The present invention relates to a measurement apparatus for measuring surface tension, the apparatus comprising a measurement head incorporating at least one measurement unit provided with at least one sensor, means for bringing at least one sample to be measured into contact with a sensor incorporated in or associated with the measurement unit in order to measure the surface tension in the sample and further comprising control means for controlling the measurement operations.

The invention also relates to a method for measuring surface tension using the relevant measurement apparatus.

From patent publication FI 982845, an apparatus for measuring small forces and displacement distances is known. This kind of apparatus is also advantageously applicable to the measurement of surface tension and surface pressure.

Particularly in the measurement of surface tension or surface pressure, the sensor must be cleaned meticulously between successive measurement cycles in order to prevent residues of the material measured in the preceding cycle possibly adhering to the sensor from being carried over to the next measurement cycle, causing error in successive measurements. In a prior embodiment, the sensor is cleaned using a flame that removes by incineration the residues of contamination from the sensor. This kind of method, however, is tedious and incompatible with automated, continuous measurement techniques.

Measurement devices suited for measuring one or more samples are being used. Such devices capable of measuring during a single cycle a plurality of samples may also be automated in regard to the transfer of samples. However, these systems still require the cleaning of sensors to be performed manually, as a separate operation during which the measurement is interrupted.

From German application publication DE 19653752, a continuously operating tensiometer system is known which is based on measuring the internal pressure of bubbles in the sample and is principally intended for measuring the parameters of washing machine detergent solutions. To a permanently installed single-sample capillary sensor is connected an ultrasound transmitter that removes contamination accumulated on the sensor during its use. To enhance the cleaning effect, the system may also utilize a permanently mounted jet nozzle suited for spraying onto the sensor either the solution being measured or any other liquid.

It is an object of the present invention to provide a measurement apparatus capable of measuring surface tension on a plurality of samples and incorporating means for cleaning the measurement unit sensors.

The apparatus according to the invention is characterized in that the apparatus, preferably its measurement head, comprises a group of measurement units, preferably identical. In a preferred embodiment of the invention, the measurement units are disposed adjacent to each other in a linear array. In another preferred embodiment of the invention, the measurement units are disposed in a matrix array, advantageously having a plurality of measurement unit rows in parallel with each other. Each measurement unit is advantageously of the type described in, for example, patent publication FI 982845. This kind of measurement unit preferably comprises a detector section mounted in the same holder as a sensor assembly. The detector section of the measurement assembly comprises a light source and a position sensor, while the sensor assembly of the measurement unit comprises a spring member with a light beam shutter and sensor probe proper connected thereto. In a preferred embodiment of the invention, the measurement probe can be, e. g., a so- called DuNouy ring or the like probe generally used in surface tension measurement, such as the Wilhelmy plate. The probe may also be a wire, advantageously affixed, e. g., to a screen member as described in cited patent publication FI 982845 or to an attachment/support element connected to said screen member.

In a preferred embodiment of the invention, the measurement apparatus according to

the invention comprises a frame mounted on a base, at least one support member mounted on the frame, such as an arm having means for attaching and connecting thereto at least one measurement unit or a measurement head comprising a plurality of measurement units, a measurement station with means for receiving and moving one or more vessels containing the samples to be measured and means for bringing the sensors incorporated in and/or connected to the measurement units into contact with the liquid samples to be measured and, respectively, bringing the sensors out of said contact, and further comprises a cleaning station including means for receiving and moving one or more vessels containing a cleaning agent and means for bringing the sensors connected to the measurement units into contact with the cleaning agent and for taking the sensors out of said cleaning contact.

In a preferred embodiment of the invention, the means of the measurement station for receiving said one or more sample vessels comprise a holder or rack suited for accommodating a vessel containing one or more samples. The holder or rack is advantageously equipped with means for receiving sample vessels of different sizes.

In a further preferred embodiment of the invention, the means for contacting the sensors incorporated in and/or connected to the measurement units with the liquid samples to be measured and, respectively, taking the sensors out from said contact, comprise means capable of moving the sample vessels or vessel support racks both horizontally and vertically in respect to the measurement head.

In a preferred embodiment of the invention, the measurement station may also be provided with heating and/or cooling means for adjusting the sample temperature for and/or during the measurement cycle.

The invention is characterized in that the measurement apparatus also includes means for cleaning the measurement unit sensors. In a preferred embodiment of the inven- tion, the means for cleaning the measurement unit sensors comprise one or more vessels suited to receive a cleaning agent and to contain the cleaning agent. In a preferred embodiment of the measurement apparatus according to the invention, the

apparatus includes means for bringing the measurement unit sensors into contact with the means for cleaning the sensors. In a still further preferred embodiment of the invention, the means for bringing the measurement unit sensors into contact with the cleaning means communicate with the control means of the measurement apparatus in order to control the cleaning cycle.

The cleaning station includes means for receiving one or more vessels containing a cleaning agent, preferably a cleaning liquid, whereby the vessel receiving means comprise a holder or rack capable of accommodating one or more vessels containing the cleaning agent. Preferably, the holder or rack is provided with means for receiving vessels of different sizes.

The method according to the invention is characterized in that the sensor incorporat- ed in and/or associated with the measurement unit of the measurement head is brought, in order to perform sensor cleaning, into contact with a cleaning agent contained in at least one vessel incorporated in or associated with the measurement apparatus. In a preferred embodiment of the method according to the invention, the sensor, for the purpose of cleaning, is brought into contact advantageously successively with a cleaning agent contained in two or more vessels incorporated in or associated with the measurement apparatus. In a further preferred embodiment of the method according to the invention, each of the vessels contains the same cleaning agent but in different concentrations or, alternatively, at least one of the vessels contains a cleaning agent different from that applied to the other vessels. Preferably, DMSO (dimethylsulfoxide), or corresponding solvents are used as a cleaning agent, e. g. in the different vessels at different concentrations, e. g., so that the concentration of the cleaning agent changes from one vessel to the next. In a preferred embodiment of the invention, cleaning may be started using the most potent cleaning agent, and milder cleaning agents are introduced stepwise. In a further preferred embodiment of the invention, the last vessel containing an agent intended to make contact with the sensors contains pure water.

The sensor cleaning technique according to the present invention is efficient, as the

amount of sample residue possibly remaining on the sensor is reduced by each immersion cycle applied.

In a preferred embodiment of the invention, the means for bringing the sensors in- corporated in and/or connected to the measurement units into contact with the cleaning agent and for taking the sensors out of the cleaning contact comprise means capable of moving the cleaning agent-containing vessels or vessel support racks in both the horizontal and vertical directions in regard to the measurement head.

Advantageously, these means for moving the cleaning agent-containing vessels communicate with the control means of the measurement apparatus in order to control the movements of the cleaning agent-containing vessels.

In a further preferred embodiment of the invention, the cleaning station may be provided with means enhancing the cleaning operation, such as ultrasound devices, for instance, adapted to make contact with the cleaning agent-containing vessels, or preferably with the bottom parts thereof. The cleaning station may also include means for adjusting and controlling the temperature of the cleaning agent.

The measurement units of the measurement heads, advantageously the detector and sensor sections thereof, are preferably adapted to communicate with a control unit located in the frame of the apparatus and serving to control the functions of the apparatus and to process measurement results. The control unit may also include memory and/or computing means as well as means for displaying and/or transmitting and/or receiving information related to the measurement results and apparatus functions. In a preferred embodiment of the invention, the control unit comprises at least one microprocessor with concomitant memory, interface and control means, as well as means, such as display and printer means, for displaying the operation of the apparatus and measurement results.

In a preferred embodiment of the invention, the means of the measurement apparatus for receiving sample vessels and for bringing the sensors of the measurement units into contact with the liquid to be measured and for bringing the sensors out of contact

with the liquid advantageously comprise a rack capable of accommodating one or more sample vessels and means capable of moving the rack with the vessels mounted thereon in both the horizontal and vertical directions in regard to the measurement head. The rack may be moved manually or, alternatively, the measurement apparatus includes rack moving means controllable by e. g. the control unit. The means for bringing the sensors into contact with the cleaning agent and out of such contact are implemented in a corresponding manner In a preferred embodiment of the measurement apparatus according to the invention, the sample vessels are placed in a measurement station of the measurement appara- tus, while the cleaning agent-containing vessels are placed in a cleaning station of the measurement apparatus. Preferably, the sample vessels are so-called well plates, having, e. g., a matrix of twelve rows of eight wells for accommodating samples.

Preferably, the number of wells in a row of the sample vessel corresponds to the number of measurement units in the measurement head, whereby also the distance between the wells corresponds to the distance between measurement units in the measurement head. Advantageously, the vessels filled with cleaning agent are, e. g., vessels having elongated cavities aligned, e. g., in an array of twelve cavities side by side, with a cavity length compatible with the overall length of a measurement unit row in the measurement head.

Both the measurement station and the cleaning station are provided with mounting elements, e. g., racks, for keeping the vessels in their intended position in the measurement station and/or the cleaning station as well as means for bringing the racks with the vessels mounted thereon into contact with the sensors of the measure- ment units of the measurement heads, and for bringing the vessels out of such a contact. Preferably, these means are adapted to move the rack with the vessels mounted thereon, controlled e. g., by the measurement apparatus control unit so that, e. g., in the measurement station the sample vessel rack is moved into a position aligning the measurement unit sensors with the wells of the sample vessel. Then, the vertical movement of the rack with its sample vessels toward the measurement head brings the sensors into contact with the samples. Respectively, when the rack with its

sample vessels is moved in the vertical direction away from the measurement head, the contact of the sensors with the liquid samples is disrupted. The force imposed on the sensor may be measured either as the rack is raised or when it is lowered or, alternatively, during both raising and lowering the rack. After the rack with its vessels is moved down into its lower position, the rack may be shifted horizontally so that the next row of wells aligns with the measurement head sensors, whereupon the above-described vertical movement of the rack can be repeated. In this fashion, the rack is alternatingly moved horizontally and vertically until all the measurements are completed for all desired rows of the sample vessel rack. The rack with the cleaning agent-containing vessels is moved in a similar fashion in the cleaning station. In a preferred embodiment of the invention, measurements are performed also during the cleaning cycles.

In a further preferred embodiment of the invention, the measurement apparatus also includes members for moving the measurement heads from the measurement station to the cleaning station and back. These members are preferably connected to one or more arms supporting the measurement heads and connected to the apparatus frame so as to be movable in regard to the frame. Thus, these members allow the support arm to be moved rotatingly, for instance, in the horizontal plane with regard to the apparatus body so that a first measurement head can be brought into a suitable position for measurements, e. g., in the measurement station, while the members respectively bring a second measurement head into a position suited for cleaning the sensors, e. g., in the cleaning station.

In a preferred embodiment of the invention, the means for bringing a measurement unit sensor into contact with a sample to be measured comprise means for moving the measurement units and means for moving the sample vessels or sample vessel racks. Respectively, the means for bringing a measurement unit sensor into contact with the cleaning means comprise means for moving the measurement units and means for moving the cleaning agent-containing vessels or vessel racks. In a further preferred embodiment of the invention, the measurement units with their sensors are moved substantially vertically, while the sample vessels and/or sample vessel racks

as well as the cleaning means vessels and/or racks containing the latter vessels are moved substantially horizontally, advantageously under the control of, e. g., the measurement apparatus control unit.

Next, the invention will be examined in greater detail with reference to the attached drawings, wherein FIG. 1 shows a side elevation view of a measurement apparatus according to the invention as seen in front of the apparatus; FIG. 2 shows a top plan view of the measurement apparatus of FIG. 1; FIG. 3 shows a block diagram of the measurement apparatus control unit; FIG. 4 shows a top plan view of an embodiment of a measurement apparatus according to the invention; and FIG. 5 shows the apparatus of FIG. 4 in front elevation view.

In the Figures, like numerals refer to like elements.

In FIG. 1, reference numeral 1 denotes a measurement apparatus and reference nu- meral 10 denotes a frame thereof with a substantially horizontal support arm 20 con- nected thereto. The connection of arm 20 to the apparatus frame is such that allows the arm 20 to be advantageously rotated horizontally in regard to the frame 10, advantageously using, e. g., means 21. Attached to support arm 20 are two measurement heads 30, advantageously as shown in FIG. 1 so that one measurement head is mounted on each end of arm 20 extending outwardly from frame 10. In a preferred embodiment of the invention, the connection of measurement heads 30 to support arm 20 is made dismountable using, e. g., suitable connector and locking elements. Measurement units 31 are advantageously adapted on measurement heads 30 using coupling elements such as suitable connectors, for instance, permitting

dismantling of the units. To both sides of frame 10 in a symmetrical position thereto are advantageously adapted means 40 for receiving sample vessels 41 and means 50 for receiving cleaning agent vessels 51. To both of these means 40 and 50 are adapted means 42 and 52, respectively, for moving sample vessels 41 and cleaning vessels 51, respectively, in regard to measurement heads 30 both horizontally and vertically. In order to make their moving easier, sample vessels 41 and/or cleaning vessels 51 are advantageously placed in holders or racks that further are mountable on the above-mentioned means provided for moving the vessels. The racks advan- tageously have a design that allows one or more sample vessels 41 and/or cleaning vessels 51 to be placed thereon. Furthermore, the racks are designed to accommodate sample vessels 41 and/or cleaning vessels of different sizes.

FIG. 2 shows the measurement apparatus 1 in a top plan view. In the sample vessel, which is denoted by reference numeral 41 and preferably is a well plate, a well 43 is provided for each sample. The distance between the measurement units 31 of the measurement head 30 corresponds to the relative distance of the wells 43 of the well plate 41 in the longitudinal direction of support arm 20. The well plate 41 may be moved in the horizontal direction by means incorporated in the measurement station, advantageously controlled by the measurement apparatus control unit, for instance, so that each one of the well rows of the place can be precisely aligned with the sensors of measurement units 31 of measurement head 30. Preserving this alignment, the well plate 41 may be further moved in the vertical direction by other means, incorporated in the measurement station and advantageously controlled, e. g., by the measurement apparatus control unit, so that the sensors of measurement units 31 make contact with the samples placed in the wells 43 of well plate 41 for measuring the surface tension of the samples. The vertical movement is preferably continued sample-specifically as defined in the specifications of the relevant measurement method. After the sensor has been immersed in the sample to a specified depth, well plate 41 is moved vertically downward, advantageously to the same position from where the upward vertical movement was started. To measure the samples in the next row of well plate 41, the well plate is shifted by the distance between the well rows so that the next row of samples to be measured is aligned with the sensors of the

measurement unit, whereupon the above-described sequence of vertical movements can be repeated.

The body 10 of measurement apparatus 1 houses a control unit. The structure of control unit 60 is shown schematically in FIG. 3. Advantageously, control unit 60 comprises a central computing unit 61, such as a microprocessor, for instance, with memory means 62, computing means, interface/control means 63 included for inter- facing the measurement units with the control unit and for controlling their functions, as well as for controlling the measurement apparatus functions, and measurement apparatus programming and function control interface means 64 such as a keyboard, for instance, interface means 65 for communication with the measurement station and interface means 66 for respectively controlling the means of the cleaning station, display means 67, and means 68 for supplying power to the control unit. The control unit may also include means 69 for transmitting and/or receiving measurement and/or control information to and from other equipment connected to the measure- ment apparatus. The interface means 65 and/or 66 are also suitable for data commu- nication of the measurement station and/or the cleaning station with the central unit 61, such as identification of sample vessels and/or cleaning vessels or their holders/racks, for instance.

The transfer operations of the horizontal and vertical movements of well plate 41 may be preprogrammed in control unit 60 and stored in memory means 62 of control unit 60 before measurements are commenced. Memory unit 62 may have a plurality of such programs stored therein, from which the user may select a suitable one using, e. g., the measurement apparatus control means. For controlling the horizontal transfer of well plate 41, the measurement station may also include sensor means that identify, e. g., the type of well plate 41, the distance between its well rows and/or the position of well plate 41 in regard to the surface tension sensors of measurement head 30. In a preferred embodiment of the invention, this information is utilized for aligning well plate 41.

The cleaning station includes means 50 for receiving a cleaning agent-containing

vessel or vessels 51, such as a holder or rack, for instance, and means for moving in both the horizontal and vertical directions this kind of rack with the cleaning agent- containing vessels mounted thereon.

In a preferred embodiment of the invention, cleaning agent vessel 51 has such dimensions that the sensors incorporated with or connected to measurement units 31 of measurement head 30 can be simultaneously brought into contact with the cleaning agent in vessels 51. Preferably, vessel 51 for holding the cleaning agent includes a plurality of elongated cavities 53 having a length greater than the overall length of the linear array of measurement units 31 of measurement head 30 in an apparatus having the measurement units 31 aligned in a linear array in the measurement head 30. Hereby, the number and/or relative distance of such elongated cavities 53 preferably correspond to the number and/or relative distance of well rows in sample vessel 41.

In a preferred embodiment of the invention, support arm 20 with measurement head 30 attached thereto is movably adapted in regard to apparatus frame 10, so that measurement head 30 may be transferred to the cleaning station after measurements, for instance. Respectively, a measurement head 30 already treated in the cleaning station in the sensor cleaning cycles of measurement unit 31 may be transferred back to the measurement station by moving support arm 20. In a further preferred embodi- ment of the invention having two measurement heads connected to a common sup- port arm 20, both measurement heads are transferred simultaneously with the move- ment of the arm so that when a first measurement head 30 enters the measurement station, the second measurement head 30 enters the cleaning station. Support arm 20 is advantageously connected to apparatus frame 10 by members 21 that allow the movement of the arm relative to frame 10 by way of, e. g., rotating support arm 20 in the horizontal plane, and further include means for locking the support arm in a stationary position and unlocking from the same. In a preferred embodiment of the invention, the measurement apparatus is provided with members 21 that, controlled by control unit 60, move measurement heads 30 supported by arm 20 from the measurement station to the cleaning station and vice versa.

In a preferred embodiment of the method according to the invention, the sensor cleaning vessel 51 has, e. g., twelve immersion cavities 53 whereto the cleaning agent is metered. The metering of the cleaning agent into wells 53 is performed thus, that the concentration of the cleaning agent in each well 53 is different, e. g., advantageously having the highest concentration in the first immersion cavity 53 to receive a sensor array. Then, the next immersion trough to receive the sensor array has a concentration lower than in the preceding one and so forth. Particularly if the cleaning agent employed is water-soluble, the last immersion cavity may be filled with pure water.

In a preferred embodiment of the invention, measurements on a measurement head 30 are also performed during the time the measurement head is being cleaned in the cleaning station. Preferably, the measurement results obtained during cleaning may be utilized for assessing and/or controlling the cleaning effect. When the surface tension value of the cleaning agent in at least one of the immersion cavities is known, these measurement results may also be employed in the calibration of measurement units 31 by way of comparing the cleaning station measurement results with earlier measurement and/or stored data retrieved from the memory means 62 of control unit 60. Assessment of cleaning efficiency and/or comparison of calibration data may also be based on surface tension measurement results obtained for different concentrations of the cleaning agent, whereby such data is advantageously kept stored in the memory means 62 of control unit 60.

FIGS. 4 and 5 illustrate a preferred embodiment of the measurement apparatus 1 according to the invention. The measurement apparatus 1 comprises a frame 10 having mounted thereon a substantially horizontal support arm 20 whose distal end directed outwardly from the apparatus frame advantageously carries on its lower side one or more measurement units 31, each including one or more measurement units 31. Surface tension sensors incorporated in or connected to the measurement units 31 extend downward from the support arm. The measurement apparatus also comprises means for receiving a sample vessel 41 and a cleaning vessel 51. In a preferred

embodiment of the invention, these means 40 and 50 are constituted by a rack in which the sample vessel or the cleaning vessel, respectively, can be mounted for moving the same in regard to the support arm 20 by means 42 or 52, respectively, incorporated in the measurement apparatus. Preferably, sample vessel 41 is, e. g., a well plate having eight wells 43 by twelve rows preferably in a matrix array. The samples to be measured are placed in wells 43 of sample vessel 41, whereupon sample vessel 41 is moved to the left as shown in FIG. 4 preferably using means 42 so that the first row of wells 43 of sample vessel 41 becomes aligned with the sensors of measurement unit 31 of measurement head 30 mounted on support arm 20, whereby one sensor coincides with one well 43 of one well plate 41. Sample vessel 41 is transferred vertically by means 42 incorporated in the measurement apparatus without disturbing the lateral position of the vessel, until the sensors of measurement unit 31 of measurement head 30 come into contact with the samples placed in wells 43. Depending on the surface tension measurement method, the vertical movements are repeated a required number of times. After the sample vessel 41 has been elevated into sensor contact the number of times required by the measurement method, the movement is stopped and a vertical downward movement of the sample vessel is started and continued at least until the physical contact of the measurement unit sensors with the samples being measured is broken, preferably finally reaching the same position wherefrom the vertical movement was commenced. To measure the surface tension of samples placed in the next row of wells 43, the sample vessel is shifted laterally to the left until the next row of samples to be measured becomes aligned with the sensors of measurement units 31 of measurement head 30. The above-described sequence of lateral and vertical movements is repeated until all the intended measurements have been carried out. Finally, sample vessel 41 is preferably moved back into its home position on the right. To clean the sensors, cleaning vessel 51 is moved, to the right in the exemplary embodiment illustrated in FIG. 4, until the cleaning-liquid-containing immersion cavity 53 thereof located farthest to the right is aligned at the row of measurement unit sensors 31 of measurement head 30. Next, the cleaning vessel is moved vertically without disturbing the lateral position of the vessel until the measurement unit sensors come into contact with the cleaning agent placed in cavities 53 of cleaning vessel 51. The vertical movement is continued until

the sensors are immersed sufficiently deep in the liquid cleaning agent. The sensors are kept in the cleaning liquid for a time depending on e. g. the type of samples measured and the cleaning agent used. Preferably, the immersion time is preset or preprogrammed into the control means of the measurement apparatus control unit.

After the lapse of the preset time, the cleaning vessel is moved vertically back to the same position from where the vertical movement was commenced. This cleaning cycle is next repeated by transferring the cleaning vessel to the right in the exemplary embodiment illustrated in FIG. 4 until the next well 53 of cleaning vessel 51 coincides with the sensor row. The above-described vertical movement is repeated.

In a preferred embodiment of the invention, the durations and depths of sensor immersion are varied at the individual wells. After the sensors have been immersed in all the cavities of the cleaning vessel, the cleaning vessel is returned to its home position. In a preferred embodiment of the invention, the sensors are immersed in so many of the adjacent cleaning-liquid-containing immersion troughs 53 of cleaning vessel 51 as is required to bring the values of surface tension measurements performed during the immersion cycles to meet the target values set for cleaned sensors. In a preferred embodiment of the invention, the lateral and/or vertical transfer movements of the sample vessels and/or cleaning vessels may be performed using means 42 and/or 52 incorporated in the measurement apparatus under the control of the measurement apparatus control unit. The measurement apparatus 1 may also be provided with means allowing the user to manually perform the above- described operations required in the transfer movements of the sample vessels and the cleaning vessels. Further, it is possible to program the measurement apparatus to perform measurements only on a limited number of wells 43 of sample vessel 41.

Respectively, it is possible to perform the cleaning of sensors by immersing the sensors in only a limited number of immersion troughs 53 of cleaning vessel 51. In the exemplary embodiments shown in FIGS. 4 and 5, the sample vessel may alter- natively be placed on the left, whereby the cleaning vessel is respectively located on the right. In a preferred embodiment of the invention, the sample vessel 41 may be located on either side of measurement apparatus 1, whereby the user may indicate the location of sample vessel 41 using, e. g., means communicating with the measurement apparatus control unit or, alternatively, sample vessel 41 or cleaning vessel 51, respectively, includes means capable of communicating with the measurement apparatus control unit for identifying the location of sample vessel 41 or cleaning vessel 51, respectively, when the vessels are placed in measurement apparatus 1.