MXPA97003886A - System for delivery of load and download quick paralychid heavy indirectly in a surti - Google Patents

Abstract

The present invention relates to a method of supplying a unit dose of liquid from a dispenser in a system comprising a liquid outlet valve means through which the liquid must be delivered, a means of a gas inlet valve through from which gas is introduced into the spout, an elongated diver plunger partially immersed in the liquid, the plunger having a specific gravity greater than the liquid and a length greater than a range within the spout through which the liquid level varies in the dispenser, and control means for receiving signals generated in a load cell that continuously detects the apparent weight of the plunger symbol, since the control means transmit instructions to the valve means, the improvement is characterized in that it comprises: a) opening the exit valve means to begin to supply the unit dose, b) open a half air intake valve to introduce pressurized air in the spout in order to maintain a superatmospheric pressure of about 790 kPa, c) receive a first signal in the control means, this first signal being proportional to the detected weight of the plunger symbol when a pre-zero reference point is detected after a greater part of the unit dose was dispensed, d) transmitting a first output signal from the control means to at least one of the gas intake valve means and the liquid outlet valve means, to interrupt the moment of the liquid in the dispenser, e) restoring a portion of that moment, f) receiving a second signal in the control means, being that this second signal corresponds to the detected weight of the diver symbol when a zero reference point is detected, and then, g) transmit a second output signal to close the outlet valve means in less than 1 second, whereby the unit dose + - 5 percent is adapted for to be stocked within a predetermined portion of time, without measuring the level or volume of liquid contained in the dispenser, or directly weighing the liquid assortment of the assortment

Description

LOADING AND QUICK RELEASE SYSTEM FOR HEAVY LIQUID INDIRECTLY IN A DISPENSER BACKGROUND OF THE INVENTION This invention relates to a batch jet system for feeding liquid to a dispenser, then accurately controlling the discharge of a desired quantity of liquid, which in the present specification is referred to as "unit dose", in a short period of time for the filling and discharging cycle, which is referred to as "cycle duration". The invention specifically relates to a system for supplying a unit dose of liquid to a mixture of receiving material in which the amount of liquid is critical. Even when a single liquid can be dispensed, in a typical application a plurality of liquid reaction modifying reagents are added, separately and usually in sequence, to a wet concrete mix that is to be transported to the place where it will be used. Taking into account that the wet concrete begins to "set" as soon as it is mixed, each liquid reagent of the mixture is loaded in a spout and afterwards. discharge on a concrete transporter truck, within a short duration cycle of approximately 2 minutes or less. Usually, the amount of liquid in a unit dose varies from less than 1 liter to more than REF: 24764 100 liters; the "cycle duration" is less than 2 minutes, preferably less than 1 minute; and the time allowed for the discharge portion (stage) of the fill and discharge cycle is less than 1 minute, preferably less than 45 seconds. The short duration of the cycle requires that liquid is charged and a critically controlled amount of the unit dose is discharged, both at a high flow rate, which results in a highly unstable level within the spout. The previous technique "based on the measurement of the level did not recognize that a stable level was not required to supply a unit dose, nor does it suggest that precision can be achieved in a short cycle without measuring the level of the liquid or the volume that it occupies inside the spout, indirectly detecting the apparent weight of liquid displaced by an elongated body, which in the present memory we refer to as "plunger diver", partially submerged in liquid. In the U.S. patent No. 4,320,775 to Stirling et al, the precision of the quantity of liquid dispensed could only be maintained if the liquid was supplied with a reduced flow rate. This was done by compensating the dynamic pressure of the liquid within the spout by automatically adjusting a flow control valve to provide a lower flow rate for a short period of time at the start of each discharge. As the dynamic pressure of the liquid decreases, the flow control valve gradually opens, thus eliminating any fluctuation of the flow rate due to the variation of the dynamic pressure of the liquid. The difficulty of indirectly detecting the weight of the liquid to be filled, then supplying the desired quantity without metering valves while maintaining a critical accuracy of ± 5 percent or better and meeting the established time requirement of less than 1 minute for the cycle, has not been addressed by the prior art. Specifically in the field of mixing a load of dry or wet concrete, the technique does not provide any suggestions on how to load and then automatically supply up to 113 liters of a liquid reaction modifying agent within less than 2 minutes, preferably less than 1 minute, and yet maintain the desired precision. Feeding and then dispensing a unit dose with such speed and precision poses a problem that is exaggerated when it comes to controlling the charge of a relatively small amount of liquid to the dispenser, and then discharging that amount. This is true in particular if you have to supply "a single unit dose", and then the spout is filled from a supply tank. The term "single unit dose" (a single unit dose) refers to the desired amount of liquid that is discharged from the dispenser, which is then reloaded with sufficient liquid to discharge another single unit dose. To avoid wasting time by feeding liquid after each discharge, and to maximize the time available for the cycle discharge portion or stage, multiple doses, from 2 to 10, can be charged to the dispenser, but typically not more than approximately six, during a single loading period, filling (in this case discharging) only unit doses. During normal operation, a concrete mix, say 7.65 m, is loaded onto a truck at a dispensing station equipped with a multiplicity of dispensers, each with a specific reacting liquid reagent that must be added according to a recipe. Such liquids may include an accelerator or retarder to modify the "set" time, water reducers, evaporation retarders, corrosion inhibitors, air retainers, freezing point modifiers and the like. If the truck travels to successive filling stations, the more reagents you have to add, the longer the total time that passes until the truck can leave for a "emptying".

Whether you have to take a single unit dose or multiple unit doses, you should only have a relatively small amount of liquid in each dispenser. If only a single single unit dose is required, the relatively small amount of liquid desired is within the range of about 0.3 liters to about 113 liters, so that the dispenser has a relatively small liquid capacity, ie , is a small dispenser, typically less than 190 liters. If desired a larger spout can be used, with a capacity for more than about six unit doses, but the problem of dispensing a small unit dose accurately from a much larger volume of liquid in the spout is magnified. Therefore, in the technique of mixing concrete, and in analogous techniques in which conditions or corresponding considerations prevail, no more than six are supplied from each dispenser, and more typically only a single unit dose, the dispenser being in turn it is loaded from a large supply reservoir containing several hundred unit doses or more. Conventional systems are available to supply a desired amount of liquid from a spout. Commonly, for example, a dispenser can be weighed before and after the delivery of the desired quantity of liquid. Many of the prior art systems are provided with means for detecting the level, volume or weight of the liquid within the spout, and for operating control means for discharging the desired amount. Alternatively, a specified amount of liquid can be discharged from a spout, typically by opening an outlet valve that measures the volume of the flow of liquid that passes through it, then closing it when the desired amount has flowed or passed through. she. In the case of small amounts of liquids, the most common is that they are filled from jets with a level glass in which the liquid level indicates the amount of liquid remaining inside the dispenser. The quantity supplied is determined by the difference against the previous level existing before the liquid was filled. A large number of gauges or flow indicators are available to measure the liquid level as it enters the dispenser (refer to "Choose the Right Flow Meter") by John W. Dolenc, Chemical Engineering Progresa, January 1996). However, to obtain the desired precision within the preset time compulsion, when the viscosity of the liquid is not constant, the selection of an adequate flow rate indicator was discarded, either because of the high initial cost or the high expense of maintenance, or both. It was therefore decided to find a different system and method for measuring the desired amount of liquid to be loaded and then dispensed. Because weighing together the liquid and the spout introduces an unacceptable degree of inprecision, it was decided to weigh only the unit dose that will be supplied. However, it was decided to weigh the unit dose only indirectly, without weighing directly neither the liquid nor the spout, using the Archimedes principle. Since the hydraulic lift of a solid is the product of the volume of the solid and the specific gravity of the liquid in which the solid is immersed, if the specific gravity of the liquid is essentially constant, then a change in volume is directly proportional to the hydraulic lift. In this way, the change in the detected weight of the submerged solid can provide the weight of the liquid within which it is submerged, as long as the volume of the spout is determined (be fixed). A straight-line relationship is obtained when the solid is an elongated body, or "plunger diver," which has a constant cross-sectional area in the horizontal plane, and the cross section of the spout is also constant. The above data is used to perform computational calculations to accurately determine the weight of the liquid discharged from the spout. The previous indirect determination of the weight of the liquid in the spout is independent of the level of liquid existing in the spout, level that fluctuates violently because the liquid is fed at high speeds under superatmospheric pressure of up to 10 bar; and it is also independent of the formation of foam in the liquid, which usually happens under high-speed conditions. In addition, in order to comply with the short duration of the cycle required, the liquid is charged and discharged under pressure, and the rate or speed at which the liquid enters and / or exits the spout causes a fluctuation of the level which, if had to be measured, would make it very difficult to maintain critical accuracy. Although there are fast-acting valves on the market, which either open or close completely (in a very short period of time), there is no suggestion that they are used in a dispensing system in which the quantity of liquid to be supplied It is critical. Such valves do not have a dosing capacity. Despite the very short time, less than 1 second, preferably less than 0.5 seconds, that such a valve requires to open or close completely, it is evident that under superatmospheric pressure the amount of liquid passing through the valve during the short time lapse that takes close (completely), negatively affects the accuracy with which you can supply a small unit dose, less than 190 liters, and as small as 0.5 liters. However, there is no suggestion in the prior art that, with the use of fast inlet and outlet action valves to respectively charge and discharge the liquid to and from the spout, the required accuracy of ± 5% or better can be met. by a sudden interruption of the moment of the mass of liquid discharged from the dispenser during a critical time interval, namely after a greater portion (> 50%) of the unit dose has been dispensed. With the expression of "suddenly interrupting the moment" we mean that the speed of the remaining mass of a unit dose in the dispenser is at least halved in less than 1 second, either by cutting off the supply of pressurizing gas to the dispenser, or by cutting off the flow of liquid leaving the spout, or both. The time during which the moment is interrupted is not narrowly critical, but is preferably less than 1 second, since a longer A time does not serve any useful purpose. Preferably the moment is interrupted near the end of the stage (portion) of discharge of the cycle, before the entire unit dose has been filled, to then restore a portion of the moment lost by the remaining liquid at the time of interruption , until the load cell detects that 100% of the unit dose was filled. SUMMARY OF THE INVENTION It has been found that irrespective of the conditions under which a liquid is supplied from a supply reservoir to a dispenser, and of the physical characteristics of the liquid, the weight of the liquid that must be dispensed with critical precision within a period of time. The preset can be precisely controlled by a controller means (also referred to as "signal processor means") that transmits signals that require the momentum of the mass of liquid passing through the dispenser to be suddenly interrupted, preferably justly before the desired amount of fluid has been dispensed ("unit dose"). Specifically, a "filling cycle" (the charging portion or stage (of the spout) of the cycle) comprises charging liquid (which will then be filled (or discharged)) to the spout, typically proceeding to open a liquid inlet valve means for the liquid in connection, to then close the valve when the amount of liquid in the spout corresponds to a predetermined reference point in relation to the force exerted by a plunger submerged in the liquid. At this point we refer to the "load" reference point. Having completed the filling cycle, the portion or stage of discharge of the cycle begins. This stage of discharge of the cycle ends when the detected weight of a discharged unit dose corresponds to a predetermined reference point, which we refer to as the reference point "zero" in relation to the force exerted at that moment by the plunger submerged in the liquid. A controller means is appropriately instructed to recognize the "load" and "zero" reference points, whether the zero reference point is set for a single unit dose or for multiple unit doses. In each case, a assorted unit dose is then detected in relation to the zero reference point for a unit dose. In a first specific embodiment, the moment is interrupted after a larger portion, preferably more than 80% of the unit dose, has been discharged from the spout under inert gas pressure. The pressurizing gas, essentially not capable of reacting with the liquid, is introduced to the spout through a solenoid valve (automatic) with rapid action of air intake. As liquid is discharged through an open liquid outlet valve, the air intake valve closes quickly in less than 1 second, remains closed for a preselected period of time and re-opens, from preferably within less than 1 second, while the discharge of a unit dose is completed, that is, until the outlet valve closes. Closing the air intake valve in an air line supplying pressurized air then interrupts the liquid moment for a preselected period, and surprisingly provides the critical accuracy of the weight of the liquid assortment that is required. In a second specific embodiment, after 80% of a unit dose has been dispensed, the gas inlet valve is kept open to maintain the pressure, but the outlet valve closes quickly in less than 1 second, is maintained closed for a preselected period and then reopened, preferably in less than 1 second, until the remaining portion of the unit dose is dispensed and the outlet valve is closed. In a third specific embodiment, after the outlet valve is opened to discharge a unit dose, and after more than 80% of a unit dose has been dispensed, the pressurization air supply is cut off upon de-energizing the solenoid of the air intake valve, - essentially simultaneously the liquid outlet valve is closed, both in less than 1 second. After a short pre-selected period, preferably less than 1 second, the solenoid is re-energized and the air intake valve opens; essentially the outlet valve is opened simultaneously. The outlet valve closes again after the filling cell detects that the unit dose was supplied. It is therefore a general object of the present invention to provide a spout that traps more liquid from which it must be discharged, under gas pressure applied upstream of the liquid, with the liquid entering through a rapid opening inlet valve and It closes quickly and exits through a rapid opening and quick closing outlet valve, and each valve opens and closes in less than 1 second, preferably in less than 0.5 seconds. Air is supplied under pressure through an air line with a quick acting valve. A control means is programmed to transmit signals to initiate the opening or closing of each valve. For a visual verification of the liquid level in the dispenser, a vertical level glass is supplied. It is a specific object of this invention to provide a dispenser that uses pressurized gas to fill the space above the trapped liquid, and to forcibly discharge a unit dose from the dispenser within the discharge period of a filling and discharging cycle limited to 2 minutes, and preferably 1 minute, under a pressure within the range of about 2.7 bar to 5 bar. The portion or stage of discharge of the cycle of preference is less than 1 minute, and more preferably less than 45 seconds. It is also a specific object of this invention to provide a dispenser having an internal volume comprised within a range that is 2 to 10 times greater than the volume of the desired quantity of liquid to be discharged, - and that of providing a dispenser. for which the ratio of its internal cross-sectional area is in the proportion of approximately 3 to 20 with respect to that of the plunger. It was also discovered that a load cell adapted to emit an analog signal through an appropriate amplifier in response to a force exerted directly below the load cell by the suspended plunger piston, surprisingly results in the ability to process the signal to through a means of controlling concrete loads at a speed that is almost four times faster than if voltage switching is used. The control means transmits signals to open and close quick acting valves to suddenly stop the moment of a unit dose, just before the unit dose has been discharged, to deliver the unit dose with the established precision and within the short period ( of time) preselected. BRIEF DESCRIPTION OF THE DRAWINGS The preceding and additional objects and advantages of the invention will be better understood by reference to the following detailed description, accompanied by schematic illustrations of the preferred embodiments of the invention, being that in the illustrations the same numerals refer to to like elements and in which: Figure 1 schematically illustrates the main components of the spout system so that a desired amount of liquid additive can be loaded and discharged quickly and accurately from a spout to a wet cement mixture found in a truck for concrete. Figure 2 is a graph with the curves on the amount of liquid that is displaced as a function of the immersion depth of the plunger, wherein the spout and elongate body each have a circular cross-section of a straight cylinder, which indicate that the weight of the displaced fluid is directly proportional to the depth of immersion of the body. Figure 3 is a simplified functional flow diagram of an analogous circuit, showing the main components and functions of the signal processing means. Figure 4 is a functional flow diagram showing the components of the system in relation to their corresponding function, connected in an analogous circuit that shows the stages of the "filling cycle" during which the liquid is charged to the spout, the function of the components being described in relation to Figure 1. Figure 5 is a diagram of functional flow that shows the components of the system in relation to their corresponding function, connected in an analogous circuit that shows the stages of the "discharge cycle" during which the liquid is discharged from the spout, being that the function of the components is described with reference to Figure 1. Figure 6 is a functional flow chart describing. the operation of the processor means (or "driver") of signals in each of two embodiments, to interrupt the moment of the mass of liquid discharging from the dispenser.

DETAILED DESCRIPTION OF THE INVENTION In each of the embodiments described below, a unit dose is determined indirectly with surprising accuracy, using a load cell of which a plunger plunger having a specific gravity greater than the one of the liquid. The high flow rate of liquid to the spout, under high pressure and at high speed, results in the plunger being moved arbitrarily, oscillating in the liquid that arrives at the connection. The precision in the measurement of the detected weight of the plunger is attributed to the availability of an appropriate load cell with adequate resolution, and to the construction of an appropriate amplification means for the load cell, and (ii) to provide a processor means of signals that we refer to in general as "medium driver", to instruct the quick action valves when to open and when to close. Appropriate computer (computer) instructions ensure that excess fluid that would be supplied during the time delay inherent to the outlet valve (the time it takes to fully shut off) does not flow through the valves after the valve He received a signal to close. By providing after a greater portion of the unit dose has been discharged for a short period of time, from at least 0.1 seconds to less than 1 second, during which the moment of the liquid mass being discharged is interrupted, the flow of excess liquid. The precise amount of time within the indicated range is not critical. In particular, a unit dose of reaction modifying reagent for a wet concrete mixture is added to a (batch of) wet concrete mixture having a volume within the range of about 0.765 m3 to 11.47 m3, just prior to «That the concrete mixture is used. The system described herein is equally applicable to accurately deliver a small amount of any other liquid into a larger mass of material where analogous considerations of precision and time prevail. Referring to Figure 1, it illustrates a dispensing system referred to in general by the reference numeral 10, which includes a spout 11 to which liquid 12 is loaded, a plunger plunger 13 suspended vertically so as to It is partially immersed until a desired amount of liquid has been charged. At least one portion of the hydraulically supported plunger 13 is submerged at all times, even after the desired amount of liquid has been discharged from the spout. The liquid has a specific gravity within the range of 0.6 to about 1.3, and is typically viscous with a propensity to foam when loaded in a spout at a rate in excess of about 1.5 m / second. More preferably, the liquid is charged at a rate comprised within the range of about 1.5 m / second to about 15 m / second, to obtain a rapid fill of the spout. The plunger plunger 13 is connected by a substantially rigid rod 14 to a load cell and extensometer 15 with rotating joints or ball joints that allow the plunger or float to oscillate as well as rotate. It was found that the accuracy of the load cell was impaired if the plunger is not allowed to rotate or rotate through an angle of at least 90 °. The load cell and the associated extensometer measure the decrease in tension exerted by the plunger 13 when liquid 12 is charged through the conduit 16, which is connected in open flow communication with the spout 11. At the spout, the space above the surface of the liquid is pressurized by air from a supply 19 of air, such as a compressor, connected to supply pressurizing air to the spout 11 through a conduit (an "air line") having a valve 21 of Quick action for air intake. Even though any other type of quick acting valve can be used, a pneumatic operation valve of the poppet series (cam or rod drive (vertical actuated valves with conical or disk seat)) is preferred, as can be obtained through the Cia. Automatic Valve Co. Air to pressurize is typically available at superatmospheric pressure, preferably within the range of 2 to 6 bar. The liquid is supplied to the bottom portion of the spout 11 from the supply reservoir 3.1, through the loading conduit 16 having a quick opening and quick closing inlet valve 23, by pumping means, preferably a pump 33 of pneumatic diaphragm, at a pressure comprised within the range of about 380 kPa to about 790 kPa. While any fast-acting liquid inlet valve can be used, what is most preferred is a pneumatically operated liquid control valve, such as a miniature pneumatic diaphragm valve (operated by air), of the BSD series, which can be obtained through the Plast-O-Matic Valves Inc. Company. The liquid to be discharged from the dispenser exits through the 1-discharge conduit 18 having a rapid opening and quick-closing outlet valve 25.; and from there to a mixing vessel 37, such as a concrete mixing truck, where the discharged liquid will be mixed with other ingredients. In order to visually verify the level of liquid 12 in the spout 11, this is provided with a level glass or level 51 tube. What is most preferred is an outlet valve which is a miniature pneumatic diaphragm valve (operated by air), similar to that used as a liquid intake valve, which can be closed or opened in 0.1 seconds. The load cell and extensometer 15 are programmed to react when they detect weight at the "load", "pre-zero" and "zero" reference points. The load cell generates analogous signals which are processed by a signal processing means 17, which selectively communicates with the quick-open and quick-closing valves which are the pneumatic operation valve 36 and the intake valve 23 of the diaphragm, in the charging cycle, and the pneumatic operation valve 21 and the diaphragm outlet valve 25 in the discharge cycle. In the specific illustration presented in this document, the signal means 17 (processor) includes computing means (computer) and amplification means 40 and 43 for the reasons that will be explained later; and, pneumatic valves (operated by air) are used. The solenoid valve 41 for pneumatically controlled air activates the pneumatic cam valve 21 and the outlet diaphragm valve 25. The solenoid valves 28 and 29 are disposed between the solenoid valve 41 for pneumatic air control and the valves 21 and 25 respectively, to allow the valves 21 and 25 to be closed independently. For this reason, valves 28 and 29 are called "intermediate" valves. The cross-sectional areas of the jet 11 and the plunger 13 are selected in relation to the amount of liquid to be weighed, so that the accuracy of the measurement is at least ± 3 percent. The weight of the plunger is adjusted so that its specific gravity falls within a range that is 10% to 100% greater than that of the liquid, typically 1.1 to 2 in the case of an aqueous liquid. It is clear that higher specific gravities may be used, although this would lead to a concomitant decrease in the accuracy in the weight of the liquid being loaded and discharged. The specific gravity of the plunger and its total weight are selected in relation to the speed of the liquid to be charged, so that the total weight allows the plunger to oscillate freely in the liquid as it is charged or fed, without appreciably affecting the sensitivity of the load cell to the weight of the liquid being charged. The dispenser typically has an internal volume comprised within a range that is 2 to 10 times greater than the volume of the quantity of liquid to be discharged; and the ratio of the internal cross-sectional area of the jet with respect to that of the plunger is comprised within the range of 3 to 20. Figure 2 is a graph of the magnitude of the output signal (millivolts) of the cell. loading with respect to the length (in inches) of immersion of the plunger, for a specific cylindrical jet having an internal volume of about 30,890 cm 3, equipped with a cylindrical plunger of approximately 68.6 cm in length having an outer diameter of approximately 4.11 cm and a weight of approximately 1.9 kg (used in the example given below). It is evident that the relationship between the output signal and the immersion depth of the plunger is linear. This information is processed to provide the amount of liquid (found) in the dispenser, and by difference, the amount of liquid dispensed. Referring to Figures 1 and 3, a schematic flow chart is shown to illustrate the overall functional interaction between the major components of the system. The load cell 15 detects a reference point and transmits an SI signal to the signal processor means 17, which can be a controlling medium such as a programmable logic controller (PLC), but which will preferably be a personal computer (PC) specifically programmed for the purpose in question, and which we therefore call a "dedicated PC" " A charging cycle starts with signal S2. When the filling level is reached as detected by the charging cell 15, the liquid is kept in the dispenser until the signal processing means starts the discharge cycle with the signal S3. Referring to Figures 1 and 4, the signal S2 energizes the solenoid valve 35, which operates the pneumatic cam valve 36 and, essentially simultaneously, opens the liquid intake valve 23. When the pneumatic cam valve 36 is opened, the main air supply of the diaphragm pump 33 also opens. Liquid 12 enters the spout 11 and continuously generates an SI signal until the plunger 13 is submerged to a preselected "fill weight" corresponding to the "load" reference point. This filling weight provides a first reference signal at the desired detected weight. Only the upper portion of the plunger is not submerged. In the (point of) fill weight there is more liquid in the dispenser than it is going to be filled. The pump 33 is switched off when the signal S2 is cut to the valve 35 for pneumatic air control. The cut of the signal S2 also closes the intake valve 23.

Referring to Figures 1 and 5, in the discharge cycle in which the third embodiment of the interruption is used, a signal S3 is sent to the solenoid valve 41 for pneumatic air control, which operates the valve 25. outlet, and simultaneously the air intake control valve 21 is opened to pressurize the spout and discharge the liquid. The intermediate valves 28 and 29 remain open. The details for this embodiment, as well as for the first and second, after the signal S3 initiates the discharge cycle, are described in Figure 6. Since the ratio of the horizontal cross-sectional area of the plunger diver with respect to the spout remains constant, and the specific gravity of the plunger is greater than that of the liquid, the weight of the liquid that is loaded in the spout is computed. From the foregoing description it will now be apparent that the batch jet system for charging very rapidly and then discharging a liquid essentially having a constant specific gravity from one charge to the next comprises; a supply tank, adapted to contain the liquid; a dispenser adapted to contain more liquid from the supply reservoir than will be dispensed in a single unit dose, the liquid being charged (to the dispenser) at a sufficiently high pressure and velocity to produce an unstable unlevel surface of the accumulating liquid at the spout, - pumping means in selective open flow communication between the supply tank and the spout; an elongate plunger adapted to submerge pendently along the charged liquid (to the spout), to a depth less than the length of the plunger measured vertically, and simultaneously to have the lower end of the plunger in a spaced-apart relationship with the bottom of the dispenser; essentially non-extensible means joined to the plunger, which can oscillate freely slope of the load cell and can rotate on the rod means in response to the forces exerted by the liquid in connection; a hermetically sealed load cell disposed within the spout, and connected to the non-extensible means; fast-acting liquid intake valve means in selective open-flow communication between the reservoir and the spout; fast-acting liquid outlet valve means in selective flow communication between the spout and the discharge outlet; fast-acting air intake valve means in open flow selective communication with the spout, to provide air at a pressure comprised within a range of about 2 bar to 5 bar; and, control means that respond to output signals from the load cell, programmed to send signals to activate the pump, to stop the pump, and to open and close the air intake valve and the inlet and outlet valves of the liquid. The load cell is adapted to measure a force exerted by the plunger, and to generate a continuous analog output signal that varies in response to forces that correspond to the load reference points, pre-zero and zero, respectively, being that the force corresponding to the charge reference point is less than the force corresponding to the pre-zero reference point, which in turn is less than the force corresponding to the zero reference point; the control means responds to the output signals corresponding to the load, zero and pre-zero reference points, so that it generates corresponding signals from the computer (computer) to start the liquid discharge from the dispenser, to interrupt the moment of the mass of liquid in the spout, and subsequently to reload the spout. Depending on the selected interruption mode, either the air intake valve means or the liquid outlet valve means respond, or both, to a computer signal (or computer) that is received when the pre-zero reference point is detected, which signal closes either or both valves. In each of the modes liquid is charged and the unit dose ± 3 percent is dispensed within less than 1 minute, without measuring the level or volume of the liquid contained in the dispenser, or weighing directly the liquid that supplies the same. The load cell is calibrated for a desired range of liquid weights to be loaded and discharged from the spout 11. As regards the reaction modifier liquids that are added to the concrete, it may be that a quantity as small as They are 3.7 mi per sack of cement that will have to be supplied in a concrete mixture that can contain only 5 sacks of cement (around 227 kilos), so that the unit dose will be 18.5 mi. On the other hand, it may be required up to 5.9 liters of accelerator per 1 bag of cement, and for a mixture of 11.5 m3 of concrete with 6 bags have to download up to 530 liters in about 45 seconds. To obtain the desired measurement accuracy within the preset time, the dimensions of the spout and the plunger (cross sections) are selected so that the desired unit dose can be discharged with an accuracy of ± 3% within 30 seconds. The dimensions of the spout and the plunger are selected according to the quantity of liquid that must be supplied. In a typical concrete plant several jets are used, each for a specific liquid. In that way, to discharge with liquid excretability in an amount comprised within a range of approximately 18.5 ml / sack to 1.5 liters / sack, with an accuracy of ± 3%, a spout preferably has a cross-sectional area comprised within a range of 176 cm2 to approximately 761 cm2, and is equipped with a plunger having a cross-sectional area comprised within a range of about 15.5 cm2 to about 39 cm2. This allows both loading in the dispenser, as well as discharging from the dispenser, a unit dose of up to approximately 5 kg, with a precision that is not less than that indicated above, within a (complete) cycle for filling and discharging approximately 15 hours. seconds to approximately 50 seconds. Returning to Figs. 1 and 3, which illustrate the specific system used in the present specification with the most preferred pneumatic valves in the field, the computing means 17 (the computer) includes amplifying means 40, 43 respectively. of the first and% second output signal, and a computer (computer) "PC" 45 programmable. The SI signal is transmitted simultaneously to the amplifiers 40 and 43. The amplifier 40 sends a signal S4 (not shown) to the PC 45, which generates two output signals S2 and S3, for the filling and discharging cycles, respectively . The amplifier 43 transmits an S5 signal (not shown) which activates the valve means to interrupt the moment of liquid being discharged. The output signal S2 of the PC 45 energizes an electrically controlled air control solenoid valve 35, which preferably has an overlap of manual control. The control air (for pneumatic valve operation) released by the air control valve 35 simultaneously (opens) a pneumatic valve 36 for quick opening and closing, and (also opens) a valve 23 for diaphragm liquid intake. The valve 36 could be a direct operated solenoid valve, but more preferably it will be a pneumatic cam and seat valve of the poppet series. (also known as "pneumatic seat valve") such as can be obtained commercially through the Cia. Automatic Valve Co. The control air operates to open or close the main source of air supply that is fed to the air diaphragm pump. In turn, the control air released by the pneumatic valve 36 of the rod and seat for active air (starts) the diaphragm pump 33. Alternatively, the output signal S2 for filling control could simultaneously drive any other pumping means, such as for example an electric motor for a centrifugal pump, and an intake valve 23 that uses electric current, - or the signal S2 could drive means hydraulics to activate the pump 33 and the intake valve 23. In this way, the filling cycle is completed. Before the start of the discharge cycle, S2 operates (closes) the solenoid 35, and the pneumatic valve 36 of the cam is de-energized, stopping the pump 33, and the intake valve 23 is closed. At the start of the discharge cycle, the outlet valve 25 is opened and liquid 12 is discharged until the PC 45 turns off the signal S3, which in turn closes the outlet valve 25. Turning to Figures 1 and 6, a first embodiment for interrupting the moment is as follows: When the load cell 15 detects the preset pre-zero reference point, the valves 25 and 21 are in the open position, being that it keeps the S3 signal open. Intermediate pneumatic valves 28 and 29 are also open, which are always open until they are instructed to close. The signal S3 keeps valves 25 and 21 open by ordering the solenoid valve 41 for pneumatic control air to provide air to open each of them. In the particular embodiment shown, the output signal to the valve 41 for pneumatic control air is generated in the amplifier 43, since the PC 45 is not programmed to provide the output signal. Preferably the control means is programmed to provide the signal, so as to avoid using the amplifier. When the plunger exerts a predetermined force at the pre-zero reference point, S3 keeps the valve 25 open, and a signal S4 generated by the internal relay of the amplifier 43 momentarily energizes the solenoid of the valve 28 for pneumatic control air normally open, so that it closes it. After approximately 0.5 seconds the signal S4 is cut off and the solenoid valve 28 is de-energized, thereby opening the air intake valve 21. The period (of time) between the energization and the de-energization of the solenoid is comprised within a range of 0.1 seconds to less than 1 second. A second embodiment for interrupting the moment is as follows: As in the one embodiment, when the load cell 15 detects the pre-set reference point pre-zero, the valves 25 and 21 are in the open position, as are the intermediate valves 28 and 29. The programmed controller means (to avoid the amplifier) provides a signal S4 energizing the normally open solenoid valve 29 for air of pneumatic control, closing it. When the valve 29 closes, the outlet valve 25 closes. After approximately 0.5 seconds the signal S4 is cut off and the solenoid of the valve 28 is de-energized, thereby opening the air intake valve 21. The period (of time) between the energization and the de-energization of the solenoid is comprised within the range of 0.1 seconds to less than 1 second. A third embodiment for interrupting the moment is as follows: As in the one embodiment, when the load cell 15 detects the preset pre-set reference point, the valves 25 and 21 are in the open position , as are the intermediate valves 28 and 29. The programmed controller means cuts the signal S3 when it is informed that the pre-zero reference point has been reached. This causes the pneumatic control air solenoid valve 41 to be de-energized, whereupon both valves 21 and 25 are closed. After about 0.5 seconds, the signal S3 is retransmitted to energize the solenoid 41 and reopen both valves 21 and 45 (it must be 25). The period between de-energization and re-energization of the solenoid is within the range of 0.1 seconds to less than 1 second. In each of the three preceding embodiments, after the moment is stopped at the pre-zero reference point and the discharge is reset to restore a portion of the liquid moment at the spout. When the zero reference point is reached, the signal S3 is turned off, whereby the valves 21 and 25 are completely closed. In specific detail, with respect to supplying a particular singular unit dose,. the spout system is calibrated for a zero reading at the "zero reference point" near the bottom of the plunger; a "load reference point" near the top (of the plunger), where the difference represents a unit dose; and a "pre-zero reference point" at 85% of the unit dose that is delivered, just above the zero reference point. To calibrate the system, whether or not the manual control overlap is provided by the computing means, the solenoid valve 35 for pneumatically controlled air is opened to energize the inlet valve 23 and charge liquid until the level in the Level glass 51 is located at a mark identified as "zero line". The calibration of the scale is then entered manually into the computer (computer) to recognize the zero line. More fluid is loaded until the "full of a unit dose" is loaded, which corresponds to a single unit dose. The unit dose is then discharged to the zero reference line, and the quantity supplied is weighed to determine the correlation between the detected weight (output signal in millivolts) and the weighed quantity. In PC 45 an input voltage is established that corresponds to the decreased force after the unit dose was supplied, which is received from the dispenser. If multiple doses are to be supplied, which are referred to as "filling to capacity", the dispenser is loaded to a level in the level glass corresponding to the total unit doses that will be supplied, as long as this level does not exceed the upper part of the plunger. To supply multiple unit doses, the output signal will be directly proportional since all the intermediate points are linearly related. The load reference point is also introduced to the computer (or computer) so that it recognizes the load reference point. Having received a unit dose, the voltage corresponding to the highest force exerted by the plunger is received by the PC, which is then ready to start the discharge cycle. Before starting the download cycle, the computer automatically performs an internal verification of the calibration to determine if the desired quantity loaded is within a pre-set precision, for example ± 3 percent. If it is outside the desired tolerance, the computer goes into a "hold" mode, which requires manual attention. If it is within the desired tolerance, start with the download cycle. Example 1 The effect of the pressure on the discharge accuracy using a fast acting valve with 0.5 seconds delay time (it takes 0.5 seconds to close completely after the closing started): To determine the effect of unloading a unit dose without interrupting the previous flow to an exit valve with 0.5 seconds of delay time before it is completely closed, the following illustrative computation is presented for the addition of a single unit dose of 473 ml of accelerator per bag of cement ( of 45.5 kgs), in a mixture of 7.65 m3 with 6 bags of concrete, that is, containing six bags of cement / m3 of concrete (7.65 m3). The unit dose is 28.4 liters of accelerator. The unit dose is discharged at a rate of 2.2 liters / second through a pipe with a nominal diameter of 2.54 cm (1 inch) which is in open flow communication with a pressurized jet at approximately 380 kPa with air. The time elapsed before the outlet valve begins to close includes the accumulated times (i) by the computer processing the load cell instructions, (ii) by the air to be moved from the valve solenoid 41 of air control of pneumatic control, before closing the solenoid, (iii) for the time it takes to transmit the pressurization air to the outlet valve 25, and (iv) for the time it takes to displace the air from the valve exit 25. Additionally, the actual closing time of the valve, after it starts, is 0.5 seconds. The elapsed time typically totals around 0.8 seconds. The amount of accelerator that is delivered in 0.8 seconds under the indicated conditions is approximately 1.75 liters, which is outside the allowable limit of ± 3% (the limit of + 3% permissible for 28.38 liters is 851 mi). The surplus assorted in 0.8 seconds is 893 mi. To compensate for the unwanted excess, the initiation of the closing of the outlet valve is signaled at the pre-zero reference point after 85% of the unit dose has been discharged, which in a specific instance is 0.11 seconds before the point of pre-established calibrated reference for the unit dose is detected by the load cell. This adjustment in 85% of the unit dose (which is the pre-zero reference point) is made in PC 45 (or amplifier 43) taking into account the position of the calibrated zero reference point, because the% Volume of liquid discharged can not be established in the applicator. Example 2 In a typical situation in which a concrete mixer truck should be filled with a specially designed concrete mix, the truck is placed to receive the liquid ingredients required for that particular designed mix. The operator enters (as data to the computer or computer) the pre-engineered designed mixture and enters the volume of the concrete batch contained within the truck. Automatically a charge cycle begins as described above. Upon detecting the charging reference point near the top of the plunger, the load cell sends a signal to the amplifier 40 indicating that the filling cycle has been completed. The discharge cycle does not start automatically until all the liquid ingredients are loaded. When the discharge cycle is already started, the moment is interrupted at each dispenser (since it is typical to use a plurality of dispensers) after approximately 90% of a unit dose has been discharged; and the discharge cycle is restarted (to continue) until the entire unit dose has been discharged. In each of the following runs the indicated accuracy of ± 3% is achieved within a total time period of the cycle of 50 seconds or less, depending on the size of the unit dose that must be supplied. To supply a small unit dose, for example 59 ml / bag of air retainer in a mixture of 7.65 m3 with 6 bags of cement, ie 3.5 liters in 10 seconds, using a spout having a diameter of 15 cm and a volume of 9832 cm3 with a plunger plunger having a diameter of 4.13 cm, the excess of liquid that would pass through an outlet valve with a delay time of 0.5 seconds and a total elapsed time of 0.8 seconds, is 218 mi . By interrupting the discharge when 3193 ml have been dispensed, the unit dose falls within the tolerance of 106 ml. To supply a large unit dose, for example 1794 ml / throttle sack in a mixture of 7.65 m3 with 6 bags of cement, ie 106 liters in 40 seconds, using a spout having a diameter of 30.5 cm and a volume of 88490 cm3 with a plunger plunger having a diameter of 5.1 cm, the excess liquid that would pass through an outlet valve with a delay time of 0.5 seconds and a total elapsed time of 0.8 seconds, is 6.5 liters, which is 3.34 liters above the tolerance. By interrupting the discharge when 95.8 liters have been dispensed, the unit dose falls within the tolerance of 3.19 liters. Example 3 Dispenser according to the prior art using a digital displacement meter: The particular meter used herein is a PFT-25 Concrete Additive Flow Transmission System meter manufactured by the Cia. Badger Meter, Inc. The meter functions as a mass flow indicator to charge a spout that operates in the "single unit dose" mode. The meter is used in combination with a computer (computer) that reads 10 counts / second. This meter is used to measure a unit dose that is introduced into a dispenser, before the unit dose is discharged to a concrete truck, since it is necessary to verify the unit dose before discharging it to the truck. The dispenser is equipped with a pair of probes, first and second (rods) placed vertically in a separation ratio, with the lower end of the first probe being a little above the bottom of the spout that the lower end of the second probe . A computer (computer) is connected to respond to the level of liquid that leaves the first probe, and then the second. A unit dose is considered as filled when the liquid level leaves the second probe. The meter has a maximum count rate of 10 counts / second, to suit the capacity of the computer, and each count corresponds to 29.6 ml, so it takes 80 seconds to load a unit dose of 23.7 liters in a pump. Ignoring that the load portion of the cycle is larger than 1 minute, and looking to discharge the unit dose in 20 seconds under an air pressure of 380 kPa, the discharge continues until the liquid level falls below a probe . When the probe stops being in contact with the liquid, the outlet valve closes. The lower part of the probe is positioned so that the delay time of 0.5 seconds is compensated for the closing of a fast acting outlet valve. Since the counts / second for the meter should be able to be read by a computer, even if the computer were able to read 15 counts / second it is clear that a total cycle time of 1 minute can not be met. Furthermore, at the end of the discharge cycle, the actual volume of liquid within the dispenser is not known, since the level may have dropped to various levels below the probe. In this wayEven though the meter can accurately load a unit dose, the quantity of the unit dose is uncontrolled, since the probe can only detect when the liquid level falls below it. Having thereby provided a general discussion, described in detail the overall method and illustrated the invention with specific examples of the best mode of carrying out the method, it will be apparent that the invention has met a long-expected need in the field of production. of concrete. It is therefore understood that undue constraints should not be imposed by reason of the specific embodiments illustrated and discussed, and particularly that the invention should not be restricted to a slavish adherence to the details set forth herein.

Claims (10)

1. CLAIMS 1. In a method for supplying a unit dose of liquid from a dispenser in a system comprising liquid outlet valve means through which the liquid must be dispensed, a gas inlet valve means through which Gas is introduced into the spout, an elongated plunger plunger partially immersed in the liquid, the plunger having a specific gravity greater than the liquid and a length greater than a range within the spout through which the piston varies. liquid level in the spout, and control means for receiving signals generated in a load cell that continuously detects the apparent weight of the plunger, being "that the control means transmit instructions to the valve means, the improvement is characterized in that it comprises, a) opening the outlet valve means to begin supplying the unit dose, b) opening an air intake valve means for introducing pressurization air into the dispenser in order to maintain a superatmospheric pressure of up to approximately 790 kPa, c) receiving a first signal in the control means, this first signal being proportional to the detected weight of the plunger when a pre-zero reference point is detected after a greater part of the unit dose has been dispensed, d) transmitting a first output signal from the control means to at least one of the gas intake valve means and the liquid outlet valve means, for interrupt the moment of the liquid in the spout, e) restore a portion of that moment, • f) receive a second signal in the control means, being that this second signal corresponds to the detected weight of the plunger when a point is detected zero reference, and then g) transmitting a second output signal to close the outlet valve means in less than 1 second; whereby the unit dose ± 5 percent is adapted to be supplied within a predetermined time portion, without measuring the level or volume of liquid contained in the dispenser, or directly weighing the dispensed liquid from the dispenser. The method according to claim 1, characterized in that the moment is interrupted by closing the air intake valve means when the pre-zero reference point is detected, and reopening the intake valve means A of air within 1 second, keeping the outlet valve means in an open position, and closing the outlet valve means in less than 1 second when the zero reference point is detected. The method according to claim 1, characterized in that the moment is interrupted by keeping the air intake valve means in the open position to keep the spout under pressure, closing the outlet valve means when the point is detected. of pre-zero reference, and reopening the exit valve means within 1 second, and closing the exit valve means in less than 1 second when the zero reference point is detected. The method according to claim 1, characterized in that the moment is interrupted by closing the air intake valve means when the pre-zero reference point is detected, and by reopening the intake valve means of air within 1 second, and essentially closing the outlet valve means simultaneously when the pre-zero reference point is detected, and reopening the outlet valve means within 1 second, and closing the outlet valve means in less than 1 second when the zero reference point is detected. 5. In a system for supplying a unit dose of liquid from a spout, comprising liquid outlet valve means through which the liquid must be dispensed, a gas inlet valve means through which gas is introduced in the spout, an elongated plunger plunger partially immersed in the liquid, being that the plunger has a specific gravity greater than the liquid and a length greater than the variation of the liquid level in the spout, and control means for receiving signals generated in a load cell that continuously detects the apparent weight of the plunger diver, being that the control means transmit instructions to the valves, the improvement that is characterized because it comprises, a) means to open the outlet valve means to begin to supply the unit dose, b) means to open a valve intake means of air to introduce pressurization air into the jet in order to maintain a superatmospheric pressure of up to about 790 kPa, c) load cell means to generate a first signal proportional to the detected weight of the plunger when a reference point is detected pre-zero after a greater part of the unit dose was filled, d) means for receiving the first signal in the control means, and transmitting a first output signal from the control means to at least one of the gas inlet valve means and the liquid outlet valve means, to interrupt the moment of the liquid in the spout for a period (of time) preselected, e) means for restoring a portion of that moment, and f) means for receiving a second signal in the control means, this second signal corresponding to the detected weight of the plunger when a zero reference point is detected, and , g) means for transmitting a second output signal to close the outlet valve means in less than 1 second; whereby the unit dose ± 5 percent is adapted to be supplied within a predetermined time portion, without measuring the level or volume of liquid contained in the dispenser, or directly weighing the dispensed liquid from the dispenser. The system according to claim 5, characterized in that the first output signal of the control means at least one of the gas inlet valve means and liquid outlet valve means interrupts the moment of the liquid for a preselected time period comprised within the range of 0.25 seconds to approximately 1 second. 7 The system according to claim 5, characterized in that the unit dose is supplied to a batch of wet concrete mixture, and because the liquid is a reaction modifying liquid that modifies the setting speed of the concrete mixture. The system according to claim 7, characterized in that the liquid is selected from the group consisting of an accelerator, a retarder, an air retainer and a water reducer. 9. In a system for loading a dispenser and discharging a unit dose of liquid from the dispenser into a discharge portion of a defined charge and discharge cycle, without directly measuring the weight of anything, or the volume or level of the discharge. liquid inside the dispenser that is charged with the liquid from a supply reservoir through liquid intake valve means and is discharged through liquid outlet valve means, in which the system includes control means to receive the liquid. signals generated in a load cell medium of which an elongated plunger is suspended which is partially submerged in the liquid, the improvement is characterized in that it comprises: (i) gas inlet valve means for controlling the gas flow of pressurization to the supplier, being the. fast-acting gas inlet valve means, in the manner of opening and closing in less than 1 second, in response to the output signals of the computing medium, (ii) the liquid inlet and outlet valve means that are each fast acting, such as opening or closing in less than 1 second, and in response to output signals from the computing means, and (iii) the load cell produces a signal that varies in response to the amount of liquid inside the dispenser that corresponds to a load reference point, to a zero reference point and to a pre-zero reference point, respectively, with the reference point being the load indicating the discharge portion and the availability of at least one unit dose, the zero reference point indicates that the unit dose was stocked, and the pre-zero reference point indicates that the greater part of a unit dose has been delivered, and (iv) that the control means this adapts to transmit a first output signal to interrupt the moment of the liquid flowing through the spout when the pre-zero reference point is detected, and to restore a portion of said moment within less than 1 second, and, transmit a second output signal to close the outlet valve means when the zero reference point is detected, whereby the unit dose ± 5 percent is adapted to be dispensed within 2 minutes. The system according to claim 17, characterized in that the portion of the moment is restored within less than 0.5 seconds, because the discharge portion of the filling and discharging cycle is less than 1 minute, because the means of valves open and close in less than 0.5 seconds and because the unit dose is delivered with an accuracy of ± 3 percent.