DD300614A7 - METHOD AND DEVICE FOR LEVEL AND DENSITY MEASUREMENT IN PRESSURE-FREE LIQUID CONTAINERS - Google Patents

Abstract

The invention relates to a method and a device for measuring the filling level and the density in pressureless fluid containers. The aim is to eliminate the influence of the constantly changing material properties of the liquids by using a self-controlling measuring process and to ensure a largely universal application. Time or pressure is measured from the motion sequence during the suction of the liquid, and the current level of liquid or the density is determined {level measurement; Density measurement; Vacuum; Print; Time differences; Pressure differences; Induction}

Description

For this 3 pages drawings

The invention relates to a method and a device for measuring the filling level and the density in pressureless liquid containers, preferably in agitators.

The known, continuously operating fill level measuring devices in liquid containers are based on the use of probes immersed in the liquid, in which, depending on the depth of immersion, measurements of physical quantities that can be detected by measurement technology occur. Typical Vertretet ^J: <* ser Füllstandsmeßverfahren are capacitive methods and methods in which the buoyancy of an immersed in the liquid the float in dependence on the depth of immersion changes. "The latter method leads to incorrect measurements, which are not recognized when the material properties of the liquids change." When probes are used, the measurement result can be falsified by the solidification of solids.

Furthermore, from DD-PS 126 747 and 263 586 known to determine the level and the density of liquids by the hydrostatic pressure is measured by means of bubble level measurement or Druckmeßumformer at defined intervals in the measuring container. In this method, the two measuring points must be below the liquid surface, so that only from a certain level can be measured. Errors of the pressure measurements are not recognizable.

that maintenance or functional and zero point checks are difficult to handle. These disadvantages are partially avoided by a method described in DE-OS 30 07 658. The attainment of the fill level limits is signaled by removing ingredient from the liquid container and detecting by a flow sensor whether a gaseous or a liquid medium is being conveyed. Thus, only reaching a level limit can be detected by this method. ·

In DE-AS 23 00 184 a device is described, with the level in liquid containers is measured by moving a float in a submerged in the liquid container at the bottom offon tube to a sealing seat with a suction pump and in the piston as Piston pump designed suction pump adjusting pressure is rated as a measure of the level. It follows that the pressure generated is significantly influenced by the vapor pressure of the sucked liquid. In addition, the application of this device requires in various containers cumbersome calibration procedures and design changes, in which influences the temperature on the Meßergobni? must be taken into account. A constructive ^': ve extension for cyclically running, car riatische measurements is difficult to solve. To ensure proper functioning, leaks in the sliding seals of the piston pump must be excluded and an absolutely leakproof float valve must be assumed. For liquids that are difficult to handle, such as suspensions, this can not be guaranteed. A simultaneous measurement of the density of the liquid with this device is not possible.

The aim of the invention is to determine the level of containers or the density of liquids or both with minimal effort, with a constant functional control of the measuring device is carried out in principle. The various disturbances, such as auxiliary power fluctuation, density ·, viscosity or level change should have no influence on the measurement result.

The object of the invention is to realize a combined level and density measurement, in which the sensitive components, such as pressure measuring and limit switches installed outside the container and periodic function and zero controls can be performed without difficulty.

According to the invention the object is achieved in that a riser dives into the liquid to be measured and in this periodically by means of vacuum or pressure, the measuring liquid from the current liquid level is promoted to an upper measuring point, woboi by measuring the duration of the movement and by the measurement of time differences

during the course of the movement or by measuring pressure values and pressure differences, the filling level and / or the

Density of the liquid is determined. For the determination of the level height in the liquid container, the times are detected, the liquid up to the reach

a lower and an upper measuring mark needed. From the measurement results, the fill level can be calculated independently of the viscosity or pressure, the viscosity and the density of the liquid.

For the determination of the density and the level height, the pressures are detected in the riser when reaching inor

set lower and when reaching an upper measuring mark. In the volume above the liquid level, e η builds up

Vacuum, which is proportional to the instantaneous height of the sucked liquid column. The time dos Achieving the measurement marks present vacuum values are detected with a fast pressure measuring device and from it

the container level and the density of the liquid are calculated.

Furthermore, it is possible to install at the riser at defined intervals in series inductors and in the Riser to place a float with magnet, so that from the number of induction voltage pulses at a Delivery stroke can also be closed to the container level. With the method according to the invention, a functional check is carried out in principle by the failure of the Messeinrichtung is immediately reported when a signal from the measuring points fails after the preset time. The invention will be explained in more detail by way of examples. The accompanying drawings show

Fig. 1: movement of the liquid by applying the suction principle Fig. 2: movement of the liquid by applying the pressure principle

Fig. 3: Generation of induction voltage pulses by moving past a permanent magnet to induction coils in the movement of the liquid

Determining the fill level in a liquid filter example 1

In Figure 1, the Verfahran is shown using vacuum: In a liquid container 1 immersed at the lower end of a suction tube 2, which is connected via an automatically operated valve 8 to a vacuum pump. Another automatically actuated valve 6 can be used to establish a connection to the atmosphere. When the measuring process is triggered, valve 6 is closed and valve 8 is opened. In the volume above the liquid level in the suction pipe, a vacuum is built up, whereby the liquid rises in the suction pipe During the rise two time measurements are triggered, vnn which ends the first t, when reaching the limit switch 3 and the second t ₂ when reaching the limit switch 4 becomes. From the results of the time measurements is by means of microelectronic circuits or by application of microtechnical Gerätetochnik the quotient

t ₂ -ti

calculated. This quotient is a measure of the height of the liquid level in the liquid container. The quotient formation eliminates errors resulting from changes in the capacity of the vacuum pump, density or viscosity changes of the liquid.

Example 2

In Figure 2, the method is shown using pressure: In a dip tube 10, a riser is retracted. At the lower end of the dip tube, a bottom valve 11 is attached. If the dip tube is pressurized by means of a valve 9, the bottom valve 11 closes and the liquid rises in the riser upwards. Analogously to Example 1, the times are counted, which pass until reaching the threshold marks 3 and 4.

Example 3 FIG. 3 shows a variant of the method using vacuum: over the entire length of the suction tube 2

are many, at equal intervals closely spaced marks in the form of induction coils 14 attached. In the

Suction tube is a float 13, which is provided with a permanent magnet 12, introduced. When the vacuum is applied to the suction tube, the float moves with the aspirated fluid to the Induction coils over to the top. As each induction coil passes, an electrical pulse is generated. The number of

counted with a suitable electronic arrangement pulses then corresponds to the distance between the liquid level and an upper limit mark, the z. B. is realized by a proximity switch, from which the container level can be determined

Determining the level and density of a liquid ir: a liquid container Example 4 Maintaining the basic principle, with a particularly simple measuring device, as shown in FIG. 1, both

the level as well as the density are determined.

To the suction pipe 2 is, with the valve 8 da.s is operated by a clock control, periodically via the throttle valve. 7 Vacuum applied. It builds up in the volume above the liquid level, a negative pressure, the current height

the sucked liquid column is proportional. By means of switching and computational means, the

Negative pressure values existing at the time limit markers 3 and 4 are reached, with a fast one Detected pressure measuring device 5 and from the container level and the density of the liquid according to the following Equations calculated:

If pt and p _{2 are} the respective negative pressures on reaching the limit contacts 3 and 4 and Ah is the distance between the two limit contacts, the density may be off

^M Ah

be calculated.

The absolute height h, the sucked liquid column from the current tank level h to the limit switch is calculated / u

h | = - or h, =

q P2 - Pi

If h, o is the height of the limit switch 3 above the container bottom, then the desired level h of the container applies

, , uu PiAh

η = Πιο - Πι = Πιο

Pj-Pi

Claims (3)

1. A method for level and density measurement in pressureless liquid containers, characterized in that by means of vacuum or pressure, the liquid by a in the liquid container (1) immersed riser pipe (2) is supported by the current liquid level, the time difference during the course of movement or the pressure differences measured between the limit switches (3; 4) and from this the level height and / or the density of the liquid can be determined. 2. The method according to claim 1, characterized in that when sucking the liquid with a magnet (12) versehener float (13) in the suction pipe at defined distances electrically isolated mounted induction coils (14) is moved past and the electrical pulses in an electrical Circuit to measure the level in the liquid container. 3. A device for level and density measurement in pressureless liquid containers, characterized in that a lower end open riser (2) is immersed in the liquid container, the upper part of the riser with two spaced-apart filling level limit switches (3,4), connected to a pump via an automatically actuated valve (8, 9) and provided with a pressure sensor (5), the fluid limit switch and the pressure sensor being connected to an electronic control and evaluation device.