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
  • G01F1/66—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 measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
  • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters

Definitions

• the present invention relates to transceiver circuits for flow meters.
• the present invention relates to low cost and power saving transceiver circuits for ultrasonic flow meters.
• EP 1 426 739 One very simple approach has been suggested in EP 1 426 739 where a single transistor acts as a buffer and an amplifier when ultrasonic signals are to be transmitted and received, respectively. It is a drawback of the circuit suggested in EP 1 426 739 that the transistor needs to be operated in class A in order to preserve linearity for both transmitted and received signals. It is well-known that operating a transistor in a class A mode of operation requires current levels that are orders of magnitudes higher compared to what is required by other types of bipolar topologies.
• a transceiver circuit for a flow meter comprising a common signal path for signals to be transmitted and/or received via one or more associated transducers, the transceiver circuit comprising a generator circuit, a signal processing circuit and an active circuit, wherein
• the generator circuit is operatively connected to an input terminal of the active circuit
• the signal processing circuit is operatively connected to an output terminal of the active circuit
• the active circuit comprises a first and a second transistor being operatively connected via their respective emitter terminals thereby forming a combined input/output terminal, said combined input/output terminal being operatively connectable to one or more associated transducers, the active circuit being adapted to act as a buffer for signals to be transmitted, and adapted to act as an amplifier for received signals, and
• the input terminal of the active circuit being operatively connected to base terminals of the first and second transistors, and the output terminal of the active circuit being operatively connected to collector terminals of the first and second transistors.
• the transceiver circuit may be operated as a front end transceiver circuit.
• the term front end is here to be understood as a circuit being operatively connected to, either directly or indirectly, the associated transducers.
• the present invention finds its use in relation to flow meters adapted to measure flow speeds of liquids and/or gasses.
• the emitters of the first and second transistors are directly connected.
• the term emitters should be understood as emitters in relation to bipolar transistors as well as sources in relation to Field Effect Transistors (FETs).
• the terms bases and collectors in relation to bipolar transistors correspond to gates and drains of FETs, respectively.
• the active circuit is adapted to act as a buffer for signals to be transmitted, and act as an amplifier for received signals.
• the aim of the buffer is to facilitate that more current may be delivered to the transducer.
• the buffer may be a unity gain buffer having a voltage gain of essentially one. It should be noted however, that the voltage gain of the buffer may differ from one.
• the active circuit forming the buffer and the amplifier may ensure that each of the associated transducers experiences an essentially constant impedance while transmitting and receiving signals.
• transducer is to be understood as either a transmitting or receiving transducer.
• piezo-electric transducers being capable of both generating and detecting ultrasonic signals may be applicable in relation to the present invention.
• transceiver circuit is to be understood as a circuit that is capable of both transmitting and receiving signals via a number of associated transducers.
• the signals being transmitted and/or received by the associated transducers may be ultrasonic signals.
• ultrasonic signals are here to be understood as signals having frequencies from 100 kHz to 10 MHz, such as preferably around 1 MHz. It should however be noted that other frequency ranges may be applicable as well.
• the proposed transceiver circuit is advantageous in that it is simple, cheap, and it has a common signal path for transmitted and received signals. Hence, delay differences in the upstream and downstream signal paths at zero flow are essentially avoided.
• the first and second transistors may be configured in a low-power consumption topology where the first and second transistors are operated in a class AB mode by a circuit adapted to set a bias point for the first and second transistors.
• the transceiver circuit may further either comprise, or being connected to, a controllable switch/multiplexer for providing signals to and/or from associated receiving and/or transmitting transducers.
• the controllable switch/multiplexer may provide signals to and from a pair of transducers. Each of said pair of transducers may be operated as a transmitting transducer as well as a receiving transducer.
• the transceiver circuit may further comprise, or being connected to, additional controllable switches/multiplexers for providing signals to and/or from associated receiving and/or transmitting transducers.
• the additional switches/multiplexers may be controlled individually so that signals may be directed to and/or from a plurality of transducers in an independent manner.
• the switches/multiplexers may be implemented as a number of different switch/multiplexer types - either as single pole, single throw (SPST) switches or as a multiplexer.
• SPST single pole, single throw
• Each element of the switch or multiplexer may be a simple integrated or discrete MOSFET switch or a more elaborated T-type switch to enhance cross talk performance between transducers. It may also be combined with short circuit switches across the transducers to further enhance cross talk between transducers.
• the generator circuit has an output impedance, Zout, which is essentially constant.
• the generator circuit is adapted to generate periodic signals, such as sinusoidal signals, square wave signals etc.
• the signals from the generator circuit may be provided in bursts having durations of an appropriate number of periods.
• the burst signals may comprise an appropriate number of periods of sinusoidal signals, square wave signals or even a single-step function.
• a negative signal feedback from an output terminal of the active circuit to the combined input/output terminal of the active circuit may be provided as well.
• the amount of negative signal feedback may be variable, such as variable on-the-fly.
• the term on-the-fly is here to be understood as variable at any time. As an example a first amount of negative feedback may be used during transmitting, whereas a second, and different, amount of negative feedback may be used during receiving.
• the present invention relates to a flow meter comprising a transceiver circuit according to the first aspect of the present invention.
• the transceiver circuit may be implemented and configured as disclosed in relation to the first aspect.
• the flow meter may further comprise a plurality of transducers being connectable to the combined input/output terminal of the active circuit. At least a number of the plurality of transducers may be adapted to both transmit and receive signals.
• transducers facilitate that signals, such as ultrasonic signals, may be sent both upstream and downstream relative to the direction of a given flow.
• An amplifier may be provided to amplify signals from the output terminal of the active circuit.
• the gain of this amplifier may be variable. This may be advantageous in relation to the following signal processing. In fact, the gain of the amplifier may be variable on-the-fly, i.e. it may be changed at any time, such as between transmitting and receiving.
• Fig. 1 shows the principle of the present invention
• Fig. 2 shows the principle of the invention including an embodiment of an output circuit
• Fig. 3 shows the principle of the invention including embodiments of a bias circuit and an output circuit.
• the present invention relates to a low cost and low power consumption transceiver circuit topology that is capable of providing a stable zero flow offset of zero in flow meters, such as in ultrasonic flow meters.
• the transceiver circuit topology of the present invention is independent on influences from temperature and varying transducer impedances.
• the present invention suggests a circuit topology with a single common signal path for both upstream and downstream signals, i.e. for signals to either transmitted or received.
• the transceiver circuit of the present invention offers that associated transducers can be operated in a reciprocal manner in order to avoid influences from different transceiver impedances.
• Fig. 1 the components of the transceiver circuit 100 of the present invention are depicted.
• the main components of the transceiver circuit 100 are the two transistors 101 and 102 which are connected via their respective emitters at point 114.
• the emitters may be directly connected as shown in Fig. 1 or they may be connected via other components, such as via resistors.
• During transmitting the two transistors 101, 102 are driven by the signal generator circuit 104 through the bias circuit 103.
• the main advantages of the transceiver circuit topology shown in Fig. 1 are as follows:
• the transceiver circuit is operated as follows:
• a low impedance transmit signal is generated at the emitters of transistors 101, 102 that during transmitting is operated as a bipolar class AB emitter follower.
• the bipolar class AB emitter follower drives one of the transducers 112, 113 through the transducer termination impedance 110 and the switch/multiplexer 111.
• the number of transducers may differ from the two shown in Fig. 1.
• the number of transducers may be three, four, five or even more.
• the number of switches/multiplexers may be more than one. In that case each of the switches/multiplexers may be controlled individually.
• the signal generator circuit 104 is not transmitting, and the signal from one of the two transducers 112, 113 is provided to the emitters of transistors 101, 102 through the switch/multiplexer 111 and transducer termination impedance 110.
• the transistors 101, 102 now work as a bipolar class AB common base amplifier through the output circuit 105.
• the output signal from the output circuit 105 may be further amplified in the signal processing circuit 107 before the final output signal 109 is provided. This further amplification may be a variable or a fixed amplification, and it may depend on whether signals are transmitted or received.
• the power supply signal is denoted 108.
• transceiver circuit shown in Fig. 1 is illustrated with bipolar transistors 101, 102, but also Field Effect Transistors (FETs) are applicable. In that case the sources of the FET's are operatively connected, either directly or via other components, such as via resistors.
• FETs Field Effect Transistors
• the transceiver circuit could optionally include a negative feedback 106 from the output of the output circuit 105 to the emitters of transistors 101, 102.
• the negative feedback 106 would increase the overall linearity of the active circuit.
• the negative feedback may be implemented in various ways, such as by using an operational amplifier, transistors, transformers etc.
• the transducers 112 and 113 are only shown schematically. In practice, the transducers 112, 113 may include various components, such as series and parallel impedances. The transducers 112, 113 may be capable of transmitting and/or receiving signals, such as ultrasonic signals.
• the switch/multiplexer 111 may be implemented as a number of different switch/multiplexer types - either as SPST switches or as a multiplexer.
• Fig. 2 shows a possible implementation of the output circuit 105 in Fig. 1.
• the transceiver circuit 200 still comprises a signal generator circuit 204, a bias circuit 203 and two transistors 201, 202 being operatively connected (directly or indirectly) via their emitters in point 214.
• the transducer termination impedance 210, the switch/multiplexer 211 and the transducer 212, 213 are similar to the components shown in Fig. 1.
• the transceiver circuit is powered by the power supply 208.
• the shown implementation of the output circuit 105 of Fig. 1 includes two capacitors 205 and 206 is depicted.
• the output signal is provided from a node between these two capacitors.
• Resistors 215 and 216 are inserted in the power supply line and the connection to ground, respectively.
• the output signal from the node between the two capacitors 205, 206 may be further amplifier in amplifier 207 before the final output signal 209 is provided. Again this further amplification may be variable or fixed, and it may depend on whether signals are transmitted or received.
• Fig. 3 shows a possible implementation of the bias circuit 203 in Fig. 2.
• the output circuit in Fig. 3 is similar to that of Fig. 2 in that it includes two capacitors 305 and 306, and the output signal is provided from a node between these two capacitors. Resistors 315 and 316 are inserted in the power supply line and the connection to ground, respectively.
• the output signal from the node between the two capacitors 305, 306 may be further amplifier in amplifier 307 before the final output signal 309 is provided. As previously stated this further amplification may be variable or fixed, and it may depend on whether signals are transmitted or received.
• the transceiver circuit 300 further includes a signal generator circuit 304, a bias circuit including two transistors 317, 318 operatively connected via their respective connectors.
• the signal generator circuit 304 provides signals to the bias circuit via the common point 303.
• the two transistors 301, 302 are operatively connected (directly or indirectly) via their emitters in point 314.
• the transducer termination impedance 310, the switch/multiplexer 311 and the transducer 312, 313 are similar to the components shown in Figs. 1 and 2.
• the transceiver circuit is powered by the power supply 308.
• pairs of matched transistors 317, 302 and 318, 301 are included.
• the pairs of matched transistors eliminate the use of emitter resistances without introducing the risk of having thermal run-away in transistors 301, 302.
• thermal run-away is to be understood as an uncontrolled increase of current flow and power dissipation leading to a destructive result.
• bias circuit 103 and the output circuit 105 may be implemented in alternative ways which may deviate from the implementations depicted in Figs. 2 and 3.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Amplifiers (AREA)
• Measuring Volume Flow (AREA)

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• 2015
  • 2015-03-11 WO PCT/EP2015/055038 patent/WO2016141982A1/en active Application Filing
  • 2015-03-11 CN CN201580077595.3A patent/CN107407584B/zh active Active
  • 2015-03-11 EP EP15709175.2A patent/EP3268700A1/en not_active Ceased
  • 2015-03-11 EA EA201791854A patent/EA033712B1/ru not_active IP Right Cessation

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