FIELD OF THE INVENTION

The invention relates to the field of consumption meters, such as high precision consumption meters for charging applications. Especially, the invention defines a low power battery driven consumption meter including a flow sensing unit.

BACKGROUND OF THE INVENTION

Battery driven consumption meters intended for long-term operation, e.g. 15-20 years, without the need for maintenance must have electronic circuits with low electric power consumption. Typical batteries for such long-term operation are Lithium type batteries, and such batteries have a limited peak current capacity. Thus, circuits requiring high power drain from the battery in short periods, such as wireless radio communication interfaces during Radio Frequency transmission, are problematic to drive with such batteries, and if possible, the power efficiency is poor.

Of course, a larger battery or application of several batteries can be used to provide a higher peak current capacity, however this solution has the disadvantages of high costs and large space requirements, and still the power efficiency is rather poor.

WO 02/091329 Al discloses, e.g. Fig.18, a meter for collecting and communicating flow data, wherein a wireless transmitter is provided for outputting the sensed data from the meter. A 3 V Lithium battery powers the wireless transmitter. Furthermore, it is described that a parallel capacitor is added to the battery to provide the peak current needed for RF transmission. Still further, it is described that periodical transmission of data reduces power consumption of internal circuits.

WO 2006/127479 A2 discloses in Fig. 1 a remote communication system wherein a high capacity battery provides power for a two-way digital radio module through a low voltage power converter. Furthermore, in Fig. 3 the high capacity battery, at typically 6 volts, provides power through a low voltage power converter to two sources in the hardware package, the digital microprocessor and the two-way digital radio module.

SUMMARY OF THE INVENTION

It may be seen as an object of the present invention to provide an improved battery driven consumption meter with low power consumption and still with the peak current capacity to drive a radio communication interface.

The present invention provides a consumption meter arranged to measure an amount of a physical entity, the consumption meter including

- a flow sensing unit, such as an ultrasonic flow sensing unit, arranged to perform a measurement on the physical entity, and to generate data representing an amount of flow accordingly,

- a radio communication interface arranged to transmit a Radio Frequency signal representing the amount of the physical quantity,

- a battery exhibiting a battery voltage, wherein the battery is arranged to generate electric supply power for the flow sensing unit and the radio communication interface, and

- a voltage converter connected to the battery so as to convert the battery voltage to a second voltage being lower than the battery voltage, wherein the radio communication interface is arranged for at least partly being powered by the second voltage.

Thus, the meter is power by a supply circuit including the battery and the voltage converter. The flow sensing unit may be powered directly by the battery voltage, or it may be powered also via the voltage converter. By converting the battery voltage, which is often fixed by the specific type of battery, it is possible to provide a lower voltage which may still be able to supply the required supply voltage to drive the radio communication interface. At the same time, an improved power efficiency can be obtained, because the lower supply voltage means that high currents drawn during RF transmission will be easier to handle for the battery, because the current drawn from the battery will be reduced compared to the situation where the full battery voltage was used to supply the radio communication interface. Thus, even though the voltage converter in itself will consume some energy, it is possible to obtain an increased power efficiency upon appropriate selection of the voltage conversion factor to suit the specific circuits in question. This is due to the fact that especially radio communication circuits consume less power when operated at a voltage lower than the typical battery voltage 3.6V for Lithium batteries. In the following, preferred embodiments with further reduction of power loss in the voltage converter will be described.

Preferably, the voltage converter includes a non-linear regulator, such as a switch-mode circuit, to convert the battery voltage to the second voltage. Such non-linear regulator is commercially available in version with very high power conversion efficiency, and thus the improved power efficiency will not be completely lost due to losses in the voltage converter in itself. A non-linear regulator will conserve the power (voltage multiplied by current), and thus reduce the current with a factor corresponding to the ration between input and output voltage of the non-linear regulator.

A sensing element arranged to sense a current consumption of the radio communication interface may be included, such as a sensing element connected so as to disable the non-linear regulator upon the sensing element sensing a current consumption of the radio communication interface being lower than a predetermined threshold value. Hereby power can be saved to drive the nonlinear regulator in situations where it is not required, because only a limited current is drawn by the radio communication interface, a current that can be handled by the battery directly, if required at all. In an implementation, a voltage across the sensing element is used to enable or disable the non-linear regulator, such as by a voltage across the sensing element providing an input to an electric switch connected to an enable input of the non-linear regulator. Especially, a single resistor can be used to implement the current sensing element.

The non-linear regulator may be connected with a feedback loop to provide the non-linear regulator with a feedback of the second voltage, and wherein a current consumption of the feedback loop is eliminated according with disablement of the non-linear regulator. Hereby power to e.g. a voltage divider serving as feedback loop, can be saved when not required, e.g. by means of an electric switch serving to connect or disconnect the feedback loop, wherein the electric switch is controlled by the sensing element, e.g. the electric switch can be controlled by a voltage across a current sensing resistor. Especially a single transistor (bipolar or FET) can be used to implement the electric switch.

An electrical by-pass connector may be included, i.e. an electric connector arranged to by-pass the voltage converter, such as an electrical by-pass connector connecting voltage input and voltage output of the voltage converter. Hereby it is possible to supply voltage directly from the battery in periods where the voltage converter is disabled. The electrical by-pass connector may include a resistor, such as the electrical by-pass connector being a single resistor connected between voltage input and voltage output of the voltage converter. The by-pass connector and the sensing element may especially be implemented by one or more common elements, such as implemented by a single resistor serving the function of current sensing element as well as a by-pass connector. Especially, the by-pass connector may be arranged to supply sufficient electric power to maintain a stand-by activity of the radio communication interface in periods where the nonlinear regulator is disabled. Thus, it is possible to maintain all registers etc. ready in the radio communication interface without the need for the voltage converter being active, and then the radio communication interface will be quickly ready for RF transmission, when required, and thus the period where the voltage converter is required is reduced, thereby saving power to drive the voltage regulator itself.

To save further power in the voltage converter when not required, the supply circuit may include a switch arranged to disconnect a supply voltage to the voltage converter, such as an electric switch operating according to an input provided by the sensing element as described earlier.

It may be required for some low voltage circuits of the meter to be supplied by an even lower voltage than the second voltage. Thus, the meter may include a linear regulator arranged to convert the second voltage to a third voltage being lower than the second voltage. The flow sensing unit and the radio communication interface may be powered by different supply voltages, such as the battery voltage and the second voltage, respectively, and wherein the flow sensing unit and the radio communication interface are interconnected via a level shifter so as to ensure proper communication voltage levels between the radio communication interface and the flow sensing unit.

The voltage converter may be arranged to generate supply power to at least one further element of the consumption meter, such as one of: a display, and an optical communication interface.

The flow sensing unit may be arranged for at least partly being powered by the second voltage. Certain types of flow sensing circuits exhibit the same significantly different current requirements as a function of time as described for the radio communication interface, e.g. circuits requiring high currents during rather short periods where power consuming measurement transducers are driven. Thus, in order to save power, such circuits may in the same way be powered by a lower voltage, i.e. the second voltage, in periods with high current requirement, while powered directly by the battery voltage in periods with lower current requirements.

The radio communication interface may be operated in a discontinuous manner, such as operated in a manner requiring significant different supply current in different periods. This is typical in a remote reading consumption meter, where the power consuming transmission only occupies a small fraction of normal operation time. The above described supply circuit embodiments where the voltage converter, preferably non-linear regulator, can be enabled and disabled according to current needs of the radio communication interface.

To obtain a power saving effect, the second voltage is preferably below 75% of the battery voltage, such as below 50% of the battery voltage, or such as below 30% of the battery voltage. With a 3.6 V battery, a preferred second voltage range will be such as 0.9 V to 2.5 V. Of course, the actual choice depends on the voltage rating of the circuits in question. The consumption meter may be: a water meter, a heat meter, a cooling meter, or a gas meter. The flow sensing unit is preferably an ultrasonic flow sensing unit.

In general the various aspects and advantages of the invention may be combined and coupled in any way possible within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 illustrates a sketch of a diagram of basic parts of an embodiment, and

FIG. 2 illustrates an electric diagram of a preferred supply circuit for a consumption meter.

DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates a consumption meter (dashed box) embodiment connected to sense an amount of fluid flow in a fluid line FL, e.g. a cold water pipe to for supply of cold water to a consumer. A flow sensing unit FSL), e.g. with an ultrasonic flow sensor, performs measurements on the fluid flow in the fluid line FL and generates a value representing a consumed amount of fluid Q. This value Q is applied to a radio communication interface RCI that transmits a Radio Frequency signal with the consumed amount value Q represented therein. All circuits of the consumption meter are supplied by electric power by a battery B mounted within a casing housing electronic components of the consumption meter. The battery B exhibits a battery voltage VB, e.g. a Lithium type battery B with battery voltage VB = 3.6 V.

In this embodiment, the battery voltage VB is applied directly to supply power input of the flow sensing unit FSL). The radio communication interface RCI is supplied with electric power via a voltage converter in the form of a non-linear regulator NR, preferably a switch mode circuit. The non-linear regulator NR converts the battery voltage VB to a lower second voltage V2. The radio communication interface RCI is the supplied with power at this reduced voltage V2. The second voltage V2 can be such as 75% or 50% of the battery voltage. Thus, the flow sensing unit FSL) and the radio communication interface RCI have different supply voltages, and this may require a level shifter connected between these to units FSL), RCI so as to convert a communication output voltage, e.g. for communicating the measured value Q, from the flow sensing unit FSL) to an appropriate input voltage level for the radio communication interface RCI. It is to be understood, however, that the flow sensing unit FSL) may in other embodiments be supplied by the second voltage V2 instead of directly by the battery voltage VB, i.e. via the non-linear regulator NR. Especially, of course the use of a non-linear voltage converter NR is advantageous in case low voltage circuit components are used, i.e. components with a rated voltage significantly below the voltage provided by the battery VB. Hereby power loss in a voltage divider can be avoided.

One advantage obtained by converting the battery voltage VB to a lower voltage V2 for supply of power to the radio communication interface RCI is that peak currents drawn by the radio communication interface RCI during RF transmission can easily be overcome by the battery B, since the current drawn from the battery B will be scaled down with the ratio between the battery voltage VB and the lower voltage V2. In this way, power efficiency can be improved.

However, the non-linear regulator NR will itself consume power, and thus to reduce this power consumption, a current sensing element CSE is introduced to sense a current consumption by the radio communication interface RCI. In a simple form such current sensing element CSE is a resistor connected to by-pass the non-linear regulator NR, i.e. between the battery voltage VB and the second voltage V2. A voltage across such current sensing resistor CSE can then be used to disable, e.g. switch off, the non-linear regulator NR when the current drawn is below a predetermined threshold value. At the same time, the current sensing resistor CSE serves as a by-pass of the non-linear regulator and thus serves to supply the battery voltage VB to the radio communication interface RCI when the current demand is low and the non-linear regulator NR is disabled. Hereby the radio communication interface can maintain a stand-by mode of operation, such as keeping register values etc. in periods between the current demanding RF transmissions, while power to the non-linear regulator NR is saved since the nonlinear regulator NR is not required in such periods.

Fig. 2 illustrated an electric diagram of an implementation of a circuit for supply of power to a radio communication interface based on power from a battery B. As seen, the non-linear regulator NR is here implemented with one commercially available switch-mode based voltage converter chip with a supply voltage input Vin, an enable input En, an output voltage output Vo, a feedback input Fb, as well as an electric ground connector Gnd. The actual output voltage V_out to supply of the radio communication interface, and possibly other circuit element of the consumption meter, is determined by means of a feedback loop connected between Vo and Fb, i.e. the voltage divider formed by resistors R18 and R19. The non-linear regulator chip NR is only active, when the enable input En is set to "high". Thus, with a low voltage on this enable input En, the non-linear regulator will enter a disabled state, i.e. an inactive state with a very low power consumption.

The current sensing element CSE described in connection with Fig. 1 is implemented with a single resistor R16 connected between supply voltage input of the radio communication interface (and possible other circuits) and supply input Vin of the non-linear regulator NR. A voltage across this resistor R16 is used as input to an electric switch Ql. The electric switch Ql is further connected to control another electric switch Q3 which serves to connect/disconnect the feedback loop R18, R19 to electric ground. Thus, along with disabling the non- linear regulator NR, this power consuming feedback loop R18, R19 can also be disabled or disconnected, thereby saving power.

In a situation where the non-linear regulator NR is disabled, i.e. with a low current consumption of V_out, and a large current is required, e.g. by RF transmission of the radio communication interface (or another circuit connected to V_out), then the voltage across resistor R16 will increase, and accordingly the electronic switch Ql will cause the enable input En to go "high" and thus enable the non-linear regulator NR. Accordingly, electronic switch Q3 will serve to connect the feedback loop R18, R19. When the non-linear regulator NR is enabled, the supply voltage V_out will equal the scaled-down voltage Vo of the non-linear regulator, e.g. 50-75% of the battery voltage VB. When only a low current is drawn from the output V_out, the output voltage V_out will increase due to current through the by-pass resistor R16. Hereby, the voltage across R16 will decrease until the electric switch Ql switches to off and thus disables the non-linear regulator. Thus, at very low current drains, the non-linear regulator NR is disabled, and R16 then serves to provide the battery voltage VB to the output V_out. At the same time, the capacitor Cl across the power supply output V_out will charge up to the battery voltage VB.

Thus, at low current requirements, the supply circuit will provide a supply voltage V_out equal to the battery voltage VB, while at high current requirements, the supply circuit will provide a supply voltage V_out equal to the output voltage Vo of the non-linear regulator NR.

To further save power in a disabled state of the non-linear regulator NR, one of its connections Vin or Gnd may be connected via an electronic switch controlled by the current sensing element CSE.

A peak current drawn from the battery B is reduced by de-coupling the battery B with capacitor C4 and resistor R20 to only a fraction of the peak current required by the radio communication interface. Altogether, the use of a voltage converter NR and the additional power consuming features described, results in a circuit design where the capacitor C4 can be rather small in size, and at the same time C4 can be implemented by a low cost component. Furthermore, the average current drawn by the battery is reduced, and thus the consumption meter will have an increased life-time with the same size of the battery B.

Tests have been performed to verify the effect of the invention. A Lithium battery with VB = 3.6 V was used to supply a radio transmitter IC (TI CC 1101) during transmission, i.e. the mode where the required supply current is highest. Two modes of operation have been tested: 1) by direct supply of the IC, and 2) by application of an embodiment of the inventive power saving circuit using a switch mode type DC-DC voltage converter to down-convert the supply voltage to V2 = 2.1 V. In mode 1) the current drawn from the battery was 29.4 mA, and the power consumption was 105.84 mW. In mode 2) the current drawn from the battery was reduced to 21.3 mA, while the power consumption was reduced to 76.68 mW. Thus, a significant reduction in maximum current drawn from the battery can be obtained, thereby allowing a small and cost effective Lithium battery to be used without driving the battery at peak currents leading to poor efficiency and thus poor battery life time.

Although the present invention has been described in connection with preferred embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims.

In the claims, the term "comprising" does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus, references to "a", "an", "first", "second" etc. do not preclude a plurality. Reference signs are included in the claims however the inclusion of the reference signs is only for clarity reasons and should not be construed as limiting the scope of the claims.