SU1282823A3 - Method for controlling ratio of mixture components - Google Patents

Abstract

The invention relates to the field of preparation of mixtures, in particular, to a method for controlling the ratio of the components of mixtures. The aim of the invention is to improve the control accuracy. The goal is achieved by the fact that, in the method of controlling the ratio of the components of the mixture, the relationship between the time of opening and closing of valves in pipelines and pulsations of flows at the pump inlet and outlet is determined. The times at which complete opening and closing of the valves in the pipelines should not coincide with the time when the flow pulsations at the pump inlet and outlet have extreme values. 1 hp ff, 2 ill.

Description

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The invention relates to the field of preparation of mixtures, in particular, to a method for controlling the ratio of the mixture components to a mixture, and can be used in industry, laboratories, hospitals and research clinics.

The purpose of the invention is to improve the accuracy of regulation.

Figure 1 shows a block diagram of a control system that implements the proposed method; Fig. 2 shows flow pulsation diagrams at the pump inlet and outlet with valve switching periods.

The control system contains tanks 1, mixing chamber 2, tubes 3, solenoid valves 4, pump 5 with inlet 6 and outlet 7 pipelines and three heads 8-10. The system also includes a control device 11 comprising a pump drive control unit 12, a control panel 4, a device 15 for controlling the ratio of the components.

The proposed control method consists in that the mixing components come from a plurality of tanks by cyclic dosing of the flow from each tank into the mixing chamber over time to form a liquid flow, as well as cyclically pumping the liquid flow. the time period of the pump operation cycle to provide the required flow rate and adjust the period of the dosing cycle time, which must be asynchronous with respect to the period of the operation cycle of the pump and its higher ha Monica.

The control system contains several reservoirs 1, each of which contains various mixable liquids or liquid media. These fluids must be mixed together in a predetermined proportion. For this, liquids are sent in the mixing chamber 2 through the tubes 3 and the corresponding solenoid valves 4. Before entering the mixing chamber, each of the liquids passes through a filter (not shown), by which solid particles are removed. Each of the solenoid valves 4 uses a high-speed solenoid which either permits or prohibits

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The flow through the corresponding tube 3 is established. The mixture is formed by periodically opening each valve 4 for a certain period of time during the total valve switching period, which is proportional to the fraction of this required fluid. From the mixing chamber, the liquid passes to the pump 5. It is possible to use a pump with three heads, since they provide a more constant level of output flow rate. Such a pump is a positive displacement pump operating with a phase displacement of 120. For each pump, the displacement of the piston is a sinusoidal function in time. The period of operation of the pump is determined by the delivery volume for one cycle of each pump head divided by the volume capacity of the system.

The inlet and outlet check valves on each head (not shown) ensure that each head supplies fluid at a certain time in the pump cycle. The outlets and inlets of the pump heads 8-10 are connected by lines 6 and 7, which separate the flow at the pump inlet and combine the flow at the outlet. Due to the work of the locking; valve flow in the cavity: the fluid of each head 8-10 is pulsating, i.e. when the fluid enters the cavity when the piston is drawn in, then it flows out of this cavity, and when the fluid is ejected from the cavity as the piston moves, it does not flow into the cavity. The exact characteristics of the flow pulsations depend on the actuator mechanism of the pistons, the compressibility of the fluid and the reaction time (speed) of the shut-off valve. Thus, the three pump pistons produced six flow pulsations at the pump inlet and outlet for each pump cycle (Figure 2). The drive control unit 12 of the pump 12 acts on the drive of the pump 13, which in turn acts on the respective heads 8-10 of the pump a. The pump drive control unit 12 operates in accordance with the desired flow rate information, which is set by the system operator on the control panel 14. The operator also sets the mix composition information that is transmitted to the device 15 with the help and the control panel. The opening and closing times of each valve is determined by the device 15 and is accomplished by applying power to different Solenoids at certain periods of time through the appropriate communication lines.

In accordance with the present invention, a problem arising from the frequency of the pump flow interacting with the switching frequency of the solenoid valves, which can lead to unexpected slow changes in fluid mixtures, is solved. The solution to the problem is to modify the valve switching period T based on the engine speed information obtained by the device 15 from the pump drive control unit 12. An example of such an undesirable interaction is given.

2, where valves 4 and

4 are presented in such a way that they cyclically open and close during period T during the period of flow.

pump t. Ripple

pump and valves (Fig. 2) are exactly in sync, so that the maximum flow rate is created when valve 4 is open. Minimum flow is created when valve 4 is opened, since the pump flow is maximum during valve 4 opening. As a result, the mixture contains more component passing through valve A than is assumed from the valve switching period.

In practice, accurate synchronization between the period of operation of the valve and the period of switching valves occurs rarely. More often, slow changes in concentration occur when the pulsations of the valves and flow shift from phase to phase.

The proposed method allows to reduce or eliminate errors in such mixing with the help of the selection

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valve switching periods that do not result in an interaction between the respective valve switching periods and flow periods 5. Preferably, errors are avoided by setting the valve switching period, which should be a function of the flow rate. More precisely, the cycle speed tO, i.e. the period of operation of the pump is adjusted to provide the desired flow rate, and then the speed of the spin cycle, i.e. the valve switching period is controlled in such a way that it is asynchronous with respect to the flow rate of the pump and exhausted to the harmonics of the flow rate of the pump.

In this way, exact compensation of the composition and flow of the liquid is maintained.

Claims (2)

Invention Formula one . The method of controlling the ratio of the components of the mixture, which includes feeding each component from the tank to the mixer through the corresponding pipeline by opening the valve installed on this pipeline for a time proportional to the proportion of that component in the total fluid flow, and pumping the total flow using a pump from the mixer to the object consumption, characterized in that, in order to improve the control accuracy, the valves are opened and closed in the pipelines at times that do not coincide with the time when the flow pulsations at the pump inlet and outlet have extreme values. 2. A method according to claim 1, characterized in that the opening and closing of the valves in the pipelines are performed at times that do not coincide with the passage time of the higher harmonics of the flow pulsations at the pump inlet and outlet. tshchsch UJIUUIMJUUUU g guuuuuu lrll V h "g / y" 3 V ff - 92 V. i. i 1 .-4M:: / V-  I - / . Tr: