FR2746180A1 - DEVICE FOR DETERMINING THE FLOW OF A FLOWING AGENT - Google Patents

Abstract

Device characterized in that the measurement voltage is fed to a frequency-voltage conversion circuit (UFW) whose frequency is a measurement of the flowing fluid and in that there is a high temperature calibration stage (HTA) , which comprises a third arrangement of resistors with at least one potentiometer, which is located in the transverse branch of the bridge and can be variably adjusted.

Description

STATE OF THE ART The invention relates to a device for determining the

  flow of a flowing agent, for example mass

  of air drawn in by an internal combustion engine, with a subs-

  trat exposed to the flowing fluid, on which is disposed a first resistance device, which is a component of a heating control circuit, with at least one resistance that can be brought to a predefined higher temperature and with a second resistance device which is connected in the form of a bridge with a diagonal lying between a supply voltage and ground and at least two resistors

  depending on the temperature which are arranged above and below

  below the heating resistance with respect to the direction of flow of the agent to be detected, so that they are regularly heated by the latter, while they are

  cooled significantly differently by the flowing fluid

  and that the measurement voltage which is established as a result of

  the temperature difference is exploited on the other diago-

  nale of the bridge to determine the flow

  We know, for example from the document DE-OS-

  43 24 040 detectors as well as corresponding operating circuits with which the flow of a flowing fluid can be determined. In the case of such mass detectors

  known, the sensing element is exposed to the flowing agent

  ment, for example an air flow in the intake pipe of an internal combustion engine. The detection element in this case comprises a heating device which, thanks to

  the supply of a regulated current is brought to a temperature above

  less than that of the agent to be determined. We associate with this dis-

  positive heating a temperature sensor of the heater, as well as a temperature sensor that detects the temperature of the flowing fluid. In the space near the heaters there are at least two resistors

  varying with temperature, which are found

  tively on one side of the heating device with respect to the direction of flow of the fluid to be detected and are regularly heated by the heating device. The resistors are however cooled differently strongly by the flowing fluid, because the resistance which is first swept by the flowing fluid is more strongly cooled than the other

  resistance. As the two resistances are the parts

  of a measuring bridge, the difference in temperature

  duit a measurement voltage on a diagonal of the bridge. Depending on this measurement voltage, the mass can be determined

flowing fluid.

  In the German patent application, not previously published, DE-P-19 542 143 there is described a supplement to the

  device known from document DE-OS-43 24 040 used for de-

  terminate the flow of a flowing fluid, which has a

  improved temperature behavior. The complement of the provision

  initially known, includes another resistance circuit

  these year bridge, which allows to have a taring at high temperature.

Advantages of the invention

  The device according to the invention which is used to determine

  ner the flow of a flowing fluid is characterized in that the measurement voltage is brought to a frequency-voltage conversion circuit whose frequency is a measurement of the fluid in

flow.

  The device has in relation to the state of the art

  that the advantage that the output signal has a frequency

  which is a function of the flowing fluid. We get this advantage

  tage by supplementing a known device used to determine the flow rate of a flowing fluid with a frequency-voltage conversion circuit, to which the measurement signal is supplied. It is particularly advantageous that the known device serving to

  determine the flow rate of a flowing fluid can be con-

  served and that the corresponding circuit must only be com-

  completed by another part of the circuit.

  One advantage is that you can

  read a taring at high temperature, being able to make it inde-

  during frequency-voltage conversion.

  According to other characteristics of the invention:

  - we have a high temperature setting stage (HTA), which

  takes a third arrangement of resistors with at least one potentiometer, which is in the transverse branch of the bridge and can be variably adjusted,

  - the tension in the diagonal of the third arrangement of re-

  resistance and the measurement voltage are superimposed one on

  the other to produce the temperature compensated output signal

  erasure, - the frequency-voltage conversion stage comprises at least one integrator connected as an operational amplifier (OP4) and a comparator (KP1) with at least two connection thresholds S1, S2, which together form a system capable of oscillating , - the comparator output (KP1) leads to a connection (FA), from which the output signal can be taken, the frequency of which depends on the mass of the flow, - the non-inverting inputs of the operational amplifier ( OP4) and the comparator (KP1) are at the fixed potential predefined by the heating circuit, - the high temperature setting stage (HTA) is made up

  as a source of intensity, which brings to the integrator an

  additional current, - the circuit is dimensioned in such a way that the charge intensity of the integrator is significantly greater than the discharge intensity, - the dimensioning of the calibration stage at high temperature is carried out in such a way that the resistor R13 via which the intensity is brought to the integrator, is currentless at the

ambient temperature.

  The invention will be described below in more detail on the basis of an exemplary embodiment shown in the single figure.

  Description of the exemplary embodiment

  The figure shows the circuit of one of the devices according to the invention used to determine the flow rate of a flowing fluid, the whole description being found by

  example on a substrate 10, and being exposed in a suitable manner

  property of the fluid to be determined, for example the air flow in

the internal combustion pipe.

  The HK heating control circuit includes a bridge installation with the resistors Rl, R2, R3, RHF and RLF,

  RHF being the temperature sensor of the heating device

  fage and RLF being the sensor of the air or fluid temperature and the value of these resistances being a function of the temperature. The resistance bridge of the HK heating control circuit is supplied with a voltage source SQ by a UK voltage. It is located between the voltage source SQ and ground. The intensity delivered by the voltage source SQ

is designated by He.

  Heating takes place using the heating resistor RH which is located on the emitter-collector path

  of a transistor Til as well as on a resistance R0l at the voltage

  UB battery charge. To stabilize the tension there is between the connection of the resistance R10 which is far from the battery and the mass a Zener diode Dl; if applicable there may be

  capacitors Cl and C2 between resistor R10 and ground.

  The connection of the RH heating resistor which is far from the battery, is connected via a resistor R5 to

the mass.

  While the first diagonal of the heating circuit bridge connection is between the voltage source SQ with the output voltage UK and ground, the second diagonal

  of the bridge is connected to the two inputs of an operational amplifier

  tional OPl, the output of which controls the base of transistor Tl.

  Between the inverting input of the operational amplifier OPl and the heating resistor RH or the emitter of the transistor Tl is still a resistor R4. Between the two inputs of the operational amplifier OPl and ground there is the case

  capacitors C5 and C6.

  The actual measurement circuit is an assembly

  bridge resistors designated as time difference bridge

  DT temperature (AT bridge mounting) with resistors RAB1, RAB2, RAUl, RAU2 and RP. These resistors are resistors

  which are a function of temperature, and which are also found

  as the RHF heating resistance at a higher temperature.

  are shown in the solid line circuit, the resistors which are at a lower temperature are hatched. The resistors RABl and RAB2 are arranged, with respect to the direction of flow of the fluid to be detected, downstream of the heating resistor RH, the resistors RAUl and RAU2 are however upstream. In another configuration of the invention one could also only insert respectively

  resistance upstream and resistance downstream of the resistance

  tance of heating, with respect to the direction of flow.

  The resistance bridge of the AT, DT circuit is located between the HTA high temperature taring step and earth.

  To supply the resistance bridge, an intensity is passed

  sity I2 of the HTA high temperature taring step at the

  power supply for resistance bridges. The other diagonal of the resistance bridge is in connection with the amplifier OP2 leading to the connection of the cursor of a potentiometer Pi which is located in parallel with the resistance RP of the measurement bridge. Between the two entries of

  OP2 amplifier and ground there may be condensa-

  C7, C8. The OP2 amplifier is an amplifier with an adjustable amplification, the digital calibration of the amplification

  is made using the VA block, which has three connections

  elements PR, DA, TA by means of which are brought by a device

  tif external operation the necessary control signals.

  These control signals may include programs, data or synchronization signals. Digital taring

  amplification takes place for example by influencing the resistance

  VR feedback from the OP2 amplifier. At the output of the amplifier OP2, the measurement voltage UM is created, which is

  brought to the frequency-voltage converter UFW.

  The frequency-voltage converter UFW includes

  lon the example of embodiment shown the setting at high temperature HTA and an area of the circuit designated by UFW1, which will

  described in more detail below.

  Both the high temperature setting stage

  MV as the UFWl area of the frequency converter circuit

  voltage is also connected to the supply diagonal of the AT bridge, Dt. The common link is a component of the feedback branch of an operational amplifier OP3, or the input

  non-inverting from which is brought by a resistor R4 the tension

  sion UK. The UK voltage is also brought to the operational amplifier OP2, it is designated in this case

like the voltage UM 0.

  The HTA high temperature taring step includes

  the resistors Rll, R12 and the resistances depending on the time

  temperature, R15, R16, which are at the higher temperature

  better. The resistors mentioned are connected in bridge with one of the sides of the bridge being earthed. In the diagonal of the measurement of the high temperature setpoint HTA is a potentiometer P2, by means of the central terminal from which a setpoint voltage UA can be taken. This voltage UA is brought by the resistor R13 to the voltage divider R6, R7 and

  in this case superimposed on the measurement voltage UM.

  The voltage UA directed by the resistor R13 of the high temperature setting step MV is brought to the inverting input of the operational amplifier OP4 whose output is driven by the resistors R8, R9 at the output of all

  circuit. The non-inverting input of the operation amplifier

  nel OP4 is connected to the non-inverting input of the amplifier

  OP1 of the HK heating control circuit and con-

  also due to the non-inverting input of a comparator KP1.

  The non-inverting input of the comparator KP1 is linked by the resistor R8 to the output of the operational amplifier OP4. Between the output of the operational amplifier OP4 and the resistor R13 is a capacitor C4. In addition, it is also possible to connect a capacitor C9 between the output of the operational amplifier OP4 and the ground, and in parallel to it.

  resistance Rll. The frequency-voltage converter is com-

  supplemented by the two resistors R17 and R18, which are found

  be output A of the circuit and output of comparator KP1. At output A, the voltage UFA occurs, the frequency FA of which is a function of the flow of the agent. If necessary there may be a

  other capacitor C3 between output A and ground. The connection

  the ground of the entire circuit is designated in the usual way by GND. Part of the circuit, which is designated by

  IC1 can be realized in its entirety in the form of a circuit

baked integrated.

  Description of the frequency-voltage converter

  The part of the circuit, which is designated by UFW,

  constitutes the frequency-voltage converter proper.

  In this case, the HTA high temperature rating bridge is not used

  at the same time as the resistance R13 as with the correction of the

  temperature increase. The operational amplifier OP4 is connected as an integrator and forms at the same time as the

  comparator KPl a system which can oscillate. Non-entry

  the operational amplifier OP4 or the inverting input of the comparator KPl, which are directly linked to

  the other is at the fixed potential, which is predefined by the HK heating control circuit. The potential is found in this way as well on the non-inverting input of the operational amplifier OP1 as also at the point of connection.

  sound between resistors R2 and RLF, which constitutes a point on the measurement diagonal of the heating control circuit. This

potential is designated by U +.

  With the voltage divisions shown we obtain

  holds the discharge intensity IE according to the equation:

IE = (U + -UM) / R6

  This intensity is constantly passing. The charging current IA, which only exists during the charging phase, is supplied via the resistor R7. The load intensity IA only passes, when the comparator output is on "high". For the load intensity IA, we have: IA = UREF / (R7 + R17 // Rl8) When the output signal of the comparator KP1 is "low", we adjust the potential at the connection point between the resistors R17, R18 and R7 on U +. In this way the resistance

R7 becomes currentless.

  The KP1 comparator conversion thresholds are

  fixed by the voltage U + as well as by the resistors R8 and R9.

  In this case we have for the first threshold: Si = (R8 + R9) / R9. U + or

R8 / (R8 + R9). S2 = U +

  In this way we have for the second threshold:

S2 = U + -R8 / R9. (UREF -U +)

  On the comparator KP1 there is consequently an os-

  triangular cillation, crossed by the amplitude AU = S1 -S2.

  When charging, we therefore have the relation:

(IA -IE). TA / C4 = AU

  Correspondingly we have during the discharge:

IE. TE / C4 = AU

  TA designating the charging time and TE the discharging time if the last two equations are satisfactory, we

  can get a relation for the FA output frequency.

We have:

IA. TA = IE. (TA + TE) = IE / FA

  For the output frequency FA we have in this way the following equation:

FA = 1 / TA. IE / IA

  By an appropriate dimensioning of the circuit represented

  felt in the figure, we have the assurance that the charge intensity IA is significantly greater than that of discharge IE. For the charging time TA we have this way:

TA = AU.C4 / (IA-IE) AU. C4 / IA

  If we enter TA in the equation presented above

above, we then have:

FA = IE

  C4.AU If we insert the intensity IE 'into the above equation, we have the following equation for the output frequency: 1 U + -Um

FA = -

R6C4 AU

  As the voltage difference AU is constant and the product of the resistance R6 by the capacitance C4 is also constant and equal to the time TM, we have for the output frequency FA: FA = 1 / TM. (U + - Um) / AU = f (Um)

  The sign of the voltage UM is negative. In this way

  the output frequency increases with increasing air mass; it is inverted on the amplifier OP2 using the operational amplifier OP3. High temperature calibration arrives on the integrator as an additional source

  current. In the case of ambient temperature the resistance

  tance R13 is aware of dimensioning without current, in the case of other temperatures it is possible by sliding the cursor on the potentiometer on the potentiometer P2 to obtain a

  compensation, such compensation having no feedback

  tion on the behavior at room temperature.

  You can make the circuit shown in figure

  if necessary also without high temperature setting stage

  ture HTH of the corresponding adaptations of the circuit then being necessary.

Claims (7)

R E V E N D I C A T IONS   1) Device for determining the flow rate of a flowing fluid   ment with a substrate (10) exposed to the flowing fluid, on which is disposed a first resistance device, which is a component of a heating control circuit, with at   minus a resistor that can be brought to a higher temperature   pre-defined and with a second resistance device   tance which is connected in the form of a bridge with a diagonal lying between a supply voltage and ground and at least two temperature-dependent resistors which are arranged above and below the resistance of   heating with respect to the direction of flow of the agent to be detected   ter, so that they are heated regularly by it, while they are cooled in a strongly   different by the flowing fluid and that the voltage of me-   sure which is established as a result of the temperature difference is exploited on the other diagonal of the bridge to determine the flow, characterized in that   the measurement voltage is supplied to a frequency conversion circuit   quence-tension (UFW) whose frequency is a measure of the fluid in flow.   2) Device according to claim 1, characterized in that   there is a high temperature setting stage (HTA), which   takes a third arrangement of resistors with at least one potentiometer, which is in the transverse branch of the   bridge and maybe variably adjusted.   3) Device according to claim 2, characterized in that   the tension in the diagonal of the third resistance arrangement   tance and measurement voltage are superimposed on each other   to produce the temperature compensated output signal.   4) Device according to any one of the preceding claims.   teeth,] 11 characterized in that the frequency-voltage conversion stage comprises at least one integrator connected as an operational amplifier (OP4) and a comparator (KP1) with at least two connection thresholds S1, S2, which together form a system capable of oscillating. ) Device according to claim 4, characterized in that the output of the comparator (KP1) leads to a connection (FA),   from which you can take the output signal whose frequency   quence is a function of the mass of the flow.   ) Device according to any one of the preceding claims.   teeth, characterized in that the non-inverting inputs of the operational amplifier (OP4) and the comparator (KP1) are at fixed potential   preset by the heating circuit.   7) Device according to any one of the preceding claims.   teeth, characterized in that the high temperature setting stage (HTA) is constituted as   source of intensity, which brings to the integrator an ad- traditional.   8) Device according to any one of the preceding claims.   teeth, characterized in that the dimensioning of the circuit is carried out in such a way that the load intensity of the integrator is substantially more   greater than the discharge intensity.   9) Device according to any one of the preceding claims.   teeth, characterized in that the dimensioning of the high temperature calibration stage is carried out in such a way that the resistor R13 via which   brought the intensity to the integrator, is currentless at the time ambient temperature.