WO1991019170A1 - Detecteur de debit et systeme de commande - Google Patents

Detecteur de debit et systeme de commande Download PDF

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Publication number
WO1991019170A1
WO1991019170A1 PCT/AU1991/000239 AU9100239W WO9119170A1 WO 1991019170 A1 WO1991019170 A1 WO 1991019170A1 AU 9100239 W AU9100239 W AU 9100239W WO 9119170 A1 WO9119170 A1 WO 9119170A1
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WO
WIPO (PCT)
Prior art keywords
fluid
flow
detector
temperature
heater
Prior art date
Application number
PCT/AU1991/000239
Other languages
English (en)
Inventor
Walter Berryman
Hugh Barr Mcdonald
Original Assignee
Mcpherson's Limited
Hybrid Electronics Australia Pty. Ltd.
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 Mcpherson's Limited, Hybrid Electronics Australia Pty. Ltd. filed Critical Mcpherson's Limited
Publication of WO1991019170A1 publication Critical patent/WO1991019170A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6847—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
    • F04D15/02—Stopping of pumps, or operating valves, on occurrence of unwanted conditions
    • F04D15/0209—Stopping of pumps, or operating valves, on occurrence of unwanted conditions responsive to a condition of the working fluid
    • F04D15/0218—Stopping of pumps, or operating valves, on occurrence of unwanted conditions responsive to a condition of the working fluid the condition being a liquid level or a lack of liquid supply
    • F04D15/0227—Lack of liquid level being detected using a flow transducer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6842—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow with means for influencing the fluid flow
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/696—Circuits therefor, e.g. constant-current flow meters

Definitions

  • This invention relates to fluid flow systems and is particularly concerned with flow sensors as used in such systems.
  • the invention is also concerned with other aspects concerning control of a pump or other flow generating device as used in such a system.
  • a flow sensor according to the invention is especially useful in fluid flow systems of the kind including a pump which draws fluid (e.g., water) from a supply source and delivers that fluid to a service outlet by way of a pressure accumulator.
  • fluid e.g., water
  • Systems of that kind are commonly used to supply water from a dam or a holding tank. It will be convenient to hereinafter describe the invention with particular reference to systems of the foregoing kind, but it is to be understood that the invention has other applications.
  • the pump of a system of the foregoing kind needs to be protected from dry-running - i.e., a situation in which there is no water available in the supply source, but the pump is nevertheless continuing to operate. Such dry running can cause serious damage to the pump and is to be avoided.
  • the pump system may include a flow sensor which is intended to detect absence of water through the pump and produce a signal which results in the pump being shut down. Flow sensors as known prior to the present invention have not been sufficiently reliable for a variety of reasons.
  • Another object of the invention in a preferred form is to provide a sensor which may be as free as possible from variation or ageing of thermally conductive adhesives used during manufacture of the sensor.
  • Yet another object of the invention in a preferred form is to provide such a sensor having effective power control means so as to ensure relatively consistent operation of the sensor over a wide variation of power supply voltage.
  • Another object of the invention in a preferred form, is to provide such a flow system with means for ensuring that the pump is primed at commencement of a pumping operation.
  • a flow sensor having a heater and temperature responsive means which is operable to respond to temperature of a fluid body.
  • the heater and the temperature responsive means may be relatively arranged so that the temperature responsive means detects transfer of heat from the heater to a fluid body with which the temperature responsive means is associated.
  • the fluid temperature detected by the temperature responsive means is an indicator of the rate of fluid flow past the sensor. That is, a high detected temperature indicates little or no flow, whereas a low detected temperature indicates high flow.
  • transfer of heat between the heater and the temperature responsive means may be via a close thermal link.
  • the temperature responsive means measures the temperature of the heater or a variable directly related to the heater temperature.
  • transfer of heat between the heater and the temperature responsive means may be via a loose thermal link.
  • a heater is used to locally heat water or fluid in the system and the temperature responsive means is located adjacent to this local source of heat.
  • the temperature responsive means senses the temperature loss in the fluid caused by fluid movement or flow.
  • the temperature responsive means measures heated fluid temperature with first order independence of the quality of the thermal link between the heater and temperature responsive means. There may be circumstances under which ambient temperature of the fluid varies to such an extent as to disturb effectiveness of the sensor. In one form of the invention, means may be provided to compensate for such ambient temperature variation.
  • Such compensating means preferably includes a thermistor, or other temperature responsive means, which detects and responds to ambient or base temperature of the fluid, and feedback means which produces a signal characteristic of that detected temperature and applies that signal to compensate the temperature responsive means and/or to control of the heater.
  • a thermistor or other temperature responsive means, which detects and responds to ambient or base temperature of the fluid
  • feedback means which produces a signal characteristic of that detected temperature and applies that signal to compensate the temperature responsive means and/or to control of the heater.
  • the arrangement may be such that a substantially constant temperature differential is maintained between the heater and the fluid ambient temperature.
  • utilizing a loose thermal link between the heater and the temperature responsive means to compensate the heater for ambient temperature variations may be dispensed with and the heater may be arranged to operate with constant power input. Heater temperature may still depend on the quality of the thermal link between the heater and temperature responsive means although the temperature rise of the fluid (and hence the output of the sensor) may be independent (to first order) of the quality of the thermal link.
  • the heater may be of the electrical resistance type and the temperature responsive means may be rendered operable by connection to an electrical power source.
  • the heater may be included in a power supply circuit for the temperature responsive means.
  • isolating means may be operative to isolate the sensor from the influence of flowing air, but not flowing water. Such isolating means thereby ensures that the desired sensor response occurs under flow conditions of the kind which are intended to be monitored.
  • the isolating means may comprise a baffle that at least alleviates the effects of fluid turbulence on the flow sensor.
  • the baffle may be adapted to provide the sensor with an environment which is substantially free of turbulence and vortices.
  • the baffle should not restrict the sensor from being subjected to fluid flow above a predetermined minimum rate.
  • One purpose of the baffle is to localize turbulence in a relatively short distance.
  • the baffle may include a relatively long space for containing and/or dissipating turbulence and a relatively short space which is substantially free of turbulence.
  • the long space may include converging means such as a frusto-conical portion.
  • the short space may include a cylindrical portion.
  • the converging means may comprise a stepped cylindrical portion.
  • the converging means preferably includes apertures within a wall or walls thereof.
  • the converging means is operative to absorb kinetic energy of a vortex within a minimum length without converting the energy into turbulent flow. Energy absorption may be achieved by causing the vortex to converge on its axis within the converging means of the long space. Selection of aperture sizes and positions along the wall or walls of the converging means combined with optimum wall thickness may ensure vortexing is confined within the long space.
  • Strategic positioning of apertures near the downstream end of the long space may allow fluid to return to the vortex.
  • SUBSTITUTE SHECT be used separately therefrom or in conjunction with other arrangements in which it is desired to reduce or alleviate the effects of fluid turbulence.
  • a fluid supply system including a pump and a pressure accumulator connected to the output side of the pump.
  • Pump control means is also provided and includes pressure responsive means and first and second timer means.
  • the pressure responsive means detects falling pressure in the accumulator and may cause operation of the pump at a predetermined minimum pressure.
  • the first timer means functions to ensure continued operation of the pump after power up for a first period of time, say 30 to 60 seconds, even though water (or other fluid to be pumped) is not passing through the pump. That is, the first timer means overrides, temporarily, any flow sensor which may be provided in the system to terminate operation of the pump under certain flow conditions (e.g., no flow).
  • the first timer means ensures that the pump can be primed before the flow sensor becomes effective to control the pump.
  • the second timer means is provided to run the pump for a second relatively short time period, say 5 to 15 seconds, after the pressure responsive means detects falling pressure. At expiration of the second time period, the second timer means operates to turn off the pump. This may ensure that the pump does not run in a dry state for an excessive period.
  • the fluid supply system of the present invention may include thermal switch means to switch off the pump or associated control system in the event that fluid or water temperature exceeds a predetermined threshold. This may be desirable because fluid or water temperature in excess of the predetermined threshold may be detrimental or may cause damage to the pump and/or its associated control system.
  • the thermal switch means may be adapted to turn off the pump eg. by disabling the pump motor switch when fluid or water temperature exceeds the abovementioned threshold temperature.
  • the thermal switch means may include latch means which may be triggered at the threshold temperature. The latch means may maintain the pump switch in a disabled state until the latch means is reset. The latch means may be reset eg. by removing and re-applying a control voltage to the latch means.
  • Figure 1 is a representation of a flow sensor according to the present invention and utilizing a loose thermal link
  • FIG. 2 is a representation of a pump system utilizing a flow sensor according to the invention
  • Figure 3 is a block diagram of a pump control system incorporating a flow sensor of the invention
  • Figure 4 is a circuit diagram of a pump control system including the flow sensor of figure 1 and incorporating the features of Figure 3;
  • Figure 5 is a representation of a flow sensor according to the invention and utilizing a close thermal link;
  • Figure 6 is a block diagram of a heater control incorporating a voltage dropping power supply
  • Figure 7 is a circuit diagram of the heater control and power supply of Figure 6;
  • FIG 8 is a circuit diagram of a pump control system including the flow sensor of Figure 5 and incorporating the heater control circuit of Figure 7;
  • Figure 9 shows one form of baffle means which may be used to isolate the flow sensor from the effects of spurious flow;
  • Figure 10 shows one form of thermal switch means.
  • FIG. 1 shows, in diagrammatic form, a flow sensor incorporating one aspect of the invention.
  • That sensor includes a heater 1, flow indicating means 2 and ambient temperature compensating means 3.
  • the flow indicating means 2 and the ambient temperature compensating means 3 each comprises or includes temperature responsive means, and in a preferred arrangement hereinafter described in greater detail, each such temperature responsive means is formed by a thermistor or similar device. It will be convenient to hereinafter refer to the flow thermistor 2 and the ambient thermistor 3.
  • Each of the three components, 1, 2 and 3, may be mounted on a respective support such as a sheet or substrate of ceramic or other insulating material. Alternatively, they may be mounted on a common support, but in such a case it is preferred to provide at least some degree of thermal isolation between the heater 1 and the flow thermistor 2, for a reason hereinafter explained. In one form thermal insulation may be provided by a barrier of silicone or the like between respective sheets or substrates of ceramic on which the heater and flow thermistor 2 are mounted.
  • the ambient thermistor 3 is shown downstream from the heater 1 relative to the direction of fluid flow as shown by the arrow 4, but it could be located upstream of the heater 1 if desired.
  • the ambient thermistor 3 is preferably positioned so as to detect the temperature of the body of fluid 5 at a location substantially unaffected by transfer of heat from the heater 1 to the fluid body 5. That is, it is the intention of the ambient thermistor 3 to detect and respond to the ambient or base temperature of the fluid body 5.
  • the flow thermistor 2 It is necessary for the flow thermistor 2 to be located relatively close to the heater 1 so as to be responsive to dissipation of heat into the fluid body 5 from the heater 1. Assuming that heater 1 operates on substantially constant power the temperature of the portion of the fluid body 5 adjacent to the heater 1 will be relatively low if the rate of fluid flow past the heater 1 is high, and will be relatively high if the fluid flow rate is low. The flow rate indicating function of the flow thermistor 2 may be impaired if there is excessive transfer of heat between the heater 1 and the thermistor 2 other than through the fluid body 5 as represented by the arrows 6. It is for that reason that it is preferred to provide at least some degree of thermal isolation between the heater 1 and the thermistor 2, and in a simple form that can involve spacial separation of those components as shown in Figure 1.
  • FIG. 1 The ideal situation as shown in figure 1 may not be a practical possibility.
  • an interface such as a substrate connects heater 1 and thermistor 2.
  • That interface/substrate eg. copper or ceramic
  • forms a heat sink to ensure adequate transfer of heat from heater 1 to thermistor 2.
  • the heater 1 Since the heater 1 must transfer heat to the fluid body 5, and the thermistors 2 and 3 must respond to the temperature of that body, it is necessary for each of those three components to have direct or indirect contact, or close association, with the fluid body 5. Indirect contact or association through an electrically insulating material such as ceramic is usually preferred.
  • the flow thermistor 2 is connected to an appropriate reference so that the extent of rise or fall in detected temperature can be determined.
  • the reference is the ambient thermistor 3, and that may be a direct or indirect line of reference.
  • FIG. 2 diagrammatically illustrates a pump system incorporating the flow sensor as described. That system includes a pump 7, a motor 8 to drive the pump, and an accumulator 9 on the output side of the pump.
  • Pressure responsive means 10 detects a fall in the pressure within the accumulator 9 below a predetermined level, and responds by causing operation of the pump motor switch 11 so that the pump 7 is started. Water, for example, is thereby drawn from the supply source 12 and pumped, by way of the accumulator 9, to a service outlet.
  • the flow sensor 13 is positioned on the output side of the accumulator 9 as shown, and responds to flow as previously described. Flow sensor 13 may be arranged to sample flow as shown or it may be arranged such that all flow passes through sensor 13.
  • a barrier or baffle 14 is provided adjacent the sensor 13 so as to protect the sensor against the influence of spurious flow as previously referred to.
  • Flow sensor 13 alternatively could be located in front of pump 7 and that location being a low pressure location may be of advantage in some circumstances. In further embodiments flow sensor 13 may be located between pump 7 and accumulator 9. In the event that the sensor 13 detects a low or no flow situation, switch 11 which may be a thyristor or silicon controlled rectifier will be operated to shut down the pump 7.
  • FIG. 3 is a block diagram which illustrates one form of pump system incorporating a flow sensor according to the present invention.
  • the blocks 15 represent the mains power input to the system.
  • the block 16 represents the mains power switch, and the block 17 represents a switch which is responsive to detection of a fall in pressure in the system.
  • Each of the switches 16 and 17 is connected to respective first and second timers 18 and 19 which are in turn connected to a temperature sensor 20 incorporating flow thermistor 2 and ambient thermistor 3 in a bridge circuit.
  • Block 21 represents a mains voltage feedback circuit adapted to provide a compensating voltage to the temperature sensor 20.
  • the compensating voltage is adapted to remove the effect of mains voltage fluctuations and consequent changes in heater output.
  • Block 22 represents the basic flow switch and may comprise a voltage comparator connected to respective arms of the bridge circuit of temperature sensor 20.
  • timer 18 When switch 16 is actuated on initial power up or subsequent restoration of power, timer 18 functions to ensure that pump 7 will continue to operate for a satisfactory period - e.g., 30-60 seconds. That ensures adequate priming of pump 7 without interruption by the influence of the flow sensor. At the end of that period the flow sensor including heater 1, temperature sensor 20 and flow switch 22, is activated and imposes its influence on the system. In the event that a fault condition
  • the second timer 19 functions to ensure that the pump will operate for a relatively shorter period eg. 5 to 15 seconds. This ensures that the pump does not run in a dry state for an excessive period.
  • timers 18, 19 is to run the flow sensor or to override it.
  • the flow thermistor 2 is represented by thermistor element R13 and ambient thermistor 3 is represented by thermistor element R12.
  • capacitor C 2 belonging to the first timing means, and capacitor C_ belonging to the second timing means are uncharged and input pins 5, 6 of op. amp 23 which may be one half of a dual FET device type TL082, are initially at positive rail voltage V + .
  • the time constant associated with the first timing means resistor
  • R.., R 2 and capacitor C_ is chosen to be about 4 to
  • R4/R5 are chosen such that the steady state voltage at input pin 5 is just below than the steady state voltage at input pin 6. Hence when capacitors C,, C_ are fully charged the voltage at output pin 7 is low.
  • the pressure responsive means 10 is represented in Figure 4 by switch SW. When pressure in accumulator 9 drops switch SW is shorted causing full rail voltage to pass across capacitor C . turning transistor Tl on temporarily. This pulls capacitor -, to ground charging it fully. With capacitor C_ fully charged input pin 6 of op. amp 23 goes low causing pin 7 of op. amp 23 and pin 2 of op. amp 24 to go high. Consequently pin 1 of op. amp 24 goes low and the pump runs. With transistor T.
  • a low voltage at pin 7 activates the flow sensor which comprises a bridge circuit made up of thermistor elements R12, R13 and resistors R15, R16 and R8. The bridge is trimmed via resistor R15 so that it balances when thermistor element R13 is cool and is indicative of an acceptable flow rate in the system.
  • Minimum flow at pump switch may be approximately 2.5 litres/min with water temperature between 2-50°C and approximately 3 litres/min with water temperature between 50-70°C.
  • Feedback resistor R18 also influences balance of the bridge circuit.
  • the function of resistor R18 is to shift the balance point of the bridge whenever the supply voltage changes thereby compensating the bridge circuit for the change in heater output due to supply voltage fluctuations.
  • the pump will keep running until low flow is sensed. Low flow causes thermistor element R13 to heat up causing the bridge circuit to unbalance sending the voltage at pin 2 of op. amp 24 low, since thermistor element R13 exhibits a negative temperature coefficient. This drives pin 1 high turning off the oscillator circuit and triac switch 11, and pump 7 stops. Positive feedback from pin 1 to pin 4 holds the pump off. The pump does not run until pressure in accumulator 9 drops and switch SW closes again retriggering pin 7 high and pin 1 low and causing the pump to run again. If pressure in accumulator 9 is low or switch SW becomes jammed in the closed position and the pump turns off because of a fault condition, it will not run because switch SW remains shorted and cannot retrigger pin 7.
  • pin 7 may be retriggered by disconnecting mains power and reconnecting it again.
  • Diode D3 (actually a transistor connected in diode configuration for low leakage) then discharges capacitor C 2 and upon power being reconnected pin 5 remains high until capacitor C 2 charges to the steady state voltage determined by voltage dividing resistors Rl, R2.
  • the time constants described above are sufficient to hold pin 5 above pin 6 for about 45 seconds and the pump runs during this period notwithstanding that a fault condition exists. The pump then stops because the fault condition will keep the bridge circuit unbalanced.
  • FIG. 5 shows, in diagrammatic form, a flow sensor incorporating another aspect of the invention. That sensor includes a heater 1, flow indicating means 25, ambient temperature compensating means 26 and heater temperature indicating means 27.
  • the flow indicating means 25, ambient temperature compensating means 26 and heater temperature indicating means 27 each comprises or includes temperature responsive means, and in the preferred arrangement hereinafter described, each such temperature responsive means is formed by a thermistor or similar device. It will be convenient to hereinafter refer to the flow thermistor 25, the ambient thermistor 26 and the temperature thermistor 27.
  • each of the four components, 1, 25, 26 and 27, may be mounted on a respective support such as a sheet or substrate of ceramic or other insulating material. Alternatively, they may be mounted on a common support.
  • the ambient thermistor 26 is shown downstream from the heater 1 relative to the direction of fluid flow as shown by the arrow 4, but it could be located upstream of the heater 1 if desired. It is preferable that the flow thermistor 25 be located between the heater 1 and the ambient thermistor 26 so as to be responsive to dissipation of heat into the fluid body 5 from the heater 1.
  • flow thermistor 25 relies on the fact that the temperature gradient existing between the heater 1 and the ambient thermistor 26 will be relatively low if the rate of fluid flow past the heater 1 is high, and will be relatively high if the fluid flow rate is low.
  • the flow rate indicating function of the flow thermistor 25 may be impaired if there is transfer of heat between the heater 1 and the Flow thermistor 25 other than through the fluid body 5 as represented by the arrows 28. It is for that reason that it is preferred to provide at least some degree of thermal isolation between the heater 1 and the thermistor 25.
  • the heater 1 Since the heater 1 must transfer heat to the fluid body 5 (directly or via a substrate/interface), and the thermistors 25 and 26 must respond to the temperature of that body, it is necessary for each of those three components to have direct or indirect contact, or close association, with the fluid body 5. Indirect contact or association through an electrically insulating material such as ceramic is usually preferred.
  • the flow thermistor 25 is connected to an appropriate reference so that the extent of rise or fall in detected temperature can be determined. In the arrangement shown in Figure 5, the reference is the ambient thermistor 26, and that may be a direct or indirect line of reference. Alternatively, the reference may be the temperature thermistor 27, and again the line of reference may be direct or indirect.
  • the connection is such as to establish a reference which is characteristic of the temperature gradient existing between the heater temperature and fluid ambient temperature as it exists at any one point in time. That gradient reference enables the system to compensate for variations in fluid ambient temperature, and in particular provides a convenient reference for the flow thermistor 25.
  • the heater temperature and ambient temperature referred to may not be the actual temperatures, but may be represented by something which is characteristic of or corresponds to the respective temperatures.
  • Figure 6 includes the heater 1, thermistors 26 and 27, switch means 29 for the heater 1, control means 30 connected between the thermistors 26 and 27 and the switch means 29 for controlling modes of operation of the heater 1.
  • the entire circuit is connected to a source of mains electrical power.
  • the two lines 31 and 32 between the heater 1 and the switch means 29 represents the two modes of operation of the heater 1 previously referred to.
  • the heater 1 forms part of the power supply circuit for the thermistors 26 and 27. It is a further feature of the arrangement that means is provided whereby the voltage applied to the thermistors 26 and 27 is maintained at a substantially constant level. Under the high current mode of operation (through line 31), the regulating means 33, which may be a zener diode, functions to maintain the voltage at the output of switch means 29 at a predetermined level.
  • the switch means 29 which may be a voltage biased silicon controlled rectifier or thyristor, responds to the load on the thermistors 26 and 27 so as to provide a current flow through the heater 1 as necessary to maintain a predetermined voltage to thermistors 26 and 27.
  • the part of the circuit through which power is supplied to the thermistors 26 and 27 functions as a voltage dropping power supply circuit.
  • FIG. 7 shows a heater control circuit which incorporates the voltage dropping circuit of Figure 6.
  • the block marked A in Figure 7 represents the aforementioned voltage dropping power supply circuit which supplies DC power to the thermistors 26 and 27.
  • the heater 1 is represented by resistance Rll and the switch means 29 of Figure 6 is represented by the SCR Ql.
  • Thermistor 26 is represented by the reference R13 and thermistor 27 is represented by the reference R12.
  • the resistance heater Rll is connected in series with an AC mains supply, and that connection is under the control of SCR Ql which when triggered drives a DC output voltage limited by the reverse breakdown voltage of zener diode D3.
  • a further diode D4 connects the DC voltage appearing across zener diode D3 to smoothing capacitor Cl.
  • the diode D3 corresponds to the regulating means 33 of Figure 6.
  • a further diode D4 may be included, depending on the selection of Ql.
  • the circuit composed of the foregoing is essentially a voltage dropping and rectifying network, and the inclusion of SCR Ql allows control of current flow to the capacitor Cl.
  • the heater Rll functions as a dropping resistance with the zener D3 limiting the output voltage, and the diode D4 and capacitor Cl providing additional rectification and filtering respectively.
  • Figure 8 illustrates application of the Figure 7 circuit to a flow sensor as described which is arranged to control operation of a pump.
  • the heater control circuit includes a comparator IC1/A and a bridge circuit, the arms of which each comprises a resistor and a thermistor.
  • One arm comprises the resistor Rl and the thermistor R12
  • the other arm comprises the resistor R3 and the thermistor R13.
  • the thermistor R12 is placed in thermal proximity to the heater Rll and provides a feedback, representing the temperature of the heater Rll, to one input of the comparator IC1/A. It will be appreciated that other means could be employed for that feedback function.
  • the thermistor R13 is preferably placed in a thermally decoupled position relative to heater Rll - i.e., it is not open to thermal influence by the heater - and in a practical application is arranged so as to provide a signal representing the ambient temperature of a fluid body, and that signal is transmitted to a second input of comparator IC1/A.
  • the ambient temperature signal is usually not fixed, but “floats" up and down according to the prevailing ambient temperature of the fluid with which the sensor is associated.
  • the thermistor R13 may be replaced by a fixed (or variable) resistance element.
  • the value of the fixed (or variable) resistance element would then determine the signal to the second input of comparator IC1/A.
  • the bridge elements R12, R13, Rl and R3 are chosen such that the bridge will balance when there exists a temperature differential Tl between thermistors R12 and R13, say 20°C.
  • Comparator IC1/A may be arranged to enable the gate of SCR Ql via diode D2 as the bridge passes its balance point.
  • the above arrangement will control the temperature of the heater Rll such that it will "track" ambient temperature as measured (detected) by the thermistor R13. That is, the temperature of the heater to be maintained at a substantially steady temperature differential Tl above ambient temperature of the fluid so as to result in a predictable temperature gradient for reference purposes.
  • Comparator IC1/A controls operation of the DC power supply in two modes
  • Control of SCR Ql is via diodes D3, D2, resistor R2 and the output of comparator IC1/A.
  • Resistor R2 provides a trigger current to the gate of SCR Ql which provides "start-up" to an otherwise inert circuit. If the comparator IC1/A output (pin 7) is low, SCR Ql operates in mode (i). When the voltage on capacitor Cl drops, the combination of D2, D3 and R2 provides gate current causing conduction of SCR Ql until Cl voltage rises again. If the comparator IC1/A output is high, resistor R2 provides continuous gate current, keeping SCR Ql fully on. This means that SCR Ql is operating in mode (ii) .
  • the heating control circuit may be disabled by forcing the cathode of diode Dl to a logic low, thereby forcing comparator IC1/A to a low output and disabling the gate of SCR Ql.
  • the cathode of diode Dl will be low when a no flow condition is sensed and pressure switch PI is not actuated.
  • FIG. 8 shows an example control system which utilises a flow sensor, as previously described, to turn off a supply pump (not shown) driven via motor 8 upon detection of an unacceptably low flow rate.
  • the control system of Figure 8 incorporates a heater control circuit as described with reference to Figure 7.
  • the flow sensor includes comparator IC1/B connected to a bridge circuit whose arms comprise thermistors R13 and R14 and resistors R3 and R4/R15/R16.
  • Thermistor R14 is physically positioned intermediate thermistors R12 and R13 relative to the direction of fluid flow, and corresponds to the flow thermistor 25 of Figure 5.
  • Resistors R15/R16 are connected to a sliding switch SW adapted to short the resistor R16, or both the resistors R15 and R16, out of the bridge circuit. Switch SW may be used for adjusting flow rate sensitivity.
  • Bridge elements, R13, R14, R3 and R4/R15/R16 are chosen or adjusted such that the bridge will balance when there exists a fixed temperature differential T2 between thermistors R13 and R14 which does not exceed the temperature differential Tl between thermistors R12 and R13 (20°C in the example given) . That is reasonable because the thermistor R14 is placed intermediate the thermistors R12 and R13.
  • Q2 is a sensitive gate triac minimizing current source requirements of CMOS NAND gate IC2/B and the power supply.
  • the pump motor must run for some minimum time when activated as set by the RC time constant of a timing circuit comprising resistor R8, capacitor C4 and buffer IC2/D (typically about 45 seconds) . Provided this minimum time has elapsed, the pump motor can then be turned off immediately flow cessation has been sensed. That time constant may be established to ensure priming of the pump as hereinafter discussed.
  • flow will be sensed by pressure in a fluid reservoir falling and actuating pressure switch- PI. This will set the latch and turn on pump motor 8. This is initally independent of the flow sensor output (ICl/B) as there can be no pull-up current provided to its open collector output until the minimum run time has elapsed as determined by the timing circuit.
  • pressure switch PI remained actuated, i.e., there existed continuous low pressure, and no flow was sensed, this would be indicative of a liquid "no head” condition at the pump and the pump must be turned off. This is ensured as both latch outputs will be forced low by the action of the pressure switch and flow sensor. This condition is stable and can maintain the motor off and the heater control circuit on.
  • the pressure switch input is protected from external noise sources by a filter comprising resistors R5, R6 and capacitor C2.
  • the latch output, IC2/B drives motor 8 on or off via triac switch Q3.
  • Resistor R9 sets the trigger current for the more sensitive gate triac Q2, which in turn sets, via resistor RIO the larger trigger current drive required by the motor triac switch Q3.
  • Figure 9 shows the flow sensor 13 positioned within flow coupling element 34. Fluid enters coupling element 34 from the top and exits at the right as indicated by the arrow 35. The lower opening provides a service access and is plugged in use.
  • the flow sensor comprises heater 1, flow thermistor 2 and ambient thermistor 3 as previously described.
  • Thermisters 2 and 3 are printed as a matched pair on a single piece of ceramic and are separated by snapping the ceramic. This avoids the need to trim the thermistors in circuit.
  • a frusto-conical baffle 36 is inserted into coupling element 34 as shown in broken outline. Baffle 36 is adapted to provide flow sensor 12 with an environment which is substantially free of turbulence and vortices. Baffle 36 does not restrict the sensor from being subjected to fluid flows above a predetermined minimum.
  • Apertures 37 included within the converging portion of baffle 36 are adapted to absorb kinetic energy of a vortex without converting the energy into turbulent flow.
  • Apertures 37 comprise slots as shown or they may be substantially circular. Apertures 38 allow fluid to return to the vortex and are important to proper functioning of the baffle. Wall thickness of the baffle should be sufficient to avoid shear of flow over the external surface of baffle 35. Generally speaking a relatively thin wall may be used where apertures 37 are small. Wall thickness may be increased as the size of apertures 37 increases. Heater 1 and flow thermistor 2 are positioned over the cylindrical or forward portion of baffle 35 which is substantially free of turbulence.
  • the thermal switch means includes a temperature responsive element in the form of thermistor R4.
  • Thermistor R4 forms a voltage divider with trim resistor R3.
  • the junction of thermistor R4 and trim resistor R3 is connected to the base electrode of transistor T2.
  • Resistor R3 is trimmed so that there is insufficient voltage to the base of transistor T2 to turn it on before the threshold temperature is reached. This provides a high impedance state of the latch between points 1 and 2.
  • thermistor R4 As the t h reshold temperature is reached the resistance of thermistor R4 becomes low enough to just turn on transistor T2 through trim resistor R3. This turns on transistor Tl and latches through resistor R2. Once latched the circuit maintains a low impedance between points 2 and 3 until negative supply voltage -V to thermistor R4 is removed and re-applied. Capacitors Cl and C 2 are inc l uded to minimize spurious latch triggering. Thermistor R4 may be mounted on a suitable support such as a sheet or substrate of ceramic or other insulating material. The complete ceramic substrate may b e active l y trimmed to provide an accurate switching temperature. This may be done by placing the substrate on a controlle d temperature hot block and trimming resistor R3 until latching occurs.
  • thermal switch means In order to turn off the pump at the threshold or latch temperature point 3 of the thermal switch means may be applied to a pump control system shown in Figure 4 to trigger capacitor C7, or alternatively to triac trigger control zener diode D4.
  • the thermal switch may be physically located with flow sensor 13 shown in Figure 9, within flow coupling element 34.
  • the thermal switch may be physically soldered to the bottom of flow sensor 13 ie. remote from the water side, to measure water temperature.
  • Thermal elements and bridge components may be inexpensively mass produceable utilizing thick film technology.
  • Thick film (or thin film) hybrid assembly ensures safety isolation consistent with suitable electrical, physical and especially thermal diffusivity properties.
  • the heater element provides the mains voltage dropping component eliminating an expensive power transformer.

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  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Positive-Displacement Pumps (AREA)

Abstract

Un détecteur servant à détecter le débit d'un fluide (4) possédant un élément chauffant (1) qui transmet de l'énergie thermique (6) à un corps fluide (5) auquel le détecteur est associé et des premier (2) et deuxième (3) détecteurs de température dont chacun d'entre eux réagit à la température du corps fluide. Le deuxième détecteur de température (3) se situe à distance du premier détecteur de température (2), créant ainsi une différence de réaction de chaque détecteur de température au moins lorsqu'aucun fluide ne passe devant le détecteur. Celui-ci comprend également des moyens capables de détecter une modification de la différence de réaction, cette modification représentant, par conséquent, une modification du débit du corps fluide. Sont également décrits: un système de pompage dans lequel le moteur de la pompe est commandé par des moyens réagissant à la pression du fluide et par un détecteur de débit pourvu de moyens de temporisation; ainsi qu'un moyen d'isolation d'un détecteur de débit comprenant un élément déflecteur pourvu de parois à ouvertures régulant le débit du fluide.
PCT/AU1991/000239 1990-06-04 1991-06-04 Detecteur de debit et systeme de commande WO1991019170A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AUPK0472 1990-06-04
AUPK047290 1990-06-04
AUPK280790 1990-10-12
AUPK2807 1990-10-12

Publications (1)

Publication Number Publication Date
WO1991019170A1 true WO1991019170A1 (fr) 1991-12-12

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WO (1) WO1991019170A1 (fr)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0528726A1 (fr) * 1991-08-16 1993-02-24 POMPES SALMSON Société Anonyme à directoire dite: Procédé et dispositif de commande d'une installation de pompage et élément modulaire de détection pour une telle installation
EP0484645B1 (fr) * 1990-11-09 1995-04-26 Hewlett-Packard Company Méthodes et systèmes pour l'identification de fluides et détermination du flux
WO2000042392A1 (fr) * 1999-01-15 2000-07-20 Kayden Instruments Inc. Dispositif a dissipation thermique commande par micro-ordinateur
EP1070940A1 (fr) * 1999-07-08 2001-01-24 Lockheed Martin Corporation Débitmètre à différence de température constante
WO2003029656A1 (fr) * 2001-10-03 2003-04-10 Davey Products Pty Ltd Systeme de commande de pompe
EP1336761A2 (fr) * 2002-02-13 2003-08-20 Schneider Electric Industrie Italia S.p.A. Dispositif de contrôle pour une pompe d'autoclave
WO2006007669A1 (fr) 2004-07-22 2006-01-26 Davey Products Pty Ltd Unite de commande, systeme et procede d'acheminement d'eau de supplement
AU2002333031B2 (en) * 2001-10-03 2007-05-17 Davey Products Pty Ltd Pump control system
DE102013021305B3 (de) * 2013-12-19 2014-10-30 Krohne Messtechnik Gmbh Schaltungsanordnung zur Temperaturüberwachung und kalorimetrisches Massedurchflussmessgerät
US20170003153A1 (en) * 2015-06-30 2017-01-05 General Electric Company Water heater appliance and a method for detecting water draws in a water heater appliance
EP3135327A1 (fr) * 2015-08-31 2017-03-01 Berlin Heart GmbH Pompe destinee au transport de liquides et procede de determination d'un debit
DE102015119832A1 (de) * 2015-11-17 2017-05-18 Xylem Ip Management Sàrl Förderpumpe zur Druckerhöhung in einer Leitung und Verfahren zum Betreiben einer Förderpumpe

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DE1403256A1 (de) * 1959-05-16 1968-10-10 Hagan Controls Corp System zur automatischen Regelung der Stroemung eines stroemungsfaehigen Mediums durch eine Zentrifugalpumpe entsprechend der Differenz zwischen den Temperaturen an deren Einlass und Auslass
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FR2500927A1 (fr) * 1981-02-27 1982-09-03 Marchal Equip Auto Disposilif de mesure du debit d'un fluide
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JPS62142890A (ja) * 1985-12-18 1987-06-26 Matsushita Electric Ind Co Ltd ポンプ装置
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DE1403256A1 (de) * 1959-05-16 1968-10-10 Hagan Controls Corp System zur automatischen Regelung der Stroemung eines stroemungsfaehigen Mediums durch eine Zentrifugalpumpe entsprechend der Differenz zwischen den Temperaturen an deren Einlass und Auslass
US3438254A (en) * 1965-10-19 1969-04-15 United Control Corp Fluid flow detector
GB1360225A (en) * 1972-10-19 1974-07-17 Distillers Co Carbon Dioxide Carbonated liquid moving apparatus
FR2246846A1 (en) * 1973-10-09 1975-05-02 Thomson Csf Linear flow meter based on thermodynamic laws - measures temp upstream and downstream of heat source in fluid flow
AU4365479A (en) * 1978-01-30 1979-08-09 Kb Vindkraft I Goteborg Flow accelerator
EP0009428A1 (fr) * 1978-09-01 1980-04-02 Baltimore Aircoil Company, Inc. Système de contrôle automatique pour pompes centrifuges
US4255968A (en) * 1979-06-08 1981-03-17 Intek, Inc. Flow indicator
FR2487973A1 (fr) * 1980-08-01 1982-02-05 Soule Sa Debitmetre thermique : procede et dispositifs electroniques permettant de mesurer l'ecoulement d'un fluide en fonction des variations de sa temperature
FR2500927A1 (fr) * 1981-02-27 1982-09-03 Marchal Equip Auto Disposilif de mesure du debit d'un fluide
US4693116A (en) * 1983-06-20 1987-09-15 Nippon Soken, Inc. Semiconductor-chip gas-flow measuring apparatus
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DE3518409A1 (de) * 1984-05-22 1985-11-28 Kabushiki Kaisha Toshiba, Kawasaki, Kanagawa Halbleiter-stroemungsmesser zur bestimmung von stroemungsmenge und -richtung eines stroemungsmittels
JPS62142890A (ja) * 1985-12-18 1987-06-26 Matsushita Electric Ind Co Ltd ポンプ装置
JPS63223392A (ja) * 1987-03-11 1988-09-16 Mitsubishi Electric Corp ポンプ装置
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Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0484645B1 (fr) * 1990-11-09 1995-04-26 Hewlett-Packard Company Méthodes et systèmes pour l'identification de fluides et détermination du flux
US5515295A (en) * 1990-11-09 1996-05-07 Hewlett-Packard Company Methods and systems for fluid identification and flow rate determination
EP0528726A1 (fr) * 1991-08-16 1993-02-24 POMPES SALMSON Société Anonyme à directoire dite: Procédé et dispositif de commande d'une installation de pompage et élément modulaire de détection pour une telle installation
WO2000042392A1 (fr) * 1999-01-15 2000-07-20 Kayden Instruments Inc. Dispositif a dissipation thermique commande par micro-ordinateur
US6318168B1 (en) 1999-01-15 2001-11-20 Kayden Instruments Inc. Thermal dispersion probe with microcomputer controller
EP1070940A1 (fr) * 1999-07-08 2001-01-24 Lockheed Martin Corporation Débitmètre à différence de température constante
WO2003029656A1 (fr) * 2001-10-03 2003-04-10 Davey Products Pty Ltd Systeme de commande de pompe
CN1293309C (zh) * 2001-10-03 2007-01-03 戴维产品股份有限公司 泵控制***
AU2002333031B2 (en) * 2001-10-03 2007-05-17 Davey Products Pty Ltd Pump control system
EP1336761A3 (fr) * 2002-02-13 2009-06-10 Schneider Electric Industrie Italia S.p.A. Dispositif de contrôle pour une pompe d'autoclave
EP1336761A2 (fr) * 2002-02-13 2003-08-20 Schneider Electric Industrie Italia S.p.A. Dispositif de contrôle pour une pompe d'autoclave
WO2006007669A1 (fr) 2004-07-22 2006-01-26 Davey Products Pty Ltd Unite de commande, systeme et procede d'acheminement d'eau de supplement
DE102013021305B3 (de) * 2013-12-19 2014-10-30 Krohne Messtechnik Gmbh Schaltungsanordnung zur Temperaturüberwachung und kalorimetrisches Massedurchflussmessgerät
US20170003153A1 (en) * 2015-06-30 2017-01-05 General Electric Company Water heater appliance and a method for detecting water draws in a water heater appliance
EP3135327A1 (fr) * 2015-08-31 2017-03-01 Berlin Heart GmbH Pompe destinee au transport de liquides et procede de determination d'un debit
WO2017037025A1 (fr) * 2015-08-31 2017-03-09 Berlin Heart Gmbh Pompe pour le pompage de liquides et procédé de détermination du débit
CN108136086A (zh) * 2015-08-31 2018-06-08 柏林心脏有限公司 用于输送流体的泵以及用于确定流量的方法
DE102015119832A1 (de) * 2015-11-17 2017-05-18 Xylem Ip Management Sàrl Förderpumpe zur Druckerhöhung in einer Leitung und Verfahren zum Betreiben einer Förderpumpe

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