US2264254A - Control apparatus - Google Patents

Description

F. c. BRANDT CONTROL APPARATUS Filed 001'.. 22, 1938 UIIIII,

Nov. 25, 1941.

Patented Nov. 25, 1941 UNITED` STATES PATENT OFFICE CONTROL APPARATUS Frederick C. Brandt. Chicago, lli., assigner to Minneapolis-Honeywell .Regulator Company, Minneapolis, Minn., a corporation of Delaware vAgm'lnmuon october 22, 193s, sel-lai No. 236,592

(ci. zas-s2) 10 Claims.

This invention relates in general to automatic' controls and more particularly to automatic controls of the pneumatic or pressure actuated type.

It is an object of this invention to provide a control device for a pneumatic or pressure actuated motor which is simple and sturdy in construction. which provides for positive proportionate positioning of the motor in accordance with changes in condition of its controller, and 'which further provides for load compensation to thereby maintain the condition being controlled at the control point of the controller irrespective of the actual load upon the system being con-I trolled. l

More specifically, it is an object of this invention to provide a follow-up control arrangement ling cell constant when the condition being controlled is at the control point of the controller. Other objects will appear from the following description and the appended claims.

For a full disclosure of this invention, reference is made to the following detailed description and to the accompanying drawing. in which Figure 1 shows a pneumatic damper motor having my invention applied thereto, and in which Figure 2` is a cross sectional view of the combined positive positioner and load compensating device.

about its pivot s thereby' biasing the'member a' against the diaphragm located in housing member 3. It will be apparent that upon increasing the air or other fluid pressure withinthe dia--` phragm. the lever arm i will'be urged upwardly against the action of spring 3, while upon decrease in such pressure the spring 3 willcause downward movement of the lever arm. The lever arm 3 may actuate valves or dampers for controlling whatever medium is desired to be controlled. Y l

Mounted upon an extension oi the base member 2 is the combined positive positioning and load compensating device III. Referring to Figure 2, this device I0. is shown as being formed of a lower housing member yI I and an uppervhousing member I2. Located in the uppelhousin'g member I2 is a diaphragmy or bellows I3. this bellows being sealed to the upper wall of member I2 and being in communication with a pipe connection I4. The lower wall of the diaphragm I3 is provided with a projection I5 which forms a vil) Referring to Figure l, reference character I indicates a damper motor of a construction weil known in the art. This motor consists of a base 2 upon which is mounted a cylindrical housing member 3 which contains an expansible and con-V tractible diaphragm for actuating a member 4 extending through the top of this housing. The

member 4 is connected to the usual lever arm 6 which is pivoted at 6 upon a bracket member 1 attached to the top of the housing. Also attached to the lever arm I is a tension spring 3. the lower end of which is attached to a suitable bracket formed on the base member 2. The spring 3 thus urges rotation of the lever arm t downwardly 5f retainer for a spring I3 the lower end of which is supported upon an adjusting nut I1 mounted in a web I8. The projection I 5 .is also attached to a stem I9 which extends through an opening20 in the adjusting nut and which is attached to acompensating diaphragm or bellows 2|. The lower end of the compensating diaphragm 2| is connected to a clevis 22 which is provided with a guide stem 23 fitting into an opening 24 in the lower housing member I I. Pivoted into the clevis 22 is a floating lever 25, the left-hand end of which is attached to a link 28 whichr in turn is pivoted to a'lever 21 fulcrumed at28 inan extension 23 of the bracket'memberl. The lever 21 is actuated in unison with the motor'lever arm 5 by means of an abutment member 3|) which may be adjustably positioned-uponth'e lever arm l.

The lower housing member II is also provided with a boss 32 providedwith a centralchamber l' 33 which communicates through a passage 34 with a pipe connectionl 36. The boss 32 also contains a valve chamber 33 containing a valve memi `ber 31 which isurged against its seat by means of a spring as shown. This valve member is provided with a guidev stem 33 received in a plug 33. The valve chamber 33 yis in communication with an air passage 40 in the lower housing mem-- ber II. This passage 40 coincides with a passage 4I in the upper housing member I2 which communicates with a pipe connection 42 providedon this housing member. The boss 32 also contains a vent valve chamber 43 which communicates with atmosphere through a vent 44 and which contains a valve member as which is identical in to the valve member 31. The valves cated as 50. This thermostat is shown as consisting of a bimetallic element 5I cooperating with a leak port 52. The leak port 52 is connected to an air supply pipe 53 through a restriction 54 and is also connected by pipe 55 to the pipe connection I4 of the device I0. Air may be supplied at lbs. per square inch pressure through the pipe 53, and the thermostat 55 Opf" erstes to vary the pressure in pipe 55 and conseduently in thediaphragm I3 of the positioning device I0 in accordance with variations in -texn-l perature at this thermostat. Assuming that the damper motor lcontrols the supply of heat to a space and that the thermostat 50 is responsive to the space temperature, this thermostat may be arranged so as to cause complete closure of the leak port 52 when space temperature rises to 71 F. This will cause a pressure of 15 lbs. per square inch to be applied to the diaphragm I3. This thermostat 50 may be also arranged to causeV the leak port 52 to be wideV open when the space temperature falls to 69 F. Thus for this value of space temperature zero pressure will be applied to the diaphragm I3 of the positioning device I0. It will therefore be apparent that the pressure in the diaphragm I3 is varied ln'aocordance with the temperature at thermostat 53. As this diaphragm I3 is biased by the spring I5 it will be apparent that the position of the stem I3 will vary in accordance with the pressure in diaphragm I3 and therefore in accordance' with the temperature at thermostat 50. Thus when the bimetallic element 5I is at an intermediate position for applying 'I1/2 lbs. per square inch pressure to the diaphragm I3, this diaphragm will assume the intermediate position shown, while expanding upon temperaturerise and contracting upon temperature fall.

With the parts in the positions shown, the

^ space temperature is approximately 70 which has caused a pressure of 'W2 lbs. pressure to be applied to the diaphragm I3. This has caused the lever arm 5 to assume midposition for thus causing the damper or valve being controlled to be half open. -If the space temperature should increase, the thermostat 50 will increase the pressure applied to the bellows I5 which will cause downward movement of the stem I3 to a position in which the tension of. spring I5 just balances the increased pressure within diaphragm I3. This downward movement of the stem I8 will shift bodily the compensating diaphragm 2| downwardly thereby causing rotation of the floating lever arm 25 about pivot 55. This will cause counter-clockwise rotation of the valve lever 45 about its pivot formed in diaphragm 41 thereby opening the valve 31. Opening of valve 31 will permit a flow of air under pressure from against theaction of spring 5 which will cause shifting of the device being controlled in a manner to decrease the supply of heat to the space. As the lever arm 5 is rotated upwardly, the lefthand extension thereof will rotate downwardly which will permit downward. movement of the lever 21 andthus causes counter-clockwise rotation of the floating lever 25 about the pivot in clevis 22. This in turn will cause clockwise rotation of the valve lever 45 for thus shifting the supply valve 31 towards closed position. When the motor movement corresponds to the downward movement of the stem I5 due to change in pressurein the diaphragm I3, the valve 31 will be. returned to complete closed position and consequently the motor will remain stationary.

Assuming a decrease in temperature at the 'thermostat 55, this thermostat will increase the air iiow through leak port 52 thereby decreasing the pressure in the diaphragm -I3 which will cause contraction oi' this diaphragm until the decrease in tension of spring I3 corresponds to the decrease in pressure in diaphragm I3. 'Ihis will cause upward movement of the stem I3, diaphragm 2i and clevis 22, for thus rotating the iloating lever 25 upwardly about pivot 55 which in turn rotates the valve lever 45 in a direction for opening valve 45. 'I'his opening of valve 45 will permit air toilow from the motorthrough the vent 44 to atmosphere. which will permit the spring 5 to rotate the lever arm 5 in a clockwise direction about its pivot 5 for increasing the supclevis 22. This will rotate the valve lever 43 counter-clockwise for moving the valve 45 towards closed position. It will be apparent that when the motor movement corresponds to the decrease in pressure in diaphragm I3, the lever 45 will have moved Just far enough to close the vent valve 45 for retaining the motor stationary.

From the description thus far it will be apparent that the device described providesy for causing the motor to assume the position demanded by the thermostat 5,0 and that the motor diaphragm is either supplied with full line pressure or is vented until it reaches the proper position. One defect in the sinple follow-up system Just described is that it requires a variation in the condition being controlled from the desired value in order to-cause movement of the motor from mid-position. Thus the thermostat 50 is desired to control at F. and will maintain the space temperature at this desired value for intermediate heating loads. However, during times of light load it is necessary to decrease the supply 0f heat and in order for the motor I to completely stop the supply of heat. the space temperature must rise to 71 F. Conversely during cold weather when maximum heating is required the space temperature must fall to 69 F. before the motor I will cause the valve or damper to be wide open. -The simple follow-up system therefore is not capable oi' maintaining the space temperature at the control point of the thermothe supply pipe 53 through pipe 51, passages 4I and 40, into the valve chamber 35 and through the valve port into chamber 33 from which it l. flows through passage 54 and pipe 53 into the motor diaphragm. This ilow of air under pressure into the motor diaphragm will cause it to4 expand for rotating the lever arm 5 upwardly stat. namely '10 F., for all load conditions.

In order to avoid this undesirable resultl and to provide a system which will maintain the condition controlled at the desired value regardless of load, the diaphragm or cell 2I is provided. This cell is formed to be normally contracted so that it will expand upon increase in pressure therein and will contract upon decrease in such pressure. The pressure applied to the cell 2| is controlled by means of a compensating valve as sembly which is formed in a boss 60, forming a part of the upper housing member I0. This boss 60 is provided with a, central chamber 6| provided with an inlet valve 62 and a vent valve 63.` These valves may be arranged similarly to thelvalves 31 and 45 'previously described. The valve chamber for valve 62 communicates through a passage 66 with the air supply passage 4|. Consequently when this valve is open, air under pressure is supplied tothe chamber 6|. The valve chamber of the valve 63 communicates withatmosphere through a port 65 and thus vents chamber 6| when open. The valves 62 and 63 are actuated by a valve lever 66 which is 'pivotally secured to a diaphragm 61 which seals the open end of chamber 6|. Valve lever 66 is actuated by the diaphragm I3 and is shown as being attached to this diaphragm by means of a spring clip 63. Leading from the chamber 6I is a passage 69 the ilow of air through which is controlled by a needle valve screw 10, this valve communicating with a ilexible tube 1| which is attached to the compensating diaphragm or cell 2l. The needle valve 10 provides for restricting communication of the chamber 6| with the compensating cell 2|. This causes the pressure within the cell 2| to change very slowly in the event that either valve 62 or 63 is open.

With the parts in the positions shown, the tem*- perature within the space is at the control point of thermostat 50, namely 70 F. This has caused the diaphragm I3 to assume intermediate posi-l tion in whichthe valve lever 66 permits both valves 62 and 63 to be closed.v Consequently,

the chamber 6| and thecompensating cell 2| remain under a constant pressure. As long as this condition remains, the cell 2| will not change in length and consequently does not change the relationship between the diaphragm I3 and they iioating lever 25. The system will therefore control as previously described and the pressure within cell 2| will remain substantially constant low '10 `which causes the motor to increase the u supply f heat. At this time the increase in heat supply is obtained due to the space temperature falling below the control point of thermostat 50. However, upon the temperature within the space falling below this control point the diaphragm I3 contracts for Acausing movement of valve lever 66 in a direction for opening the vent valve 63. This will vent the chamber 6I and permit venting oi the -compensating cell 2| at a very slow rate as determined by the adiustment of screw 10. This slow venting o f cell 2| will cause counter-clockwise rotation of the iioating lever 25 about pivot 56 thus tending to open valve 65 for decreasing the pressure in the motor diaphragm -thereby increasing the supdue to the rising space temperature will continue until it re-assumes intermediate position at which the space temperature is at '10 F. and the valves 62 and 63 are closed. The pressure within the compensating cell 2| will now remain'constant until another change in the heating load.

The thermostat 50 and follow-up arrangement will therefore continue to control the motor position for counteracting temporary iiuctuations in space temperature.

In the event that the heating load upon the system decreases, the space temperature will rise and the thermostat 50 and follow-up mechanism willl cause an immediate change in position of the damper or valve formaintaining the space temperature within the control range of the thermostat. However, due to the decreasing load the space temperature will temporarily rise above 70 F. and consequently the bellows I3 will cause the valve lever 66 to open the supply valve 62 thereby slowly increasing the pressure in the compensating cell2 I. The resulting slow expansion of the cell 2| will cause rotation of the oating lever 25 about pivot 56 in a direction for opening valve 31 and supplying additional air to the motor. Expansion -of the cell 2| thus causes the supply of heat to the space to be slowly decreased, which permits the space temperature to fall back to the control point of thermostat 50 at which time the valve v6| will again be closed and the'cell 2| will remain at its new length. f

If desired, the tube 1| may also communicate with an external chamber for thus further decreasing the rate of pressure change within the compensating cell 2|.

From the foregoing description it will be apparent that I have provided a control device which will positively position a pneumatic motor in accordance with the demand of -its controller and which also compensates for changes inload upon the system in a manner to maintain the condition being controlled at the center of the control range of the controller or in other words,`

at the desired control point. It will also be apparent thatl this compensation is obtained by the use of a'variable linkage comprising an expansible cell, the pressure in which is directly controlled by the condition responsive device in a manner to cause a slow and continuous compensating action until the value of the condition is returned tothe exact desired value.

ply of heat to the space. This action of increasrising, which will cause expansion of the diaphragm I3. This expansion of diaphragm I3 While throughout this description itfhas been assumed that the device is utilized for con--` trolling a heating system and deilnite values of pressure and temperature have been mentioned, it will be understood that the invention is not limited to heating systems and may be used for controlling any condition. Also it will be understood that the various values of temperature and pressure may be varied as desired for diilerent types of installations. Also while my improved load compensating arrangement is of especial utility in combination withthe follow-up system which provides for a quick initial response, it

'will be apparent that this compensating arrangement vis of utility in systems not, utilizing positive follow-up. As manymodiilc'ations which are within the scope of this invention will occur 'to those skilled in the art, I desire to be limited only by the scope of the appended I claim as my invention: 1. In a control systemQin combination, a con'-4 trol device to be variably positioned, reversible motor means for actuating said control device',

claims.

said reversible motor means comprising an expansible chamber having a movable wall, motor control valve means for selectively causing movement oi said motor means in either direction and for stopping said motor means in any one of a plurality of 4intermediate positions, a condition responsive means, connecting means by means of which the movement of said condition responsive means is mechanically transmitted to said motor control valve means to cause said motor control valve means to move in a manner to cause the movable wall of said motor means to move proportionately to change in condition at said condition responsive means,l a variable linkage in said connecting means between said condition responsive means and said motor control valve means comprising a cell adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said cell, and means connected for actuation by said condition responsive means for positioning said compensating valve means in a manner to vary said linkage when the condition being controlled is not at the control point oi said condition responsive means.

. 2. In a control system, in combination, a control device to be variably positioned, reversible motor means for actuating said control device. said reversible motor means comprising an expansible chamber having a movable wall, motor control valve means for selectively causing movement o1' said motor means in either direction and for `stopping said motor means in any one oi a plurality of intermediate positions, a condition responsive means, connecting means by means of which the movement oi said condition responsive means is mechanically transmitted to said motor control valve means to cause said motor control valve means to move in a manner to cause the movable wall of said motor means to move proportionately to change in condition at said condition responsive means, a variable linkage in said connecting means between said condition responsive means and said motor control valve means comprising a cell adaptedato expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure appliedto said cell, said compensating valve means including inlet and exhaust valves for admitting fluid to said cell or for exhausting said cell, and means connected for actuation by said condition responsive means for positioning said compensating valve means in. a manner to close said supply and exhaust valves when the condition being controlled is at the control point 'or said condition responsive means while opening one or the other of said valves when said condition means deviates from .said control point.

plurality of intermediate positions, a pressurey actuated device, a source of fluid at a pressure differingA from atmospheric, a condition responsive cf ntroller connected to said pressure actuated device and to said source for varying the pressure appliedl to said pressure actuated device in proportion to change in the condition to which said controller responds, connecting means by means ci which the movement o! said condition responsive means is mechanically transmitted to said motor control valve means to cause said motor control valve means to move in a manner to cause the movable wall of said motor means to move proportionately to change of said condition, a variable linkage in said connecting means between said condition responsive means and said motor control valve means comprising a cell adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said cell, and means connected for actuation by said vpressure actuated devicefor positioning said compensating valve means in a manner to vary said linkage when the condition being controlled deviates from the control point of said condition responsive controller.

4. In a control system, in combinationJL a control device to be variably positioned. reversible motor means for actuating said control device, said reversible motor means comprising an expansible chamber having a movableD wall. motor control valve means for selectively causing movement of said motor means in either direction and for stopping said motor means in any one o! a plurality or intermediate positions, a pressure actuated device, a source o! iluid at a pressure dinering from atmospheric, a condition responsive controller connected to said pressure actuated device and to said source for varying the pressure applied to said pressure actuated device in proportion to change in the condition to which said controller responds, connecting means by means o! which the movement of said condition responsive means is mechanically transmitted to said motor control valve means to cause said motor control valve means to move in a manner to cause the movable wall oi said motor means to move proportionately to change oi said condition, a variable linkage in said connecting means between said condition responsive means and said motor control valve means comprising a cell adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure spplied to said cell, said compensating valve means includinginlet and exhaust valves for admitting nuid to said cell and for exhausting said cell, and means connected for actuation by said pressure actuated device for positioning said compensating valve means in a manner to close said supply and exhaust valves when the condition being controlled is at the control point of said condition responsive controller, while opening one or the other oi' said valves when said condition deviates from said control point.

5. In a control system, 4in combination, a control devlce to be variably positioned, reversible motor means for actuating said control device.

said reversible motor means comprising an expansible chamber having a movable wall, valve means for controlling the application of pressure to said expansible chamber, a condition responsive means, a follow-up device actuated upon movement of said motor means, said condition responsive means and said follow-up device being mechanically connected to said valve means and conjointly controlling said valve means for thereby causing movement of said motor means in proportion to changes in the condition to which the' condition responsive means responds, compensating means associated with said valve means for controlling said valve means conjointly with said condition responsive' means and said follow-up device for varying the relationship between said condition responsive means and said motor means, said compensating means comprising a cell in the connection between said condition responsive means and said valve means adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said cell, and means connected for actuation by said condition responsive means for positioning said compensating valve means in a manner to vary the pressure in said cell when the condition being controlled deviates from the control point of said condition responsive means.

6. In a4 control system in combination, a control device to be variably positioned, reversible motor means for actuating said control device, said reversible motor means comprising an expansible chamber having a movable wall, valve means for controlling the application oi pressure to said expansible chamber, a condition responsive means, a follow-up device actuated upon movement of said motor means, said condition responsive means and said follow-up device being mechanically connected to said valve means and conjointly controlling Vsaid valve means for thereby causing movement of said motor means in proportion to changes in the condition to which the condition responsivemeans responds, compensating means associated with said condition responsive means for adjusting said condition responsive means, said compensating means comprising a cell in the connection between said condition responsive means and said valve means adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said cell, and means connected for actuation by said condition responsive means for positioning said compensating valve means in a manner to vary the pressure in said cell when the condition being controlled deviates from the control point of said condition responsive means.

7. In a control system. in combination, a control. device to be variably positioned. reversible motor means for actuating said control device,

said reversible motor means comprising an expansible chamber having a movable wall, valve means for controlling the application oi' pressure to said expansible chamber, a condition responsive means, a follow-up device actuated upon movement ot said motor means, said condition responsive means and said follow-up device conjointly controlling said valve means for thereby causing movement of said motor means in proportion to changes'in the condition to which the condition responsivemeans responds, compensating means associated with said valve means -ior controlling said valve means conjointly withl said condition responsive means and said followupR device for varying the relationship between said condition responsive means and said motor means, said compensating means comprising a cell adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said cell including inlet and exhaust valves for admitting iluid to said cell and for exhausting said cell, and means connected for actuation by said condition responsive means for positioning said compensating valve means in a ma er to close said inlet and exhaust valves when the condition being controlled is at the control point of said condition responsive means,

while opening one or the other o! said valves when said condition deviates from said control point.

8. In a control system in combination, a con- I trol device to be variably positioned, reversible motor means for actuating said control device,

said reversible motor means comprising an expansible chamber having a -movable wall, valve means for controlling the application o! pressure to said expansible chamber, a condition responsive means, a follow-up device lactuated upon movement of said motor means, said condition responsive means and said follow-up device being mechanically connected to said valve means and conjointly controlling said valve means for thereby causing movement of said motor means in proportion to changes in the condition to whichl i compensating valve means in a manner to close said inlet and exhaust valves when the condition being controlled is at the control point of said condition responsive means, while opening one or the other of saidvalves when said condition deviates from said control point.

9. In a control system, in combination, a control-device to be variably positioned, reversible motor means tor actuating 'said control device,

said reversible motor means comprising an expansible chamber having a movable wall, a condition responsive device, a source of iluid under pressure differing from atmosphere, a control line, said condition responsive device .being connected to said source and to said control line for varying the pressure in said control line in accordance with the value oi* the condition to which said condition responsive device responds, positive positioning means for controlling said reversible motor means in a manner to cause movements oi said motor proportionate to changes in pressure in said control line, said positive positioning means comprising valve means for controlling the pressure applied to said motor means.

.pressure actuated means connected to said control line, and follow-up means actuated by said motor means, said pressure actuated means and .said follow-up means conjolntly controlling said valve means, an expansible cell associated with said positive positioning means for adjusting said positive positioning means, said cell being adapted to expand and contract upon changes in pressure applied thereto, compensating valve means for controlling the pressure applied to said' cell. and means actuated by changes in pressure in said control line for actuating said compensating valve means in a manner to change the pressure applied to said cell when the condition being controlled deviates from the control point of said condition responsive device.

l0. In a control system, in combination, a coni trol device to be variably positioned, reversible 6 epesses dition responsive device, a source of duid under pressure differing from atmosphere.v a control line. said condition responsive device being oonnected to said source and to said .control line for varying the pressure in said control line in accordance with the value or the condition to which said condition responsive device responds,

positive positioning means for controlling said.

reversible motor means in a mannerto cause movements oi said motor proportionate todo changes in pressure in said control line. said positivo positioning means comprising valve means for controlling the pressure applied to said motor means, pressure actuated means connected to said control line. and follow-up means 15 actuated by said motor means, said pressure actuated means and said follow-up means conjointly controlling said valve means, an expansible cell associated with said positive positionins means for adjusting said positive positioning means, said cell being adapted to expand and contract upon changes ln pressure applied thereto. and compensating valve means for controlling the pressure applied to said cell, said compeneating valve means including inlet and exhaust' control point.

FREDERICK C. BRANDT.

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