CZ20031074A3 - Method of and system for controlling the ratio of a variable lead parameter and an adjustable lag parameter for a lag-lead process - Google Patents

Abstract

In a method of and system for controlling the air/gas ratio in a lag-lead combustion plant the lead and lag parameters are monitored to provide lead and lag signals representative of the values of the parameters. These are compared to provide an error signal representative of the deviation of the ratio of the lead and lag parameters from a preselected ratio. The lag parameter is then adjusted to reduce the deviation in response to the deviation exceeding a preselected deviation.

Description

A method and a system for controlling the ratio of a variable supply parameter to an adjustable retention parameter in the process of controlling these parameters

Technical field

BACKGROUND OF THE INVENTION The present invention relates to a method and a system for controlling the ratio of variable supply parameter and adjustable retention parameter in a process for controlling these parameters, generally referred to as the lag-lead process, and more particularly, but not exclusively. air / gas) in a gas combustion plant.

State of the art

It is known that the air to gas ratio in a gas combustion plant should be kept constant in order to achieve maximum efficiency of the plant. To maintain the ratio of air to gas, regulators of this ratio are used, which are to be maintained even when the amount of gas supplied is reduced or increased and which are to adjust the air flow accordingly, usually by means of a valve in the air duct.

A problem with existing regulators for the ratio of air supply to gas supply is the difficulty of adjusting the air supply value to exactly match the gas supply value. The present invention is therefore directed to providing an improved method and system for controlling the air / gas ratio.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved method for controlling the ratio of variable supply parameter and adjustable retention parameter in a process for controlling these parameters, and a system for controlling the ratio of variable supply parameter and adjustable parameter.

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- retention in the process of controlling these parameters, which method and system achieve accurate control of the gas and air supply relative to each other so as to achieve a constant maximum effective ratio for a given purpose.

The present invention solves a method for controlling the ratio of a variable feed parameter to an adjustable retention parameter in a process for controlling these parameters, the subject matter of the invention comprising: monitoring a feed parameter and generating a feed signal representative of a feed parameter value; monitoring the lag parameter and producing a signal representing the value of the lag parameter; comparing both of these signals and generating an error signal representing a deviation from the preselected ratio of the feed parameter to the containment parameter; setting a lag parameter to reduce this deviation in response to a deviation in excess of the preselected deviation.

The invention is also directed to a method comprising comparing an error signal with a preselected threshold and adjusting the lag parameter in response to the error signal in excess of the preselected threshold.

The invention is further directed to a method comprising comparing an error signal with an error range determined by a first, upper preselected threshold and a second, lower preselected threshold, and adjusting the lag parameter in response to the error signal falling outside the error range.

The invention is also directed to a method comprising: adjusting the lag parameter to reduce the ratio of lag and lead parameters in response to an error signal that is above the error range; and adjusting the lag parameter to increase the ratio of lag parameters to supply in response to an error signal that is below the error range.

The invention is further directed to a method wherein the first, upper preselected threshold is a positive value and the second, lower preselected threshold is a negative value; a positive error signal indicates an increase in the air / gas ratio from the preselected ratio and a negative error signal indicates a decrease in the air / gas ratio from the preselected ratio; and that the method comprises: adjusting the containment parameter to reduce the ratio of the parameters • · · ·

-3 retention and supply in response to a positive error signal exceeding a first, upper preselected threshold; and adjusting the lag parameter to increase the ratio of lag and lead parameters in response to a negative error signal exceeding a second, lower preselected threshold.

The invention is also directed to a method wherein the threshold or each of the preselected thresholds is a fixed value.

The invention is further directed to a method wherein the threshold value or each of the threshold values is a function of the value of the containment parameter.

The invention is also directed to a method wherein the step of comparing the error signal to the or each threshold comprises adjusting the threshold in dependence on the value of the lag parameter and comparing the error signal to the adjusted threshold.

The invention is also directed to a method comprising: providing a tracking table for storing a plurality of threshold values; and a step of adjusting said threshold value comprising selecting one of said thresholds depending on the value of the lag parameter.

The invention is further directed to a method wherein the threshold or each of the thresholds comprises a plurality of threshold levels; and the step of comparing the error signal to the or each threshold value comprises selecting a threshold level for that threshold value depending on the value of the lag parameter and comparing the error signal to the selected threshold level.

The invention is further directed to a method comprising: providing a tracking table for storing a plurality of threshold levels; and a threshold setting step comprising selecting one of these threshold levels depending on the value of the lag parameter.

The invention is also directed to a method wherein feed and containment parameters are feed fluid flow and delay values in an industrial process; and where the method comprises: measures • · · 9

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- valve delay means for regulating the flow of retention fluid; monitoring the position of said valve means to delay opening or closing said valve means; monitoring the flow of retention fluid when the valve means is opened or closed; comparing the change in position of these valve means with the change in flow rate of the retained fluid; and adjusting a threshold in response to this comparison indicating a change in the characteristic of the valve means.

The invention is also directed to a method wherein the threshold setting step comprises setting thresholds or levels in the tracking table.

The invention is further directed to a method wherein the feed parameter is a flammable gas flow rate; the lag parameter is the air flow rate; and the process is a combustion process.

The invention is also directed to a control system for arranging a containment and supply control in a process having a variable supply parameter and an adjustable containment parameter, the system comprising: supply monitoring means for monitoring the supply parameter and generating a supply signal representative of the supply parameter value; containment monitoring means for monitoring the containment parameter and providing a containment signal representative of the value of the containment parameter; comparing means for comparing feed and containment signals and producing an error signal representing a deviation of the ratio of feed and containment parameters from a preselected ratio; and adjusting means for adjusting said lag parameter to reduce said deviation in response to a deviation exceeding a preselected deviation.

The invention is further directed to a control system further comprising: a threshold value means for providing a preselectable threshold value; comparing means for comparing the error signal to a preselectable threshold; and that the adjusting means is operable to adjust the lag parameter in response to an error signal exceeding a preselectable threshold.

· · Φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ

The invention is also directed to a control system wherein the threshold value means comprises first, upper threshold value means for providing a first, upper preselected threshold value and a second, lower threshold value means for providing a second, lower preselectable threshold value, thereby defining a error range; the comparing means is operable to compare the error signal to an upper and a lower preselectable threshold; and the adjusting means are operable to adjust the lag parameter in response to an error signal falling outside the error range.

The invention is also directed to a control system wherein the adjusting means are operable to adjust the lag parameter to reduce the ratio of feed and lag parameters in response to an error signal that lies above the error range and to adjust the lag parameter to increase the ratio of feed and lag parameters in response to the error a signal that is below the error range.

The invention is further directed to a control system wherein the first, upper preselected threshold is a positive value and the second, lower preselected value is a negative value; a positive error signal indicates an increase in the ratio of supply and containment parameters from this preselected ratio, and a negative error signal indicates a decrease in the ratio of supply and containment parameters from this preselected ratio; and the adjusting means are operable to decrease the ratio of the feed and contain parameters in response to a positive error signal exceeding the first, preselected threshold value, and to increase the ratio of the feed and contain parameters in response to a negative error signal exceeding the second, lower preselected threshold.

The invention is also directed to a control system wherein the threshold or each threshold is a fixed value.

The invention is further directed to a control system wherein the threshold value or each of the threshold values is a function of the value of the containment parameter.

The invention is also directed to a control system which further comprises adjusting means for adjusting a threshold value as a function of the value of the containment parameter and wherein the comparative

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-6 means are operable to compare the error signal with the set threshold value.

The invention is further directed to a control system wherein the threshold value means comprises a tracking table for storing a plurality of threshold values; and the threshold value adjusting means is operable to adjust the threshold value by selecting one of the threshold values depending on the value of the lag parameter.

The invention is also directed to a control system, further comprising: adjusting means for adjusting a threshold value as a function of the value of the containment parameter; and that the threshold or each of the thresholds comprises a plurality of threshold levels; wherein the threshold value adjusting means is operable to adjust the threshold value by selecting one of the threshold levels depending on the value of the lag parameter; and the comparison means is operable to compare the error signal to the allowed threshold level.

The invention is further directed to a control system wherein the threshold value means comprises a tracking table for storing a plurality of threshold values; and the value adjusting means is operable to adjust the threshold value by selecting one of the threshold values depending on the value of the lag parameter.

The invention is further directed to a control system wherein the supply and containment parameters are flow rates of the supplied and retained fluid in the process; and wherein the control system comprises: a containment valve means for controlling the flow of the containment fluid; position monitoring means for monitoring the position of the containment valve means when opening or closing the containment valve means and providing a position signal representing them; wherein the containment monitoring means is operable to monitor the flow rate of the containment fluid when opening and closing the containment valve means, and a flow value signal representing them is provided; and wherein the control system further comprises: storage means for storing sampled values of the position and flow signals representing a preselected characteristic of the containment valve means; second comparing means for comparing the position of the valve

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-7 valve retaining means and retained fluid flow as the retaining valve means are moved by stored values; and second adjusting means for adjusting the threshold value in response to the comparison indicating a change in the characteristic of the containment valve means.

The invention is also directed to a control system wherein the supply and containment parameters are flow rates of the feed fluid and the fluid retained for the process; and the control system comprises: valve retention means for controlling the flow of retention fluid; positioning monitoring means for monitoring the position of the containment valve means when opening and closing the containment valve means and providing a position signal representing them; wherein the containment monitoring means is operable to monitor the flow rate of the retained fluid when opening and closing the valve means and providing a flow value signal representing them; and wherein the control system further comprises: storage means for storing sampled values of the position and flow signals representing a preselected characteristic of the containment valve means; second comparing means for comparing the flow rate of the retained fluid during movement of the valve means by a stored value corresponding to the monitored position of the retaining valve means; and second adjusting means for adjusting the threshold value in response to the comparison indicating a change in the characteristic of the valve means.

Finally, the invention is also directed to a control system wherein the feed parameter is a combustion gas flow rate; the lag parameter is the air flow rate; and the process is a combustion process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a typical gas combustion apparatus;

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Fig. 2 is a block diagram of an air / gas ratio controller used in the apparatus of Fig. 1;

FIG. 3 is a block diagram of a control system with a preferred air / gas ratio controller arrangement according to one aspect of the invention;

FIG. 4 is a block diagram of a preferred air / gas ratio controller according to another aspect of the invention;

Fig. 5 is a block diagram of a modification of the controller of Fig. 4;

FIG. 6 is a graph depicting a valve position change using control voltage;

FIG. 7 is a graph showing a derivative of the valve characteristic of FIG. 6; and FIG. 8 is a graph showing the relationship between the valve derivative and the total deadband value.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a typical gas combustion apparatus 10. It consists of three main parts, a temperature regulator 12, an air / gas ratio control system 20, and a burner 40 arranged, for example, in an oven or furnace 41.

The temperature controller 12 is able to control the temperature of the furnace 41, either by monitoring a predetermined temperature profile or by allowing the user to define a desired temperature profile. E.g. for increasing the temperature, the temperature controller 12 adjusts the gas supply valve to increase the flow of gas supplied to the burner 40, and the air / gas ratio control system 20 adjusts the gas flow to attempt to maintain a substantially constant ratio of air and gas flow to the burner 40.

FIG. 2 shows a typical arrangement of an air / gas ratio control system 20. The control system 20 comprises a gas valve 22 connected to the gas supply line. 44 4444 44 4444

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-924 to change the gas flow. The gas flow sensor 26 is arranged downstream of the gas valve 22 and monitors the gas flow through the gas line 24. Similarly, the air valve 28 is arranged in the air inlet air line 30 to change the air flow and downstream of the air valve 28 is arranged downstream. a measuring sensor 32 for monitoring air flow through the air duct 30.

The gas valve 22 is connected and arranged to receive signals from the temperature controller 12 to adjust the gas flow value. The air valve 28 is connected and arranged to receive signals from the air / gas ratio regulator 34 to adjust the air flow value as a function of the gas flow value. The air / gas ratio controller 34 receives signals from both the gas flow sensor 26 and the air flow sensor 32 and compares these air and gas flows to adjust the air valve 28 to maintain the desired air / gas ratio.

The purpose of the combustion process is to function as efficiently as possible, and the air / gas ratio regulator 34 must control the air valve 28 to react as soon as possible to changes in the gas valve 22.

Such a system is commonly referred to as the "lag-lead system", which is a relatively complicated term "system for regulating the ratio of variable supply and adjustable retention parameters", which means gas supply and air retention. In this system, the flow rate parameters are changed and accordingly the required flow rate parameters must be adjusted by keeping the air flow supply so that the air / gas ratio is kept substantially constant.

The air and gas flow values are measured by the gas and air flow sensors 26, 32 of the overall control system 20. Flow samples are measured at a predetermined sampling rate at regular time intervals. The gas supply parameter is typically sampled faster, more often than the air retention parameter, and can be sampled every 20 milliseconds, for example. The air retention parameter should be set by its sampling to match the air intake parameter and can typically be set to, for example, ······················ · · ··· · · ······························ 19 ·

- 10 sampling every 120 milliseconds. The typical sampling range of the lag parameter is between 100 ms and 500 ms. In a natural gas combustion system, the air / gas ratio is typically maintained in the order of 10: 1, known as the stoichiometric gas ratio. Temperature changes in the reference signal result in adjustment of the gas valve 22 by the temperature controller 12. This changes the gas flow rate and thus the air / gas ratio to such an extent that it deviates from the desired value. This change is monitored by the air / gas ratio regulator 34 and results in the air valve 28 being adjusted to return the air / gas ratio to the desired value.

If a change in the air / gas ratio (i.e., this deviates from the setpoint) is detected by sampling both the air and gas flow, the controller 34 will begin to move the air valve 28 in the necessary direction (i.e. either towards full opening or close) until the following sample is taken.

However, if the air / gas ratio error is less than the air / gas ratio change achieved by moving the air valve 28 within one sampling interval (between taking the first sample and the next sample), the air valve 28 exceeds the desired position and the required flow rate is not reached. air. On further sampling, the controller 34 detects a reverse error and moves the air valve 28 in the opposite direction, i.e., to the fully open position if the previous movement was made towards the closed position or towards the closed position if the previous movement was made towards the position openly. Again, the air valve 28 may be moved beyond the required position during the sampling interval and set to a position close to or identical to the original position, i.e. the position at the beginning of the air / gas ratio setting. This closing and opening of the air valve 28 will be repeated as long as the air / gas ratio error remains substantially the same or less than the change achieved by the movement of the air valve 28 during one sampling interval. Thus, the air valve 28 and consequently the air flow values will oscillate around the level required to achieve the necessary air / gas ratio. These oscillations are known as limit cycles.

However, if the error in the air / gas ratio exceeds a certain threshold (defined by the change in the air / gas ratio achieved by the movement of the air valve 28) 99 99 9999 9 9999 9 9 9 • 9,999,999,999 • 99,999,999

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- 11 during one sampling interval), no limit cycles will occur. However, if the error lies below the threshold level, limit cycling occurs. For valves having a linear characteristic, i.e. having a linear response, the threshold level is constant over the entire range of operation of such a valve. However, many solenoid valves have a non-linear response, and the air flow rate varies non-linearly relative to the control signal. As a result, the change in air flow rate as the air valve 28 moves towards the fully open or fully closed position during one sampling interval varies depending on the position of the air valve 28 within its operating range (see FIG. 6). Subsequently, the threshold level defining the value of the area under which the limit cycling occurs will vary during the operation of the air valve 28.

Since the motorized valve actuator acts as an integrator, a change in flow rate during one sampling interval may be indicated by derivative of the valve characteristic (Fig. 7). The valve characteristic curve differential shows how much the valve moves (and thus changes the value of the air flow) during one sampling interval, depending on the original position of the valve within its operation. Since errors in the air / gas ratio can have both negative and positive values, it is necessary to establish both positive and negative derivative curves centered around zero to determine the threshold level. As shown in FIG. 8, this effectively causes a so-called " error wrapping curve " to which limit cycling occurs (FIG. 8). This occurs when:

e (Ts, u) | S (u)

O) where:

δ (u) is a derivative of the valve characteristic at any given position (u);

2 * 6 (u) represents the dead band value;

Ts is the sampling time; and u is the valve position.

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- 12 Conversely, limit cycling does not occur when:

| e _(Ts , _U ) | Ó (u) | ................................................. ( 2)

In order to reduce or substantially eliminate the limit cycling of the air / gas ratio regulator 34, it is desirable to ensure that the air valve 28 does not change if the error is within the error envelope of the air valve 28, in other words when the equation is applicable (1). In a preferred embodiment of the invention, this is achieved by applying a so-called "dead zone" as described below.

Giant. 3 shows a block diagram of a portion of a control system 90 with a preferred embodiment of an air / gas ratio controller 100. The controller 100 has a first comparator 102 which is coupled and adapted to receive two input signals, a first of the gas flow sensor 26 connected to the non-inverting input of the comparator 102 and a second of the air flow sensor 32 connected to the inverting input. The output of the first comparator 102 is coupled to both the non-inverting input of the second comparator 104 and the inverting input of the third comparator 106.

The positive and negative fixed thresholds of the value means 108, 110, the purpose of which is explained below, are connected to the non-inverting and inverting inputs of the second and third comparator means 104, 106. Their output is always connected to and output from the respective operational amplifier 112, 114. is always connected to a respective relay 116, 118 causing movement of the air valve 28.

During operation of the combustion apparatus 10, the gas and air flow rates to the burner 40 are measured by the flow sensors 26, 32, which generate signals Sg, Sa corresponding to the respective flow rate and send them to the air / gas ratio controller 100.

The gas flow signal Sg and the air flow signal Sa are transmitted to the first comparator 102, namely the gas flow signal Sg to the non-inverting input and the signal 4 '. 4 · 4 9 · 9

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- 13 airflow Sa to inverting inlet. The comparator 102 compares these signals and generates an error signal e as a function of the comparison.

The error signal e represents the difference between the actual air flow detected by the measurement sensor 32 and the desired air flow to produce a stoichiometric air / gas ratio with a normal gas flow rate. Since the metering sensor 32 would normally produce an airflow signal Sa, which is ten times greater than the gas flow signal Sg produced by the gas measuring sensor 26 for the stoichiometric ratio (i.e., the airflow value is tens greater than the gas flow value), the flow signal value Sa The airflow is set to the same level as the gas flow signal Sg for the stoichiometric ratio. This can be achieved by a simple voltage divider in the airflow sensor 32.

The error signal e. Is transmitted to the non-inverting input of the second comparator means 104 and to the inverting input of the third comparator means 106, each comparing the value of the error signal e. With fixed positive and negative thresholds generated by the positive and negative circuits of the value means 108, 110.

If the error signal value is greater than or equal to the positive threshold value, the comparator 104 applies the control signal by the first op-amp 112 to the first relay 116, which supplies the air valve 28 to move it in the first direction to its fully closed position. Similarly, if the error signal value is less than or equal to the negative threshold value, the comparator 106 applies the control signal by the second op-amp 114 to the second relay 116 which supplies the air valve 28 to move it in the opposite direction to the fully open position.

However, if the error signal value is less than a positive threshold and greater than a negative threshold, the second and third comparator means 104, 106 will not be affected and the air valve 28 will not be adjusted.

The threshold value means circuits 108, 110 are set to an error signal range within which the controller 100 does not perform any corrective action. If the value of * * «· ν ··· changes» »♦,« ·· &

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14 of the gas flow and the temperature of the burner 40 increases or decreases, resulting in a change in the air / gas ratio away from the desired value. This results in an error signal generated by the comparator 102, which signal represents the difference between the actual air / gas ratio and the desired air / gas ratio. It is therefore desirable that the change in the air flow rate required to return the air / gas ratio to the desired level is less than the change represented by the range of the error signal set by the threshold value means 108, 110, whereupon the error signal e reaches this range. and the air valve 28 remains intact. This error is judged to be zero and the air valve 28 is not reset. This threshold range set by the threshold value means 108, 110 circuits is called the "deadband". In practice, this reduces the occurrence of limit cycling in the air flow and allows the desired air / gas ratio to remain narrower.

The deadband value affects the performance of the air / gas ratio regulator 100, which in turn affects combustion efficiency. It is therefore very important to choose the right value of the deadband. If the dead band value is too high, the limit cycles will decrease but the accuracy of the air valve 28 control will also decrease. Conversely, a low threshold gives good accuracy but increases the occurrence of limit cycles. It is therefore preferred that the dead zone is selected as small as possible, but without causing limit cycling.

From this description, it is apparent that if the deadband value is a change in the airflow value that is slightly greater than the movement of the air valve 28 (change in the air flow value) in a single sampling interval, then the air valve 28 can be adjusted without limiting cycles. A constant deadband value can therefore be used for valves with linear characteristics. For non-linear enveloping error curve valves as shown in Fig. 8, the use of a constant deadband is not effective, because in some parts of the valve operating range limit cycling may occur even when the deadband is used.

The solution is to vary the deadband value according to the valve characteristic over the valve operation range. It has been found that the optimal value of the deadband for a given valve position is equal to twice the differential value of the valve characteristic at that position.

· 4 · 44 · 4 · 4 · 4 · 4 · 4 · 4 · 4 · 44 · 4 · 4 t <«·· · * · · · · · · · · · · ·

Since the dead zone is located around zero, the upper and lower thresholds of the dead zone (set by the positive and negative circuits of the threshold value means 108, 110) correspond to the positive and negative derivative curves of the valve. In this way, the dead zone selection is achieved precisely according to the envelope error curve of the valve. The regulator 100 thus adjusts the air valve 28 at the moment

D (u)

I (Ts, u) | - Even where D (u) = δ (u) a represents the deadband value defined by the envelope error curve at a given valve position (u), which is the area where limit cycling does not occur even in the absence of the dead band, the area is greater than or equal to the change in flow caused by the valve setting during one sampling interval. Conversely, the regulator 100 does not adjust the air valve 28 at the moment

D (u)

I £ (Ts, u) | <| - I

In this case, the error lies within the dead zone, which is the area in which the limit cycling would occur if the air valve 28 were reset and the dead zone was not present.

The solution is to vary the dead band depending on the characteristic of the valve within its operating range.

Figure 4 shows a second embodiment of an air / gas ratio controller 200 as part of control system 190. In Figures 3, 4 and 5, the same reference numerals designate the same parts. As can be seen, the controller 200 is similar to the controller 100 of Figure 3, but the fixed circuitry of the threshold value means 108, 110 is replaced by the variable circuitry of the threshold value means 208, 210, each containing an observation table. The variable value threshold means 208, 210 are coupled and arranged to receive a signal from the air valve position sensor 222 via an operational amplifier. · · · · · · ····

16220. The position sensor 222 can only be designed to monitor the voltage on the air valve 28 to move it between the open and closed positions.

Before actuating the control system, the characteristic of the air valve 28 is measured and the differential curve of Fig. 7 determines the envelope error curve of Fig. 8 for a given air valve 28. The plurality of different thresholds or levels are then taken from the envelope of Fig. 8; positive and negative values for the selected positions of the air valve 28. Positive values are stored in the observation table of the threshold value means 208 and the negative values are stored in the observation table of the threshold value means 210.

During operation, as the position of the air valve 28 changes, a threshold value in the observation table that is compared to the error signal is selected based on the position signal from the air valve position sensor 28.

The value generated by each variable circuit of the threshold value means 208, 210 is thus a function of the position of the air valve 28 and hence the value of the air flow. As the position of the air valve 28 changes, the value of the air flow also changes during each sampling interval. The characteristics of the air valve 28 are effectively stored in an observation table in each circumference of the threshold value means 208, 210. This table provides the characteristics at a given position of the air valve 28 and thereby determines the value of the deadband for that position. The dead zone thus changes according to the current position of the air valve 28.

As in the previous embodiment, if the error signal e is calculated by the comparator 202 and lies within the range defined by the instantaneous positive and negative threshold values generated by the threshold value means 208, 210, the error is judged to be zero and no air valve corrective action 28 .

However, if the error value is outside the envelope curve, the air valve 28 is set as described.

• · · ·

Since the deadband value is always greater than the flow rate change caused by the movement of the air valve 28 during one sampling interval, the occurrence of limit cycling is minimized. In addition, the accuracy of the air / gas ratio regulator 200 is increased. This achieves a significant increase in combustion efficiency since the air / gas ratio is maintained optimal.

Obviously, various modifications and improvements of the present invention can be achieved. This may be modified so that the movement of the air valve 28 is continuously monitored to determine if its characteristic has changed, e.g., by wear. When this occurs, this information is provided to the threshold value means 208, 210 to modify the deadband value for each valve position. An example of such a modification is shown in Figure 5.

One of the relays, in this case relay 116, which controls the valve toward its fully closed position, is connected to the inlet of the multiplier 300. The output of the airflow sensor 32 and the valve position sensor 222 is also coupled to the multiplier 300. the parameter calculator 302, the output of which is connected to the variable circuitry of the threshold value means 208, 210. The parameter calculator 302 may be a conventional microprocessor, e.g. of the MATLAB type.

Prior to actuation of the control system, the characteristic of the air valve 28 is measured and the corresponding curve shown in FIG. 6 is stored in the parameter calculator 302. This can be accomplished by moving the air valve 28 from one position to another, e.g. positions fully closed and monitoring the position sensor 222 and the air flow measurement sensor 32, which parameters are stored in the parameter calculator 302 as continuously variable or discrete values.

When the relay 116 for moving the air valve 28 towards its fully closed position is actuated, the parameter calculator 302. also affects the parameter calculator 302 while the air valve 28 closes. The signals of the airflow sensor 32 and the position sensor 222. flow value with the previous flow value. If the flow deviation is monitored, »φ φ · φ φ φ φ φ φ φ φ φ φ

- 18 this would indicate ο possible wear on the valve mechanism. The parameter calculator 302 then sets the threshold values in the observation tables of the threshold value means circuits 208, 210 relative to the monitored valve position to account for changes in the valve characteristics that occurred. Also, the movement of the valve towards its fully open position can be used to update the observation tables by taking into account wear, in which case the parameter calculator 302 is influenced by the relay 118.

Although the present disclosure relates to a gas supply and airflow retention control system with appropriate parameters, the present invention may also be used to control or control the air supply and flow retention or gas supply or any other corresponding lag-lead system. .

It will also be appreciated that while preferred embodiments of the present invention relate to combustion of gas with air in a furnace, furnace or combustion plant, the present invention is also applicable to control, control or regulation systems of two fluids in gaseous or liquid form with a single medium supply. and retaining the second medium.

Industrial applicability

The invention is particularly useful in the manufacture, assembly and operation of systems and devices for controlling the supply and retention of liquid media in gaseous or liquid form.

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Claims (25)

PATENT CLAIMS A method for controlling the ratio of a variable supply parameter to an adjustable containment parameter in a process for controlling these parameters, comprising: monitoring the lead parameter and producing a signal representative of the lead parameter value; monitoring the lag parameter and producing a signal representing the value of the lag parameter; comparing both of these signals and generating an error signal representing a deviation from the preselected ratio of the feed parameter to the containment parameter; and adjusting the containment parameter to reduce this deviation in response to a deviation exceeding a preselected deviation. 2. The method of claim 1 comprising comparing the error signal to a preselected threshold and adjusting the lag parameter in response to the error signal in excess of said preselected threshold. The method of claim 1 or 2, comprising comparing the error signal with an error range determined by a first, upper preselected threshold and a second, lower preselected threshold, and adjusting the lag parameter in response to said out-of-range error signal. mistakes. The method of claim 3, comprising: adjusting the lag parameter to reduce the ratio of the lag parameters and the lead in response to an error signal that is above the error range; and adjusting the lag parameter to increase the ratio of lag parameters to supply in response to an error signal that is below the error range. * · · · · · · · · · · · · · · -205. The method of claim 4, wherein the first, upper preselected threshold is a positive value and the second, lower preselected threshold is a negative value; a positive error signal indicates an increase in the air / gas ratio from the preselected ratio and a negative error signal indicates a decrease in the air / gas ratio from the preselected ratio; and that the method comprises: adjusting the lag parameter to reduce the ratio of lag and lead parameters in response to a positive error signal exceeding a first, upper preselected threshold; and adjusting the lag parameter to increase the ratio of lag and lead parameters in response to a negative error signal exceeding a second, lower preselected threshold. The method of any one of claims 2 to 5, wherein the threshold or each of the preselected thresholds is a fixed value. The method of any one of claims 2 to 5, wherein the or each of the threshold values is a function of the value of the lag parameter. The method of claim 7, wherein the step of comparing the error signal to the or each threshold comprises adjusting the threshold in dependence on the value of the lag parameter and comparing the error signal to the set threshold. The method of claim 8, comprising: providing a tracking table for storing a plurality of threshold values; and a step of adjusting said threshold value comprising selecting one of said thresholds depending on the value of the lag parameter. The method of claim 7, wherein the or each of said thresholds comprises a plurality of threshold levels; and the step of comparing the error signal to the or each threshold value comprises selecting a threshold level for that threshold value depending on the value of the lag parameter and comparing the error signal to the selected threshold level. -21 The method of claim 10, comprising: providing a tracking table to store a plurality of threshold levels; and a threshold setting step comprising selecting one of these threshold levels depending on the value of the lag parameter. Method according to any one of claims 1 to 11, characterized in that the supply and containment parameters are the supply fluid flow and delay values in an industrial process; and wherein the method comprises: providing delay valve means to regulate the flow of retained fluid; monitoring the position of said valve means to delay opening or closing said valve means; monitoring the flow of retention fluid when the valve means is opened or closed; comparing the change in position of these valve means with the change in flow rate of the retained fluid; and adjusting a threshold in response to this comparison indicating a change in the characteristic of the valve means. The method of claim 12 dependent on claim 9 or 11, wherein the step of adjusting the threshold value comprises adjusting the threshold values or levels in the tracking table. Method according to any one of claims 1 to 13, characterized in that the feed parameter is a flammable gas flow rate; the lag parameter is the air flow rate; and the process is a combustion process. A control system (34) for arranging a containment and supply control in a process having a variable supply parameter and an adjustable containment parameter, characterized in that the system comprises: supply monitoring means (26) for monitoring the supply parameter and generating a supply signal representative of the supply parameter value ; containment monitoring means (32) for monitoring the containment parameter and producing a containment signal representing the value of the containment parameter; comparing means (102) for comparing the supply and containment signals and generating an error signal representing a deviation of the supply and containment ratio from a preselected ratio, and adjusting means (116, 118) for adjusting the containment parameter to reduce this deviation in response to a deviation exceeding chosen. 0 0 00 00 0000 Φ Φ * Φ Φ Φ Φ Φ Φ 0000 0 0 0 0 0 0 0 0 · 00 · 00 0 Φ · ΦΦ ΦΦ 0 0 0 -2216. The control system of claim 15, further comprising: threshold value means (108, 110) for providing a preselectable threshold value; comparing means (104, 106) for comparing the error signal to a preselectable threshold; and that the adjusting means (116, 118) are operable to adjust the lag parameter in response to an error signal exceeding a preselectable threshold. The control system of claim 16, wherein the threshold value means comprises first, upper threshold value means (108) for providing a first, upper preselected threshold value, and second, lower threshold value means (110) for providing a second, lower threshold value. preselectable thresholds, thereby defining an error range; the comparing means (104, 106) are operable to compare the error signal to an upper and a lower preselectable threshold; and the adjusting means (116, 118) are operable to adjust the lag parameter in response to an error signal falling outside the error range. The control system of claim 17, wherein the adjusting means (116, 118) are operable to adjust the lag parameter to reduce the ratio of feed and lag parameters in response to an error signal that is above the error range and to set the lag parameter to increase. the ratio of supply and containment parameters in response to an error signal that is below the error range. 19. The control system of claim 18 wherein the first upper preselected threshold is a positive value and the second lower preselected value is a negative value; a positive error signal indicates an increase in the ratio of supply and containment parameters from this preselected ratio, and a negative error signal indicates a decrease in the ratio of supply and containment parameters from this preselected ratio; and the adjusting means (116, 118) are operable to decrease the ratio of feed and contain parameters in response to a positive error signal exceeding the first, preselected threshold and to increase the ratio of feed and contain parameters in response to a negative error signal exceeding the second, lower preselected threshold value. 4 4444 4 4 4 4 4 4 4 4 4 4 4 4 4 -23 The control system of any one of claims 16 to 19, wherein the threshold or each of the thresholds is a fixed value. A control system according to any one of claims 16 to 19, characterized in that the threshold value or each of the threshold values is a function of the value of the containment parameter. The control system of claim 21, further comprising adjusting means (222) for adjusting the threshold value as a function of the value of the lag parameter, and wherein the comparing means (104, 106) are operable to compare the error signal to the set threshold value. The control system of claim 22, wherein the threshold value means comprises a tracking table (208,210) for storing a plurality of threshold values; and the threshold value adjusting means (222) are operable to adjust the threshold value by selecting one of the threshold values depending on the value of the lag parameter. The control system of claim 21, further comprising: adjusting means (222) for adjusting a threshold in dependence on the value of the lag parameter; and that the threshold or each of the thresholds comprises a plurality of threshold levels; wherein the threshold value adjusting means (222) is operable to adjust the threshold value by selecting one of the threshold levels depending on the value of the lag parameter; and the comparator means (104, 106) are operable to compare the error signal to the allowed threshold level. The control system of claim 24, wherein the threshold value means comprises a tracking table (208, 210) for storing a plurality of threshold values; and the value adjusting means (222) are operable to adjust the threshold value by selecting one of the threshold values depending on the value of the lag parameter. Control system according to any one of claims 15 to 25, characterized in that the supply and containment parameters are the flow rates of the supplied and retained fluid. 9 9 9 9 9 99 99 9 9 9 9 · -24ν process; and wherein the control system comprises: a containment valve means (28) for controlling the flow of the containment fluid; position monitoring means (322) for monitoring the position of the containment valve means (28) when opening or closing the containment valve means (28) and providing a position signal representing them; wherein the containment monitoring means (32) is operable to monitor the flow rate of the containment fluid when opening and closing the containment valve means (28), and a flow value signal representing them is provided; and wherein the control system further comprises: storage means (302) for storing sampled position and flow signal values representative of a preselected characteristic of the containment valve means (28); second comparing means (302) for comparing the valve position of the valve retaining means (28) and the flow rate of the retained fluid while moving the retaining valve means (28) using stored values; and second adjusting means (302) for adjusting the threshold value in response to the comparison indicating a change in characteristic of the containment valve means (28). 27. A control system as claimed in any one of claims 15 to 25 wherein the supply and containment parameters are flow rates of the feed fluid and the fluid retained for the process; and the control system comprises: valve retention means (28) for controlling the flow of retention fluid; positioning monitoring means (322) for monitoring the position of the containment valve means when opening or closing the containment valve means and providing a position signal representing them; wherein the containment monitoring means (32) is operable to monitor the flow rate of the retained fluid when opening or closing the valve means (28) and providing a flow value signal representing them; and wherein the control system further comprises storing means (302) for storing sampled values of the position and flow signals representing a preselected characteristic of the containment valve means; second comparing means (302) for comparing the flow rate of the retained fluid during movement of the valve means by a stored value corresponding to the monitored position of the retaining valve means; and second adjusting means (302) for adjusting the threshold value in response to the comparison indicating a change in the characteristic of the valve means. ···· Φ · φ · Φ · · · · · · · · φ · φ · φ · φ · φ · φ · φ · · · · · φ · φ · φ · φ · φ · φ · · · φφ φφ Control system according to any one of claims 15 to 27, characterized in that the feed parameter is a value of the flow rate of the combustion gas; the lag parameter is the air flow rate; and the process is a combustion process.