Method for Calibrating a Temperature Measuring Unit Based on Ultrasonic Measurement, Method for Measuring the Temperature of a Medium, Temperature Measuring Unit and Ultrasonic Flowmeter

Abstract

A method for calibrating a temperature measuring unit based on ultrasound measurement includes: establishing an empirical functional relationship between the medium temperature of a medium to be measured and the velocity of sound of a measurement signal passing through the medium to be measured; capturing at least the velocity of sound of the measurement signal, the temperature measured by means of a temperature sensor, and the time variation of the sensor temperature at at least two measuring points, wherein the at least two measuring points have a different medium temperature; determining the medium temperature from the measured temperature, taking into account the time variation of the sensor temperature, so that at least two pairs of values and exist; running a compensating curve through the pairs of values which corresponds to the empirical functional relationship; and storing the functional relationship.

Claims

1. A method for calibrating a temperature measuring unit based on ultrasound measurement, wherein the temperature measuring unit has an ultrasound measuring device with at least one ultrasound transmitter and at least one ultrasound receiver, wherein a temperature sensor is provided, the method comprising: establishing an empirical functional relationship T.sub.M(c) between the medium temperature T.sub.M of a medium to be measured and the velocity of sound c of a measurement signal passing through the medium to be measured; capturing at least the velocity of sound c of the measurement signal, the temperature T.sub.sensor measured by means of a temperature sensor, and the time variation of the sensor temperature dT/dt at at least two measuring points, wherein the at least two measuring points have a different medium temperature T.sub.M; determining the medium temperature T.sub.M from the measured temperature T.sub.sensor, taking into account the time variation of the sensor temperature dT/dt, so that at least two pairs of values (T.sub.M1, c.sub.1) and (T.sub.M2, c.sub.2) exist; running a compensating curve through the pairs of values which corresponds to the empirical functional relationship T.sub.M(c); and storing the functional relationship T.sub.M(c) in the temperature measuring unit.

2. The method according to claim 1, wherein, at at least two measuring points, the temporal variation of the sensor temperature dT/dt and/or the temporal variation of the measured velocity of sound dc/dt is below a fixed limit value.

3. The method according to claim 1, wherein, when determining the medium temperature T.sub.M from the sensor temperature T.sub.sensor, a time constant τ describing the inertia of the temperature sensor is additionally taken into account.

4. The method according to claim 3, wherein, for determining the medium temperature T.sub.M, the time constant τ is estimated from the measured sensor temperature T.sub.sensor in such a way that the at least two pairs of values (T.sub.M1, c.sub.1) and (T.sub.M2, c.sub.2) have a functional relationship.

5. The method according to claim 4, wherein the medium temperature T.sub.M is determined from the measured sensor temperature T.sub.sensor by means of the relationship T.sub.M=T.sub.sensor+τ*dT/dt; and wherein the time constant τ is estimated in such a way that the at least two pairs of values (T.sub.M1, c.sub.1) and (T.sub.M2, c.sub.2) have a functional relationship.

6. The method according to claim 1, wherein the pressure of the medium is additionally measured at each measuring point and a functional relationship T.sub.M(c,p) is established between the medium temperature T.sub.M, the velocity of sound c and the pressure p of the medium.

7. A method for measuring the temperature of a medium with a temperature measuring unit, wherein the temperature measuring unit has an ultrasonic measuring device with at least one ultrasonic transmitter and at least one ultrasonic receiver, the method comprising: calibrating the temperature measuring unit with a calibration method including the following steps: establishing an empirical functional relationship T.sub.M(c) between the medium temperature T.sub.M of a medium to be measured and the velocity of sound c of a measurement signal passing through the medium to be measured; capturing at least the velocity of sound c of the measurement signal, the temperature T.sub.sensor measured by means of a temperature sensor, and the time variation of the sensor temperature dT/dt at at least two measuring points, wherein the at least two measuring points have a different medium temperature T.sub.M; determining the medium temperature T.sub.M from the measured temperature T.sub.sensor, taking into account the time variation of the sensor temperature dT/dt, so that at least two pairs of values (T.sub.M1, c.sub.1) and (T.sub.M2, c.sub.2) exist; running a compensating curve through the pairs of values which corresponds to the empirical functional relationship T.sub.M(c); and storing the functional relationship T.sub.M(c) in the temperature measuring unit; measuring the velocity of sound c of the measurement signal passing through the medium to be measured; and determining the temperature of the medium from the stored relationship T.sub.M(c).

8. The method according to claim 7, wherein the temperature measuring unit has a temperature sensor; wherein, during operation, the temperature of the medium is determined at least at times both by means of the velocity of sound c and by means of the temperature sensor; and wherein the temperature T.sub.M determined by means of the velocity of sound c is compared with the sensor temperature T.sub.sensor.

9. The method according to claim 8, wherein if the temperature T.sub.M determined via the velocity of sound c deviates from the sensor temperature T.sub.sensor in the case in which dT/dt is below a specified limit value, the temperature measuring unit is automatically recalibrated according to the calibration method and/or a message is output with regard to the measured deviation.

10. A temperature measuring unit for measuring the temperature of a medium, comprising: at least one ultrasonic measuring device, wherein the ultrasonic measuring device has at least one ultrasonic transmitter and at least one ultrasonic receiver; and a control and evaluation unit; wherein a relationship T.sub.M(c), established according to a calibration method, between the medium temperature T.sub.M of the medium to be measured and the velocity of sound c of a measurement signal is stored in the control and evaluation unit; wherein the calibration method includes the following steps: establishing an empirical functional relationship T.sub.M(c) between the medium temperature T.sub.M of a medium to be measured and the velocity of sound c of a measurement signal passing through the medium to be measured; capturing at least the velocity of sound c of the measurement signal, the temperature T.sub.sensor measured by means of a temperature sensor, and the time variation of the sensor temperature dT/dt at at least two measuring points, wherein the at least two measuring points have a different medium temperature T.sub.M; determining the medium temperature T.sub.M from the measured temperature T.sub.sensor, taking into account the time variation of the sensor temperature dT/dt, so that at least two pairs of values (T.sub.M1, c.sub.1) and (T.sub.M2, c.sub.2) exist; running a compensating curve through the pairs of values which corresponds to the empirical functional relationship T.sub.M(c); and storing the functional relationship T.sub.M(c) in the temperature measuring unit; and wherein, during operation, the temperature measuring unit determines the current temperature of the medium T.sub.M from the measurement of the velocity of sound c of a measurement signal and from the stored relationship T.sub.M(c).

11. An ultrasonic flowmeter, comprising: a measuring tube; an ultrasonic measuring device having at least one ultrasonic transmitter and at least one ultrasonic receiver; and at least one temperature measuring unit, wherein the temperature measuring unit is designed so that, during operation, the ultrasonic flowmeter determines, on the one hand, the flow velocity of the medium from the transit time of a first measurement signal which passes through the medium both in the direction of flow and against the direction of flow, and determines, on the other hand, the temperature of the medium by measuring the velocity of sound c of the first measurement signal or of a second measurement signal.

12. The ultrasonic flowmeter according to claim 11, wherein the at least one ultrasonic transmitter and the at least one ultrasonic receiver of the temperature measuring unit are identical to the at least one ultrasonic transmitter and the at least one ultrasonic receiver of the ultrasonic flowmeter for determining the flow of the flowing medium.

13. The ultrasonic flowmeter according to claim 11, wherein the ultrasonic flowmeter has, in addition to the temperature measuring unit, at least one further ultrasonic transmitter and at least one further ultrasonic receiver, which form the ultrasonic measuring device for measuring the flow of a medium flowing through the measuring tube.

14. The ultrasonic flowmeter according to claim 11, wherein the temperature measuring unit is arranged on the measuring tube such that the ultrasonic transmitter and the ultrasonic receiver are arranged substantially planar to the measuring tube inner wall.

15. The method according to claim 2, wherein, when determining the medium temperature T.sub.M from the sensor temperature T.sub.sensor, a time constant τ describing the inertia of the temperature sensor is additionally taken into account.

Description

DESCRIPTION OF THE DRAWINGS

[0057] There is now a plurality of possibilities for designing and further developing the methods according to the invention, the temperature measuring unit according to the invention and the ultrasonic flowmeter according to the invention. For this, reference is made to the description of preferred embodiments in conjunction with the drawings.

[0058] FIG. 1 illustrates the temperature curve of an abruptly changing medium temperature and the adaptation of the temperature of a temperature sensor.

[0059] FIG. 2 illustrates a first embodiment of a method according to the invention for the calibration of a temperature measuring unit.

[0060] FIG. 3 illustrates the temperature curve of the temperature of the medium T.sub.M and the temperature of a sensor T.sub.sensor during temperature changes.

[0061] FIG. 4 illustrates the functional relationship between the velocity of sound c and the temperature of the medium T.sub.M.

[0062] FIG. 5 illustrates the temperature curve of the temperature of the medium T.sub.M and the temperature of the sensor T.sub.sensor in the case of sudden and continuous temperature changes of the medium as well as the simultaneously detected velocity of sound c.

[0063] FIG. 6 illustrates a second embodiment of a method for calibrating a temperature measuring unit.

[0064] FIGS. 7a to 7c illustrate the relationship between the velocity of sound c and the calculated medium temperature T.sub.M at different estimates of the time constant τ.

[0065] FIG. 8 illustrates an embodiment of a temperature measuring unit and an ultrasonic flowmeter.

[0066] FIG. 9 illustrates a method for measuring the temperature of a flowing medium.

DETAILED DESCRIPTION

[0067] FIG. 1 shows the behavior of a temperature sensor 12, in the case where the medium to be measured changes its temperature abruptly. It can be seen from the illustration that after an initial agreement of the temperature, the temperature sensor 12 can only follow the abrupt change of the medium temperature T.sub.M with a delay. After a time interval, the sensor temperature T.sub.sensor again matches the medium temperature T.sub.M.

[0068] FIG. 2 shows a first method 1 for calibrating a temperature measuring unit 3. The temperature measuring unit 3 comprises an ultrasonic measuring device 10 and a temperature sensor 12. The ultrasonic measuring device 10 comprises an ultrasonic transmitter and an ultrasonic receiver, wherein the ultrasonic receiver is arranged to receive a measurement signal 11 transmitted by the ultrasonic transmitter after passing through the medium. The temperature sensor 12 is arranged to measure the temperature of the medium.

[0069] In a first step 5, at least the velocity of sound c of a measurement signal, the temperature T.sub.sensor measured by means of a temperature sensor 12 and the variation over time of the sensor temperature dT/dt are determined at at least two measurement points, wherein the at least two measurement points have a different medium temperature T.sub.M.

[0070] In a next step 6, the medium temperature T.sub.M is determined from the measured temperature T.sub.sensor, taking into account the time variation of the sensor temperature dT/dt, so that at least three pairs of values (T.sub.M1, c.sub.1), (T.sub.M2, c.sub.2) and (T.sub.M3, c.sub.3) exist. According to this embodiment, the sensor temperature T.sub.sensor is recorded on each measurement point under the condition that the time variation of the measured temperature dT/dt is below a specified limit. In this case, this ensures that the measured sensor temperature T.sub.sensor corresponds to the medium temperature T.sub.M in the best possible way.

[0071] In a next step 7, the empirical functional relationship T.sub.M(c) is determined by forming the compensation curve through the pairs of values. The compensation curve corresponds to a polynomial fit through the pairs of values.

[0072] Then, the empirical functional relationship T.sub.M(c) is stored 8 in the temperature measurement unit 3.

[0073] FIG. 3 shows the curve of the change of the medium temperature T.sub.M, the sensor temperature T.sub.sensor as well as the velocity of sound c for recording the individual value pairs (T.sub.M1, c.sub.1), (T.sub.M2, c.sub.2) and (T.sub.M3, c.sub.3) according to the method shown in FIG. 2.

[0074] FIG. 4 shows the individual value pairs (T.sub.M1, c.sub.1), (T.sub.M2, c.sub.2) and (T.sub.M3, c.sub.3) together with the compensation curve describing the empirical functional relationship T.sub.M(c) between the medium temperature T.sub.M and the speed of sound c.

[0075] FIG. 5 shows the curve of the change in the medium temperature T.sub.M, the sensor temperature T.sub.sensor and the speed of sound c for recording the individual pairs of values (T.sub.M1, c.sub.1), (T.sub.M2, c.sub.2) and (T.sub.M3, c.sub.3), wherein, in contrast to the embodiment shown in FIGS. 2 to 4, the sensor temperature values T.sub.sensor, which lie in the course of a temperature change, are also taken into account. This has the advantage that the time required to determine the value pairs (T.sub.M1, c.sub.1) to (T.sub.Mn, c.sub.n) can be minimized.

[0076] FIG. 6 shows a further embodiment of a method 1 according to the invention for calibrating a temperature measuring unit 3. In a first step 5, at least the velocity of sound c of a measurement signal, the temperature T.sub.sensor measured by means of a temperature sensor 12 and the variation over time of the sensor temperature dT/dt are determined at at least two measurement points, wherein the at least two measurement points have a different medium temperature T.sub.M.

[0077] In a next step 6, the medium temperature T.sub.M is determined from the measured temperature T.sub.sensor, taking into account the time variation of the sensor temperature dT/dt. In an advantageous manner, the transition between the at least two medium temperatures T.sub.M is also taken into account in the embodiment shown for establishing the relationship sought between the speed of sound c and the medium temperature T.sub.M.

[0078] For this, the time constant τ of the temperature measuring unit is first estimated 9 with the help of the correlation T.sub.M=T.sub.sensor+τ*dT/dt in such a way that the values T.sub.M and c determined in this way give a smooth, i.e. unambiguous, functional correlation.

[0079] The correlation T.sub.M(c) determined in this way is then stored 8 in the temperature measuring unit 3. With the help of this correlation, the medium temperature can be determined particularly accurately and quickly during further operation by measuring the speed of sound c.

[0080] The following FIGS. 7a to 7c show the result of different estimations of the time constant τ for the best possible establishment of a correlation between the medium temperature T.sub.M and the velocity of sound c.

[0081] FIGS. 7a and 7b show the correlation between T.sub.M and c, for the case when the time constant τ was not estimated correctly. A smooth correlation between T.sub.M and c cannot be seen.

[0082] FIG. 7c shows a smooth correlation between the medium temperature T.sub.M and c. A functional relationship between T.sub.M and c can be established via the compensation curve of the values shown, so that the medium temperature T.sub.M can be determined via the measurement of the velocity of sound c.

[0083] FIG. 8 shows a temperature measuring unit 3 comprising an ultrasonic measuring device 10, with two ultrasonic transducers 18, each designed as a transmitter and receiver, for transmitting and receiving a measuring signal 11. In addition, a temperature sensor 12 is provided, which determines the temperature of the medium located in the measuring tube 13. Furthermore, a control and evaluation unit 14 is provided, which determines the temperature of the medium from the measured velocity of sound of a measuring signal 11.

[0084] In addition, the temperature measuring unit 3 is designed in such a way that it can determine not only the medium temperature T.sub.M via the present velocity of sound c. Rather, the temperature measuring unit 3 can monitor, during operation, whether the temperature values determined via the speed of sound are correct, or whether an adjustment of the estimate of τ by communicating with the temperature sensor 12 and thus a recalibration is required. In this respect, the temperature measuring unit 3 is equally suitable for detecting changes in the process conditions, such as a change of media.

[0085] The ultrasonic measuring unit 10 shown is likewise arranged and designed in such a way that the flow velocity of the medium can be determined by measuring the difference in transit time of the measuring signal 11 in and against the flow direction of the flowing medium. In this respect, FIG. 8 likewise shows an ultrasonic flowmeter 4 which, in an advantageous manner, can simultaneously determine the medium temperature T.sub.M particularly quickly.

[0086] FIG. 9 shows a method 2 for measuring the temperature of a flowing medium by means of a temperature measuring unit 3 calibrated with a method 1 according to the embodiment shown in FIG. 2 or 6.

[0087] In a first step 15, a measurement signal 11 is emitted into the medium. In a next step, the velocity of sound c is determined from the transit time of the measurement signal 16. The medium temperature T.sub.M is determined 17 from the velocity of sound c according to the stored relationship T.sub.M(c).

[0088] The illustrated method for measuring the temperature of a medium has the advantage that it enables a particularly accurate and fast temperature measurement.