Method for the verification of pipettes

Abstract

A verification of a pipette results in a release or a warning message. A liquid measuring container (110) receives the pipette liquid volume (V.sub.P) to be verified. A loading cell (120) is connected to the liquid measuring container in a force-transmitting manner. The loading cell outputs a measurement signal (ms) corresponding to the weight force (F.sub.G) acting thereon. A processing unit (130) detects and processes the measurement signal (ms), determines a first weight force (G.sub.t1) at time point (t.sub.1) and determines a second weight force (G.sub.t2) at time point (t.sub.2). The pipette liquid volume is calculated and the calculated value is assigned to a pipette volume class (K.sub.i) having a defined class nominal value (VK.sub.i). The processing unit tests whether or not an absolute value of the volume difference (ΔV) is within a predetermined tolerance value (T) for the assigned pipette volume class. The processing unit outputs the test result.

Claims

1. A method for verifying pipettes, wherein the result of the verification is a release or a warning message, the method comprising the steps of: providing a liquid measuring container to receive a pipette liquid volume to be verified, a loading cell, connected to the liquid measuring container in a force-transmitting manner, the loading cell configured to output a measurement signal corresponding to a weight force acting on the loading cell, and a processing unit for receiving and processing the measurement signal; determining a first weight force from the measurement signal at a first time point t.sub.1 of a last stable measurement point by the processing unit, wherein said last measurement point is chronologically prior to the receiving of the pipette liquid volume to be verified; determining a second weight force from the measurement signal at a second time point t.sub.2 of a new measurement point by the processing unit, wherein said new measurement point is chronologically after the receiving of the pipette liquid volume to be verified; calculating the pipette liquid volume in the processing unit according to the formula:
V.sub.P=ρ.sup.−1×(G.sub.t2−G.sub.t1); wherein: V.sub.P is the pipette liquid volume; ρ is the density of the pipette liquid; G.sub.t1 is the weight force at the first time point; and G.sub.t2 is the weight force at the second time point; assigning the calculated pipette liquid volume to one of at least two pipette volume classes having a defined class nominal value respectively, wherein the assignment by the processing unit takes place in such a way that an absolute value of a volume difference between the pipette liquid volume and the class nominal value is as small as possible; testing, in the processing unit, whether or not the volume difference has an absolute value that is less than a predetermined tolerance value for the class nominal value of the assigned pipette volume class; and outputting a test result from the processing unit as a release when the volume difference is less than the predetermined tolerance value, or as a warning message when the volume difference is greater than the predetermined tolerance value.

2. The method of claim 1, wherein: the test is carried out by the processing unit based on a predefined number of times the pipette liquid volume to be verified is received.

3. The method of claim 1, wherein a measurement signal is a measurement signal when the measurement signal is within a signal band having a predetermined time length and predetermined signal level.

4. The method of claim 1, wherein the method is fully automated, such that the receiving of the pipette liquid volume to be verified into the liquid measuring container triggers the verification by the processing unit, and after outputting the test result, the processing unit is ready to receive and verify a next pipette liquid volume to be verified.

5. The method of claim 1, further comprising the steps of: determining an evaporation rate of the liquid in the liquid measuring container by processing the measurement signal over a preceding time period which terminates at the latest at time point; calculating the evaporation volume between time point ti and time point t2; and calculating the pipette liquid volume according to the formula:
V.sub.P=ρ.sup.−1×(G.sub.t2−G.sub.t1+c.sub.v×(t.sub.2−t.sub.1)) wherein: c.sub.v is the evaporation rate; t.sub.1 is the first time point; and t.sub.2 is the second time point.

6. The method of claim 5, wherein the time period (Δtv) is at least and inclusive of ten seconds, and at most and inclusive of ten times the time difference between time point t.sub.1 and time point t.sub.2.

7. The method of claim 5, wherein: based on a reference value, the validity of the evaporation rate is checked.

8. The method of claim 1, wherein: when the weight force difference is less than a predetermined value, the method is ended without a result output.

9. The method of claim 1, wherein: when the weight force acting on the loading cell is greater than a predetermined value, the method is ended with an output of a warning message.

10. The method of claim 1, wherein: if the measurement signal has not reached a stable state within a defined time period, the method is ended with an output of a warning message.

11. The method of claim 1, wherein: the test result is output in the form of a visual, acoustic and/or electrical signal.

12. The method of claim 1, wherein: the test result is output as a visual signal by means of a multicolour LED for each pipette volume class.

13. The method of claim 12, wherein: after the output of the test result and after a defined output time period of the visual signal, all LEDs flash simultaneously to signal the verification as ended and readiness for another verification.

14. The method of claim 1, further comprising the steps of: providing an identification sensor for identifying a pipette, and a database system for storing the test results of a verification; detecting an identification feature of the pipette, with which a pipette can be uniquely identified; and storing the test result of the verification of the pipette in the database system.

15. A device for the verification of pipettes, comprising a liquid measuring container for receiving a pipette liquid volume to be verified, a loading cell connected to the liquid measuring container in a force-transmitting manner, which outputs a measurement signal corresponding to the weight force acting on the loading cell, and a processing unit for detecting and processing the measurement signal of the loading cell, wherein the processing unit comprises software instructions, which when executed, configure one or more processors of the processing unit to: determine a first weight force from the measurement signal at a first time point t.sub.1 of a last stable measurement point by the processing unit, wherein said last measurement point is chronologically prior to the receiving of the pipette liquid volume to be verified; determine a second weight force from the measurement signal at a second time point t.sub.2 of a new measurement point by the processing unit, wherein said new measurement point is chronologically after the receiving of the pipette liquid volume to be verified; calculate the pipette liquid volume in the processing unit according to the formula:
V.sub.P=ρ.sup.−1×(G.sub.t2−G.sub.t1); wherein: V.sub.P is the pipette liquid volume; ρ is the density of the pipette liquid; G.sub.t1 is the weight force at the first time point; and G.sub.t2 is the weight force at the second time point; assign the calculated pipette liquid volume to one of at least two pipette volume classes having a defined class nominal value respectively, wherein the assignment by the processing unit takes place in such a way that an absolute value of a volume difference between the pipette liquid volume and the class nominal value is as small as possible; test, in the processing unit, whether or not the volume difference has an absolute value that is less than a predetermined tolerance value for the class nominal value of the assigned pipette volume class; and output a test result from the processing unit as a release when the volume difference is less than the predetermined tolerance value, or as a warning message when the volume difference is greater than the predetermined tolerance value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Details of the force measuring device according to the invention, the force measuring module according to the invention, and the method according to the invention are given based on the description of the embodiment examples shown in the drawings. Shown are: FIG. 1 a schematic structure of an embodiment of the inventive device;

(2) FIG. 2 a measurement signal course when receiving the pipette liquid volume to be verified;

(3) FIG. 3 determination of a stable measurement signal by the processing unit; and

(4) FIG. 4 a diagram of the calibration- and verification interval of a pipette.

(5) Features with the same function and similar configuration are provided with the same reference numbers in the following description.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) FIG. 1 schematically shows the device 100 for the verification of pipettes. The device 100 shown here consists of a liquid measuring container 110, a loading cell 120, and a processing unit 130. The liquid measuring container 110 has an opening 111, through which the pipette liquid volume V.sub.P to be verified can be introduced by the pipette P. Care must be taken here to ensure that the pipette liquid volume V.sub.P to be verified is introduced all at once from the pipette P into the liquid measuring container 110, or at least dropwise, so that the measurement signal ms of the loading cell 120 is indicated as stable by the processing unit 130 only after the complete emptying of the pipette P (see description relating to FIG. 3). The liquid measuring container 110 is connected to the loading cell 120 in a force-transmitting manner, so that it exerts a weight force F.sub.G acting on the loading cell 120, which is continuously output to a processing unit 130 as a measurement signal m.sub.S. The processing unit 130 is used for detecting and processing the measurement signal m.sub.S of the loading cell 120 and for performing the method. The test result (R.sub.P) is output in the form of a visual, acoustic and/or electrical signal.

(7) The introduced pipette liquid remains in the liquid measuring container 110, which is filled more and more by each further verification. When the weight force F.sub.G of the liquid measuring container 110 acting on the loading cell 120 reaches an upper limit, this is recognized by the processing unit 130 based on the measurement signal ms and signalled to the user. Until the upper limit is reached, the method runs uninterruptedly, that is, the processing unit 130 assesses the measurement signal ms of the loading cell 120 without interruption. Thus, the user only introduces the pipette liquid volume V.sub.P into the liquid measuring container 110, whereby the measurement signal m.sub.S of the loading cell 120 is triggered. This triggering starts the verification method as described below with reference to FIG. 2.

(8) Based on the measurement signal course from FIG. 2, the inventive method will now be described in more detail. The measurement signal course is shown before and after the receiving of the pipette liquid volume to be verified, which is recognized by the fact that the measurement signal between time point t.sub.1 and time point t.sub.2 is unsteady or that it is triggered.

(9) The process is started by the user introducing the pipette liquid volume V.sub.P to be verified into the liquid measuring container 110. The triggering of the measurement signal now starts the measurement signal assessment. From the stable measurement signal ms at the time point t.sub.1 of a last stable measurement point M.sub.t1, a first weight force G.sub.t1 is determined by the processing unit. This weight force corresponds to the amount of liquid already present in the liquid measuring container 110. From the stable measurement signal ms at the time point t.sub.2 of a new stable measurement point M.sub.t2, a second weight force G.sub.t2 is determined by the processing unit 130. This weight force corresponds to the sum of the liquid amount already present in the liquid measuring container 110 plus the introduced pipette liquid volume V.sub.P to be verified. The pipette liquid volume V.sub.P can now be calculated according to the formula V.sub.P=ρ.sup.−1×(G.sub.t2−G.sub.t1).

(10) The calculated pipette liquid volume V.sub.P is assigned to a pipette volume class K.sub.i having a defined class nominal value V.sub.Ki. The device may be pre-set to a few volumes, e.g., 20 μl, 100 μl, 200 μl and 1000 μl, each with its own tolerance. The assignment takes place in such a way that the absolute value of a volume difference ΔV between the pipette liquid volume V.sub.P and the class nominal value V.sub.Ki is as small as possible. Now it can be checked whether or not the absolute value of the volume difference ΔV is within a tolerance value T for the class nominal value V.sub.Ki of the assigned pipette volume class K.sub.i. When the volume difference ΔV is within the tolerance value T, a release takes place as an output of the test result, otherwise a warning message takes place when the volume difference ΔV is outside the tolerance value T.

(11) A measurement signal ms is indicated as stable by the processing unit 130 (see FIG. 3) when it is within a signal band S having a time-defined length ts and having a maximum signal difference or signal level Δm.sub.S. This means that from the time point of a measurement signal value, all measurement signal values, preceding over a certain time, may deviate at most by a defined difference. The definition of these parameters significantly affects how fast the processing unit 130 determines a stable measurement point M.sub.ti. Here, it should be considered that the user should introduce the pipette liquid volume V.sub.P to be verified into the liquid container 110 without interruption as much as possible. Also, in the case of an accidental interruption, the processing unit 130 should not output the measurement signal ms as stable too early (by the parameter selection). The measurement signal ms at time point to is not indicated as stable, because said signal has not always been within the signal band S.sub.A over the preceding time period ts. On the contrary, it differs at time point ts and at time point t.sub.2, at which the measurement signal m.sub.S is indicated as stable.

(12) Furthermore, the method can further determine an evaporation rate c.sub.v of the liquid present in the liquid measuring container 110 by processing the measurement signal m.sub.S, by detecting the weight loss over a preceding time period Δtv which terminates at the latest at time point t.sub.1. With this evaporation rate c.sub.v, the evaporation volume V.sub.v between time point t.sub.1 and time point t.sub.2 can now be determined. Taking these values into account, the pipette liquid volume V.sub.P can be calculated more accurately according to the formula: V.sub.P=ρ.sub.−1×(G.sub.t2−G.sub.t1+c.sub.v×(t.sub.2−t.sub.1)).

(13) The determination of the evaporation rate cv always takes place by means of a stable measurement signal after time point t.sub.2 and before time point t.sub.1, in which the duration over a time period Δtv is at least and inclusive of ten seconds, and/or at most and inclusive of ten times the time difference between time point t.sub.1 and time point t.sub.2. In the time period Δtv, the determination of the evaporation rate c.sub.v can also be carried out continuously. Based on a reference value, the validity of the evaporation rate c.sub.v can be checked.

(14) Now it can happen that the weight force difference ΔG.sub.t is smaller than a predetermined value. In this case, the method is ended without an output of a result. Also, a weight force F.sub.G acting on the loading cell 120 may be greater than a predetermined value, in which case the method is ended with an output of a warning message. If these parameters are defined too narrowly for the determination of a stable measurement point M.sub.ti, there is the possibility that the measurement signal ms cannot assume a stable state for the processing unit 130 within a defined time period. The method is then ended with an output of a warning message.

(15) Each of the predefined volumes may be displayed by three LEDs, e.g., green, orange and red. When a new result is output, the corresponding LED is switched to a steady light for a certain time period. After the expiration of this time period, the LED is switched to a flashing mode, which further signals the result to the user, but also displays readiness for the next test. When the liquid measuring container 110 is full, the result is displayed as described above, but in addition all other LEDs flash, for example in red, with a short-on long-off pattern.

(16) The method is fully automated and only the operation of the pipette by the user is required. The device 100 recognizes the process and displays the result without any additional user interaction.

(17) In FIG. 4, the calibration and verification interval of a pipette is shown. A pipette is calibrated at the factory before it is delivered to the user. Between two regular calibrations of a pipette, verifications—also called quick tests—are carried out according to the inventive method. The frequency of these quick tests is recommended to the user through a risk assessment which is based on two specific criteria: A) the impact of pipetting on the user's business and B) the pipetting/pipetting process tolerance. From this, it can be deduced at which time interval a pipette must be subjected to a calibration, and what tolerance is to be maintained during the pipetting process.

(18) Between the calibrations of a pipette, the inventive method is now used to give the user an immediate feedback that the pipette is still sufficiently accurate and ready for use. If the feedback is negative, the pipette can be subjected to a calibration already before the expiration of the calibration interval. Such early detection can prevent critical impact on the user's business.

(19) Depending on the user's business, it may also be considered to extend the calibration interval in order to reduce the cost of a more expensive calibration and in order to reduce the time when the pipette is not available.