FI94676C - Method and apparatus for calibrating liquid measuring equipment - Google Patents

Description

94676

METHOD AND APPARATUS FOR CALIBRATING THE LIQUID MEASURING APPARATUS

The present invention relates to a method and an apparatus for calibrating a liquid measuring apparatus according to the preamble of claim 1.

Today, only a small proportion of tanks for the storage of fuel distributed at service stations are equipped with 10 surface sensors that provide information on the height of the liquid surface. There are several known solutions, for example a magnetostrictive sensor in which the position of a floating float is measured, or a (most commonly used) capacitive method in which by measuring the capacitance of different capacitors with respect to others it is possible to find out where the liquid surface is. Such equipment is quite complex in terms of electronics, and the reliability of operation is insufficient, as certain fuel additives interfere with the capacitive process in particular.

U.S. Patent No. 4,914,962 discloses a transducer-based transducer that can be used to measure a liquid level. The liquid level transducer disclosed in said publication measures the liquid level by measuring the buoyancy of a unit of weight set at a certain height in the container and partially immersed in the liquid. The transducer body acts as an upper attachment point for the thin steel strip and at the same time as an attachment point for the hinge connecting the body to the lower support, which serves as the lower attachment point of the strip and at the same time also the attachment point of the weight unit bracket. A unit consisting of a winding and a permanent magnet is placed near the strip, by means of which the strip is made to vibrate. . · · At its resonant frequency and to produce an electrical output signal for surface measurement. Attached to the bracket is a 35 bracket cable on which the weight unit is hung. The weight unit is cylindrical and has a constant diameter over the entire fluid surface range.

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The float technique according to said US patent achieves a simple structure. In addition, the equipment is highly resistant to fuel additives because the float can be made of a material that is not affected by the additives. The device-5 can be calibrated by taking a stick measure from the liquid surface in the tank and recording it. The surface reading given by the apparatus is then determined and compared with the 'stick size'. Other similar calibration methods may be used.

10 The operation and manufacture of such a float is simple, but with such a solution it is not possible to reveal a (small) error due to the dispersion of the specific gravity of fuels, which is about ± 0.6% for diesel fuels and even ± 1.5% for petrol-15. The scatter of the specific gravity may cause an error of up to 1 to 2 cm in the measurement of the height of the liquid surface based on the buoyancy.

The object of the present invention is to improve the accuracy of a floating apparatus for measuring liquids according to the prior art. In the calibration method according to the invention, discontinuities are arranged on the outer surface of the float, where the outer diameter of the float changes. These discontinuities are used to match the measured values "* .25" determined by the measuring sensor to the actual mechanical dimensions of the float according to the claims below.

The discontinuous float according to the invention makes it possible to monitor the actual height points, so that it can be detected if the tank has moved or some other disturbances have occurred. In addition, the self-calibration according to the invention is easy to handle mathematically and can be taken into account in the normal gradual emptying event of the tank after each filling operation.

35 Also when filling the tank, the same method can be used, for example, by recording the measurement signal with respect to time 3 94676 at regular intervals and analyzing the curve at the end of the filling operation.

In the following, the invention will be described in more detail by means of Example 5 with reference to the accompanying drawing, in which

Figure 1 shows an apparatus according to the invention for measuring the level of fuel in a fuel tank.

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Figure 2 shows the focus curve showing the discontinuities.

Figure 1 shows a cylindrical fuel tank 1, 15 with fuel up to the surface 2. At the top of the tank 1 there is one unit 3 for measuring equipment. Attached to the connection 3 is a cylindrical protective tube 4 extending from the bottom and extending to the bottom of the tank 1. Inside it, a cylindrical float 5 extending from the bottom extending from the bottom to the lower end of the protective tube 4 is placed.

A sensor unit 6 acting as a surface transmitter is placed on the float 5. It comprises a round, thin and flexible metal-25 dirt 8 running between the cover part 7 at the upper end of the float 5, which is tensioned at its outer edge on a flange 9 around the cover part 7 and a sensor 10 connected to the cover part. is a metal wire oscillating at a certain frequency inside a thin vertical metal tube and a magnetic unit 30 with magnets inside attached to the metal tube in the middle thereof. Such a sensor is, for example, the structural tension measuring probe P-200 manufactured by Geonor A / S. In addition, the sensor unit has a protective cap 11.

The float 5 is affected by a buoyancy equal to the weight of the amount of fuel frozen syr-35. The buoyancy is transmitted via the membrane 8 to the force measuring sensor 10. The sensor 10 is further connected by a control cable 12 to a control unit located in the case of Fig. 1 in a dispensing machine 13.

When the equipment is switched on, the wire in the pipe starts to vibrate according to the signal from the control unit. After a few seconds, the oscillations reach a constant amplitude, and the wire continues to oscillate as long as the sensor is on. The output of the sensor 10 is an alternating voltage alternating voltage, from which the frequency is measured by a control unit.

10 The frequency is still used to determine the height of the liquid in the tank.

For calibration, two discontinuities 14 and 15 are arranged in the float 5, which are, for example, cylinders with an outer diameter 15 larger than the outer diameter of the float 5, one in the middle of the float 5 in Fig. 1 and one upwards so that both are in the liquid surface 2 range. The diameter of both discontinuities 14, 15 is constant. For example, in the case of Figure 1, the length of the cylinders is about 1/10 of the height of the float 5. The lower and upper ends of each cylinder 14 and 15 thus form discontinuities A to D on the outer surface of the float 5, where the outer diameter of the float 5 changes discontinuously and whose heights hA - hD in the height direction (arrow 16) from the lower end of the tank 1 (horizontal axis 17) •• 25 are known. The discontinuity points A to D in diameter are used as calibration points on the basis of which the calibration curve determined by the measuring equipment can be refined as follows.

30 In the case of an oscillating wire, a factor depending on the difference between the squares of the frequencies and the amount of liquid leaving the tank 1 can be used as the focusing factor of the calibration curve ·· used for measuring the surface height.

li 5 94676 fl-fl Κ-Λτ where K is the focusing factor, fi and f0 are two consecutive frequency values and AV is the change in volume of the liquid. Fig. 2 shows the focusing curve 21 of the tank 1 in a coordinate system in which the vertical axis has a focusing factor K and the horizontal axis has a height.

5 At the beginning of the horizontal axis there is a maximum level of the fuel level in the tank 1 and at the end a minimum h, ^. As can be seen from the curve, the discontinuities appear clearly larger than nearby values. At points of discontinuity, the derivative of the calibration curve is discontinuous.

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In the system according to the invention, the change in the volume of the liquid AV is obtained independently of the level measuring device as feedback information from the measuring device through which the liquid flow leaving the tank passes. Such a measuring device can be, for example, a distribution meter 19 connected to the tank 1 by a supply line 18, from which the information is further transmitted by a cable 20 to the control unit of the vending machine 13.

With the calibration curve used to measure the liquid level, the points of discontinuity can be determined accurately with the system according to the invention after the liquid surface 2 has moved past them by fitting the focus curve 21 with discontinuity points hA '- hD' obtained from derivative changes or the above equation,

25 to correspond to the actual heights hA of the discontinuities A to D

- hD. This can be done mathematically, for example by the least squares method. It should be noted that the actual heights hA - hD of the discontinuities 14, 15 from the bottom of the tank 1 are always known very precisely for mechanical reasons.

It will be clear to a person skilled in the art that the various embodiments of the invention are not limited exclusively to the above-described 6,94676 character, but may vary within the scope of the claims set out below.

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Claims (4)

A method of calibrating an apparatus for measuring the height of the liquid surface in a cistern (1), wherein in the measuring apparatus a cylindrical float (5) located in the cistern (1) of at least the height of the cistern (1) and an adjacent one is used. The float is provided with a sensor unit (13) provided with the sensor unit (6) and 10, where the pressure acting on the measuring equipment's float (5), which is equal to the weight of the displaced fuel quantity, is conveyed to the sensor unit (6), whereby the height of the liquid (2) and amount in the container (1) can be determined in the control unit 15 (13) by means of said pressure, characterized in that at least one discontinuity portion (AD) is arranged in the float (5) within the variation interval 20 of the liquid surface (2). the diameter of the outer casing surface of the float is changed so that the amount of liquid from the cistern (1) or to the cistern entering the amount of liquid is measured in a manner independent of the measurement of the surface height and that at least one the discontinuity portion (hA.-hD.) of the float determined in measuring the surface height of the liquid is brought to correspond to the actual discontinuity portion value (hA-hD) by means of the measurement of the amount of liquid, which is. *: * regardless of the measurement of the surface height. 2. Apparatus for calibrating an apparatus for measuring the height of the liquid surface in a cistern (1), where a cylindrical float (5) located in the cistern (1) of at least the height of the cistern (1) is used, and one in a connection to the float provided with a sensor unit (13) provided with the sensor unit (6) and 5, where the pressure acting on the float (5) of the measuring equipment, which is equal to the weight of the displaced fuel quantity, is conveyed to the sensor unit (6), the height (2) and amount of the liquid in the tank (1) can be determined in the control unit 10 (13) by means of said pressure, characterized in that the float (5) is provided with at least one discontinuity portion (AD) within the variation interval of the liquid surface (2). , where the diameter of the outer casing surface of the float is changed, that the device is provided with a device (19) for measuring the amount of liquid with which the amount of liquid from the cistern (1) or to the cistern entering the liquid one is measured in a manner independent of the measurement of the surface height and that the control unit (13) controls at least one such discontinuity portion (hA, -hD,) on the float as determined by the measurement of the surface height of the liquid to correspond to the actual discontinuity portion value (hA-hD) by means of the measurement of the amount of liquid, which is independent of the measurement of the surface height. Device according to claim 2 for calibrating an apparatus for measuring the height of the liquid surface in a cistern (1), characterized in that the float (5) is provided with one or more discontinuous portions (14,15) whose length is substantially less than the length of the float, in which / which the discontinuities arise and whose outer diameter at least in any range 12 94676 deviates from the outer diameter of the float within the variation range of the liquid surface (2). 4. Device according to claim 2, characterized in that the sensor unit (6) is provided with a power sensor (10) based on a vibrating vibration element, which vibration element can be caused to vibrate according to the control from the control unit (13). «* · · • · · li