DE19517236C2 - Method and device for monitoring the flow of flowing media - Google Patents

Method and device for monitoring the flow of flowing media

Info

Publication number
DE19517236C2
DE19517236C2 DE1995117236 DE19517236A DE19517236C2 DE 19517236 C2 DE19517236 C2 DE 19517236C2 DE 1995117236 DE1995117236 DE 1995117236 DE 19517236 A DE19517236 A DE 19517236A DE 19517236 C2 DE19517236 C2 DE 19517236C2
Authority
DE
Germany
Prior art keywords
temperature
flowing medium
heating element
flow
temperature measuring
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
DE1995117236
Other languages
German (de)
Other versions
DE19517236A1 (en
Inventor
Walter Dipl Ing Reichart
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
IFM Electronic GmbH
Original Assignee
IFM Electronic GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by IFM Electronic GmbH filed Critical IFM Electronic GmbH
Priority to DE1995117236 priority Critical patent/DE19517236C2/en
Publication of DE19517236A1 publication Critical patent/DE19517236A1/en
Application granted granted Critical
Publication of DE19517236C2 publication Critical patent/DE19517236C2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow
    • G01F1/68Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using thermal effects
    • G01F1/684Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/688Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
    • G01F1/69Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element of resistive type
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow
    • G01F1/68Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using thermal effects
    • G01F1/684Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/688Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow
    • G01F1/68Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using thermal effects
    • G01F1/696Circuits therefor, e.g. constant-current flow meters
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow
    • G01F1/68Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using thermal effects
    • G01F1/696Circuits therefor, e.g. constant-current flow meters
    • G01F1/698Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
    • G01F1/6986Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters with pulsed heating, e.g. dynamic methods

Description

The invention relates to a method for monitoring the flow of flowing Me serve, with the help of at least one partially influencing the flowing medium Heating element, with the help of at least one at least predominantly from the Heating element unaffected portion of the flowing medium affected first Temperaturmeßelementes and with the help of at least one at least predominantly from affected by the heating element proportion of the flowing medium second temperature measuring element, in which with the inclusion of the together depends on the flow velocity of the flowing medium and the Temperature difference between the first and the second temperature measuring element a measuring signal proportional to the flow velocity of the flowing medium gnal is generated. The invention further relates to a device for implementation of the method according to the invention, namely a so-called flow meter.

Flow meters as calorimetric flow monitors have been around for a long time gem and known in many embodiments (see, for example, the German Offenle 24 47 617, 26 29 051, 32 13 902, 32 22 046, 34 24 642, 37 13 981, 38 11 728, 38 25 059, 39 11 008, 39 43 437 and 44 06 541).

In the kalorimetri known from German Offenlegungsschrift 34 24 642 flow monitor is the difference between the temperatures of a warm flowed through boundary layer of the flowing medium to the temperature of the un influences the flowing medium evaluated to the speed of the to determine flowing medium. The temperature difference described is pro proportional to the heat transfer coefficient α. The heat transfer coefficient α is again a function of the speed of the flowing medium and the Temperature of the portion of the flowing medium unaffected by the heating element to.

In the case of the methods known from the prior art for monitoring the currents With flowing media, it is often assumed that the influence of temperature the proportion of the flowing medium which is not influenced by the heating element will, d. H. the temperature of the flowing medium in front of the flow switch is neglected, i.e. the heat transfer coefficient α and thus the measured  Temperature difference directly proportional to the flow speed of the flow the medium is.

Cause of the described simplification of the influences on the heat transfer co efficient α and thus the measured temperature difference is the structure of the previously known flow switch. In general, the measurements of tempera difference made on the basis of bridge circuits in which PTC's, NTC's or other temperature-dependent components used as temperature measuring elements will. With almost all temperature-dependent components it is problematic that this have a non-linear characteristic, which also goes from component to component scatters. On the one hand, this leads to a limited interchangeability of these components, e.g. B. as part of maintenance work, on the other hand to difficulties in construction of a precisely working flow switch. In particular, the known construction parts problematic in that their non-linearity and component dispersion a correction of the dependence of the heat transfer coefficient and thus the measured temperature difference from the temperature of the heating element un influenced portion of the flowing medium is almost impossible.

The lack of possibility to compensate for the dependence of the heat transfer coefficient α or the measured temperature difference from the temperature the unaffected portion of the flowing medium may depend gig of the flowing medium actually monitored, be serious.

In Fig. 1 of the drawing, the heat transfer coefficient α is shown depending on the Ge speed of the flowing medium at temperatures of 10, 25 and 80 ° C for water. One can clearly see the great dependence of the heat transfer coefficient α on the temperature of the uninfluenced portion of the flowing medium, on the other hand, the non-linearity of this dependence. It is therefore only possible to use one of the known flow monitors for water without errors if the temperature of the portion of the flowing medium uninfluenced by the heating element is known.

In addition to the known temperature-dependent components described so far, so-called dynamic temperature meters, which operate according to the "proportional to absolute temperature" method (PTAT method), are generally known as temperature meters (cf. Elektor 1/93, Ing. Harro Kühne, "Dynamic Temperature Meter ", Pages 54 to 58). These dynamic temperature meters work on the physical principle that the difference in voltage drop across a semiconductor junction with two different forward currents corresponds directly to the product of a constant, the absolute temperature and the natural logarithm of the quotient or the ratio of the forward currents. Expressed mathematically, this physical principle is:

The dynamic temperature meters work in such a way that a semiconductor junction is alternately acted upon with two different forward currents. Older known methods use the described physical principle in that that two identically constructed semiconductor junctions, which are on the same tempe rature are subjected to different forward currents. The be Known dynamic temperature meters are characterized by the fact that they have a rela tiv large measurement signal that no adjustment is necessary that the voltage diff reference is directly proportional to the absolute temperature and that the sensor elements are interchangeable without adjustment.

The invention is based on the object, the known methods and ago directions for monitoring the flow of flowing media ten that the measuring accuracy even with varying temperatures of the heating ment unaffected portion of the flowing medium is significantly increased.

In the method according to the invention, the object outlined above is thereby solved that as a temperature measuring element each a let-through current half conductor transition or several forward current-applied semiconductor junctions same temperature are used that at least per temperature measuring element a voltage difference between two forward voltages at different through let flow is determined and that a compensation of the loading influence of the relationship between the flow velocity of the stream  menden medium and the temperature difference by the un of the heating element influenced temperature of the flowing medium by controlling the Forward currents of the semiconductor junction or the semiconductor junctions depending on the temperature of the flowing medium unaffected by the heating element is taken. According to the invention it has been recognized that so-called dy Named temperature meters not only because of their well-known properties are particularly suitable for use as temperature measuring elements in a process suitable for monitoring the flow of flowing media, but also beyond Have properties that are irrelevant in general use, they but make it particularly suitable for use in such a process. The control of the forward currents of the semiconductors proposed according to the invention Transitions depending on the temperature of the heating element unaffected flowing medium is particularly advantageous because the compensation thus achieved tion of influencing the relationship between flow velocity of the flowing medium and the temperature difference due to that of the heating element unaffected temperature of the flowing medium with high reproducibility speed and precision is guaranteed.

An advantageous embodiment of the method according to the invention is thereby ge indicates that the compensation is based on a linear or non-linear control tion of the ratio of the forward currents of at least one temperature measuring element depending on the temperature of the flowing Me unaffected by the heating element diums is made. By directly controlling the relationship of the Let-through currents of one of the two temperature measuring elements thus become sensitive speed of this temperature measuring element depending on the temperature of the Controlled heating element unaffected flowing medium. This ensures that the measurement signal generated by the inventive method is independent of is the temperature of the flowing medium unaffected by the heating element. If she Control is linear or non-linear, is from the relationship between the Heat transfer coefficient and the temperature of the heating element not be influenced flowing medium.

Another particularly advantageous embodiment of the method according to the invention rens is characterized in that as a temperature measuring element in certain  Time intervals with different forward currents of semiconductors gear is used. This measure ensures a particularly simple structure of the temperature measuring element, since in this case only one per temperature measuring element Semiconductor transition is necessary. The offset error is preferably one of the Output signals of the temperature measuring elements amplifying differential amplifier Suppressed with the help of a chopper network. The use of a chopper network is possible because the temperature difference is the difference between the signals of the two tempera tower elements as a dynamic signal. By the described measure is the measuring accuracy of the inventive method for monitoring the Flow of flowing media further increased.

In detail, there are now a variety of ways to Ver the invention drive and the device for monitoring the flow stream designing and developing media. On the one hand, reference is made to this the claims 2 to 4 subordinate to claim 1, on the other hand the description of a preferred embodiment in connection with the Drawing. In the drawing shows

Fig. 2 is a block diagram of an embodiment of a circuit for Ver realization of the inventive method,

Fig. 3 is a schematic representation of a semiconductor junction to Erläute tion of the underlying physical principle of temperature measurement,

Fig. 4 is a circuit diagram of a sensor bridge for realizing the temperature difference measurement and

Fig. 5 is a circuit diagram of the sensor bridge shown in Fig. 4 in connection with a chopper network downstream of a differential amplifier.

Fig. 2 shows a block diagram of an embodiment of a circuit for the realization of the inventive method. In this embodiment, a sensor system 1 is provided for determining the temperature difference, evaluation electronics 2 for evaluating the temperature difference supplied by the sensor system 1 , control electronics 3 and an output stage 4 serving to amplify the output signal of the evaluation electronics 2 . As already described in the introduction, we take compensation measures carried out by the control electronics 3 via the evaluation electronics 2 back to the sensor system 1 , namely to the ratios of the forward currents alternately present at a semiconductor junction for certain periods.

The semiconductor junction 5 shown schematically in FIG. 3 is polarized in the forward direction in the method according to the invention, as is known for dynamic temperature meters, the forward currents I 1 / I 2 periodically taking different values. The difference between the voltage drops U pn determined at the semiconductor junction 5 for the different forward currents I 1 / I 2 is directly proportional to the absolute temperature of the semiconductor junction 5 .

In Fig. 4 is a circuit diagram of a sensor bridge is shown, with the help of the flow rate of the flowing medium proportional temperature difference is determined. In the sensor bridge shown, the first temperature measuring element 6 consists of a reference semiconductor junction 7 and a switched reference constant current source 8 . Analogously, the second temperature measuring element 9 consists of a sensor semiconductor transition 10 and a likewise switched sensor constant current source 11 . In the circuit diagram of a sensor bridge shown in Fig. 4, the series resistors are switched synchronously and thus different forward currents are forced for the semiconductor junctions. The accuracy of the ratios of the forward currents can be set very precisely via the resistors arranged in the reference constant current source 8 and in the sensor constant current source 11 . In Fig. 4 is not shown the possibility of controlling the ratios of the forward currents of one of the temperature measuring elements 6 , 9 depending on the unaffected by the heating element temperature of the flowing medium. This can be ensured, for example, by the arrangement of further switchable resistors in the reference constant current source.

In Fig. 5 of the drawing, the sensor bridge shown in Fig. 4 is finally shown with egg nem downstream differential amplifier 12 and an associated chopper network 13 .

Claims (5)

1. A method for monitoring the flow of flowing media, with the aid of at least at least one heating element partially influencing the flowing medium, with the help of at least one at least predominantly influenced by the heating element unaffected portion of the flowing medium first temperature measuring element and with the help of at least one at least predominantly by the Heating element be influenced portion of the flowing medium influenced second Temperaturmeßele mentes, in which, taking into account the relationship between the flow velocity of the flowing medium and the temperature difference between the first and second temperature measuring elements, a flow signal of the flowing medium proportional measurement signal is generated by characterized in that as a temperature measuring element each a pass-through current semiconductor transition or several pass-current-applied semiconductor transitions at the same temperature ur be used that each Temperaturmeßele element at least one voltage difference between two forward voltages at different forward currents is determined and that compensation for influencing the relationship between the speed of the flow medium of the flowing medium and the temperature difference by the unaffected by the heating element temperature of the flowing medium by a controller the forward currents of the semiconductor junction or the semiconductor junctions is made depending on the temperature of the flowing medium unaffected by the heating element.
2. The method according to claim 1, characterized in that the compensation a linear or non-linear control of the ratio of the passage currents at least one temperature measuring element depending on the heating element unaffected temperature of the flowing medium is made.
3. The method according to any one of claims 1 or 2, characterized in that as Temperature measuring element in certain time intervals with different Passing currents applied semiconductor transition is used.  
4. The method according to claim 3, characterized in that the offset error the output signals of the temperature measuring elements amplifying differential amplifier is suppressed with the help of a chopper network.
5. Device for realizing the method according to one of claims 1 to 4, with a heating element partially influencing the flowing medium, with an at least predominantly influenced by the heating element unaffected by the proportion of the flowing medium first temperature measuring element ( 6 ) and with at least predominantly from the portion of the flow influenced by the heating element influencing the medium, the second temperature measuring element ( 9 ), taking into account the relationship between the flow rate of the flowing medium and the temperature difference between the first and the second temperature measuring element ( 6 , 9 ) a the flow rate of the flowing medium measurement signal proportional can be generated, characterized in that the temperature sensor (6, 9) each have a durchlaßstrombeaufschlagten semiconductor junction (7, 10) or more semiconductor durchlaßstrombeaufschlagte transitions (7, 10) at the same Temperature has that means are available through which at least one voltage difference between two forward voltages for different forward currents can be determined per temperature element ( 6 , 9 ) and that means are available through which compensation for influencing the relationship between the flow rate of the flowing medium and the temperature difference is effected by the temperature of the flowing medium unaffected by the heating element by controlling the forward current or the forward currents of the semiconductor junctions depending on the temperature of the flowing medium uninfluenced by the heating element.
DE1995117236 1995-05-15 1995-05-15 Method and device for monitoring the flow of flowing media Expired - Fee Related DE19517236C2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE1995117236 DE19517236C2 (en) 1995-05-15 1995-05-15 Method and device for monitoring the flow of flowing media

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE1995117236 DE19517236C2 (en) 1995-05-15 1995-05-15 Method and device for monitoring the flow of flowing media

Publications (2)

Publication Number Publication Date
DE19517236A1 DE19517236A1 (en) 1996-11-21
DE19517236C2 true DE19517236C2 (en) 1998-12-24

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Family Applications (1)

Application Number Title Priority Date Filing Date
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3196679A (en) * 1962-05-22 1965-07-27 Lockheed Aircraft Corp Fluid no-flow detection apparatus
US3968685A (en) * 1973-02-16 1976-07-13 Her Majesty The Queen In Right Of Canada As Represented By The Minister Of National Defence Transistor anemometer
DE3424642A1 (en) * 1983-07-11 1985-01-31 Gen Motors Corp Solid air flow probe
DE3518409A1 (en) * 1984-05-22 1985-11-28 Toshiba Kawasaki Kk Semiconductor flow meter for determining flow amount and direction of a flow medium

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3196679A (en) * 1962-05-22 1965-07-27 Lockheed Aircraft Corp Fluid no-flow detection apparatus
US3968685A (en) * 1973-02-16 1976-07-13 Her Majesty The Queen In Right Of Canada As Represented By The Minister Of National Defence Transistor anemometer
DE3424642A1 (en) * 1983-07-11 1985-01-31 Gen Motors Corp Solid air flow probe
DE3518409A1 (en) * 1984-05-22 1985-11-28 Toshiba Kawasaki Kk Semiconductor flow meter for determining flow amount and direction of a flow medium

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DE-Z: Elektor 1/93, S. 54-58 *

Also Published As

Publication number Publication date
DE19517236A1 (en) 1996-11-21

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Date Code Title Description
OP8 Request for examination as to paragraph 44 patent law
D2 Grant after examination
8363 Opposition against the patent
8365 Fully valid after opposition proceedings
8320 Willingness to grant licenses declared (paragraph 23)
8339 Ceased/non-payment of the annual fee