Method

Abstract

A method for determining the concentration of constituents in a fluid, such as cutting fluids or HFC fluids, using refractometry by means of a laser (22) of a measuring device that uses the transmitted light principle, consists of at least the following method steps: - specifying a peak value for the laser light received by refraction on a photodiode line (46) using a homogeneous fluid to be transilluminated, and - keeping the peak value constant despite the occurrence of disturbances by adapting - the duty cycle of the laser (22) and / or - the current intensity for the laser (22) and / or - the sensitivity of the photodiode line (46) using an evaluation apparatus (59).

Description

[0001] Proceedings

[0002] The invention relates to a method for determining the concentration of components in a fluid, such as cooling lubricants or HFC fluids, using 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 target value, water and / or cooling lubricant is 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 method that can compensate for a multitude of possible disturbances that may occur during the measurement. This object is achieved by a measuring method having the features of patent claim 1 in its entirety.

[0004] The method according to the invention uses a laser of a measuring device for refractometry, which operates according to the transmitted light principle, carrying out at least the following method steps:

[0005] Specifying a peak value for the laser light received by refraction on a photodiode array using a homogeneous eluent to be transilluminated, and

[0006] Keeping the peak value constant despite the occurrence of disturbances by adjusting

[0007] - the duty cycle of the laser and / or

[0008] - the current for the laser and / or

[0009] - the sensitivity of the photodiode array using an evaluation device.

[0010] In this way, a reliable concentration determination in fluids is achieved even when various disturbances occur during the measurement. The laser used allows collimation, i.e. a parallel alignment of otherwise divergent light beams, which leads to an 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".

[0011] Within the scope of the method according to the invention, such a disturbance can be formed by turbidity of the fluid, which leads to a loss of intensity of the peak value of the received laser light at the photodiode array. Another possible disturbance is formed by finely dispersed particle contamination, which results in a widespread increase in intensity due to laser scattering on the photodiode array. Further disturbances are formed by larger particles or air bubbles that are moved along with the fluid to be measured and lead to the brief occurrence of measured value peaks on the photodiode array, the measured value of which is smaller than the peak value measured during refraction by a homogeneous fluid.

[0012] A further disturbance is formed by contamination on a laser-transparent wall of the sample chamber with which the process is carried out and along which the fluid is passed, which are jointly traversed by the laser light, whereby the contamination is detected by the photodiode array by a path offset compared to the regulated peak value in the usual refraction.

[0013] Regardless of the disturbance variable occurring in each case, it can be reliably detected using the measurement method according to the invention and compensated for by carrying out the method as described above.

[0014] In a further preferred embodiment of the method according to the invention, it is provided that, for a measurement operation with the measuring device, the device is calibrated to a predeterminable refractive index value using a reference fluid. Preferably, a reference fluid, such as water, whose refractive index behavior is known is used for the calibration.

[0015] In a further preferred embodiment of the method according to the invention, it is provided that during a rinsing operation of the measuring device, the sample chamber is rinsed with the reference fluid, that a comparison is made between the actual and the target value of the respective refractive index value, and that any deviation in the calibration is taken into account, and if the deviation is too large, an error message is output. In this way, calibration can take place together with a rinsing operation of the measuring device. In a further preferred embodiment of the method according to the invention, it is provided that the measuring device is monitored by the higher-level evaluation device, which preferably also performs control and / or regulation tasks in addition to measured value acquisition, and evaluates the measurement data from externally connected additional measuring devices, such as temperature, pressure, viscosity, electrical conductivity, pH value, etc.and that, depending on the measurement data obtained, external actuators such as hydraulic pumps, valves, level switches, etc. are controlled. In this way, a largely automated measurement process operation is possible and a large number of additional monitoring tasks can be included in the control of a processing machine as the consumer.

[0016] Preferably, the measuring device is connected to a secondary branch of a hydraulic supply circuit that supplies fluid to a hydraulic consumer. The measuring device is connected to or disconnected from the supply circuit by means of a valve control. In this way, the actual measuring process with the respective measuring device can be separated from the fluid supply of a consumer connected to the supply circuit, which helps facilitate maintenance work.

[0017] In particular, the method according to the invention is advantageously characterized in that, when there is no concentrate in the fluid, the fluid is fed into the fluidic supply circuit by means of a supply device under the monitoring of a measuring device.

[0018] The method according to the invention is explained in more detail below using an exemplary embodiment, including the measuring device. Figure 1 shows the essential components of the measuring device in a schematic diagram, not to scale, in the form of a longitudinal section;

[0019] Figures 2 to 5 show different possibilities of carrying out measurements according to the transmitted light principle;

[0020] Figures 6, 7, 8 and 10 show different types of operation of the measuring device using flow charts; and

[0021] Figure 9 in the form of a hydraulic circuit diagram the

[0022] Integration of the measuring device into a hydraulic measuring and supply circuit.

[0023] 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.

[0024] 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.

[0025] 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 usually 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 fiber 22 is inserted into a device housing 20 of the measuring device, the upper fiber 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 the easer 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 variety of designs.

[0026] 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 orientation 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. A temperature measurement is necessary for temperature compensation in refractometry.

[0027] 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 possibly in the case of 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 air. Viewed in a fictitious vertical projection within the plane of the drawing in Figure 1, the light source in the form of the laser 22 is located at the beginning of the sample chamber 10, and the beginning of the sensor device 26 is located 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 laser 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, so that a measuring device of this type can be accommodated even in cramped installation conditions. This also facilitates the retrofitting of existing systems with the measuring device.

[0028] 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.

[0029] 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, which serve to supply and discharge a flushing medium DL into a further storage tank CM2.

[0030] 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.Should the refractometry performed using the measuring device determine 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 actuating the supply pump P2 via the concentrate container CM3. The 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.

[0031] 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.

[0032] In the following, the measuring device according to the invention will 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 glass wall 28. A second refraction n2 then occurs at the glass wall 28 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 is made, in which the vertical distance between the sensor surface 46 and the glass wall 28 is changed, the sensitivity can be adjusted. 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 laser diode or laser 22 can be controlled with variable intensity by a control and / or regulating device (not shown in detail) in the form of the process control 59. Preferably, however, the laser 22 regulates the intensity independently.

[0033] 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 laser 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 laser 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, of 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 the 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.

[0034] 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 different from this are the briefly tapered peaks of varying intensity, which result from a change in refraction caused by the particles 74 mentioned above or the introduction of air bubbles. These disturbances can also be compensated for after their individual detection and do not interfere with the concentration determination of the fluid used with the measuring device.

[0035] The illustration in Figure 5 again relates to a different disturbance variable within the scope of the concentration measurement, in which a transparent, flat contamination with a changed refractive index n3 occurs on the glass wall 18 with its refractive index n2. Accordingly, Figure 5 shows the peak curve 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 shown in Figure 5 with the same measured value height are shifted in the horizontal direction 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. In this respect, this disturbance variable can then also be calculated out again within the scope of the fluid concentrate determination.

[0036] 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:

[0037] OPEN = Establish flow to the measuring device by opening valves V1 and V2

[0038] MES = Measurement 1 is carried out for a specified time (Fluid = cooling lubricant or HFC)

[0039] CLOSED = Stop the flow to the measuring device by closing valve V1 and valve V2

[0040] 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) OFF = Evaluation of measurement 2 from CAL and signaling (measurement OK, recalibration, maintenance required)

[0041] SP3 = Closing of valves V3 and V4

[0042] 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.

[0043] 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. Method for determining the concentration of components in a fluid, such as cooling lubricants or HFC fluids, using refractometry with a laser (22) of a measuring device based on the transmitted light principle, comprising at least the following process steps: Setting a peak value for the laser light received by refraction on a photodiode array (46) using a homogeneous eluid to be illuminated, and keeping the peak value constant despite the occurrence of disturbances by adjustment - of the laser's duty cycle (22) and / or - the current for the laser (22) and / or - the sensitivity of the photodiode array (46) using an evaluation device (59).

2. Method according to claim 1, characterized in that the disturbance variable is formed from a turbidity of the fluid, which results in a loss of intensity of the peak value of the received laser light at the photodiode array (46).

3. Method according to claim 1 or 2, characterized in that the disturbance is formed from a finely dispersed particle contamination, which results in a broad increase in intensity due to laser scattering on the photodiode array (46).

4. Method according to one of the preceding claims, characterized in that the disturbance variable is formed from larger particles (74) or air bubbles which are moved along with the fluid to be measured and which lead to the brief occurrence of measurement peaks on the photodiode array (46) whose measurement value is smaller. than the peak value measured during refraction through a homogeneous fluid.

5. Method according to one of the preceding claims, characterized in that the disturbance is formed from contamination on a laser-transparent wall (18) of a sample chamber (10), along which the fluid is passed, which are jointly traversed by the laser light, and that the contamination is detected by the photodiode array (46) by a path offset (Ax) compared to the adjusted peak value at the usual refraction.

6. Method according to one of the preceding claims, characterized in that, for a measurement operation with the measuring device, the device is calibrated to a predefinable refractive index value (Brix) using a reference fluid.

7. Method according to one of the preceding claims, characterized in that in a rinsing operation of the measuring device a rinsing of the sample chamber (10) with the reference fluid takes place, that a comparison takes place between the actual and the target value of the respective refractive index value (Brix), and that any deviation in the calibration is taken into account and an error message is issued if the deviation is too large.

8. Method according to one of the preceding claims, characterized in that the measuring device is monitored by the higher-level evaluation unit (59), which evaluates the measurement data from externally connected, additional measuring devices (38), such as temperature, pressure, viscosity, electrical conductivity, pH value etc. and that, depending on the measurement data received, external actuators are controlled, such as hydraulic pumps (P1 ,P2), valves (V1 ,V2,V3,V4), level switches (62) etc.

9. A method according to any one of the preceding claims, characterized in that a measuring device is connected in a branch of a hydraulic supply circuit (16) that supplies a hydraulic consumer (BM) with fluid, and the measuring device is connected to or disconnected from the supply circuit (16) by means of a valve control (V1, V2).

10. A method according to any one of the preceding claims, characterized in that, if there is no concentrate in the fluid, it is fed into the fluidic supply circuit (16) by means of a supply device (P2, CM3).

Images