GB2557351A - Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element - Google Patents
Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element Download PDFInfo
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- GB2557351A GB2557351A GB1620871.2A GB201620871A GB2557351A GB 2557351 A GB2557351 A GB 2557351A GB 201620871 A GB201620871 A GB 201620871A GB 2557351 A GB2557351 A GB 2557351A
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- 230000018109 developmental process Effects 0.000 description 3
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Classifications
-
- 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
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
- G01K7/10—Arrangements for compensating for auxiliary variables, e.g. length of lead
- G01K7/12—Arrangements with respect to the cold junction, e.g. preventing influence of temperature of surrounding air
- G01K7/13—Circuits for cold-junction compensation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K15/00—Testing or calibrating of thermometers
- G01K15/005—Calibration
-
- 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
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
- G01K7/021—Particular circuit arrangements
-
- 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
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
- G01K7/026—Arrangements for signalling failure or disconnection of thermocouples
-
- 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
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
- G01K7/10—Arrangements for compensating for auxiliary variables, e.g. length of lead
-
- 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
- G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
- G01K7/10—Arrangements for compensating for auxiliary variables, e.g. length of lead
- G01K7/12—Arrangements with respect to the cold junction, e.g. preventing influence of temperature of surrounding air
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
Abstract
The invention is concerned with a measuring device 10 comprising a thermocouple element 11, an electronic circuit 12 and wires 13,13' for connecting cold-end electrodes 14 of the thermocouple element 11 with the measuring circuit 12, wherein the electronic circuit 12 comprises a voltage measuring circuitry 17 that is designed to measure a thermo-voltage 18' generated at the cold-end electrodes 14 and transmitted to the electronic circuit 12 over the wires 13,13'. The invention is characterized in that one of the cold-end electrodes 14 is connected to one of the wires 13' over a temperature sensing element 34, wherein a driving circuitry 19 is designed to drive a measuring current I through the sensing element 34 over the wires 13,13', wherein the measuring device 10 is designed to generate a temperature signal that is a function of an absolute temperature of the sensing element 34. The sensing element may be a positive temperature coefficient resistor. The measuring device may comprise means for determining leakage resistance 36 for use in calibration: voltage source 19 generates a pre-defined voltage 20 at the wire 13 that it is connected to, wherein the pre-defined voltage 20 results under the condition that the leakage resistance 36 that is effective between the thermocouple element 11 and the ground potential 23 is above a pre-defined threshold, and wherein the voltage measuring circuitry 17 is designed to measure the actual voltage 20 at the wire 13 while the switch 24 is opened. Switches 24, 25, 26 allow measurement of the thermo voltage fig. 1, temperature signal fig. 2 and observation of the leakage resistance fig. 3.
Description
(54) Title of the Invention: Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element
Abstract Title: Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element (57) The invention is concerned with a measuring device 10 comprising a thermocouple element 11, an electronic circuit 12 and wires 13,13' for connecting cold-end electrodes 14 of the thermocouple element 11 with the measuring circuit 12, wherein the electronic circuit 12 comprises a voltage measuring circuitry 17 that is designed to measure a thermo-voltage 18' generated at the cold-end electrodes 14 and transmitted to the electronic circuit 12 over the wires 13,13'. The invention is characterized in that one of the cold-end electrodes 14 is connected to one of the wires 13' over a temperature sensing element 34, wherein a driving circuitry 19 is designed to drive a measuring current I through the sensing element 34 over the wires 13,13', wherein the measuring device 10 is designed to generate a temperature signal that is a function of an absolute temperature of the sensing element 34. The sensing element may be a positive temperature coefficient resistor. The measuring device may comprise means for determining leakage resistance 36 for use in calibration: voltage source 19 generates a pre-defined voltage 20 at the wire 13 that it is connected to, wherein the pre-defined voltage 20 results under the condition that the leakage resistance 36 that is effective between the thermocouple element 11 and the ground potential 23 is above a predefined threshold, and wherein the voltage measuring circuitry 17 is designed to measure the actual voltage 20 at the wire 13 while the switch 24 is opened. Switches 24, 25, 26 allow measurement of the thermo voltage fig. 1, temperature signal fig. 2 and observation of the leakage resistance fig. 3.
Fig, 2
Description
Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element
The invention is concerned with a measuring device comprising a thermocouple element and an electronic circuit. The thermocouple element and the electronic circuit are connected via electrical wires. The invention also comprises a method for measuring an absolute temperature at a. so-called hot-end side of a thermo coup1e elernent.
A thermocouple element for high temperature sensoi an produced on the basis of a so-called mineral-insulated cable. A mineral-insulated cable can comprise a sheath of tubular shape in which to wires can be arranged that form a so-called thermocouple. For electrically insulating the wires with regard to the sheath, the space between the wires and the sheath can be filled with a mineral powder, e.g. magnesium oxide or aluminum oxide. At a so called cold-end side of the thermocouple element, the thermocouple wires generate a thermo-voltage on the basis of the thermoelectric effect. The value of the thermo-voltage is a function of the temperature difference between the cold-end side of the thermocouple element and the opposite hot-end side. The end of the wires at the cold-end side are called cold-end electrodes in the sequel.
Temperature sensors based on a thermocouple element are designed in such a way that the thermocouple element is connected to the electronic circuit by means of a special cable, a so-called extension cable that provides wires with thermo-electrical properties that are the same as those of the wires of the thermocouple element itself. This arrangement allows to ef35 festively shift the cold-end of the thermocouple element from the cold-end electrodes of the thermocouple to a connection point on the electronic circuit itself.
As was already explained, the thermo-voltage is a function of a relative temperature. In order to obtain a value for the absolute temperature at the hot-end side of the thermocouple element, the absolute temperature of the cold-end side, where the thermo-voltage is measured, must be determined. To this end, the electronic circuit itself generally provides an additional temperature sensor that is designed to measure the absolute temperature at the connection point, where is connected on the electronic circuit.
However.
extension caoie
| same n | material | as the thermocouple wires, the m, | aterial | costs | are |
| high. | As an a | Iternative, a compensation cable | can be | used. | The |
| wires | of the | compensation cable provide simil | ,ar ther | - |
mo-electrical properties as one of the wires of the thermocouple element. However, using a compensation cable loses measurement accuracy.
It is an object of the present invention, to provide a measuring device for measuring an absolute temperature at a hot-end side of a thermocouple element.
The object is achieved by the subject matter of the independent claims. Advantageous developments with convenient and non-trivial further embodiments of the invention are specified in the following description, the dependent claims and the figures .
The invention provides a measuring device that can be used as a temperature sensor. The measuring device comprises a thermocouple element and an electronic circuit. Wires are provided for connecting cold-end electrodes of the thermocouple element with the measuring circuit. The electronic circuit comprises a voltage measuring circuitry that is designed to measure a thermo-voltage that is generated at the cold-end electrodes by the thermocouple element and that is transmitted to the electronic circuit over the wires. In the prior art, those wires must be provided by the described extension cable or the compensation cable, which would ·!
result in high production costs and/or loss of measurement accuracy. The reason for choosing those special cables is, that the point of measuring the thermo-volt age must be the same as the point of measuring the absolute temperature using the additional temperature sensing element. In the prior art the temperature sensing element is consequently placed in the electronic circuit.
In order to avoid the high costs of providing an extension cable or a compensation cable, the invention provides the following instead. One of the cold-end electrodes of the thermocouple element is connected to one of the wires over a passive temperature sensing element.
The passive temperature sensing element, comprises a temperature-dependent electric property, especially the electric resistance that is a function of the absolute temperature of the temperature sensing element. In order to measure this temperature-dependent electric property, the electronic circuit comprises a driving circuitry that is connected to the sensing element over the wires and that is designed to drive a measuring current through the passive temperature sensing element over the wires. In other words, the wires are not only used for receiving the thermo-voltage at the electronic circuit. Additionally, the wires are also used to transfer or conduct the measuring current from the electronic circuit to the cold-end electrodes in order to drive the measuring current through the temperature sensing element. By driving the measuring current through the temperature sensing element, an electric quantity, e.g. the electric voltage, results in dependence on the temperature-dependent electric property of the temperature sensing element.
The measuring device is designed to generate a temperature signal that is a function of the absolute temperature of the passive temperature sensing element. For example, the electric voltage can be measured that results from the measuring current flowing through the temperature sensing element. The temperature signal is then a voltage signal.
The invention provides the advantage that the thermo-voltage generated at the cold-end electrodes of the thermocouple element itself can be transferred or transmitted to the electronic circuit by means of ordinary wires, as the absolute temperature of the cold-end electrodes is measured or known by means of the temperature sensing element connected to one of the cold-end electrodes directly. Any temperature difference between the cold-end electrodes of the thermocouple element on one side and the electronic circuit on the other side does not have an effect on the evaluation of the thermo-voltage. As a voltage measuring circuitry any known circuitry can be used as it is already provided in thermocouple-based temperature sensors known in the prior art.
The invention also comprises optional embodiments that provide features which afford additional technical advantages.
Preferably, the pas temiperature sensing
I. v_. j. j.
i s ci
PTC-resistor (PTC?, - positive temperature coefficient) , Such an element provides a precise measurement of the absolute temperature .
The voltage measuring circuitry and the driving circuitry can be arranged on a. common printed circuit board (PC?B) . The wires connect the printed circuit board to the thermocouple element over a. distance. In other words, the temperature sensing element is detached from the printed circuit board. Nevertheless, the absolute temperature of the temperature sensing element can be determined by transferring the measuring current through the wires to the temperature sensing element such that temperature-dependent electric property of the sensing element can be determined over the wires.
As the absolute temperature can be measured at the cold-end electrodes of the thermocouple element itself, the wires can be made of the same material, especially copper or aluminum. This reduces the production cost of the measuring device.
For driving the measuring current comprise a voltage divider that is The voltage divider can connect a supply unit to a ground potential, to a region between two resistors voltage divider provides the adve resistance value of the temperatui by measuring the voltage between electronic circuit.
:, the driving circuitry can connected to one of the wires, power supply unit, or voltage The one wire can be connected ; of the voltage divider. A rntage that determining the :e sensing element is possible the wires on the side of the
For measuring the voltage, the voltage measuring circuitry can be used. In other words, the same circuitry that, is used for measuring the thermo-voltage can also be used for measuring the voltage evoked by the measuring current. Naturally, this is not possible at the same time. In other words, measuring the thermo-voltage and measuring the voltage evoked by the measuring current is performed at different time intervals. For switching between the two measurements, a switch can be provided. In other words, for switching or controlling the measuring current, the one of the wires can be coupled to a ground potential over a switch. Closing the switch will cause the measuring current to flow from the voltage divider through the wires and the temperature sensitive element and the switch to the ground potential. Opening the switch will block the measuring current and the voltage generated between the wires corresponds to the thermo-voltage generated by the thermocouple element between the cold-end electrodes. Closing; the switch will result in an additional voltage evoked by the measuring current in the temperature sensing element.
In order to control the measurements, a control circuitry may be designed to open the switch for measuring the thermo-voltage by means of the voltage measuring circuitry and to close the switch for measuring the voltage evoked by the measuring current in the temperature sensing element. The voltage measuring circuitry then generates the temperature signal that is the signal which is a function of the absolute temperature of the passive temperature sensing element. The control circuitry may be provided on the basis of a microcontroller.
S ‘•A
The measuring device may also be designed to perform, a. third measurement. To this end the voltage divider can be designed to generate a predefined voltage at the wire that it is connected to. However, this pre-defined voltage results under the condition that a leakage resistance that, is effective between the thermocouple elements and the ground potential is above a pre-defined threshold. In other words, by opening the switch and thus decoupling the wires from the ground potential, a certain minimum voltage should result at the wire connected to the voltage divider if the leakage resistance is above the threshold. Otherwise, with a leakage resistance below the threshold, the voltage will have a. lower value than the pre-defined voltage. Accordingly, the voltage measuring circuitry is designed to measure the actual voltage at the wire while the switch is opened. This results in a control signal that, can be used to determine or check the leakage resistance.
In order to determine the leakage resistance more precisely, e.g. for calibrating the measuring device, a second switch can be provided that is designed to provide an electrical short, circuit between the wires. By short-circuiting the wires, the measurement of the actual voltage of the wire that is connected to the voltage source is independent of the thermo-voltage . In other words, the leakage resistance can be determined at any temperature as the temperature of the thermocouple element has no influence on this measurement.
The measuring device allow method for determining an a: of a thermocouple element.
s to perform the following inventive bsolute temperature at a hot-end side As is known from the prior art the thermocouple element generates a thermo-voltage between cold-end electrodes of the thermocouple element., wherein the thermo-voltage is a function of a difference between the absolute temperature at. the hot-end side and the absolute temperature at.
the cold-end electrodes. Wires transmit or transfer the thermo-voltage to the electronic circuit. A voltage measuring circuitry of the electronic circuit measures the thermo-voltage at the wires. Thus, the temperature difference between the cold-end electrodes and the hot-end side of the thermocouple element can be determined by measuring the thermo-voltage. As one of the cold-end electrodes is connected to one of the wires over a passive temperature sensing element a driving circuitry of the electronic circuit can drive a measuring; current through the passive temperature sensing element over the wires. The measuring current will also flow through the wires of the thermocouple element. On the basis of the measuring current the measuring device generates a temperature signal that is a function of the absolute temperature of the passive temperature sensing element. The temperature signal describing the absolute temperature of the passive temperature sensing element can be the voltage that results from driving the measuring current through the wires and the temperature sensing element. For thermo-voltage can also be considered this measurement, the as this mav influence the measurement
As the passive tewerature sensing elemei is locate!
it one the cold-end electrodes, the absolute temperature of the cold-end electrodes is thus known. As the difference between the absolute temperature at the cold-electrodes and the absolute temperature of the hot-end side is also known from the measurement of the thermos-voltage alone, the absolute temperature of the hot-end side can be determined on the basis of the absolute temperature of the passive temperature sensing element and the difference between the described absolute temperatures.
The invention also comprises further developments of the inventive method that comprise features as they have been already described in connection with the further developments of the measuring device. For this reason, the features are not described again here.
In the following an exemplary implementation of the invention is described. The finures show:
Fig. 1 a schematic illustration of an embodiment of the inventive measuring device in a first measuring mode;
Fig. 2 a schematic illustration of the measuring device in a second measuring mode; and
Fig.
a schematic illustration of third measuring mode.
measuring crevice m a
The embodiment explained in the following is a preferred embodiment of the invention. However, in the embodiment, the described components of the embodiment each represent individual . LJ. v_. mo lently of each other and which each develop the invention also independently of each other and thereby are also to be regarded as a component of the invention in individual manner or in another than the shown combination. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.
In the figures elements that provide the same function are marked with identical reference signs.
Fig. 1 shows a measuring device 10 comprising a thermocouple element 11 and an electronic circuit 12 and’wires 13 that connect cold-end electrodes 14 of the thermocouple element 11 with contact electrodes 15 of the electronic circuit 12. Electronic circuit 12 can be, e.g., based on a printed circuit board 12' .
The thermocouple element 11 can be arranged in a distance 16 to the electronic circuit 12 the distance can be greater than 5 cm, especially greater than 10 cm. The thermocouple element 11 can be based on a mineral-insulated cable.
The electronic circuit 12 comprises a voltage measuring circuitry 17 that is designed to measure a voltage 18 between the contact electrodes 15. The voltage measuring circuitry 17 can be designed a:
is known from the prior art. The voltage measuring circu:
Generate:
itage signal V as a function of :age 18.
| Additionally, | the el | ectronic circuit. 12 | can compr | ise ; | a voltage |
| divider 19 whi | ch is | connected to one of | the wire | s 13 | and i s |
| designed to pr | ovide | a voltage 20 in the | wire 13. | The | voltage |
| divider 19 can | compr | ise resistors 21, 22 | for divi | ding | a supply |
voltage VO in the known manner in order to provide the voltage 20. The voltage divider 19 can connect the supply voltage VO to a ground potential 23. Voltage divider 19 represents a driving circuitry for driving measuring current I.
Further, the electronic circuit 12 can comprise switches 24, 25, 26. The switches can each be provided, e.g., as a transistor or as a relay. The switches 24, 25, 26 can be controlled by a control circuitry 27. Switch 24 can be controlled to either connect wire 13' with the ground potential 23 or to disconnect the wire 13' from, the ground potential 23. Switch 25 can be controlled to either provide a short circuit, between the wires 13, 13' or to electrically disconnect the wires 13, 13' . The switch 26 can be controlled to either connect the wire 13 with the voltage measuring circuit or to connect the voltage measuring circuitry 17 with the ground potential 23.
Fig.
iWS le measuring device 10 in a measurinu mode Ml for measuring a therm.o-volt.age 18' as voltage 18. To this end, control .rcuitry 27 controls swit: .sconnects wire 13' from 1 :es 24 to 26 such that switch 24 ne ground pot6-+- + ° 1 a ·v_ial 23, switch , 13' and switch 2 6 connects voltage measuring circuitry 17 to wire 13. Voltage divider 19 does not have an influence on the measurement of the voltage measuring circuitry 17.
The thermo-voltage 18' is generated by two thermocouple wires 28, 29 which are connected by a jointing 30 at a so-called hot-end side 31 of the thermocouple element 11. Thermo-voltage 18' is a function of the difference of temperatures at. hot-end side 31 and the so-called cold-end side 32 at which cold-end electrodes 14 are connected to wires 13, 13' .
Wires 13, 13' transfer the thermo-voltage 18' to contact 5 electrodes 15. Wires 13, 13' can be wires made of copper or aluminum and can be made of the same material.
The voltage measured by voltage measuring circuitry 17 in measuring mode Ml is thus a function of the temperature dif10 ference,
In order to measure the absolute temperature at hot-end side 31, a prior art measuring probe would have to use different wires instead of the wires 13, 13'. The wires would have to be those of an extension cable or a. compensation cable as described previously. Further, electronic circuit 12 would have to provide a temperature sensor 33 at the point of measuring thermo-voltage fi ’
-L >-> «
The measuring device 10 does not need such a temperature sensor 33 inside the electronic circuitry 12 and no specific type of wires. Instead, the absolute temperature is measured at. the cold-end electrodes 14 wcithout the need of any additional wiring.
To this end, measuring device 10 provides a second measuring mode M2 that is illustrated in Fig. 2. In measuring mode M2 the difference with regards to switches is that switch 24 connects w’ire 13' wmth ground potential 23.
Thus, voltage divider 19 drives a measuring current I through wires 13, 13' and wires 28, 29 of thermocouple element 11. Wire 13' is connected to cold-end electrodes 14 via a passive temperature sensing element 34. Sensing element 34 can be, e.g., a PTC-element, for example a PTC-resistor. An electric resistance of sensing element 34 is a function of absolute temperature of the sensing element 34. Thus, a voltage 35 caused by measuring current I at sensing element 34 is a function of the absolute temperature of the sensor 34, Conseguently, the voltage 18 measured by voltage measuring circuitry 17 between contact electrodes 15 is a function of the absolute temperature of the sensor 34 as well. From, the measured voltage 18 and the pre-defined resistance values of resistors 21, 22 of the voltage divider 19, the resistance value of sensing element 34 can be derived and finally the temperature of sensing element 34.
As sensing element 34 is arranged next to one of the cold-electrodes 14, the absolute temperature at code-end electrodes 14 can be determined in measurement mode M2. As from the measurement in measurement mode Ml the difference between the absolute temperatures at code-end side 32 and hot-end side 31 is known, the absolute temperature at hot-end side 31 of thermocouple element 11 can be determined in the known wav.
Fig. 3 illustrates a third measurement mode M3 for supervising or checking a value of a leakage resistance 36. Leakage resistance 36 is not an electric element, but can result, e.g. from moisture that can have reached thermocouple wires 28, 29 of thermocouple element 11. If the value of leakage resistance 36 is above a predefined threshold, voltage 20, as generated by voltage divider 19 has a predefined value, if no current is flowing through the thermocouple element 11. In order to block any current, switch 24 is opened such that wire 13' is disconnected from ground potential 23. Switch 25 is closed to provide the short circuit between wires 13, 13? . Switch 26 is switched such that voltage measuring circuitry 17 is connected to ground potential 23 in order to measure voltage 20. In other words, voltage measurement circuitry 17 is connected to ground potential at one electrode and to voltage divider 19 over another electrode and over switch 25.
With leakage resistance 36 above said threshold, the only significant electric current flows through resistor 22 resulting in a predefined value for voltage 20. However, if leakage resistance 36 is below the given threshold, voltaoe 20 results lower value than the predefined value ai resistance 36 acts like an additional resistore leakacre connected in parallel to resistor 22. This can be detected using voltage measuring circuitry 17 . If the measured voltage is below a certain threshold, a signal can be generated indicating that, the leakage resistance 36 is too low. Additionally or alternatively, a. calibration can be performed such that, the value of leakage resistance 36 is considered or compensated in measurement modes Ml and/or M2 .
Overall, the measurement probe 10 can be provided at lower costs compared to a measurement probe that uses an extension cable or a. compensation cable which must provide wires that are made of specific, expensive materials, instead of simple copper wires 13, 13'. The problem of replacing the cables of special alloys by conventional copper wires is solved by locating a passive temperature sensing element 34 in series with the wires 28, 29 of the thermocouple element 11 itself and by providing a switch for switching from the acquisition mode or measuring mode Ml for measuring the thermo-voltage 18' to a measurement, mode M2 where the resistance of the passive temperature element 34 and subsequently the absolute temperature of the cold-end side 32 is determined.
This provides savings in material costs as no cable of expensive materials must be provided and yields an increase in measurement accuracy as the temperature can be measured directly at the cold-end side 32 of the thermocouple element 11 itself. This also results in an improved accuracy since the accuracy of the cold-end temperature measurement at code-end side 32 may be improved with respect to measurements on the printed circuit board of the electronic circuit 12 itself, as no side effects, like temperature gradients and self-heating, can influence the measurement. Further, the dynamical behavior of the cold-end side 32 of the thermocouple element 11 provides a smaller time constant than the electronic circuit 12 was PCB 12' such that changes in temperature can be detected faster. Additionally, the printed circuit board 12' itself can be manufactured with less cost, as the thermal management of the printed circuit board 12' can be simplified, as no temperature sensor 33 must be considered.
Thus by providing the temperature sensitive element 34 cold-end side 32 together with driving circuitry in the the voltage source 19 and the switch 21 provides the poss of using wires 13, 30' that can be made of copper or al i.e. they had unit need to be adapted to the materials o at the form of ibility uranium, f wires
28, 29 of thermocouple element 11.
Overall, the example shows how in a thermocouple-based high temperature sensor the use of extension and compensation cables can be avoided.
Claims (10)
1. Measuring device (10) comprising a thermocouple element (11) and an electronic circuit (12) and wires (13, 13') for connecting cold-end electrodes (14) of the thermocouple element (11) with the measuring circuit (12), wherein the electronic circuit (12) comprises a voltage measuring circuitry (17) that is designed to measure a thermo-voltage (18') generated at the cold-end electrodes (14) by the thermocouple element (11) and transmitted to the electronic circuit (12) over the wires (13, 13'), characterized in that one of the cold-end electrodes (14) is connected to one of the wires (13') over a passive temperature sensing element (34), wherein the electronic circuit (12) comprises a driving circuitry (19) that is connected to the sensing element (34) over the wires (13, 13') and that is designed to drive a measuring current (I) through the sensing element (34) over the wires (13, 13'), wherein the measuring device (10) is designed to generate on the basis of the measuring current (I) a temperature signal that is a function of an absolute temperature of the sensing element (34).
2 . Measuring device (10) according to claim 1, wherein the sensing element (34) is a PCT-resistor.
3 . Measuring device (10) according to any of the preceding claims, wherein the voltage measuring circuitry (17) and the driving circuitry (19) are arranged on a common printed circuit board (12') and wherein the wires (13, 13') connect the printed circuit board (12') with the thermocouple element (11) over a distance (16) .
4 . Measuring device (10) according to any of the preceding claims, wherein the wires (13, 13') are made of the same material, especially copper or aluminum.
5. Measuring device (10) according to any of the preceding claims, wherein for driving the measuring current (I) the driving circuitry (19) comprises a voltage source (19), e.g. a voltage divider (21), that is connected to one of the wires (13).
6. Measuring device (10) according to claim 5, wherein for controlling (switching) the measuring current (I), another one of the wires (13') is coupled to a ground potential (23) over a switch (24) .
7. Measuring device (10) according to claim 6, wherein a control circuitry (27) is designed to open the switch (24) for measuring the thermo-voltage (18' ) by means of the voltage measuring circuitry (17) and to close the switch (24) for measuring a voltage (18) caused by the measuring current (I), wherein the voltage measuring circuitry (17) generates the temperature signal as a voltage signal.
8. Measuring device (10) according to any of the claims 6 to 7, wherein the voltage source (19) is designed to generate a pre-defined voltage (20) at the wire (13) that it is connected to, wherein the pre-defined voltage (20) results under the condition that a leakage resistance (36) that is effective between the thermocouple element (11) and the ground potential (23) is above a pre-defined threshold, and wherein the voltage measuring circuitry (17) is designed to measure the actual voltage (20) at the wire (13) while the switch (24) is opened.
9. Measuring device (10) according to claim 8, wherein a second switch (25) is provided that is designed to provide an electrical short cut between the wires (13, 13') for measuring the actual voltage (20) at the wire (13) independently of the thermo-voltage (18' ) .
10. Method for determining an absolute temperature at a hot-end side (31) of a thermocouple element (
11), wherein
- thermocouple element (11) generates a thermo-voltage (18') between cold-end electrodes (14) of the thermocouple element (11), the thermo-voltage (18) being a function of a difference between the absolute temperature at the hot-end side (31) and an absolute temperature at the cold-end electrodes (14),
- wires (13, 13') transfer the thermo-voltage (18' ) to an electronic circuit (
12), and
5 - a voltage measuring circuitry (17) of the electronic circuit (12) measures the thermo-voltage (12') at the wires (
13, 13'), characterized in that
- one of the cold-end electrodes (
14) is connected to one of the wires (13') over a passive temperature sensing element (34) and
10 - a driving circuitry (19) of the electronic circuit (12) drives a measuring current (I) through the passive temperature sensing element (34) over the wires (13, 13'), and
- on the basis of the measuring current (I) the measuring device (10) generates a temperature signal that is a function of the
15 absolute temperature of the sensing element (34).
Intellectual
Property
Office
Application No: GB1620871.2 Examiner: Ms Danielle Jones
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1620871.2A GB2557351A (en) | 2016-12-08 | 2016-12-08 | Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1620871.2A GB2557351A (en) | 2016-12-08 | 2016-12-08 | Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB201620871D0 GB201620871D0 (en) | 2017-01-25 |
| GB2557351A true GB2557351A (en) | 2018-06-20 |
Family
ID=58222053
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1620871.2A Withdrawn GB2557351A (en) | 2016-12-08 | 2016-12-08 | Method for measuring an absolute temperature at a hot-end side of a thermocouple element and measuring device comprising the thermocouple element |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2557351A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114324455B (en) * | 2021-12-11 | 2025-08-01 | 河南昊泰新材科技有限公司 | Carbon-point quality detection device |
| CN115452179B (en) * | 2022-11-07 | 2023-02-14 | 四川天利科技有限责任公司 | Multi-channel real-time self-calibration thermocouple cold end temperature measurement method |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1125030A (en) * | 1955-04-21 | 1956-10-23 | Advanced training in thermoelectric devices used for measuring or regulating temperatures on board mobile vehicles and aircraft | |
| GB1518594A (en) * | 1975-05-02 | 1978-07-19 | Siemens Ag | Temperature-measuring apparatus |
| CN2234085Y (en) * | 1995-08-08 | 1996-08-28 | 胡渭标 | Thermocouple cold junction temperature compensation circuit |
| CN102798481A (en) * | 2012-08-22 | 2012-11-28 | 哈尔滨汽轮机厂有限责任公司 | Cold junction compensation temperature measurement method of thermocouple |
-
2016
- 2016-12-08 GB GB1620871.2A patent/GB2557351A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1125030A (en) * | 1955-04-21 | 1956-10-23 | Advanced training in thermoelectric devices used for measuring or regulating temperatures on board mobile vehicles and aircraft | |
| GB1518594A (en) * | 1975-05-02 | 1978-07-19 | Siemens Ag | Temperature-measuring apparatus |
| CN2234085Y (en) * | 1995-08-08 | 1996-08-28 | 胡渭标 | Thermocouple cold junction temperature compensation circuit |
| CN102798481A (en) * | 2012-08-22 | 2012-11-28 | 哈尔滨汽轮机厂有限责任公司 | Cold junction compensation temperature measurement method of thermocouple |
Also Published As
| Publication number | Publication date |
|---|---|
| GB201620871D0 (en) | 2017-01-25 |
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