DE2229171A1 - Level control system - using continuous radiant heat measurement of material - Google Patents

Abstract

Esp. the material is in the vacuum transfer chamber between two stages of a worm type plasticiser and extrusion press and the output signal of the sensor in that chamber is fed to a speed regulator unit whose thyristor output stage is used to control a motor, esp. dc motor, driving the worm of the first (plasticiser) stage. Double closed loop control may be incorporated, the first difference element accepting the sensor signal and a desired temp. signal whilst the second has as secon input the signal from a tachogenerator coupled to the drive motor. Smooth, automatic control is achieved.

Description

Method and device for level control by continuous Measuring the radiant heat of a conveyed material.

The invention relates to a method and an apparatus to keep the level of heated conveyed goods constant, especially plastic material, by level control, which is in a, from a machine g- ^ fed container is degassed and then exits the container.

Known means and measures for the filling level of refillable loading containers to be checked, whereby the delivery is interrupted when the target value is reached, are based on the capacitive detection method, the ultrasonic scanning method, the tuning fork measuring method and the radioactive measurement method known.

Most plastic materials have too low a dielectric constant in order to achieve a sufficiently large change in capacitance between two electrodes for the To bring about measured value acquisition, which serve the goal of a level control. the Ultrasonic scanning is separated from the purpose because of the intended evacuation measure of the conveyed material degassing. When using a transmitter similar to a tuning fork, which is excited to mechanical vibrations at a resonance frequency this is attenuated when the sensor is covered with filling material.

This actuates a relay in the electronic circuit, that can initiate a corresponding level control.

However, a regulation is only available in the case of relatively large ones Containers possible in which the material does not pass through the area of the tuning fork flows through. In the case of small containers, the material flowing through dissolves Signal that leads to incorrect switching. In the case of viscous material to which one A number of plastics counts, the tuning fork will also turn out after a short time to add.

The intended effect comes when the level rises and falls therefore not applicable. The radioactive measurement is required regarding the Safety precautions are relatively complex and can be used with small vacuum container dimensions cannot be used for reasons of space requirements.

Another known control method is to use a feed container to be connected to a suction conveyor.

The filling level is determined by an over the material requirement of the consumer horizontal conveying capacity of the suction conveyor in connection with the differential pressure ratios between pressure at the funnel inlet and outlet and by a specific arrangement the suction and feed line regulated. This method is with a heated and Do not use evacuable container.

It is also known to measure the level of a container through a container Controlling the material flowing through by means of a temperature sensor as a transmitter, where the encoder is connected to a controller (US Pat. No. 2,861,159) Regulator is a filling pump in connection with one arranged in the delivery line Valve operated according to the on-off method. When the level is low, the filling pump is switched on and switched off when the fill level is high. These Type level control detects the level heights of a minimum and maximum level and does not include continuous adjustment; it is also subject to fluctuations in terms of the filling volume and the filling pressure. These fluctuations are disadvantageous if the container is assigned to a continuously material processing machine.

The aim of the invention is that a certain selectable level kept constant in an evacuable container and that resulting deviations from this level quickly and constantly detected and by constant regulation of the delivery rate of the machine feeding the container, the specific filling level is restored heated material in the container qualitatively and quantitatively can be degassed cheaply. Another aim of the invention is the level control with simple, few and reliable means precisely and regularly to undertake.

This aim is achieved according to the invention in that one of the radiant heat the filling level of the present conveyed good, in particular plastic material, more adequate Actual value measured continuously in the container, this actual value with a specified, a selectable level compared to an adequate setpoint and that depends on the Difference value a continuous output signal is generated, through which a speed change the working machine brought about and the fill level by continuous Changing the flow rate is kept constant.

It is possible to do the comparison in a speed controller or in a Temperature controller and then in a speed controller.

The solution found makes the actual fill level exact detected and the resulting deviations precisely and quickly dependent on the measured temperature value continuously regulated so that they are linked to a constant level Operating conditions are optimal. You can do the degassing, the pressure, the Temperature, the residence time and the bulk density in the container as well as the intake behavior of the conveyed goods for the further processing machine. The measurement and control method according to the invention is simple, accurate and inexpensive to carry out.

An apparatus for carrying out the method according to the invention preferably consists of an evacuable container, in particular a vacuum chamber, between separate screw stages of a known cascade screw press se is arranged. According to the invention there is a tempe raturmeßelement or device in the container containing the conveyed material. It's on a speed controller for an electric motor drive connected to the machine feeding the container. This machine is the screw press forming the first screw stage of the cascade screw press. The electric motor drive is a known direct current motor; he's through a thyristor control, in which the speed controller device is included, dependent speed can be changed from the measured temperature value.

For the controlled system is for the purpose of a stable control behavior a differentiating or returning member is provided which is associated with the governing device is.

According to a modified embodiment of the device is between a temperature controller in addition to the temperature measuring element and the speed controller intended.

The temperature controller is a setpoint adjuster and also the speed controller a setpoint adjuster is assigned.

Furthermore, the feed machine can preferably be a tachometer a Tachometer generator. This is connected to the speed controller. These Devices for keeping the fill level constant include commercially available components and devices that are convenient and simple to solve the technical problem Circuit arrangement are summarized. The construction effort is proportionate low The one advantage is that the temperature sensitive sensor is accurate and continuously the radiant heat of the level detected and that the intended Medium does not affect the heated material flowing through or the evacuation process and that conversely this does not have a disturbing influence on a simple and favorable one Take measured value acquisition.

The further advantage is that a desired fill level can only be brought about in a simple manner by changing the setpoint value can. With the level control measures belonging to the state of the art, one is such a change with mechanical adjustment measures of a sensor or with the help of connected to another required sensor. The linking of the temperature measuring equipment with the speed control means in connection with a thyristor controlled container feeding machine is highly effective in terms of continuous, accurate and quick adjustment method to keep the level constant. The electrical elements can also be easily retrofitted to every container and feeding machine System can be provided that does not yet work according to this control method. Element protection is not sought after for the components mentioned.

Embodiments of the invention are shown in the drawing and explained.

1 shows a schematic diagram of a screw press installation with a temperature measuring element and thyristor control with speed controller; FIG. 2 is a schematic diagram corresponding to FIG. 1 with additional temperature controller.

In a screw press cascade 1, which consists of a first screw stage forming screw press 2 and a screw press forming the second screw stage 3 with the vacuum chamber 4 arranged between the screw presses, is plastic material processed in the first screw stage as an agglomerate in the vacuum chamber got. This heated agglomerate is degassed on the way through the vacuum chamber. A kind of loose pile arises in front of the inlet opening to the second screw stage, whose level is kept at a certain selectable constant level so that the agglomerate linger in the vacuum chamber for a certain period of time, degassed and can be drawn into the second screw stage.

Both screw presses 2 and 3 are powered by adjustable DC motors driven, they are denoted by 5 and 7.

In the container wall of the vacuum chamber 4 there is an in the chamber interior protruding temperature measuring element 10, it can also be a temperature measuring device, which measures the radiant heat of the level. The radiant heat is continuous measured. This means that all deviations from the selected fill level are also recorded recorded. According to FIG. 1, this measuring element is connected to a speed controller 9. The actual value determined in each case (radiant heat), which is available as an input signal, is compared with a specified target value (fill level).

Due to the comparison difference, an output signal is im Speed controller whose value becomes smaller when the input signal increases with the level gets bigger. A decreasing actual value voltage at element 10 corresponds to a decreasing one Speed of rotation of the screw of the screw press 2. This means that the screw press conveys less agglomerate into the vacuum chamber. It follows that the level falls in the vacuum container. The radiant heat is thereupon lower and thus becomes also the measured temperature value and the corresponding input signal in the speed controller 9 smaller. The value of the output signal of the speed controller increases accordingly. The speed of the screw of the screw press is caused by the thyristor control 8 2 changed. This increases the delivery rate of the agglomerate. Because of that the level in the vacuum container rises. Purpose of the measurement and control method according to the The invention is to keep the set, selectable level constant and at resulting changes by continuously regulating this level again bring about.

According to FIG. 2, in addition to the embodiment according to FIG. 1, there is a temperature regulator device 1i is provided to which the measuring element 10 is connected. The determined actual value (Radiant heat), which is present as an input signal, is given a preset Setpoint (fill level) compared. The setpoint setting element is 12 it is also connected to the device 11.

The output signal of the device 11, which is available e.g. as an output voltage, is the input signal, analogue as input voltage, for another setpoint setting Element 13.

This is assigned to the speed controller 9 for the thyristor control. A tachometer generator assigned to the screw press 2 is also attached to the speed controller 6 connected. The regulation takes place on the one hand via the temperature controller and via the tachometer generator on the other hand in the speed controller.

The desired level change takes place at the setpoint adjuster 12 and the tachometer generator arrangement results in a control-technically favorable one Speed change.

Claims (5)

Claims W Process for keeping the fill level of heated conveyed goods constant, in particular plastic material that is in one, fed by a work machine Container is degassed and then exits the container, by level control, characterized in that one of the radiant heat of the fill level of the present Conveyed material adequate actual value measured continuously in the container, this actual value compared with a predetermined, a selectable filling level adequate target value and that a continuous output signal is generated depending on the difference value, which brings about a change in the speed of the driven machine and the fill level is kept constant by continuously changing the flow rate) according to claim 1, characterized in that the actual value is combined with the nominal value in one, speed controller included in a thyristor control is compared. 3) Method according to claim 1 and 2, characterized in that the Actual value is compared with the setpoint in a temperature controller and that proportional a signal for the change in speed of the driven machine is generated for the difference value by means of which a further actual value-setpoint comparison is carried out by tachometer control. 4) Device for performing the method according to claim 1 and 2 with an evacuable container, in particular as a vacuum chamber between the Screw stages of a cascade screw press is arranged, and with means for Regulating the fill level in the container, characterized in that the radiant heat the filling level of the material to be conveyed continuously measuring element (1C) or device is arranged in the container (4), which continuously signaling an actual value is connected to a speed governor device ()) which is driven by an electric motor (#), in particular a well-known DC motor, for which the first screw stage forming screw press (~) is connected to the cascade screw press (1), and that the electric motor through a thyristor control (y), in which the speed controller device (9) is included, the speed can be changed depending on the signaled measured temperature value is. 5) Modified device according to claim 4 for performing the method according to claim 1 to 5, characterized in that the temperature measuring element (ia) or -gercit is connected to a temperature control device (11) to which a setpoint adjuster (12) is assigned, the output signal of the device (ii) as the input signal for a further setpoint adjuster (13) assigned to the speed controller (9) serves, and that a known tachometer generator (6) is connected to the direct current motor (5) which is connected to the speed control device t9).