US3751215A - Deviation proportional analog pulse controlling apparatus - Google Patents

Abstract

An automatic timer actuator relay is operably connected to continuously and alternately hold a switch of a transmitting controller in an automatic memory output signal tracking position only for a brief period of time and to hold the switch in a manual memory signal retention position for a much longer period of time so that the output deviation proportional error signal (P.V.-S.P.) that this controller is transmitting to a master cascade controller as a set point input signal can only occur over extremely short and widely spaced intervals of time during which a process is being controlled.

Description

United States Patent [191 Hucke DEVIATION PROPORTIONAL ANALOG ZONE Primary Examiner-Eugene G. Botz Attorney-Arthur H. Swanson ct al.

[57] ABSTRACT An automatic timer actuator relay is'opcrably connected to continuously and alternately-hold a switch of a transmitting controller in an automatic memory output signal tracking position only for a brief period of time and to .hold the switch in a manual memory signal retention position for a much longer period of time so that the output deviation proportional error signal (P.V.-S.P.) that this controller is transmitting to a master cascade controller as a set point input signal can only occur over extremely short and widely spaced intervals of time during which a process is being controlled.

10 Claims, 3 Drawing Figures PREHEATING ZONE PULSE CONTROLLING APPARATUS [75] Inventor: Ernest'llucke,Glenside, Pa. [73] Assignee: Honeywell Inc., Minneapolis, Minn.

I221 Filed: June 12, 1972 [2] 1 Appl. No.: 262,017

52 0.5. CI. 432/49, 235/1501 [51] Int. Cl. F27b 7/00 [58] Field of Search 432/49; 330/9; 235/1501, l5l.l

[56] References Cited UNITED STATES PATENTS 3,443,235 5/1969 Newboldus. 330/9 3,556,496 l/l97l Hucke 432/49 X 200 JQ i f 2gcALemm l nl -519 2o4' I n4 IO i -22o g I zloi 2i2 i 44 i l l .DEVIATION PROPORTIONAL ANALOG PULSE CONTROLLING APPARATUS BACKGROUND OF THE INVENTION One of the many basic process'control systems on which the aforementioned automatic timer actuated relay switching apparatus can be usefully employed is in the furnace profile temperature control that has an ancillary signal producing means which is set forth in the Ernest Hucke US. Pat. No. 3,556,496. In the aforementioned referred to patent a temperature measuring control apparatus is employed which has opposing ancillary set point adjusting loop circuits for regulating the heat required to convert a granular material, for example a cement mix into quality clinker which control apparatus is responsive to changes taking place in the overall temperature profile of the furnace and whose action is not adversely effected when e.g. sudden upsets, such as a sudden surge of heat of the material being passed into the furnace occurs which causes lengthening or shortening of the calcinating and burning zones.

The wet process and grinding-mill feeders are other examples of basic process control systems in which the aforementioned timer relay switching apparatus can be beneficially employed to minimize the adverse effect that lag has had on the end products that are produced by either of these feeders.

PROBLEMS When an upset in a processoccurs that is due to, for example, an abnormal amount of combustion air, temperature fluctuation or a radical change in the moisture content of the material being fed into a kiln an extreme surge in the heat of the kiln will occur at the inlet buming end of the kiln.

A heat upset of this type will often occur at the entrance end of the kiln where a granular mix such as cement is introduced for converting it into clinker.

In many cases it has been found that conventional sensing and controlling instruments over react when upsets of the aforementioned type occur and thereafter during the timethese instruments are attempting to effect a control of the process that will bring the furnace back to a desired preselected temperature profile. It has been difficult due to the aforementioned over reaction of the controlling instruments to produce a good quality end product with the least amount of heat and heat burn through and which at the same time will minimize the wear and tear on the inner brick wall and the shell of the kiln.

Similar problems'exist in process control systems that are employed to control a heated process material which because of the undesired lag in the system make it difficult to control.

SUMMARY OF THE INVENTION The aforementioned problems which arise during an upset condition are solved by providing 1, a timedautomatic control switching circuit which will allow a signal that is proportional to the deviation between the process variable and the setpoint signal to be fed as an electrical error signal from a transmitting controller into a master controller while this error signal is stored in a continuous updating manner in the memory of the transmitting controller when the latter controller is on automatic control for short periods of time such as 15 seconds.

2. To thereafter switch the transmitting controller to manual control so that no error signal will be transmitted to the master controller and the magnitude of the error signal at the time of switching will be ietained in the memory of the transmitting controller.

3. To feed the error signal that exists immediately before the last .shift from an automatic to manual switch occurs as an electrical set point signal into the master controller for another period of time, e.g. 15 seconds, so that the previous magnitude of the error signal that was retained in the memory of the master controller can be switchedand then updated or ramped to a magnitude that will allow the desired temperature profile kiln to be achieved and by 4. continuously repeating the aforementioned error signal switch cutting in and switch cutting out operation performed by the automatic control switching circuit as noted under No. 1-3 supra.

The aforementioned unique timer actuated switching circuit will thus allow the set point of a master controller to be altered when the transmitting controller is switched to automatic control and during the short period thereafter that the timer allows it to remain in this position before it is switched back to a manual operating position.

The desired control action effected by the aforementioned process controllers will not therefore be ad versely affected by any undesired over reaction that occurs in the process or by any shift which may occur in master controller and how a calcinating zoned.

temperature transmitting circuit shown in dotted line form can be substituted for the master set point transmitter;

FIG. 2 shows an automatic timer actuated relay connected so that it can continuously move a switch of a transmitter controller from an automatic position where it remains for a preselected periodic time to a manual or error signal memory storing position where it remains for another different period of time.

FIG. 3 shows a simplified form of the present invention in which the aforementioned type of automatic timer actuated relay is employed with a transmitting controller that is shown receiving a single P.V.-S.P. error signal from a transmitter rather than from one or more trim circuits as is shown in FIG. 1.

Referring now the drawings indetail there is shown in FIG. 1 a control apparatus 10 for making optimum use of the heat required to convert a granular cement mix or other similar material 12 into a material such as a clinker 14' having a preselected density and hardness prior to, during and after a furnace upset.

This control apparatus 10 employs a master indicating controller 16 that receives a process variable signal by way of a conductive electrical connection 18 from plate 26, that is located in a conduit 28 that supplies fuel from a source, not shown, to a burner 30.

The control apparatus also employs a set point indicating transmitter 32. The master set point transmitter 32 is connected to an AC power supply 34 and has two conductors 36, 38 connected across a resistance 40 and an electrical conductive transmission line 42, 44. These lines 42, 44 are in turn connected by way-of a voltage to current transducer 46, and electric transmitting line 48 to transmit the set point signal to the burning zone temperature transmitter 50 which in turn will alter the signal being transmitted through the electrical transmission line 52 to the master controller 16.

A process variable electric loop circuit 54 having current flowing in the direction of the arrow 56 is shown with one end of its electrical conductors 58, 60, 62 connected to a thermocouple to current transducer 64 which in turn has a pair of electrical leads 68, 68

connected to a protecting well enclosed thermocouple 70 that is employed to sense the temperature of the right end or preheating zone 72 of the furnace 74. The electrical circuit for the thermocouple to cur'rent transducer 64, its thermocouple 70 may be of the type disclosed in detail in the Edward T. E. Hurd I11 U.S. Pat No. 3,562,729. a

The other end of the conductor 88,62 is connected to a process variable vertical scale indicator 76 for indicating the magnitude of the temperature of the preheating zone 72.

The manually adjusted set point electrical loop circuit having a current flowing in the direction of the arrow 80 is shown with its conductors 82 to 84 con nected at one end to a manually adjustable vertical scale set point indicator 86 and at its other ends to the master signal transmission line 44.

The indicator 86 in turn receives alternating current power through conductors 87, 88 from a suitable AC power supply source 89. The wiper 90 and resistance 92 form the potentiometer 94 in the process variable electrical loop 54 and the wiper 96 and resistance 98 form a potentiometer 100 in the manually adjustable set point electrical loop 78. A connection 104 can therefore be employed for manually moving wipers 90, 96 jointly along their respective resistances 92, 98 to increase or decrease the resistance in the process variable and set point loop circuits 54, 78 by rotation of the knob 106.

The switch 108 is initially kept in a closed position during the initial heating up stages of a kiln and until a manual adjustment of the set point adjustment wheel 110 of the master set point transmitter 32 has been established which retains the flame heat being added to the furnace at a value that will produce a good quality clinker 14. This clinker 14 is formed just prior to the time it'is passed out the left burning zone end of the rotary furnace or kiln 74, as this kiln is rotatably driven by a conventional electric motor '112 and reduction drive 114.

During this initial period of time, the vertical scale type process variable indicator 76 will indicate the temperature that is present in the preheat zone of the furnace 74. As soon as the furnace 74 starts to produce a good quality clinker the manually adjustable set point adjusting knob 116 is moved to an ancillary set point control-indicating position that matches the value that is shown on the process variable indicator 76. The

switch 108 is then openedand since the instantaneous setting of the process variable and set point indicators 76, 86, at that time are equal the opposing loop circuits 54, 78 will be of the same magnitude so that no change in the set point signal being transmitted by the master set point transmitter 32 through leads 42,44 will occur due to the electrical output of these loops .54, 78.

After the switch 108 hfas been opened the thermocouple then senses a cooling off of the cement mix entering the preheating zone due to, for example, an upset such as an abnormal increase in the cement mix that is fed into the furnace 74 by the conveyor 118. The value of current being sent through the process variable loop 54 will thus be changed from the value of the current passing through the electrically opposing set point loop 78 and an ancillary error signal will be introduced that will change the magnitude of the set point signal being transmitted by the master set point transmitter 32 by way of the conductors 42, 44, 48 to transmitter 50. This in turn will alter the signal being transmitted to the master controller 16. This action will thereby cause the set point of the master controller 16 to change its set point and an error signal which is representative of the differences in magnitude of its process variable and altered set point signals to be sent by conductor transmission line 119 to the motorized valve 119. To allow, for example, more fuel to be sent to the burner 30 to heat the increased quantity of cement mix flowing into the right end of the furnace 74.

As this increase in cement mix passes into the calcinating zone its temperature may be raised by the last heatadding control action to a value thatexceeds a temperature level at which a good quality clinker can be produced.

If this undesired higher temperature condition should occur another pair of set point process variable opposing electrical loops 120, 122, whose representative current flow is in the direction of the arrows 124,126, are employed that are the same type and function in the same manner as the process variable and set point loops 54, 78 previously described. The process loop 120 has, for example, a vertical scale indicator 128 similar to indicator 76 and the thermocouple 130, thermocouple leads 132 and the thermocouple to current transducer 134, are similar to the previously described parts 70, 68 and 64.

A pair of leads 136, 138, are shown connecting the transducer 134 with associated slip rings 140, 142 that are in turn fixedly mounted by insulating support members, not shown on the outer surface of the kiln 74.

The output signal produced by the transducer 134 in response to the temperature sensed by the thermocouple is taken from the slip rings 140, 142, by means of brushes 144, 146 and electrical leads 148, 150.

Part way between the opposite ends of the leads 148, 150 there is shown a voltage to current converter 152. This voltage to current converter compares the input voltage signal against the reference bias voltage applied to a complementary connected transistor amplifier. The magnitude of the input voltage will affect the conduction of the transistor circuit and produce a proportional output current.

The set point loop 122 has an indicator 158that is connected to an AC source 160 by way of conductors 162, 164, similar to the previously described set point indicator 86, its AC source 89 and conductors 87, 88.

Resistors 166, 168 wipers 170, 172, conductor 174, manual connection 176, its associated knob 178 and switch 180 function in the same manner as that previously described under the description of the opposing circuits 54, 78.

A suitable position of the wiper 90 of the process variable potentiometer 94 and the wiper 96 of the set point potentiometer 100 shown in FIG. 1 that is found to produce a good quality clinker may be, for example, 100 ohms resistance with settings on the manual resistance values from the joint or individual settings of the wipers 170, 172 at the, second mentioned control station. In this way greater importance can be given to a particular control station in the determination of the total overall corrective ancillary error signal that is introduced by that particular selective one of several control stations.

As an alternative part of the aforementioned control system an automatic set point master controller 194 shown in dotted line form can take the place of the manually adjusted master set point transmitter 32. When this automatic set point m-g,ster controller 194 is employed it it connected to a suitable power source, for example AC source 34, and receives a signal whose magnitude varies in accordance with changes in temperature, of the calcinating zone as sensed by the thermocouple 196. The thermocouple 196 has a pair of leads 198 connected to a thermocouple to current transducer 200 which may be similar to the previously described parts 130, 132, 134.

Y A pair of leads 202, 204 are shown in dotted line form connecting the transducer 200 with associated slip rings 202', 204' that are in turn fixedly mounted by insulating support members, not shown, on the outer surface of the kiln 74'.

The output signal produced by the transducer 200 in response to the temperature sensed by the thermocouple 196 is taken from the slip rings 202, 204 by means of brushes 206, 208 and electrical leads 210, 212.

The pair of conductors 214, 216, in turn, are shown connecting the automatic set point master controller 194 to opposite sides of the resistance 40 in transmis-s sion conductor 42.

A radiationvpyrometer 218 which may be of the type disclosed in the T. R. Harrison U.S. Pat. No. 2,357,193 is employed to take a measurement of a temperature representative of the clinker 14 being fed through the burning zone of the kiln 74 and to send a signal proportional to this temperature by way of electrical transmission line 220 to a millivolt to current transducer 222. The circuit employed in the millivolt to current transducer 222 is similar to that disclosed in the Edward T. E. Hurd lll U.S. Pat. No. 3,562,729: I

The current flowing fro rn thetransdiicer 222 is transmitted by a suitable conductor means 224 to a single mode transmitter 50 as a process variable (P.V.) input signal.

The controlling transmitter 50 receives the set point signal flowing into it by way of conductor 48, compares the aforementioned process variable with this set point signal and produces and transmits an error signal. or in other words a signal representative of the difference between the magnitude of the process variable (P.V.) and set point (S.P.) signal that it receives, as a set point intput signal by way of the conductor 52 to the master three mode controller l6.

The master controller 16 in turn electrically com pares the input process variable signal (P.V.) it receives from the differential pressure to current transducer 20 by way of conductor 18 with the previously mentioned error signal in the form of a set point signal (S.P.) and produces and transmits another error signal equal to the difference in the two input signals by master way of the conductor 119 to the motorized valve 1 19'. The signal applied to the motorized valve 119' in the aforementioned 30 manner will regulate the flow of the fuel that is allowed to pass through conduit at 28 to the burner 30 to a desired value that will continue to produce a good quality clinker 14.

It should be noted that the circuitry employed for the manually adjusted vertical scale set point indicators 86, 158, the vertical scale process variable indicators 76, 128, the manually adjusted set point master transmitter 32, the automatically adjusted set point-transmitting controller 194, the single mode-transmitting controller 50 and the three mode master-indicating controller 16 is covered by the circuitry shown in the Newbold U.S. Pat. No. 3,443,235, filed Feb. 19, 1965. 7

It should be understood that the wipers 90, 96, and/or 172 can be jointly or individually manually adjusted to other resistance values, for example 50 ohms or 150 ohms, to obtain'a lower or higher range of ancillary DC voltage value that can be introduced into the transmission lines 42, 44. This may be desirable to correct for any undesired heating or cooling'of the material 12 as it passes through the furnace'if it is of a different quality and quantity to the material just described.

The U.S. Pat. No. 3,556,496 of Ernest Hucke, issued on Jan. 19, 1971 discloses how the individual adjustment of the aforementioned wipers can be accomplished. Furthermore, it should be understood that resistance values lower than the '50 ohmtvalues or higher than the 150 ohm values can be used where a process requires a different range in ancillary signal than that described supra and which is shown on the drawings to correct the temperature condition of the material 12 passing through any particular portion of the furnace so that preliminary desirable steps will be taken to obtain a good quality clinker before the material 12 reaches the burning zone of the furnace 74.

It should also be understood that the joint or individual settings of the wipers 90, 96 of the first mentioned S P.-P.V. control station shown on the right side of FIG. 1 can be set at different potentials and the master set point transmitter 32 that is required to obtain this quality clinker is twelve milliamps. The set point-adjusting knob 116 in FIG. 1 is then manually adjusted to line up the indicator with the same value as that shown on the process variable indicator scale 192 that has been found to produce a good quality clinker. The part of the ancillary signal that will then be produced by the left set point loop 78 will be 1.2 and the other part of this ancillary signal that will then be produced by the right process variable loop 54 will be 4, 8, 1.2, 1.6 or 2.0 volts depending on whether the process variable value on indicator 76 is 4, 8, l2, 16, or 20 milliamps.

Depending on the values of the algebraic sum of the voltages produced by the right process variable and left set point loops 54, 78, a DC signal will be produced that will either buck, aid or have no effect on the set point signal being transmitted through the transmission lines 42, 44, by the transmitter 32.

While the current range of the thermocouple- tocurrent transducers 64 and 134 is dependent on many factors, a range that has been used satisfactorily is from O to ma. If the current flowing is twelve ma for instance and the resistance of the part of the slidewire 92 below the slider 90 is 100 ohms then the voltage across this part is clearly 1.2 volts. Obviously with the setpoint indicator 86 also giving 12 ma and the slider 96 similarly adjusted (as must be the case as so far described), the voltages will be balanced.

Should the current produced by the transducer 64 now fall to say 8 ma, then the voltage across the lower part of the slide-wire will fall to 0.8 volts. A modifying voltage of 0.4 volts will therefore now be present.

If instead of being 100 ohms the resistance of the lower parts of the slidewires 92 and 98 had been 50 ohms the associated voltages would have been 0.6 volts. If now the current falls to 8 ma then a modifying voltage of 0.2 volts will be present.

Thus adjustment to the position of the sliders 90, 96 170 and 172 results in a change in sensitivity. Since the pairs of sliders 90, 9 6, 170,172 are independently adjustable, greater importance can be given to the preheating zone or vice versa.

FIG. 2 shows the previously referred to three mode transmitting controller 50 having a manual automatic memory switching apparatus 228 which is of substantially the same construction as that shown in FIG. 4 of the previously mentioned W. F. Newbold U.S. Pat. No. 3,443,235.

The process variable signal (P.V.) transmitted from the transducer 222, shown in FIG. I, is fed by means ofa conductive transmission line 224 to an error amplifier 230 that is connected to the aforementioned memory switching apparatus 228.

The set point (S.P.) transmitted from the transducer 46 is also shown being fed by the conductive transmission line 48 into an error amplifier 230.

The output of the error amplifier 230 is sent through a conductor 232 to an error signal integrating variable resistor 234, a resistor 236 and a capacitance 238. The

P.V. and SP. integrated signals are then added together by means of a summating unit 240 to produce an error signal.

An adjustable gain potentiometer 242 is connected by way of a conductor 244 and capacitance 246 to the summator 240. A conductor 248 is also shown extending between the summating unit 240 and the switching apparatus 228. The switching apparatus 228 contains a first switch blade 250 and a second switch blade 252 that are connected to a mechanical link 254 for joint movement therewith between their associated automatic contacts 256, 258 and their associated manual contacts 260, 262.

The mechanical link 254 forms a movable part of an electrical relay 264 which in turn is connected to a power supply 266 by means of a conductor 268 and a mechanical switch 270 as shown or which may alternatively be a solid state switch.

The blade 272 of the switch 270 is in turn connected for movement between an open and closed position in a prescribed manner by means ofa mechanical link 274 of an adjustable time cycle timer 276. The mechanical link 274 in turn is actuated in a timed sequence by a motor 278 to open and close the relay activated switch 270. The time the switch 270 is allowed to remain in an open position and in a closed position is accomplished by manually adjusting the pointer 280 to a desired value along the timing scale 282. While this mechanical adjustment of the pointer 280 takes place the mechanical connection 284 between the pointer 280 and motor 278 will also be moved so that the motor 278 .will be timed in the same manner as that indicatedonthe scale 282.

When the blade 272 is brought into engagement with its associated contact 270 and the timer-276 is in a closed position, the coil 264 will be energized. This act will cause mechanical link 254 and switch blades 250, 252 to be moved upwardly from the manual switch closed position shown in FIG. 2 into the automatic switch closed position. When the switch has been placed in the latter position the blades 250, 252 will be brought into contact with the associated contacts 256; 258. When the switching apparatus 228 is in this automatic position the'magnitude of the error signal will be transmitted from the summing unit 240 through conductors 248, blade 250, contact 256, conductors 286, 288 to the error amplifier 290,conductor 292, the regular amplifier 294 and by way of conductor 52 as a set point signal to the master three mode controller 16 shown in FIG. I.

It can also be seen that while the switching apparatus 228 is in its automatic position for a preferred short period of time for example, 15 seconds, the output signal being transmitted by way of conductor 52 will also be fed back by way of conductor 296 so that the magnitude of the output error signal will be continuously stored in the memory capacitor 298. In other words, the error signal will be tracked by the memory capacitor 298.

When the switching apparatus 228 is then moved to the manual position for a preselected longer period of time, for example 15 minutes, the output error signal will be cut off and no error signal will therefore be transmitted from the transmitting controller 50 to the master controller 16. It should be noted that the error signal that was being transmitted by the transmitting controller 50 immediately before the timing relay effected a shift from automatic to manual control will be the signal that is stored or in other words retained in the memory capacitor 298 during the entire time the controller remained in a manual operating position.

When the controller 50 is switched back to automatic the selected set point of this controller is compared against the then cut in process variable signal and a signal proportional to the difference in this now cut in RV. signal and the selected S.P. signal is ramped to a new error signal level due to the inherent adjustable reset action of the controller 50. This action will in turn ramp the master controller 16 to the aforementioned new error signal level.

FIG. 3 shows one example of how the manual to automatic memory timer actuating switch circuit 228, 226 that is shown in FIG. 2 for the transmitting control-. ler 50 can also be beneficially employed in another type of process control system such as the dryer control system which is shown in this FIG. 3.

FIG. 3 shows fuel being controlled by a cascade three mode master controller 16 operating on a motor operated fuel valve 119. The P.V. input to the master controller 16 is a process variable signal representative of the exhaust gas temperature as sensed by the optical pyrometer 218. This process variable signal is also a reflection of material thruput as well as a reflection of the inherent moisture and surface moisture of the process material 14',

Product exit temperature determines the tolerable moisture of the material 14'. This is measured by a radiation pyrometer 218.

It is desirable to modify the set point of the fuel controller 16 from the product exit temperature to maintain this temperature at a definite value but residence time, commonly referred to as lag time of the material in the drying kiln 74, is a main obstacle that must be overcome to accomplish this feat.

To provide a solution to the aforementioned problem the sensor 218 is employed to measure the temperature of the product exiting from the kiln and to produce a process variable input signal for the controller transmitter 50 whose output is employed to adjust the set point of the master controller 16. A timer 276 is employed to switch remotely from automatic to manual operation. On automatic, a deviational proportional adjustable reset action will update the control loop and on manual the signal will hold at its last value as has already been previously explained under the description of FIG. 1.

It should be understood that such a control system can also be used in other processes than the one shown in FIG. 3 where e.g. lag is present.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A deviation proportional cascade controlling ap-. paratus to maintain a stable control of a process so that a good quality end product can be produced while an upset occurs in the process, comprising a transmitting controller, a master controller, a switching circuit connected with said transmitting controller and an automatic timer relay operably connected with the switching circuit to periodically switch the transmitting controller from a manual to automatic position and to thereby produce an output signal for transmitting to the master controller which signal is alternately of a nonchangeable and variable magnitude.

2. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position and said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position.

3. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error sig nal as a set point signal for transmission to the master controller when the circuit is in an automatic position,

said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller.

4. The deviational proportional cascade control apparatus as defined in claim-lvwherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said a switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of the temperature of exhaust gases emitted from said process and being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller.

5. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable sig nal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position.

6. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is pr0p0rtional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process ll to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position, and wherein said transmitting controller is a controller that is operable to produce proportional and reset control and which has a means for adjusting the magnitude of its set point to a preselected value.

7. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position, and wherein said transmitting controller is a controller that is operable to produce proportional and reset control and which has a means for adjusting the magnitude of its set point to a preselected value, and wherein the reset action of said transmitting controller provides a means of ramping the error signal being sent to the master controller to a new error signal level while said timer relay switches said switching circuit of the transmitter controller from its manual to its automatic switching position.

8. The deviation proportional cascade controlling apparatus as defined in claim 1, wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops from an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with a change taking place in the product being produced by the process.

9. The deviation proportional cascade controlling apparatus as defined in claim 1, wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops form an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with temperature changes taking place in different zones of a furnace through which said product is transmitted.

10. The deviation proportional cascade controlling apparatus as defined in claim 1 wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops form an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with a change taking place in the product being produced by the process, and wherein a pair of said opposing set point-process variable loops are associated with two heating zones of the process which precedes the final end zone of the process, said apparatus being operably connected with the transmitting controller to alter the magnitude of the set point signal being transmitted by the transmitting controller to alter the magnitude of the set point signal being transmitted by the transmitting controller in accordance with the temperature of the last two mentioned zones and wherein the product being produced by the process is a granular material.

Claims (10)

1. A deviation proportional cascade controlling apparatus to maintain a stable control of a process so that a good quality end product can be produced while an upset occurs in the process, comprising a transmitting controller, a master controller, a switching circuit connected with said transmitting controller and an automatic timer relay operably connected with the switching circuit to periodically switch the transmitting controller from a manual to automatic position and to thereby produce an output signal for transmitting to the master controller which signal is alternately of a non-changeable and variable magnitude.

2. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position and said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position.

3. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust saId control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller.

4. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of the temperature of exhaust gases emitted from said process and being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller.

5. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position.

6. The deviational proportional cascade control apparatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position, and wherein said transmitting controller is a controller that is operable to produce proportional and reset control and which has a means for adjusting the magnitude of its set point to a preselected value.

7. The deviational proportional cascade control apParatus as defined in claim 1 wherein the switching circuit is a memory switching circuit which receives and summates a first signal whose magnitude is proportional to a first characteristic of the product being processed and a set point signal, said switching circuit being further operable to employ said output error signal as a set point signal for transmission to the master controller when the circuit is in an automatic position, said memory switching circuit being further operable to retain changes occurring in said first signal when said switching circuit is in a manual position, said master controller being further responsive to a second input process variable signal whose magnitude is representative of a second characteristic related to the quality of the product and said master controller being further operably connected to a control element in the process to adjust said control element in accordance with the difference in magnitude of the signals that are being transmitted to said master controller and wherein said automatic timer relay is operably connected to the memory switching circuit to periodically switch the circuit from its manual memory signal retention position to its automatic memory output error signal tracking position, and wherein said transmitting controller is a controller that is operable to produce proportional and reset control and which has a means for adjusting the magnitude of its set point to a preselected value, and wherein the reset action of said transmitting controller provides a means of ramping the error signal being sent to the master controller to a new error signal level while said timer relay switches said switching circuit of the transmitter controller from its manual to its automatic switching position.

8. The deviation proportional cascade controlling apparatus as defined in claim 1, wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops from an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with a change taking place in the product being produced by the process.

9. The deviation proportional cascade controlling apparatus as defined in claim 1, wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops form an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with temperature changes taking place in different zones of a furnace through which said product is transmitted.

10. The deviation proportional cascade controlling apparatus as defined in claim 1 wherein said output signal is a preselected set point signal and wherein at least one pair of electrical circuit opposing set point process variable loops form an ancillary signal producing circuit is operably connected with the transmitting controller to algebraically alter the magnitude of said set point signal that is being transmitted by the transmitting controller to the master controller in accordance with a change taking place in the product being produced by the process, and wherein a pair of said opposing set point-process variable loops are associated with two heating zones of the process which precedes the final end zone of the process, said apparatus being operably connected with the transmitting controller to alter the magnitude of the set point signal being transmitted by the transmitting controller to alter the magnitude of the set point signal being transmitted by the transmitting controller in accordance with the temperature of the last two mentioned zones and wherein the product Being produced by the process is a granular material.

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