The invention relates to a device for setting a flow rate of liquid flowing through a drip. Drips are applied as flow rate-determining element in for instance an infusion, but also in other applications, such as in titration. The flow rate of an infusion can be precisely determined by applying an infusion with a cylinder and a mechanically driven piston. Although the flow rate of such an infusion can be set very accurately, the costs of such devices are high. In an infusion provided with an adjustable drip the accuracy is mediocre, this usually depending on the person carrying out the setting.

The object of the invention is to provide means with which the flow rate of a device provided with a drip can be set more accurately.

This object is achieved in that the device is adapted to generate at an adjustable frequency a repetitive signal discernible by human senses, the frequency of this signal being related to the frequency of the droplets in the drip at the desired flow rate.

Use is made here of the situation that the droplet size of the drip is always the same, so that the drip frequency of the droplets is a good measure for the flow rate. The frequency of the drip can usually be set by a restriction in a part of the tube between container and drip which is situated upstream of the drip. This restriction is usually controlled with a slide. It is however difficult for a person operating the restriction to find the correct setting of the restriction. Setting is greatly simplified by providing a signal. The person first sets the frequency of the signal and then adjusts the restriction to a position such that the frequency of the falling droplets is the same as that of the signal. It is noted that the droplet size also depends on the form of the drip; microdrippers are for instance known which have a droplet size three to four times smaller than that of a normal drip. It will be apparent that the desired flow rate is calculated by dividing the quantity of liquid to be administered by the time duration within which this quantity must be administered.

The invention also relates to an associated method for setting the flow rate of liquid flowing through a drip, wherein the following steps are performed of: setting a frequency on a device adapted to generate at an adjustable frequency a repetitive signal discernible by human senses, discerning the signal and adjusting the drip until the frequency with which the droplets fall into the drip corresponds to the frequency of the droplets in the drip at the target flow rate. According to a first preferred embodiment the signal comprises a sound signal.

Although visually discernible signals such as illuminating LEDs are not precluded, the signal preferably comprises a sound signal. A sound signal is not only readily discernible, but when perceiving such a signal the user can use other senses for discerning the droplets. When perceiving the sound signals the user can thus see in very simple manner what the number of droplets per unit of time is. Use of visually discernible signals is possible, but does require the light source to be placed in the vicinity of the drip. It is also possible to apply a combination of a visual and an auditory signal. Another preferred embodiment provides the measure that the device is provided with selection means for selecting liquid data and the desired flow rate, and data-processing means for calculating the frequency of the signal on the basis of at least the selected liquid data and the selected flow rate. The user hereby need not know the drip frequency of the droplets of the relevant liquid; only properties which are relevant to the droplet formation, such as viscosity, surface tension and density, need be selected. When use is made of drips with different properties this is preferably also entered and taken into account in the calculation. The selection means can also be adapted to select the quantity of liquid and the time duration within which this quantity of liquid must be administered. The digital computer itself then calculates the desired flow rate.

This embodiment likewise provides a method in which the frequency is set by selecting properties of the liquid and selecting the flow rate.

^"■' It is however even easier if the device comprises a memory in which names of liquids with associated data are stored, if the selection means are adapted to select the name of a liquid and the data-processing means are adapted to calculate the desired frequency from data of the selected liquid stored in the memory and the selected flow rate. This greatly simplifies operation; this is because a user need only enter the name of the liquid to be administered, such as 'physiological saline solution', after which the device automatically selects the data of the relevant liquid and uses these to calculate the interval. The nature of the drip is preferably also entered here.

This embodiment likewise provides a method in which properties of the liquid are selected by selecting the name of the liquid.

It is recommended that the time duration between the falling of two droplets

corresponds to the period of the frequency of the signal generated by the device. It cannot however be precluded that the frequency of the signal is for instance twice as high, which means that a droplet should fall at every second sound signal. It will be apparent that this is also possible at more than two sound signals, and that it is also possible for a sound signal to occur at every second droplet.

An important field of application lies in determining the flow rate of an infusion. The device is thus preferably adapted to determine the frequency of a drip of an infusion.

According to yet another embodiment, the device is implemented in a handheld electronic computer such as a PDA or a mobile telephone. This is after all already provided with a computer, a memory, input or selection means and with means for generating a signal, both auditory and visual.

The above device relates only to setting of the flow rate, wherein a certain measure of inaccuracy cannot be prevented, particularly when the setting is carried out hastily and insufficient synchronization is achieved. A preferred embodiment therefore provides the measure that the device is coupled to a measuring device for determining the flow rate of the drip. It is hereby possible to check for correct setting.

This embodiment likewise provides a method in which, after the flow rate of the drip has been set, the flow rate of the drip is measured and after a period of time a comparison is made as to whether the measured flow rate corresponds to the set flow rate.

The measuring device preferably comprises a weighing member for determining the weight of the quantity of liquid present in a container, this container being coupled to the drip whose flow rate must be set, coupling means for coupling the container to the weighing member, a computer coupled to the weighing member for calculating the flow rate of the liquid flowing through the drip, a memory connected to the computer for storing the values measured by the weighing member, and visual display means for displaying the flow rate of the liquid flowing through the drip calculated by the computer.

This embodiment likewise relates to a method in which the flow rate is measured by measuring the weight of a container from which the liquid is supplied to the drip and measuring the relevant weight after a period of time, and subsequently dividing the difference by the time duration between the two weight measurements.

According to a further preferred embodiment the computer is adapted, depending on measured values stored in the memory, to disregard or take into account measured values originating from the weighing member. Because measured values lying outside predetermined limits are disregarded for further calculation, a flow rate can be calculated which is even more reliable. This is because highly deviating measured values lying outside predetermined limits entail a great risk of these values being unrealistic and for instance being caused by external factors, such as a movement of the device as a result of a disturbance. Such highly deviating measured values are excluded from the calculation by this measure. Because the user can for instance determine the limits him/herself, the device is flexible in use. According to this embodiment measured values lying outside predetermined limits are disregarded. The present invention will now be elucidated with reference to the accompanying drawings, in which:

Figure 1 shows a diagram of the device according to the invention;

Figure 2 is a perspective schematic view of a combination according to the present invention, which is also adapted to measure flow rate;

Figure 3 is a block diagram of the combination shown in figure 2; and

Figure 4 is a perspective schematic view of an alternative embodiment. Figure 1 shows a diagram of a device according to the invention. This device, designated as a whole with 30, comprises a computer 31 , an input member 32, for instance in the form of a keyboard or a 'touch screen', a memory 33, an oscillator 34, a loudspeaker 35 and a display 36. The oscillator can otherwise be incorporated in computer 31.

The operation of the device is as follows: According to a simple embodiment, during input the desired frequency is entered into input member 32. This frequency is then for instance read from a table or from an specification on the packaging of the liquid to be dispensed. This frequency is fed to digital computer 32, which drives oscillator 34 at this frequency, from which oscillator the output signal is fed to the loudspeaker. It will be apparent that after a period of time computer 32 stops the signal to the oscillator and the signal no longer sounds from loudspeaker 35. It is of course also possible to use the input member to switch off the oscillator.

According to a subsequent embodiment, the user selects various values of significance to the droplet size, such as specific mass and viscosity and the nature of the drip, by means of input member 32, which can show a relevant options menu when formed by a touch screen. These signals are then fed to digital computer 31, after which computer 31 retrieves from memory 33 the frequencies associated with these values and activates oscillator 34 at the relevant frequency. When the input member is formed by a keyboard, it is also attractive for a visual panel, 'display', to be present in order to visualize the menu. It will be apparent that instead of entering a desired flow rate it is likewise possible to enter a desired quantity of liquid to be administered and a time duration within which this liquid must be administered, preferably via a relevant options menu.

According to an alternative embodiment, only the name of the. liquid to be administered need be entered into input member 32, after which digital computer 31 retrieves the relevant values of liquid properties or directly retrieves the frequency from the memory and activates oscillator 34 at the thus obtained frequency.

Although such functions can be performed by a specific apparatus, it is attractive if they are performed by an apparatus that is already commercially available, such as a PDA or a 'smartphone'. Such devices do after all already comprise a digital computer 31, an input member 32, a display 36, a memory 33 and a loudspeaker 35. Such an apparatus also usually provides the option of communicating with other devices by means of 'Bluetooth' or other communication medium, as will be found important in the embodiment to be elucidated hereinbelow.

Figure 2 shows a device 1 for determining the quantity of liquid present in a container for medical use, such as an infusion bag 2, provided with a passage 2a for liquid, which can be closed by a tap (not shown). Device 1 comprises a housing 3 to which coupling means in the form of a hook 4 are fixed via a weighing member (not shown in this drawing) embodied as weight sensor for the purpose of determining the weight of infusion bag 2. The device also comprises a memory placed in the interior of housing 3, and therefore not shown in this drawing, for storing weight data, and a data-processing unit. A display 5, a control panel 6 and a light source are situated on an outer side of housing 3. The device further comprises fixation means (not shown in this drawing) for coupling device 1 to an infusion rod (not shown).

Figure 3 shows a block diagram which shows how the different components of the device of figure 1 are mutually connected. Infusion bag 2 is releasably connected to hook 4. Hook 4 is connected to weighing member 8, which is embodied for instance as a Hall sensor. Weighing member 8 is connected to data-processing unit 10. Display 5, control panel 6, signalling means embodied as a LED 7 and memory 9 are likewise connected to data-processing unit 10. It is noted here that the signalling means can also comprise a beeper or other auditory signalling member. Display 5, control panel 6, LED 7, weighing member 8, memory 9 and data-processing unit 10 are also connected to battery 12 in order to obtain the required energy. This battery is preferably formed by a rechargeable battery, but can also be formed by a non-rechargeable battery. A power supply circuit connectable to the mains can be applied instead of a battery. The device operates as follows. Once an infusion bag 2 has been coupled to hook 4, weighing member 8 measures the weight of infusion bag 2 and generates an associated signal. This signal representing the measured weight is stored in memory 9. Data- processing unit 10 can be operated by means of control panel 6 such that the flow rate is determined on the basis of weight data stored in memory 9. In order to determine a flow rate a user at least partially opens the tap, whereby liquid flows out of infusion bag 2 through passage 2a. Weighing member 8 measures the weight of the infusion bag at a frequency of 1 Hz, after which the signals representing these values are transmitted to data-processing unit 10 and stored in memory 9. Data- processing unit 10 calculates the flow rate on the basis of data stored in memory 9 by the user relating to the specific mass of the liquid entered beforehand into the memory, the difference in weights of infusion bag 2 measured at at least two mutually differing times, and the time difference between these times. This is then displayed on display 5. On the basis of the displayed flow rate the user can open the tap further or partially close it if the value of the displayed flow rate lies respectively below or above the value desired by the user.

Making use of control panel 6 the user can enter the desired quantity of liquid to flow out of infusion bag 2, after which data-processing unit 10 determines and displays on display 5 the time remaining on the basis of the weight of infusion bag 2, the

determined flow rate and the desired quantity of liquid to flow out of the infusion bag.

Further reference data can be entered into memory 9 making use of control panel 6.

Examples of further reference data are: the initial weight of infusion bag 2, the weight of infusion bag 2 after a quantity of liquid has flowed through passage 2a, the quantity of liquid which has flowed through the passage, the time duration before the desired quantity of liquid has flowed through passage 2a (time remaining), a lower limit and upper limit of the flow rate of the liquid, and so on. If a value determined by device 1 now differs from the lower limit or upper limit set by the user, data-processing unit 10 will activate the blue LED 7 such that it begins to flash. The device can optionally be adapted such that LED 7 then first generates a signal if the determined flow rate differs from the lower or upper limit by more than a value preset by a user. This can optionally be accompanied by a sound signal, for which purpose the signal means are provided with a loudspeaker. Device 1 can also be adapted such that it generates a signal to a central monitoring system (not shown).

The combination of a measuring device as described above and the device for setting the flow rate of a liquid flowing through a drip is attractive for setting the drip. The advantages increase when the measuring device is connected to the setting device so that the results of the measuring device can be used to modify the frequency in order to achieve a greater accuracy. It will otherwise be apparent that the measuring device can also be used on its own.