Measuring apparatus

Abstract

2. Measuring apparatus for determining the concentration of constituents in a fluid, such as cooling lubricants or HFC hydraulic liquids, by refractometry, characterized in that the fluid present for measuring is guided through a sample chamber (10), which is connected to a fluid inlet (12) and a fluid outlet (14) and which is at least partially transparent such that the beams of a light source, preferably in the form of a laser (22), passing through the sample chamber (10) containing the fluid at least partially experience a refraction and can be detected by a sensor device (26) outside the sample chamber (10).

Description

[0001] measuring device

[0002] The invention relates to a measuring device for determining the concentration of components in a fluid, such as cooling lubricants or HFC hydraulic fluids, by refractometry.

[0003] DE 10 2010 028 319 A1 discloses a method for controlling the concentration of the water-mixed cooling lubricant in a machine tool, along with an associated device. These devices are used to measure both the refractive index of the water-mixed cooling lubricant by refractometry and the electrical conductivity of the water-mixed cooling lubricant. The values ​​determined from both measurements are combined to form a controlled variable. If the controlled variable deviates from the setpoint, water and / or cooling lubricant are added. To determine the refractive index of the water-mixed cooling lubricant, the device uses a digital refractometer that has an FED as a light source and a CCD sensor as a detector.Based on this prior art, the invention seeks to create an improved measuring device that can compensate for a multitude of disturbances occurring during measurement. This object is achieved by a measuring device having the features of patent claim 1 in its entirety.

[0004] Because, according to the characterizing part of patent claim 1, the fluid to be measured is guided through a sample chamber which is connected to a fluid inlet and a fluid outlet and which is at least partially transparent in such a way that the rays of a light source, preferably in the form of an easer, which pass through the sample chamber with the fluid are at least partially refracted and can be detected by a sensor device outside the sample chamber, a spatial separation of light source, sample chamber and sensor device results, and in this way a multitude of adjustment and correction options arise, so that the measuring device can be used for a wide variety of measuring tasks and calibrated for these.Since the fluid to be examined is guided through a sample chamber, the sample is also decoupled from the actual measuring device, consisting of the light source and the sensor device, so that measurements can be taken without interference, independent of the actual supply circuit for a hydraulic consumer. Preferably, a light source in the form of an easer is used, which, compared to the otherwise conventional EED technology, enables collimation, i.e., leads to a parallel alignment of otherwise divergent calibration beams, resulting in improved measurement resolution on the part of the sensor device, usually formed by a photodiode row, which is also technically referred to as a "diode array."

[0005] The fiber also allows the introduction of a higher radiation output, so that reliable measurement value acquisition is guaranteed in every case, even if the fluid is cloudy and / or the partially transparent sample chamber is contaminated. In a preferred embodiment of the measuring device according to the invention, the sample chamber is delimited on the side facing the sensor device by a translucent wall, preferably in the form of a glass wall, and the light source is accommodated in a receiving space of a device housing and is at least partially flowed over by the fluid before entering the sample chamber. It has proven advantageous if turbulence occurs in the fluid flow as it flows through the sample chamber. This is important in order to clean the glass wall of the sample chamber of contaminants and to always exchange the sample fluid in the measuring or sample chamber.

[0006] Preferably, the light source emits light at an oblique angle, preferably 40°, to the fluid flow direction in the sample chamber, and the surface area of ​​the sensor device and its position relative to the light source are selected such that, in transmitted light, the light rays impinging on the sensor device at different angles are detected. In this way, the refractometer can be operated with transmitted light, relative to the light source, depending on the measurement task, without having to make major changes to the measurement setup itself.

[0007] In a further preferred embodiment of the measuring device according to the invention, the sensor device is part of a sensor chamber of a sensor housing which, when filled with a gas, preferably air, creates a spatial distance between the sample chamber with its translucent wall and the sensor surface of the sensor device. Preferably, viewed in a fictitious vertical projection, the light source is arranged at the beginning of the sample chamber and the beginning of the sensor device is arranged at the end of the sample chamber. In any case, by appropriately selecting the said spatial distance and the respectively selected projection plane for the arrangement of the sensor device, the latter can be adjusted both vertically and horizontally in order to adapt the sensitivity or the measuring range.

[0008] In order to ensure a preferably turbulent fluid flow, it is provided that between the fluid inlet and the fluid outlet, at least partially, a fluid channel with individual channel sections runs in a supply housing, so that a turbulent flow through the sample chamber occurs through multiple deflections.

[0009] In a further preferred embodiment of the measuring device according to the invention, the overall housing of the device is composed of individual housing parts, consisting of the supply housing with parts of the fluid channel, the device housing with the light source, and the sensor housing with the sensor device. Due to the multi-part housing construction, the measuring device can be quickly disassembled and reassembled for maintenance and cleaning purposes. A kind of modular principle is also implemented for the overall housing, which in practice makes it easier to retrofit hydraulic devices already delivered and in operation with the measuring device according to the invention.

[0010] In a further preferred embodiment of the measuring device according to the invention, it is provided that it is connected via a switchable valve to a pressure supply device, such as a hydraulic pump, which draws its fluid from a storage tank and hydraulically supplies a processing machine as a consumer. The input side of the processing machine is connected via a branch to a fluid line between the hydraulic pump and the switchable valve, and the output side of the processing machine opens into a return line at a branch point, which is connected to the fluid outlet in the supply housing and leads to the storage tank. In this way, the measuring device in the secondary branch can be decoupled from the actual pressure supply for the hydraulic consumer, so that measurements can be taken at discrete time intervals outside of the operation of the hydraulic consumer.For this purpose, it is preferably provided to insert a further switching valve into the section of the return line between the fluid outlet in the supply housing and the branch point into which the output side of the processing machine flows.

[0011] In a further preferred embodiment of the measuring device according to the invention, a third and a fourth switching valve are connected to the inlet line for the fluid inlet and to the return line from the fluid outlet, respectively, which serve to supply and discharge a flushing medium. In this way, the measuring device can be freed of contaminants by means of a flushing process, independent of the operation of the processing machine.

[0012] In the following, the measuring device according to the invention is explained in more detail using an exemplary embodiment as well as the measuring methods to be carried out with the measuring device. The figures show, in a schematic and not to scale representation, the

[0013] Figure 1 shows the essential components of the measuring device in the form of a longitudinal section;

[0014] Figures 2 to 5 show different possibilities of carrying out measurements according to the transmitted light principle;

[0015] Figures 6, 7, 8 and 10 show various types of operation of the measuring device using flow charts; and Figure 9, in the form of a hydraulic circuit diagram, shows the integration of the measuring device into a hydraulic measuring and supply circuit.

[0016] The measuring device shown in Figure 1 with its essential system components is shown in its normal operating position. The measuring device is used to determine the concentration of components in a fluid, such as cooling lubricants or HFC hydraulic fluids, using refractometry. Hydraulic fluid is regularly used to transfer energy in the form of volume flow and / or pressure in hydraulic systems within the framework of fluid technology. Such hydraulic oils are usually made from mineral oil with appropriate additives. HFC is one of the flame-resistant hydraulic fluids and regularly contains water glycols with a water content of over 35% as well as a polyglycol solution. Such HFC hydraulic fluids are regularly intended for use in hard coal mining and in civil aviation.Furthermore, they are increasingly being used in military vehicles such as tanks, which may be exposed to enemy fire. Cooling lubricants or metalworking fluids reduce friction through lubrication, thus reducing tool wear, workpiece heating, and energy consumption during machining. In both cases, the specified concentration of HFC and metalworking fluid must be maintained to ensure reliable operation. The measuring device according to the invention serves to maintain the respective concentration.

[0017] The fluid being measured by the measuring device is passed through a sample chamber 10, which is connected to a fluid inlet 12 and a fluid outlet 14. The possible flow direction is indicated in Figure 1 by arrows at the inlet 12 and the outlet 14. Both the fluid inlet 12 and the fluid outlet 14 are connected in the usual way to a fluid supply circuit 16, as shown by way of example in Figure 9.

[0018] The actual sample chamber 10 defines a cuboid-shaped chamber volume with a flat extension, and, as viewed in the direction of Figure 1, is bounded from above by a translucent glass wall 18. This wall is typically formed from a thin-walled, rectangular glass pane, which is bounded on the outer circumference by square sealing rings at the top and bottom relative to adjacent housing parts of the measuring device, in order to reliably prevent any unwanted escape of fluid from the sample chamber 10 into the environment. Adjacent to the sample chamber 10, a laser 22 is inserted into a device housing 20 of the measuring device, the upper laser exit surface of which exits toward the sample chamber 10 into a fluid-carrying inclined channel 24.In this way, the rays of a light source, here in the form of laser 22, pass through the sample chamber 10 containing the respective fluid, and the respective rays thereby undergo a first refraction n, which will be explained in more detail below. The rays refracted in this way are detected by a sensor device 26 outside the sample chamber 10. The sensor device 26 has a photodiode row as a light-sensitive sensor, which is also technically referred to as a diode array. In this respect, CCD sensors in particular, but also CMOS sensors, can be used. These are light-sensitive electronic components based on the internal photoelectric effect and are commercially available in a wide variety of designs.

[0019] As can further be seen from Figure 1, the light source in the form of the laser 22 is accommodated in a stationary manner at one end in an associated receiving space 28 in the device housing 20, so that before the fluid enters the actual sample chamber 10, the outlet cross-section for the laser beams is overflowed by the fluid, in which it flows from a horizontally running line section 30 parallel to the longitudinal alignment of the sample chamber 10 into the inclined channel 24. The line section 30 is closed on its right-hand side by a plug 32 as viewed in the direction of Figure 1, and otherwise, vertically running line sections 34 and 36 open from below into the corresponding horizontal line section 30, which continues further to the right behind the plug 32 as viewed in the direction of Figure 1 and opens into the vertical line section 36, to which the fluid drain 14 is connected.The fluid inlet 12, on the other hand, flows from the left into the vertical line section 34 for the fluid supply to the sample chamber W. Beyond the vertical line section 36, the horizontal line section 30 continues to the right and is closed at this point by a sensor 38, which can, for example, be a measuring device for parameters such as pressure, temperature, viscosity, pH, conductivity, etc. Sensors 38 that enable two or more different such parameter measurements can also be used here. Temperature measurement, in particular, is necessary for temperature compensation in refractometry.

[0020] As can further be seen from Figure 1, the light source in the form of the laser 22 emits light at an oblique angle of approximately 40° to the horizontal fluid flow direction in the sample chamber 10. The rectangular, planar extent of the sensor device 26 is selected with regard to its position relative to the light source such that, both in the transmitted-light method preferred here and in the case of a possible grazing incidence of the light rays at different angles, these are preferably completely encompassed by the sensor device 26. For the purpose of calibrating the measuring device and in particular for adapting the sensor device 26 to the actual measuring conditions within the measuring device, the sensor device 26 can be adjusted both horizontally and vertically relative to the light exit point of the laser 22, as shown in Figure 2.For this purpose, it is sufficient to loosen and retighten screws of an adjustment device 40 to which the sensor device 26 is fixed and by means of which it can be positioned relative to a stationary sensor housing 42. In this respect, the sensor housing 42, as part of the overall housing, adjoins the top of the device housing 20. In particular, the plate-shaped sensor device 26 opens into a cuboid-shaped sensor chamber 44 of the sensor housing 42, which can be provided with a gas and, when filled in this way, creates a spatial distance between the sample chamber 10 with its translucent wall 18 and an exposed sensor surface 46 of the sensor device 26. For the sake of simplicity of illustration, both the laser 22 and the sensors in the form of the device 26 and the respective measuring device 38 are shown in Figure 1 without the associated wiring.Depending on the wavelength and refractive indices to be applied to the sensor device 26, a different working gas, for example, in the form of xenon, can be accommodated in the sensor chamber 44 instead of Easer. Viewed in a fictitious vertical projection within the plane of the drawing in Figure 1, the light source in the form of the Easer 22 is arranged at the beginning of the sample chamber 10, and the beginning of the sensor device 26 is arranged at the end of the sample chamber 10.This results in particularly good measurement data acquisition across the entire range, and the inclined position of the easer 22 produces a good diffraction pattern or interference pattern when irradiating the fluid in the sample chamber 10. Furthermore, due to the oblique angle of incidence of the laser beams on the sensor surface 46, the installation space for the sensor housing 42 and thus for the entire measuring device can be kept small, allowing such a measuring device to be accommodated even in cramped installation conditions. This also facilitates the retrofitting of existing systems with the measuring device.

[0021] The channel sections 34, 36 extending between the fluid inlet 12 and the fluid outlet 14 at least partially form a fluid channel 48 in a supply housing 50. Accordingly, the overall housing of the device is composed of individual housing parts, in particular consisting of the supply housing 50 with parts of the fluid channel 48, the device housing 20 with the light source, here in the form of the laser 22, and the sensor housing 42 with the sensor device 26. This results in a modular design for the overall housing of the measuring device, which allows the measuring device to be connected to a wide variety of machines and device parts by adapting individual components.

[0022] As already mentioned at the beginning, the measuring device is part of a fluid supply circuit 16, and this can be connected to a pressure supply device such as a hydraulic pump P1 via a switchable valve V1. The motor-driven hydraulic pump P1 draws fluid, such as cooling lubricant or HFC fluid, from a storage tank CM1 and hydraulically supplies a conventional processing machine BM as a consumer. The relevant processing machine BM is connected on its inlet side via a branch 52 into a fluid line between the hydraulic pump P1 and the switchable valve V1. The outlet side of the processing machine BM, in turn, opens at a branch point 54 into a return line, which is connected to the fluid outlet in the form of the fluid drain 14 in the supply housing 50 of the measuring device and leads to the storage tank CM1.A further switching valve V2 is provided in the aforementioned section of the return line between the fluid outlet 14 in the supply housing 50 and the branch point 54 into which the output side of the processing machine BM flows. Furthermore, a third switching valve V3 and a fourth switching valve V4 are connected in the inlet line to the fluid inlet 12 and in the return line from the fluid outlet 14, respectively. These valves serve to supply and discharge a flushing medium DL into a further storage tank CM2.

[0023] A control line 56 runs between the processing machine BM and the measuring device, the housing of which is shown in Figure 10 with the housing parts 20, 42 and 50. This control line is used to transmit the measured data and enables a rinsing process depending on the machine and / or measuring device status. The measurement parameter acquisition, which is at least partially realized via the sensor 38, outputs its measured data via an additional measuring line 56 to a processor control 59 (not shown in detail) as the higher-level system, as shown in Figure 10. In addition to the usual measured values ​​of pressure, temperature and viscosity, it is also possible to record the pH value of the fluid and its electrical conductivity via the sensor 38 or further sensors 1, 2, ...x (not shown). Starting from a further control line 60 according to Figure9, the measuring device can control a further fluid pump P2, which, if necessary, removes missing concentrate detected by the measuring device from a concentrate container CM3, wherein the fill level in the concentrate container CM3 is monitored by a level switch 62, which is coupled to the processor control 59 of the measuring device by means of a further measuring line 64.If, during the refractometry performed using the measuring device, it is determined that lubricant components are missing from the cooling lubricant supply for the BM processing machine or that HFC is missing from the supply of an HFC hydraulic fluid, the missing components can be introduced into the storage tank CM1 by activating the supply pump P2 via the concentrate container CM3. The then correctly concentrated cooling lubricant or HFC hydraulic fluid is then delivered to the BM processing machine, with a refractometry measurement also being continuously performed using the measuring device during the concentration process. The actuating devices designated as external actuators 1, 2, ... y in Figure 10 correspond, among other things, to components P1 and P2 as well as valves V1, V2, V3, V4, etc.

[0024] If contamination occurs, particularly in the sample chamber 10, the supply circuit 16 can be shut off using valves V1, V2, and by opening valves V3 and V4, the sample chamber 10 can be rinsed by supplying a suitable rinsing medium DL including compressed air, thus cleaning it of particulate contamination, which is then collected in the storage tank CM2 for further processing or disposal. After the rinsing process has been completed, valves V3 and V4 can be spring-actuated to their initial position shown in Figure 9, i.e., brought into their blocked position, and after opening valves V1 and V2 again and connecting the fluid supply circuit 16, the measuring device is then again available for refractometry measurements.

[0025] In the following, the measuring device according to the invention will now be explained in more detail using the associated measuring method. Figure 2 basically shows such a measurement according to the transmitted light principle. The laser 22 shown in Figure 1 emits a collimated laser beam 70, which undergoes a first refraction n1 at the interface between the sample chamber 10 and the disk-like glass wall 18. A second refraction n2 then occurs at the glass wall 18 in the shape of a conventional glass pane. Figure 2 describes the signal change of the line array or the sensor surface 46 at different liquid concentrations. If a vertical adjustment takes place, in which the vertical distance between the sensor surface 46 and the glass wall 28 is changed, an adjustment option for the sensitivity results. If the sensor surface 46 can be shifted horizontally, the measured value range can be adjusted.In the basic representation of the measured value acquisition with the curve shown in Figure 2, a homogeneous fluid is examined in the sample chamber 10; however, it is also possible to examine turbid fluids. This is fundamentally possible because the easer diode or the fiber 22 with variable intensity can be controlled by a control and / or regulating device (not shown in detail) in the form of the process controller 59. Preferably, however, the fiber 22 regulates the intensity independently.

[0026] Figure 3 shows an example of such a measured value curve due to turbidity of the fluid in the sample chamber 10, with the thick measured value curve showing the original measured value curve and the thin measuring line relating to the loss of intensity due to turbidity of the fluid. In order to regain the previous peak value detection despite the loss of intensity, according to the thick curve in Figure 3, an adjustment to the fiber 22 is necessary, for example by adjusting the duty cycle or control level, which is technically referred to as the duty cycle, or by increasing the current strength for the easer diode. A further adjustment option is to change the refresh rate, or the refresh rate, which is technically also referred to as the shutter frequency, on the photodiode row or diode array in the form of the sensor device 26.An adjustment of the laser intensity or detector sensitivity with regard to the occurrence of possible turbidity of the fluid in the sample chamber 10 is shown as an example in the flow diagram in Figure 6. To carry out this adjustment cycle, the initial prerequisite is to determine a peak value as a reference, i.e., to specify a peak value for the light received by refraction on the photodiode line (diode array) in the form of the sensor device 26 using a fluid to be homogeneously illuminated in the sample chamber 10, as shown in Figure 2. The actual calculation of the turbidity, including output values, is obtained, as shown in Figure 7, by recording the measured values ​​with regard to the duty cycle and the current intensity for the laser 20, including determining the shutter frequency of the diode array of the sensor device 26.In this way, the disturbances caused by turbidity can be compensated within the scope of the usual measurement.

[0027] In addition to the turbidity mentioned above, according to the illustration in Figure 4, contamination can also occur as a further possible disturbance in the fluid of the sample chamber 10, for example in the form of finely dispersed particles 72 such as can regularly occur in emulsions or in the form of larger particles 74 including air bubbles in the moving volume flow within the sample chamber 10. The measured value curve is shown on the far left in Figure 4 as it results from a broad increase in intensity due to the laser scattering, caused by the finely dispersed particles 72 in the fluid flow, starting from an average peak value 78 with a rounded measured value curve as it results from the usual refraction by fluid n1 and glass pane n2.Clearly distinguishable from this are the briefly tapered peaks of varying intensity, which result from a changed refraction caused by the particles 74 mentioned or the introduction of air bubbles. These disturbances can also be compensated for after they have been individually detected and do not interfere with the concentration determination of the fluid used with the measuring device. The illustration in Figure 5, in turn, relates to a different disturbance within the scope of the concentration measurement, in which a transparent, flat contamination with a changed refractive index n3 appears on the glass wall 18 with its refractive index n2. Accordingly, Figure 5 shows the peak profile on the sensor surface 46 (diode array) without contamination 82 in dashed lines, and the right-hand curve is the evaluation with the dirt deposited on the glass pane 18.Accordingly, the two peak curves of the same measured value shown in Figure 5 are shifted horizontally by a value Ax, which can be evaluated and thus allows a conclusion to be drawn about the degree of contamination 42 on the glass pane 18. This disturbance can also be eliminated in the context of the fluid concentration determination.

[0028] For all disturbances described above, such as turbidity of the fluid, particle contamination, or contamination of the glass wall 18, a rinsing process for the sample chamber 10 can be carried out, as already described for Figure 9, with the corresponding process being shown in principle in Figure 8. A measurement and rinsing process can basically proceed as follows:

[0029] OPEN = Establish flow to the measuring device by opening valves V1 and V2

[0030] MES = Measurement 1 is carried out for a specified time (Fluid = cooling lubricant or HFC)

[0031] CLOSED = Stop the flow to the measuring device by closing valve V1 and valve V2

[0032] SP1 = Start rinsing process by opening valves V3 and V4 SPÜ = Rinse the sample chamber 10 for a specified time SP2 = End rinsing process, leaving valves V3 and V4 open CAL = Measurement 2 is carried out for a specified time (Fluid = rinsing fluid, water or air)

[0033] OFF = Evaluation of measurement 2 from CAL and signaling (measurement ok, recalibration, maintenance required) SP3 = Closing of valves V3 and V4

[0034] The refractometer described above for measuring the concentration of the concentrate of a cooling lubricant or an HFC liquid or other fluids whose concentration of components is to be monitored performs individual, discrete measurements, whereby the refractive index for determining the concentration of cooling lubricant is between 0 and 25% Brix (refractive index value) and that of HFC is between 30 and 50% Brix. As part of a self-diagnosis, there is the option of regularly internally checking the sensor device 26 for the validity of the measurement data. If, for example, peak values ​​(hotspots) cannot be detected on the diode array or the sensor surface 46 due to excessive turbidity in the fluid, the sensor device 26 should no longer output measured values, and this should be displayed via the status of the sensor device 26.

[0035] Furthermore, so-called inline calibration is possible with the measuring device. After rinsing the sample chamber 10 or the measuring cell, a reference measurement is performed in water or air. If a deviation from the expected value of the rinsing fluid is measured, the sensor device 26 is automatically recalibrated. For this purpose, the measured value with rinsing fluid is used as the new zero point. In addition, the warning "Clean refractometer" or similar is issued. By evaluating the deviation from the original value during commissioning, according to the embodiments shown in Figures 2 to 5, a prediction can also be made regarding the replacement of the laser 22 and / or the glass wall 18 in the form of damage to the glass pane. This has no equivalent in the prior art.

Claims

Patent claims 1. Measuring device for determining the concentration of components in a fluid, such as cooling lubricants or HFC hydraulic fluids, by refractometry, characterized in that the fluid to be measured is guided through a sample chamber (10) which is connected to a fluid inlet (12) and a fluid outlet (14) and which is at least partially transparent such that the rays of a light source, preferably in the form of a laser (22), which pass through the sample chamber (10) with the fluid, at least partially undergo refraction (n) and can be detected by a sensor device (26) outside the sample chamber (10).

2. Measuring device according to claim 1, characterized in that the sample chamber (10) is bounded on its side facing the sensor device (26) by a translucent wall, preferably in the form of a glass wall (18), and that the light source is received in a receiving chamber (28) of a device housing (20) and is at least partially overflowed by the fluid before entering the sample chamber (10).

3. Measuring device according to claim 1 or 2, characterized in that the light emission from the light source is at an oblique angle, preferably of 40°, to the fluid flow direction in the sample chamber (10) and that the planar extent of the sensor device (26) and its position relative to the light source are selected such that both preferably in the case of transmitted light and in the case of a possible grazing incidence of the light rays at different angles these are detected by the sensor device (26). Measuring device according to one of the preceding claims, characterized in that the sensor device (26) is part of a sensor chamber (44) of a sensor housing (42), which, filled with a gas, preferably air, creates a spatial distance between the sample chamber (10) with its translucent wall and the sensor surface (46) of the sensor device (26). Measuring device according to one of the preceding claims, characterized in that, viewed in a hypothetical vertical projection, the light source is arranged at the beginning of the sample chamber (10) and the beginning of the sensor device (26) is arranged at the end of the sample chamber (10). Measuring device according to one of the preceding claims, characterized in that a fluid channel (48) with individual channel sections (34, 36) runs at least partially between the fluid inlet (12) and the fluid outlet (14) in a supply housing (50).Measuring device according to one of the preceding claims, characterized in that the overall housing of the device is composed of individual housing parts, consisting of the supply housing (50) with parts of the fluid channel (48), the device housing (20) with the light source, and the sensor housing (42) with the sensor assembly (26). Measuring device according to one of the preceding claims, characterized in that it is connected via a switchable valve (VI) to a pressure supply device, such as a hydraulic pump (PI), which draws its fluid from a storage tank (CM1), which hydraulically supplies a machine tool (BM) as a consumer, and whose inlet side is connected via a branch (52) to a fluid line between the hydraulic pump (PI) and the switchable valve. (VI) is connected and that the output side of the machining center (MC) opens into a return line at a branch point (52) which is connected to the fluid outlet (14) in the supply housing (50) and leads to the storage tank (CM1).

9. Measuring device according to one of the preceding claims, characterized in that a further switching valve (V2) is connected in the section of the return line between the fluid outlet (14) in the supply housing (50) and the branch point (54) into which the output side of the machining center (MC) opens.

10. Measuring device according to one of the preceding claims, characterized in that a third (V3) and a fourth switching valve (V4) are connected in the supply line to the fluid inlet (12) and in the return line from the fluid outlet (14), respectively, which serve to supply and discharge a rinsing medium (DL).

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