.
This embodiment also provides a method of the kind referred to above, wherein the temperature measurement circuit is regularly switched on and off with a duty cycle smaller than 1/1000.
Because of their excellent properties it is attractive to use measurement resistors comprising a platinum alloy. Hence according to a preferred embodiment, the measuring resistor is a Pt-element, such as a Pt100-, a Pt1000 or a Pt5000-element.
The invention will be further elucidated herein below on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein shows; figure 1: a diagram of a temperature measurement circuit according to the prior art; figure 2: a diagram of a temperature measurement circuit according to a first embodiment of the invention; figure 3: a diagram of a temperature measurement circuit according to a second embodiment of the invention; figure 4: a diagram of a temperature measurement circuit according to a third embodiment of the invention; and figure 5: a diagram of a temperature measurement circuit according to a fourth embodiment of the invention. A prior art temperature measurement circuit using a resistor as temperature sensor is depicted in figure 1. This prior art circuit comprises a DC voltage supply source 1 and a measurement resistor 2 of which the resistance Rm is temperature dependent, as is the case with most resistors made of metal. It is attractive to use metals as the temperature dependency is often nearly linear over large temperature ranges. This is contrary to temperature sensors of the types which are known as NTC- or PTC-resistors which are made of semiconductors and which have a linear behaviour over limited temperature ranges.
The circuit further comprises a current source 3, which is connected to the measurement resistor 2 to direct a constant current through the measurement resistor 2. This current through the measurement resistor 2 generates a voltage over the measurement resistor 2 which is dependent only on the resistance Rm of the measurement resistor 2 and hence of its temperature. The circuit comprises also an A/D-converter 4 and the junction of the measurement resistor 2 and the current source 3 is connected to the input 5 of the A/D-converter 4, allowing the voltage over the measurement resistor 2 to be supplied to the A/D-converter 3. The supply voltage is a DC voltage, preferably stabilized. The digital output signal of the A/D-converter 4 represents the temperature of the measurement resistor 2. The current source 3 comprises several transistors or operational amplifiers, bearing in mind that the current generated by the current source 3 must be constant to ensure an accurate measurement of the temperature.
The circuit in figure 2 deviates from the prior art by the replacement of the current source 3 by a reference resistor 6 having a resistance Rr. Further the A/D-converter 4 is adapted to take into account the magnitude of the voltage over the series connection of the reference resistor 6 and the measurement resistor 2 in the processing of the input signal. When the voltage over the series connection of the resistors 2 and 6 equals the supply voltage, there is no need for a separate connection, as is depicted in figure 2, but in situations in which the voltage over the series connection between the resistors 2 and 6 is unequal to the supply voltage, a separate connection is required to provide this voltage to the A/D-converter 4.
The voltage over the measurement resistor 2 satisfies the formula:
Um = Us. Rm / (Rr + Rm), in which Us is the voltage over the series connection of the reference resistor 6 and the measurement resistor 2. The dependency on a current source in prior art has been replaced by a dependency on a voltage which can easily be compensated in the A/D-converter 4.
The formula discussed above assumes that the currents through both resistors 2 and 6 are equal. In real life there is a deviation from this ideal situation by the current drawn by the input 5 of the A/D-converter 4. This current is small, as common A/D-converters have a high input impedance. Nevertheless the current is a disturbing factor in the accuracy of the measurement. To make this current as small as possible, preferably a conditioning circuit 7 is connected between the junction of the two resistors 2 and 6 and the input 5 of the A/D-converter 4. This conditioning circuit 7 has a high input resistance, relative to the resistance Rm of the measurement resistor 2 so that the input current is neglectable relative to the current through the measurement resistor 2.
It is however also possible that the conditioning circuit 7 fulfils other functions such as the compensation of nonlinearities of the temperature dependency of the measurement resistor 2.
In many situations the measurement resistor 2 is located remote from the other components of the measurement circuit. This avoids the other components, and in particular the reference resistor 6 being subject to the temperature to be measured. Such a situation entails relative long wires between the reference resistor 6 and the other components. These long wires have resistances causing inaccuracies as the currents flowing through these wires cause offset voltages. The embodiment of figure 4 substantially reduces these offset voltages by providing an extra wire 9 between the measurement resistor 2 and the input 4 of the A/D-converter 5. This avoids the offset voltage over the wire 10 connecting the reference resistor 6 with the measurement resistor 2. The current flowing through the wire 9 connecting the measurement resistance 2 with the input 4 of the A/D-converter 5 is small, so that the offset voltage over this wire is neglectable. The wires 9, 10 and the wire connecting the measuring resistor to the ground are united in a cable 8.
The temperature measurement circuit can be switched on constantly, although in most situations it is sufficient to make measurements from time to time only. This does save power, but it also reduces ageing of the components, in particular of the measurement resistor 2 and of the reference resistor 6. It is possible to completely switch off and on the whole measurement circuit on a regular basis, but it is also possible to switch off the current through the reference resistor 2 and measurement resistor 6 only and leave the rest of the measurement circuit components switched on.
Figure 5 shows a circuit in which the resistors 2, 6 and the other components 4, 7 can be switched on an off. This circuit comprises a switch 11 connected in series with the reference resistor 6 and the measurement resistor 2. The switch 11 is controlled by a control circuit 12, with is also adapted to control the A/D-converter 5 and the conditioning circuit 7. The control circuit is adapted to keep the switch 11 opened most of the time and to close it regularly for short times to allow a temperature measurement to be made. Hence the current through the measurement resistor 2 runs only for short periods thus reducing ageing of the measurement resistor 2. The same argument counts for the reference resistor 6. To achieve this advantage of reduced ageing, the duty cycle of the switch cycle should be small.
However it is also possible to regularly switch off the complete circuit, saving electrical power, although some time is needed after switching on to reach a stable situation in which the temperature measurement can be performed.
Further it is feasible to have the time between measurements not completely constant, but to make it dependent on measured values.
It will be clear to a skilled person that numerous variations are possible on the discussed embodiments, such as the combination of features of several embodiments, as the scope of the present patent application and resulting patent is only determined by the claims.

Claims (16)

1. Schakeling voor het meten van de temperatuur, omvattende: - een meetweerstand met een temperatuurafhankelijke weerstandswaarde en die is geschakeld om als een temperatuursensor te fungeren; - een met de meetweerstand verbonden stroomelement die is ingericht om een stroom door de meetweerstand heen te leiden; en - een A/D-omzetter waarvan de ingangsaansluiting is verbonden met één zijde van de meetweerstand, en die is ingericht voor het opwekken van het digitale uitgangssignaal, met het kenmerk, dat het stroomelement een referentieweerstand omvat, waarvan een eerste zijde is verbonden met die zijde van de meetweerstand die is verbonden met de ingangsaansluiting van de A/D-omzetter en waarvan een tweede zijde is verbonden met een referentie-ingangsaansluiting van de A/D-omzetter.A circuit for measuring the temperature, comprising: - a measuring resistor with a temperature-dependent resistance value and which is connected to act as a temperature sensor; - a current element connected to the measuring resistor and adapted to conduct a current through the measuring resistor; and - an A / D converter whose input terminal is connected to one side of the measuring resistor, and which is adapted to generate the digital output signal, characterized in that the current element comprises a reference resistor, a first side of which is connected to that side of the measuring resistor which is connected to the input terminal of the A / D converter and of which a second side is connected to a reference input terminal of the A / D converter. 2. Schakeling voor het meten van de temperatuur volgens conclusie 1, met het kenmerk, dat de weerstandswaarde van de referentieweerstand ten minste één orde van grootte groter is dan de weerstandswaarde van de meetweerstand.2. A temperature measuring circuit as claimed in Claim 1, characterized in that the resistance value of the reference resistance is at least one order of magnitude greater than the resistance value of the measuring resistance. 3. Schakeling voor het meten van de temperatuur volgens conclusie 1 of 2, met het kenmerk dat de tolerantie van de referentieweerstand gelijk is aan of groter is dan de tolerantie van de meetweerstand.3. A temperature measuring circuit as claimed in Claim 1 or 2, characterized in that the tolerance of the reference resistance is equal to or greater than the tolerance of the measuring resistance. 4. Schakeling voor het meten van de temperatuur volgens conclusie 1, 2 of 3, met het kenmerk, dat de tweede zijde van de referentieweerstand en de referentie-ingangsaansluiting van de A/D-omzetter met de voedingsspanning zijn verbonden.4. A temperature measuring circuit as claimed in Claim 1, 2 or 3, characterized in that the second side of the reference resistor and the reference input terminal of the A / D converter are connected to the supply voltage. 5. Schakeling voor het meten van de temperatuur volgens conclusie 1, 2, 3 of 4, met het kenmerk, dat de A/D-omzetter een ingangsweerstand heeft die tenminste één orde van grootte groter is dan de weerstandswaarde van de meetweerstand.5. A temperature measuring circuit as claimed in Claim 1, 2, 3 or 4, characterized in that the A / D converter has an input resistance which is at least one order of magnitude greater than the resistance value of the measuring resistance. 6. Schakeling voor het meten van de temperatuur volgens één van de voorafgaande conclusies, met het kenmerk, dat tussen de verbinding tussen de referentieweerstand en de meetweerstand en de ingangsaansluiting van de A/D-omzetter een conditioneringsschakeling is geschakeld.Circuit for measuring the temperature according to one of the preceding claims, characterized in that a conditioning circuit is connected between the connection between the reference resistor and the measuring resistor and the input terminal of the A / D converter. 7. Schakeling voor het meten van de temperatuur volgens één van de voorafgaande conclusies, met het kenmerk, dat de meetweerstand op afstand van de andere componenten van de temperatuurmeetschakeling is geplaatst.A temperature measuring circuit according to any one of the preceding claims, characterized in that the measuring resistor is spaced apart from the other components of the temperature measuring circuit. 8. Schakeling voor het meten van de temperatuur volgens conclusie 7, met het kenmerk, dat de ingangsaansluiting van de A/D-omzetter en de eerste zijde van referentieweerstand door afzonderlijke draden met de meetweerstand zijn verbonden.A temperature measuring circuit according to claim 7, characterized in that the input terminal of the A / D converter and the first side of the reference resistor are connected to the measuring resistor by separate wires. 9. Schakeling voor het meten van de temperatuur volgens conclusie 8, met het kenmerk, dat een aard-referentieaansluiting van de A/D-omzetter en een algemene aarde door afzonderlijke draden met de meetweerstand zijn verbonden.9. A temperature measuring circuit as claimed in Claim 8, characterized in that an earth-reference connection of the A / D converter and a general earth are connected to the measuring resistor by separate wires. 10. Schakeling voor het meten van de temperatuur volgens één van de voorafgaande conclusies, gekenmerkt door een besturingsschakeling,die is ingericht voor het regelmatig in- en uitschakelen van de door de meetweerstand heen vloeiende stroom, waarbij de inschakelverhouding kleiner is dan 1/1000.A temperature measurement circuit as claimed in any one of the preceding claims, characterized by a control circuit which is adapted to regularly switch on and off the current flowing through the measuring resistor, the switch-on ratio being less than 1/1000. 11. Schakeling voor het meten van de temperatuur volgens conclusie 10, gekenmerkt door een met de referentieweerstand in serie geschakelde schakelaar die is ingericht om door de besturingsschakeling te worden bestuurd.A temperature measuring circuit according to claim 10, characterized by a switch connected in series with the reference resistor and adapted to be controlled by the control circuit. 12. Schakeling voor het meten van de temperatuur volgens conclusie 11, met het kenmerk dat de besturingsschakeling is ingericht voor het in- en uitschakelen van de A/D-omzetter.12. A temperature measuring circuit according to claim 11, characterized in that the control circuit is adapted to switch the A / D converter on and off. 13. Schakeling voor het meten van de temperatuur volgens één van de voorafgaande conclusies, met het kenmerk dat de meetweerstand een Pt100-, a Pt1000 of een Pt-5000-element is.Circuit for measuring the temperature according to one of the preceding claims, characterized in that the measuring resistor is a Pt100, a Pt1000 or a Pt-5000 element. 14. Werkwijze voor het meten van de temperatuur, omvattende: - het verschaffen van een als een temperatuursensor fungerende meetweerstand; - het door de meetweerstand heen leiden van een stroom; en - het over de meetweerstand staande spanning leiden naar de ingangsaansluiting van een A/D-omzetter die een digitaal uitgangssignaal opwekt, met het kenmerk, dat de stroom door de meetweerstand wordt bepaald door een referentieweerstand waarvan een eerste zijde is verbonden met die zijde van de meetweerstand die is verbonden met de ingangsaansluiting van de A/D-omzetter en waarvan een tweede zijde is verbonden met een referentie-ingangsaansluiting van de A/D-omzetter.A method for measuring the temperature, comprising: - providing a measuring resistor acting as a temperature sensor; - conducting a current through the measuring resistor; and - conducting the voltage across the measuring resistor to the input terminal of an A / D converter which generates a digital output signal, characterized in that the current through the measuring resistor is determined by a reference resistor whose first side is connected to that side of the measuring resistor connected to the input terminal of the A / D converter and a second side of which is connected to a reference input terminal of the A / D converter. 15. Werkwijze volgens conclusie 14, met het kenmerk, dat de stroom door de meetweerstand regelmatig wordt in- en uitgeschakeld met een inschakelverhouding die kleiner is dan 1/1000.Method according to claim 14, characterized in that the current through the measuring resistor is regularly switched on and off with a switch-on ratio of less than 1/1000. 16. Werkwijze volgens conclusie 14, met het kenmerk, dat de temperatuurmeetschakeling regelmatig wordt in- en uitgeschakeld met een inschakelverhouding die kleiner is dan 1/1000.A method according to claim 14, characterized in that the temperature measurement circuit is regularly switched on and off with a switch-on ratio that is smaller than 1/1000.
NL2017179A 2016-07-15 2016-07-15 Temperature measuring circuit obviating calibration NL2017179B1 (en)

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NL2017179A NL2017179B1 (en) 2016-07-15 2016-07-15 Temperature measuring circuit obviating calibration
PCT/NL2017/050453 WO2018012965A1 (en) 2016-07-15 2017-07-06 Temperature measuring circuit obviating calibration

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NL2017179A NL2017179B1 (en) 2016-07-15 2016-07-15 Temperature measuring circuit obviating calibration

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2637985A1 (en) * 1988-10-14 1990-04-20 Collet Gerard Method and apparatus for measuring resistance, particularly for temperature measurement
GB2267967A (en) * 1992-06-17 1993-12-22 Status Instr Limited Apparatus for temperature measurement
US20050083069A1 (en) * 2002-02-18 2005-04-21 Alain Pasty Recording module with a universal input for measurement of physical parameters
EP2664905A2 (en) * 2012-05-15 2013-11-20 E.G.O. ELEKTRO-GERÄTEBAU GmbH Temperature measuring device, electrical apparatus equipped with such a temperature-measuring device and method for measuring temperature
EP2924405A1 (en) * 2012-11-22 2015-09-30 Hitachi Automotive Systems, Ltd. Intake air temperature sensor and flow measurement device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2637985A1 (en) * 1988-10-14 1990-04-20 Collet Gerard Method and apparatus for measuring resistance, particularly for temperature measurement
GB2267967A (en) * 1992-06-17 1993-12-22 Status Instr Limited Apparatus for temperature measurement
US20050083069A1 (en) * 2002-02-18 2005-04-21 Alain Pasty Recording module with a universal input for measurement of physical parameters
EP2664905A2 (en) * 2012-05-15 2013-11-20 E.G.O. ELEKTRO-GERÄTEBAU GmbH Temperature measuring device, electrical apparatus equipped with such a temperature-measuring device and method for measuring temperature
EP2924405A1 (en) * 2012-11-22 2015-09-30 Hitachi Automotive Systems, Ltd. Intake air temperature sensor and flow measurement device

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