Safety workbench and method for the calibration thereof

Abstract

The present invention relates to a safety workbench, in which, for the purpose of calibrating the safety workbench before beginning regular operation, a device control unit is implemented to cause measurement means to ascertain an actual measured value, which is representative of a flow velocity achieved at normal fan performance, an analysis unit is implemented to compare the actual measured value to a starting setpoint value and, in case of an established deviation, to correct a stored starting limiting value in accordance with the deviation, or means for controlling the fan are implemented to operate the fan at a fan performance corresponding to a stored starting limiting value, a device control unit is implemented to cause the measurement means to ascertain an actual limiting measured value which is representative of the flow velocity achieved at the set fan performance, and a storage unit is implemented to store the actual limiting measured value as the corrected limiting value. Furthermore, the present invention relates to a corresponding calibration method.

Claims

1. A safety workbench having: a working chamber, enclosed by a housing, having a work opening located in the housing front side and settable using an adjustable front pane, at least one fan for delivering an air flow into the safety workbench, a device control unit, comprising a fan control configured to control the at least one fan, a storage unit configured to store at least one starting limiting value comprising at least one of a lower alarm limit and/or an upper alarm limit as at least one stored starting limiting value, which deviates by a predefined amount from a starting setpoint value, which corresponds to a specific flow velocity of the air flow delivered by the at least one fan at a predefined normal fan performance, an analysis unit, and at least one measurement device configured to ascertain a measured value, which is representative of the flow velocity of the air flow delivered by the at least one fan, wherein for the purpose of calibrating the safety workbench, (i) the device control unit is implemented to cause the measurement device to ascertain an actual measured value, which is representative of a flow velocity achieved at a measuring instant by the at least one fan set to operate at the starting setpoint value, the analysis unit is implemented to compare the actual measured value to the starting setpoint value and, in case of an established deviation between the actual measured value and starting setpoint value, to correct the at least one stored starting limiting value in accordance with the established deviation, and the storage unit is implemented to store the at least one corrected starting limiting value ascertained by the analysis unit, or (ii) the fan control the at least one fan is implemented to operate the at least one fan at a fan performance corresponding to the stored starting limiting value, the device control unit is implemented to cause the at least one measurement device to ascertain an actual limiting measured value, which is representative of a flow velocity achieved at a measuring instant by the at least one fan at the fan performance set, and the storage unit is implemented to store the ascertained actual limiting measured value as the corrected starting limiting value.

2. The safety workbench according to claim 1, wherein the normal fan performance is a fraction of the maximum fan performance.

3. The safety workbench according to claim 1, wherein the at least one measurement device is implemented to measure the flow velocity directly, and is an anemometer or is implemented to ascertain a pressure differential over the at least one fan.

4. The safety workbench according to claim 1, wherein a starting measured value obtained at a fan performance not corresponding to the normal fan performance, which is representative of a flow velocity achieved by the at least one fan, is stored as the starting limiting value in the storage unit.

5. The safety workbench according to claim 4, wherein the device control unit is implemented to cause the at least one measurement device to ascertain the actual measured value which is comparable to the starting setpoint value and the starting measured value stored as the at least one starting limiting value.

6. The safety workbench according to claim 1, wherein the analysis unit is implemented to calculate a difference between starting setpoint value and actual measured value and to correct the at least one stored starting limiting value by this difference.

7. The safety workbench according to claim 1, wherein the at least one starting limiting value is a fraction of the maximum fan performance.

8. The safety workbench according to claim 1, wherein the device control unit is implemented to cause the at least one measurement device to ascertain an actual measured value for a normal fan performance.

9. The safety workbench according to claim 1, wherein an upper starting limiting value, which deviates upward by a predefined amount from the starting setpoint value, and a lower starting limiting value, which deviates downward by a predefined amount from the starting setpoint value, are stored in the storage unit.

10. The safety workbench according to claim 9, wherein the safety workbench is implemented to perform a correction separately for each of the starting limiting values to ascertain an upper and a lower actual limiting measured value and to store the corrected limiting values in the storage unit.

11. The safety workbench according claim 1, wherein the safety workbench has multiple fans including an exhaust air fan and a circulating air fan and the safety workbench is implemented to perform a calibration separately for each of the fans.

12. The safety workbench according to claim 1, wherein the safety workbench has a safety monitoring system, which outputs a visual and/or acoustic alarm, if the analysis unit establishes a deviation out of the range which is fixed by actual measured value and corrected limiting value or corrected upper and corrected lower limiting value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be explained in greater detail in the following on the basis of drawings. These drawings are solely schematic and are only used to explain a preferred exemplary embodiment of the present invention, without the present invention being restricted to this example. In the drawings:

(2) FIG. 1 schematically shows a safety workbench according to the present invention in a perspective view;

(3) FIG. 2 schematically shows a cross-section through the safety workbench according to the present invention shown in FIG. 1, and

(4) FIG. 3 schematically shows a circuit diagram of the device control unit of the safety workbench according to the present invention for performing a calibration method.

DETAILED DESCRIPTION

(5) FIGS. 1 and 2 show a safety workbench (1) according to the present invention, which may be used for processing microbiological cultures, for example. In its basic construction, the safety workbench (1) corresponds to that known from the prior art. The safety workbench has a housing (2), which encloses a working inner chamber (3). An adjustable front pane (5) is situated on the housing front side (4), which is mounted in such a way that it may be pushed up and down essentially parallel to the housing front side. By pushing down the front pane (5), the work opening (6) located on the housing front side may be made smaller or closed entirely. The height of the work opening (6) thus results from the gap between the bottom side of the front pane (5) and the working chamber floor plate of the housing (2).

(6) Two fans are provided in the safety workbench (1), namely an exhaust air fan (7), which conveys a specific volume component of the air (8) delivered into the interior of the safety workbench (1) out of the safety workbench as an exhaust air flow (18). The exhausted exhaust air (18) is replaced by outside air (19), which flows in through the work opening (6) into the working inner chamber (3) of the safety workbench (1).

(7) In the interior of the safety workbench, the air flow (8) is delivered by a circulating air fan (16), which conducts transported air through an opening (20) in the work plate (21) and through channels, which are located in an area below the work plate (21) and behind the rear wall (22) delimiting the working inner chamber (3), via a filter (23) from top to bottom in the direction toward the work plate (21).

(8) In order that a sufficient personal and/or product protection is ensured in the safety workbench, circulating air and exhaust air must be conveyed by the corresponding fans at the predefined flow velocity through the safety workbench. Because the flow velocities of the circulating air and exhaust air are also a function of the ambient conditions such as the air pressure, for example, it must be ensured that the flow velocities are in the predefined velocity ranges independently of the installation location of the safety workbench (1). Correspondingly, these limiting values must be set again at the installation location of the safety workbench. In the safety workbench according to the present invention, this is performed using an automatic calibration method. The sequence is to be explained in greater detail in the following for exemplary purposes on the basis of FIG. 3.

(9) The calibration method is only shown here for the exhaust air fan (7). A corresponding calibration procedure may be performed for the circulating air fan (16) before the calibration procedure for the exhaust air fan (7) or subsequently thereto. The procedure of the first calibration after the installation of the safety workbench at its new working location is described here. The calibration method is executed by the device control unit (9), which may be a control unit already typically present in a safety workbench.

(10) As soon as the safety workbench (1) is connected to the local power network and impinged with voltage for the first time, an inquiry starts in a processor (not shown in greater detail) of the device control unit (9), which checks whether a calibration method as already been performed for the safety workbench. The response to this inquiry is coded in a software switch, which is set to 0 at the factory, which states that in this case no calibration has yet occurred.

(11) Because of the obtained response, the calibration routine is started by the device control unit (9). The fan is started in a first step by means (10), integrated in the device control unit (9), for controlling the fan (7) and caused to run at a fan performance predefined for the normal operation of the safety workbench. For example, the normal fan performance is set to 70% of the maximum possible fan performance. After a predefined time has passed since the starting of the fan (7), it is ascertained with the aid of the measurement means at which flow velocity the fan (7) delivers air through the inner chamber of the safety workbench.

(12) The flow velocity of the air quantity delivered by the fan (7) is determined in that a pressure differential which builds up via the fan (7) is measured. To measure this pressure differential, a barometric cell (14) and (15) is situated in each case upstream from the fan (7) and downstream therefrom. Barometric cell (14) measures the pressure upstream from the fan (7), and barometric cell (15) measures the pressure downstream from the fan. Both barometric cells are situated at a small distance to the fan (7). The ascertained pressure values are transmitted by the barometric cells (14) and (15) to an analysis unit (12), which is situated in the device control unit (9). A pressure differential, which is output to the storage unit (11) and stored therein, is calculated in the analysis unit (10) from the ascertained values.

(13) In a next step, the means (10) for controlling the fan (7) activate it in such a way that the fan (7) runs at a performance which corresponds to the predefined lower limiting value of the fan performance, i.e., the lower alarm limit. The lower alarm limit may be fixed at a fan performance of 60% of the maximum possible fan performance, for example. The fan performance at the lower alarm limit is thus 10% less than during normal operation of the fan. After the fan (7) has run for a time at 60% of the maximum possible performance, pressure values are measured again by the barometric cells (14) and (15), and the ascertained measured variables are transmitted to the analysis unit (12). A pressure differential is again calculated from the two values therein. This pressure differential is representative of the still just permissible lower flow velocity of the fan (7). This value is stored as the new lower alarm limit in the storage unit (12).

(14) If an upper limiting value corresponding to an upper alarm limit for the fan performance is also stored for the fan (7), this upper alarm limit is now approached by the fan. For example, the maximum permissible performance of the fan may be fixed at 80% of the maximum fan performance. The maximum permissible fan performance is thus 10% more than the normal performance of the fan. The means (10) for controlling the fan (7) correspondingly now activate the fan (7) for the correction of the upper alarm limit in such a way that it is operated at 80% of its maximum performance. After passage of a predefined time period, pressure values are again measured using the barometric cells (14) and (15), these values are subtracted from one another in the analysis unit (12) to provide the pressure differential over the fan (7), and the calculated value is stored as the upper alarm limit in the storage unit (11).

(15) After corrected flow velocities in the form of pressure differential values have been obtained both for the normal operation of the fan and also for the alarm limits, within which safe operation of the safety workbench is still just ensured, the calibration method is terminated. The switch originally set to 0 in the software is now automatically set to 1, so that the calibration method is not started once again unintentionally. The device control unit (9) now changes the device parameters over to normal operation. One may work in the safety workbench (1) in the typical way. It is ensured that the fixed alarm limits are set correctly corresponding to the surrounding parameters of the safety workbench. Thus, unintended false alarms are not triggered, although the safety workbench is actually still in safe operation, and vice versa, triggering an alarm is not missed because of incorrectly set alarm limits, although the safety workbench already no longer operates at adequate flow velocities.

(16) A safety monitoring system (17) is integrated in the device control unit (9) to monitor the safety workbench. During normal operation of the safety workbench (1), flow velocity measurements are performed continuously or at fixed intervals. This is performed here, as already during the calibration method, by ascertaining pressure differential values for the fans (7) and (16). The current pressure differential data ascertained during the operation is compared to the values corrected by the calibration method. If a measured value ascertained for one of the fans deviates out of the permissible area defined by the corresponding alarm limits, a visual or acoustic alarm is triggered by the safety monitoring system (17). The alarm device (24) outputs an alarm signal.

(17) In FIG. 3, the means (10) for controlling the fan (7), the storage unit (11), the analysis unit (12), and the safety monitoring system (17) are all integrated in the device control unit (9). However, this is solely exemplary. The individual components may also be installed spatially separate from one another in the safety workbench (1). It is also possible that various control, analysis, or storage functions are assumed by the same device, although separate components are shown for this purpose here. Typically, the required means are already present in any case in typical systems of safety workbenches, so that no additional components are needed but rather these systems must solely obtain additional functionalities.

(18) Finally, a simplified variant of the calibration method described above is to be presented, which may also be performed using the control unit schematically illustrated in FIG. 3. The first steps of the calibration method are identical to the preceding method. Up to ascertaining a pressure differential for the fan at normal fan performance (i.e., 70% of the maximum fan performance here), the calibration methods correspond. A pressure differential is thus obtained from the measurement procedure at normal fan performance, which corresponds to a flow velocity at the installation location of the safety workbench. This pressure differential value is now compared in the analysis unit (12) to a pressure differential value for the fan at normal performance stored in the storage unit (11), which corresponds to the fan performance at the production location of the safety workbench. For example, the pressure differential for the fan (7) at the production location of the safety workbench was 50 Pa. The pressure differential for the fan in normal operation measured at the working location of the safety workbench during the calibration procedure was 40 Pa, for example. The difference between both pressure differential values is now ascertained in the analysis unit (12). 50 Pa40 Pa=10 Pa results. This value is stored in the storage unit (11). Moreover, pressure differential values for the fan (7), which were ascertained at the production location for the fan (7) at the upper and lower alarm limits, are stored in the storage unit (11). For example, a pressure differential of 35 Pa was ascertained for the fan (7) at reduced performance, which corresponds to the lower alarm limit. The ascertained differential value of 10 Pa is now subtracted from this value. A corrected pressure differential value for the lower alarm limit of the fan (7) at the current installation location of 25 Pa thus results. This ascertained corrected pressure differential value for the lower alarm limit is stored in the storage unit (11) and used as the newer lower alarm limit for the safety monitoring by the safety monitoring unit (17) during the regular operation of the safety workbench. The same procedure is used for the upper alarm limit. The pressure differential value stored at the factory for the upper alarm limit is thus corrected downward by 10 Pa, stored, and used as a new limiting value (upper alarm limit) in the safety monitoring of the safety workbench during regular operation. In this calibration method variant, the upper and lower alarm limits are thus no longer actively approached and measured again, but rather only one measurement is still performed at normal fan performance and a correction of the upper and lower alarm limits is performed on the basis of the ascertained deviation. The termination of the calibration method again corresponds to the method described at the beginning.

(19) The described calibration method may not only be started automatically when the safety workbench is first put into operation. It is also possible and advisable to perform further calibrations of the alarm limits when repair work has been executed on the safety workbench. This is true in particular for repair work which may influence the flow velocity inside the safety workbench. The replacement of filters, and the replacement or repair of fans may be cited here as examples. To start the calibration procedure, the switch set in the software, which is set to 1 after the safety workbench is put into operation and calibrated for the first time, is reset back to 0, so that the calibration routine may start. Of course, it is also fundamentally possible that the calibration routine does not start automatically, but rather must always be started manually. If desired, authorizations may be given out for this purpose, so that only authorized individuals may perform a calibration.