AN ARRANGEMENT FOR EXECUTION OF A CONTROL PROCEDURE, ESPECIALLY FOR SUPPRESSING DISTURBING INFLUENCES

Abstract: The invention regards an arrangement for the execution of a control procedure in order to give a magnitude, sensed by means of one or more sensing means a constant value or a course varying according to a given rule, "the preference value", said control taking place under influence of some means with a known transfer function. The new part of the invention is that the sensing means is arranged to transfer to an amplifyer a control pulse of electric nature, and that the amplifyer comprises one or more amplifyer means, each of them having two inputs as well as reaction circuit from the output of said amplifyer, connected to one of the inputs. Filters are provided in the reaction circuit of such a type that they will give the amplifyer a transfer function which has same general character as the inversed shape of the transfer function of the controlled magnitude.

Description: An arrangement for execution of a control procedure, especially for suppressing disturbing influences Most technical control procedures have for their purpose to cause a given way of operation of some arrangement, system, machine or the like Thereby, it is assumed, that this operation will vary in a way more or less out of control and that a control should be made either for keeping the operation at a constant value or to have it to vary according to a program, previously set. The first mentioned will be the most usual. Below, the given value or the value varying according to a given program will be called the "the preference Value" of the operation. Even if the control of this preference value is made in such a way that it is expected to be maintained, the control will nevertheless be disturbed by two different circumstances. First, it proves that the correction of the erraneous value so that it will assume the preference value will take place very slowly, and this may in many a case mean an essential disadvantage. Second, it proves that during the run of the correction procedure out side influences, often called "disturbing influences" or simply "disturbances", will influence the planned and intended control. Therefore, this will in part run too slowly, in part and in addition thereto not run in the intended way. Below, a couple of typical examples shall be mentioned: In systems for feedingwarmwater to a tap-off system, for instance in a living house, it has been usual to collect from a heat exchanger fed with hot water from a boiler warmw'ater to tubing system, comprisin a number of tap-off places. One or more feeder conduits from a cold water network are connected to this tubing, so that successively, when warm water is tapped off will cold water be fed but this will then cool down the warm water in the distribution circuit. Hitherto, one has usually expected that by the action of the heat exchanger warm water will be created by heat fed with the hot water to the primary side of the heat exchanger, but this feed of heat usually takes place rather slowly and an inconveniently long period of time will lapse until ohe water in the distribution circuit to the tap-off places has again assumed the desired temperature, which is, in this case, the prefe ence value. If the warm water supply conduit is subjected to a tap-off of constant and moderate speed of movement, which is also preferably contiguous, then the operation for feeding heat from the hot water boiler and through the heat exchanger would follow a give program easily stated. Unfortunately, however, one cannot count with this, but th? tap-off will instead usually last for short periods of time and, thereby, not even have a constant speed of movement but a very variable speed of movement, and the time during which the tap-off takes place, may vary rather much. These circumstances cause such disturbances as mentioned above. Another, however less important disturbance is created from the boiler from which the hot water is fed to the heat exchanger requiring some time for re-heating the water to to the value indicated by the boiler thermostate, and this time will also be variable to some extent dependent upon if the water in the tap-off conduit has been strongly cooled or only cooled to a small extent, as well upon the speed of its cooling. Another example may be mentioned: Nowadays one uses to a great extent so called climatization systems for maintaining or creating, respectively, a given agreeable temperature inside of a building. If this temperature should rise or sink, the climatization system shall act to restore it to the preference value. In some cases, it is allready known how the mathematical functionisshaped indicating the relation between heat fed and the existing need for feeding heat. In other cases, one may easily on experimental basis state this function such as it would exist under normal strady circtumstances. Firstly, however, the correction of the temperature in the building to its preference value will take place rather slowly, and, second, also in this case there will exist disturbances changing the functional relations, for instance if one opens a window in the room in which the teperature is sensed and lets in cold out-side air so that a quick cooling of the air will enter, which is indicated for compensation to the preference value, or if one starts some machine device in same room which will, by the heat given off, change the said functional relation. Many other circumstances also may act as disturbances. Amongst them should be mentioned the out door temperature, because at lower out door temperature will the heating take place more slowly, further the existing wind pressure on the out side of the building because there will bazaar a cooling effect at strong wind pressure. Further the moisture of the air, the mass of solid constituents in the building, existing heating from sun shine directed onto the building and much more will have an influence. The present invention regards an arrangement intended to do away with at least the first mentioned inconvenience but preferably with both of the above mentioned inconveniences, which means that by the arrangement according to the present invention shall anyway the course of control be accelerated, but, preferably, in addition thereto, shall this course of control follow a function known in advance, taking regard to tise functions of such disturbing circumstances, examples for which having been mentioned above. Thus, the invention regards an arrangement for the execution of a control for giving a magnitude sensed by one or more sensors a constant course or a course varying according to a pre-determined rule, below referred to as the "preference value", said control taking place under influence of means having a known transfer function. According to the intentzon-i*he:sensor means is arranged to transmit to an amplifyer a control pulseofelectric character, and the amplityer comprises one or more amplifyer means each of them having two inputs and a reaction circuit conneted to one of said inputs from the output of same amplifyer, filters being provided in the reaction circuit of such a kind that they will give the amplifyer a transfer function having same general charcter as the inversed function of the transfer function of the controlled magnitude. Of course, the invention is not limited to the two possibilities of use mentioned above, but it may be used in a very great number of control procedures of the most different types. As a chosen example, the use of the invention will be described below in the first mentioned case of controlling the warm water tempe rupture in a warm water distributipn conduit fed from a heat exchanger said heat exchanger being fed in one way or another on its primary side with heat, usually by its primary side getting hot water from a boiler Thereby, the invention will be further explained in connection to the attached drawings in which Fig 1 shows a schematical picture of a very simple such warm water distribution conduit, Fig 2 and 3 show a couple of diagrams for explaining the operation of the invention, Fig 4 shows a diagram in very simplified form of the arrangement for solving the problem forming basis of the invention, and Fig 5 shows a wiring diagram of an amplifyer contained in the arrangement according to Fig 4. Fig 6, finally, shows a diagram of a more advanced system for same purpose, mainly corresponding to the way of explanation in Fig 1. The invention, however, is neither limited to the specific uses or to the specific srrangements thus described as examples, but all different kinds of modifications may be made within the frame of the invention. In Fig 1, the warm water distribution conduit is indicated by 10. It is in a way known per se arranged as a closed loop in which the worm water is kept circulating by means of a pump 11. A number of tap off places 12 are schematically indicated. For replaceing the tapped off water the loop 10 is connected by means of the conduit 13 to a water distribution net work. In the usual way, there is included in the conduit 13 firstly a shut off valve 14 and eecondly a back valve 15, but they have, of course, no decisive importance for the present invention. The loop 10, finally, runs through the secondary 16 of a heat exchanger 17 the primary 18 of which is fed by hot water. 6f course, the primary 18 may be replaced by some other suitable source for feeding heat to the warm water distribution loop 10. So far the invention is earlier known. Now, it is obvious thct if water is tapped off at anyone of the tap off places 12, then warm water will be removed from the loop 10 and for replaceing this warm water cold water will be fed through the conduit 13, and there will be a cooling of the water in the loop 10. A heat exchanger of the type shown at 17 will normally work the way that a constant but weak transfer of heat will take place from the primary 18 to the secondary 16 to compensate for the loss of heat which cannot be avoided by heat being given off from the conduit 10 to the surroundings, e.g. the walls of the house and so on, as long as no tap off takes place, and a stationary thermodynamic state of balancy will therefore exist. When warm water is tapped off so that the temperature of the wator in the loop 10 inclusive of the secondary 16 of the heat exchanger 17 sinks, the difference of temperature between the primary and the secondary of the heat exchanger 17 will increase, and more heat is transferred from the primary to the secondary, until the state of balancy is again restored. Different heat exchangers have different transfer functions for heat, With "transfer function" in this case is understood the mathematical relation T W f'(t) for transfer of heat in which T is the temperature in the heat exchanger secondary and t is the time. Therefore, one cannot give any common rule for the heat transfer common to all such heat exchangers, but this may easily be stated for each separate heat exchanger or still better for each separate system, and one may thereafter set up a program according to which one accelerates give off of heat so that the stationary state will be achieved quicker than would have been the case in the traditional arrangement said above to be known. The transfer function corresponding to this program, however, is influenced by the speed of the tap oftçand/or by the amount of water tapped off and by otier--circumstonces. For this purpose, one introduces in some place demonstrative to the warm water distribution conduit 10, preferably immediately after its exit from the heat exchanger 17, a sensor means 19 which senses the existing temperature and transforms the indication into an electric current or voltage, distinctly indicating the temperature of the warm water at the place concerned in the warm water conduit 10. Also this sensor means has a transfer function E = f"(T,t), in which E is, for instance, an electric voltage. The two mathematic functios f' and f", most probably, are not identical The sensor 19 is connected to a device 20 in which the created indicational voltage or current is treated in accordance with the. program which has, in advance, been set up for the transfer of heat in the heat exchanger 17. In this treated form, incitament to the correction is transferred to a controller 21 mechanically influencing a valve 22 and/or electrically influencing a pump (not shown in the drawing) or in other way taking care of a quicker feed of heat carrier medium and/or feed of heat carrier medium of a higher temperature to the primary of the heat exchanger 17. In a way, which will be evident from the following, the apparatus 20 is programmated to create a transfer funciion which, as to its general character as closely as possible agrees with the inverted form of the transfer functions of the heat exchanger 17 and of the sensor 19. Thereby it should be observed that the invention is not limited to the specifically described embodyment according to Fig 1, but that it may also be used in many other cases, and that the said transfer functions may assume the most different forms so that no general form con be stated for them for common use, but one will have either to know in advance the transfer functions or in some suitable way experimentally or by earlier measurements to state the transfor functions. One example for means for this purpose will be given in the following in connection with the description of the device 20. Thus, the device 20 is shaped in such a way that it will register tendencies in the sensor 19, and, guided by them, create a prognosis of the deviation of the preference value, said prognosis being transferred to the controller 21, such that the transfer of heat will take place essentially quickerSEhcn would;hove been the case, if there had been no arrangement of sensor 19, device 20, controller 21 and valve 22. In such a case, as a matter of fact, the transfer of heat would have been controlled exclusively by the difference between the temperature, sensed by the sensor, and the preference value, as described above. With other words, one could say that one has knowing the transfer function made a prognosis and introduced the inverse form of the transfer funciion into the system whereby one has got the result that the correction of the temperature took place essentially quicker. It is without decisive importance to the invention in what way this quicker correction has been created. For instance, it may as shown in Fig 1 be provided by opening a larger through let area in a valve but it may instead or in addition thereto be provided by increasing the power of a pump and/or by increasing the temperature of the hot water fed to the primary of the heat exchanger or in any deliberate other way. The choice of such a way will be within the usual knowledge of the man skilled in the art. In this way, one has by means of the invention dor away with the first mentioned disadvantage of too slow a correction of the temperature of the warm water by correction of the occuring drop of temperature in the warm water distribution loop, but one could not, by these means, do awaywith the other one of the said disadvantages, viz the influence of disturbances ct one type or another, for instance the disturbance emanating from a difference in character of the transfer functions of the heat exchanger and the sensor. As example for a disturbance, the irregular change of the temperature of the water in the loop 10 was mentioned, dependent upon if the tap off takes place with a high volume speed or with a low speed and dependent upon the duration of the tap off. The sensing of the quicker or slower decrease of the temperature of the water in the loop 10 may take place in many different ways. In the present case it takes place by using the temperature sensor means connected into the ccnduit 10, the indication of which in the form of an electric voltage or current being transferred to the device 20. If the temperature of the cold water does not vary too much one could instead cf the said arrangement connect Åa n4ns 24 in the cold water feeder conduit. This means 24 will indicate inh;-form of on electric current or voltage an adequate valueofthe'feed of cold water which will, in turn, adequately indicate the decrease of temperature. This means 24 is connected to the device 20. The indication from the means 19 used or 24 or the like thereby will influence the transfer function in such a way that a compensation will be created for the disturbing influence concerned. Thus, it is important to the invention that the general character of the transfer function of the heat exchanger 17 as well as the one of the disturbing influences of said transfer function is known. These influences, likewise, are called transfer functions. They may be of very different kind for different disturbing influences. In a way which will be apparent from the following, therefore, compensation has to be made separately for each of them. Below, the compensation for one of the disturbing influences will be further clarified, viz. the one, caused by dissimilar shape of the transfer unction of the sensor means 19. The further disturbances perhaps existing, of course, also should be compensated for, and thereby one will have, by measurement or be earlier experience to know the general character of the influence of said disturbing influences on the transfer function of the heat exchanger. In Fig 2 a curve is shown as an example of the transfer function of the heat exchanger 17. Along the vertical axis, the temperatur of the water on the secondary side 16 of the heat exchanger 17 is plotted, for instance as it exists at the connection point of the sensor 19, and along the horizontal axis time is plotted at normal correction in a way known per se. In the chosen-example, it has been assumed that the transfer funcion, as often is the case, will follow a curve of continuous change of the slope, so that one may construct a time constant T'. The device 20 is of such a kind that it will create a control operation for the controller 21 by hwhihch viz the heat transfer will fol- In wnicn low a curve indicated in Fig 3/the time constant has been decreased from the value T' to the value T". With some approximation one may assume that an observable decrease of the temperature of the warm water has occurred and that the correction of the temperature along the known principles would take place very slowly as evident from the curve according to Fig 2. The change of the time constant T' of Fig 2 into the time constant T" of Fig 3, then, could be said to be a re-shaping of the function in inverse shape according to which the decrease of the temperature initially took place. In the way mentioned above, this will cause a quicker compensation of the decrease of temperatur of the water in the loop 10 perhaps existing. Further, however, the temperature transfer in the heat exchanger 17 will be influenced by disturbances, in the chosen example thus disturbances due to variably quick decrease of temperaturg observed either by means of the sensor 19 or the sensor 24. In Fig 4, in shematical form, an arrangement is shown, which may be used for the purpose of the device 20. Principally, the arrangement 'according to Fig 4 comprises two amplifyers 25 and 26, each being programmated per se to a transfer function, the one of them, e.g. the amplifyer 25, to the transfer function of the heat exchanger 17, and the other one, e.g. the amplifyer 26, to the transfer function of the sensor 19. These amplifyers are coupled for reaction in a way, which is known for instance from Graeme, Tobey and Huelsman, Operational Amplifyers, Design and Applications MscGraw- Hill Book Company, 1971, pages 455 - 457, said amplifyers having two inputs 27', 27" and 28', 28" counteracting each other. Here, first, the operation of the amplifyer 25 will be described. Thus, the indication from the sensor means, e.g. the sensor 19, is impressed onto the input circuit 27', whereas a reaction circuit is connected to the ihput circuit 27". The reaction circuit comprises a resistor 29 and a condenser 30 in parallel, but this, of course, only is to be regarded a chosen embodiment of a filter, comprising one of the means for providing the transfer function, the other means comprising, in the chosen example, a series connection of a resistor 31 and a condenser 32 provided between the the imput 27" and ground. By adjustment of the resistance value of the resistor 29 and the capacity of the condensor 32, one may create the inverse function of a great number of transfer function, existing in practice. The resistor 29 and the condensor 32 have been shown with the usual indication for adjustable means. However, the intention is that they should either be ad3u.t.y'oe fpJr.l!toogree with a known transfor function or automaticallybe re-adjusted to agree with perhaps occu rinindications from transmitters not shown in the drawing in the form of sensors or the like. The condensor 30 mainly acts as a decoupler condensor, and the resistor 31 mainly acts as a damper for occuring oscillations. The shown arrangement, in which the inverse transfer function, see Figs 2 and 3, of the heat exchanger has been simulated as to its general character by means of the resistor 29 and the condenser 32, will give a similarity which is acceptable in many a case, but if in one or more cases the transfer function should be essentially different, the man skilled in the art will know, on basis of his usual skill another construction of the filter satifying the demand for similar shape with the inversed transfer function of other character. As mentioned above, the amplifyer 26 is intended to create compensation for the transfer function, shaped in another way, of the sensor 19. The resistor34 of the amplifyer 26 is connected in parallel with a condensor 35 to the input circuit 28", and this is grounded via a series coupling of a resistor 36 and a condenser 37. As in the coupling of the amplifyer 25, the transfer function of the amplifyer 26 is determined, in first place, by the resistor 34 and the condenser 37, whereas the resistor 35 in first place forms a de-coupling condenser and the resistor 36 forms a damper resistor for oscillations perhaps occuring. By adjustment of the values of the combination of the resistor 34 and the condensor 37 one may provide a filter giving a transfer function oftheamplifyer 26, which will, as to its general character, be in accordance with the inversed relations of the transfer function of the sensor 19. As in the arrangement according to the above mentioned litteratur reference, the reaction thus takes place to amplifyers having two inputs counteracting each other 27' 27" and 28', 28" respectively. As the heat exchanger 17 and the sensor 19 are assumed to have different transfer functions, one should provide separate amplifyers for them. Thereby, these amplifyers are reactively connected via filters causing an inverts imitation-of the transfer functions concerned. In the embodiment Xb#oribed xnWconnection with Fig 4 it has been assumed that this irnitationof the transfer functions concerned could be provided by means of simple filters comprising the resistor 29 and the condensor 32 or the resistor 34 and the condensor 37, respectively. This, however, should only be understood as a chosen example Other transfer functions will require filters of a different type, In dimensioning the means taking care of the reaction past the amplifyers 25 and 26 and so on, of course, one will have to ensure in some way known per se that the reaction must not be so strong that self oscillation is created. The output from the amplifyer 26, in this case, is directly or indirectly connected to the controller 21, which receives a signal from the indicator of the preference value 38 and controls the valve 22. If there should exist seve-ral parts of the system, each having its own transfer function, between the means controlling the operation and the sensor means, one will have to connect in a way, shown in Fig 4, further amplifyers 39 of same type as the amplifyer 26 along with the means pertaining thereto, especially the filter forming means, said kilters, which may for instance comprise a resistor and a condenso allthough they may also be built up in some other way, should, of course, have suitable transfer functions to create the inverse imitations of the transfer functions of the parts concerned. The man skilled in the art will immediately understand how such a connection of further amplifyers will take place. Operational amplifyers of the type appearing at 25 and 26 in Fig 4 nowadays are made as standard articles, usually in a completely moulded in state, and they are available in open trade. When using the present invention one may use any deliberate one of these known operational amplifyers, provided that it has two inputs counteracting each other One example for such an operational amplifyer in shown in Fig 5. Thus, this operational amlifyer has two input conduits 39 and 40, respectively, corresponding for instance to the two inputs 27', 27" in Fig 4. Each of the two input signals over the conduits 39 and 40 is amplified in the tNpobofinoìomplifyer-according to Fig 5 by means of two transistors in cascade, viz. as far as regards the input conduit 39 the transistors 41 and 42 and as far as regards the input conduit 40 the transistors 43 and 44. They get common operational voltage from the mains conductor 45 past a rectifyer 46. For stabilization of the two transistor groups 41 - 42 and 43 - 44, respectively, they are grounded via one transistor 47 and 48 respectively, each. The reaction voltage then will exist in amplified form in the conduit 49. Usually, this voltage will scarcely be sufficiently strong to be used as control voltage for the controller 21, Fig 1, and therefore it is further amplified in a transistor 50 getting its voltage from the mains 45 past the rectifyer 51. The transistor 50 is by-passed by means of a de-coupling condenser 52. The amplified output voltage therefore will exist in the conduit 53. In Fig 6 an alternative embodyment of the arrangement according to Fig 1 is shown. It is obvious that the invention shall not be limited to the specific embodiment shown in Fig 1. However, it should be observed that the invention shall even not be limited to compensation of temperature in a system for delivery of warm water to tap-off places, but that it has an essentially more extensive possibility of use. One example of such a use has been mentioned in the pre-amble, viz. for controlling the feed of heat to a system for climatization of a building. In the arrangement according to Fig 6, warm water is collected to the warm water loop and the different tap off places from a water heater 55 with an electric heater winding or a hot water loop f6 fec from a boiler. The water heater comprises a tank of large volume. The output conduit 57 is connected to a three-way valve 58, the output of which is connected to the warm water loop 54 and its tap-off places 59. Near the output from the three-way valve 58 a sensor 60 for the temperature of the water in the conduit 54 is provided, and its indication circuit runs to an apparatus 61 corresponding to the device 20 in Fig 1. The pump 62 takes care of circulation in the warm water loop 54. From the output side of the pump 62 a first conduit 63 runs to the input side of the warm water loop 54 at a place close to the connection place of the sensor 60, and a second conduit 64 runs to the water heater 55. In each of the two last mentioned conduits a back current valve 70 and 71, respectively as well as a shut off valve 72 and 73, respectively, is connected. The cold water conduit 74 connected to the cold water system, likewise comprises a back current valve 75 as well as a shut off valve 76. As in the arrangement according to Fig 1, the apparatus 61 may be influenced not only by the temperature in the warm water distribu tion conduit 54 but also by one or more indications of disturbing influences. From the apparatus 61 a conduit 77 runs to a motor 78 for adjustment of the three-way valve 58 so that this valve will at need for a restitution of the temperature of the warm water in the loop 54 be re-adjusted to feed a greater quantity of water heated in the water heater 55 via the conduit 57 or vice versa. If there should be no temperature drop in the warm water distribution conduit 54, then the circulation would run from the place of connection of the sensor means 60 and the conduit 63 past the tap off places 59 and through the pump 62, the shut off valve 72, the back current valve 70 and the branch conduit 63. In reality, however, even if no taF off of war water should take place, there will be a smaller temperature drop due to heat leaking away to the surroundings, for instance to the walls of the building and so on. The temperature drop is sensed by means of the sensor 60, which administrated its indication to the apparatus 61 which is of the type shown in Fig 4. By this, an incitament is transmitted to the motor 78 of the three way valve 58 for such re-adjustment of said valve, that a correction of the temperature of the warm water will take place in quick order and taking regard to the really existing drop of temperature as well as to any disturbing influences, perhaps occuring. Thereby, cold water is fed from the conduit 74 to one input of the three way valve 58, and also hot water from the water heater 55 to another input of same three way valve. Mixed water of correct temperature, thereafter, will be fed out to the warm water loop 54 by a third connection to the three way valve.

Claims: Claims 1. An arrangement for the execution of a control procedure in order to give a magnitude, observed by means of one or more sensors (e. g. 19,60) a constant value or a value varying according to a predetermined rule, below referred to as the "preference value", said control taking place under influence of a means (e. g. 17) having a known transfer function, c h a r a c t e r i z e d t h e r e b y that the sensor (19, 60) is arranged to transfer to an amplifyer (20) a control incitqment of electric type, and that the amplifyer (20) comprises one or more amplifyer means (25, 26) each of them havingtwo inputs (27', 27" and 28', 28", resp.) and a reaction circuit connected to one of said inputs (27", 28") from the output of same amplifyer (25, 26), filters (e.g. 29, 30, 31, 32) beings provided'in said reaction circuit of such a kind that they will give to the amplifyer a transfer function having same general character as the inverse shape of the transfer function of the controlled magnitude. 2. An arrangement according to claim 1 in which the deviation from the preference value is dependent also upon disturbing influences, c h a r a c t e r i z e d thereby that a plurality, e.g. two amplifyers (25, 26) with reaction of the type mentioned above are connected in cascade to the correction means, one of said amplifyers (25) being provided with a filter (29, 30, 31, 32) in its reaction circuit adjusted in accordance with the inverse shape of the general character of the transfer function of the controlled magnitude, the other one or ones of the amplifyers (e.g. 26) being provided each with its filter (34, 35, 36, 37) in the reaction circuit, adjusted in accordance with the inverse shape of the general character of the transfer function of each separate disturbing influence. 3. An arrangement according to claim 1 or 2, c sn a r a c t e r i z e d thereby that a resistor (e.g. 29) and a condensor (e.g. 32) are contained in the Filters contained in the reaction circuit or circuits, repectively, said resistor and condensor in common being adjusted at least substantially to make sure the desired transfer function. 4. An arrangement according to claim 3, c h a r a c t e r i z e d thereby that a de-coupling condensor (e.g. 30) is connected in parallel to the resistor contained in the filter, and that a damping resistor (31) is connected in series with the condensor (32) connected between the reaction input and ground. 5. An arrangement according to any of the above claims, c h a r a c t e r i z e d thereby that one or more of the adjustable filters are are controlled each from its transmitter for adaption to the transfer function concerned.

Inventors: SEIDLITZ, JOACHIM
Applicants: TOUR & ANDERSSON AKTIEBOLAG
Application year: 1984
Main classification: G05D23
IPC codes: G05D23