Table Of ContentSeminar on Pneumohydraulic Automation
(First Session)
PNEUMATIC A N D
HYDRAULIC
CONTROL SYSTEMS
In Two Volumes
VOLUME 1
U N D E R T H E E D I T O R S H I P O F
M.A. A I Z E R M A N
Doctor of Technical Sciences
T R A N S L A T E D F R O M T H E R U S S I A N B Y
P . L I N N I K
T R A N S L A T I O N E D I T E D B Y
J . K . R O Y L E A N D F . P . S T A I N T H O R P
P E R G A M O N P R E S S
O X F O R D · L O N D O N · E D I N B U R G H · N E W Y O R K
T O R O N T O · S Y D N E Y · P A R I S · B R A U N S C H W E I G
Pergamon Press Ltd . , Headington Hil l Hal l , Oxford
4 & 5 Fitzroy Square, London W . 1
Pergamon Press (Scotland) Ltd. , 2 & 3 Teviot Place, Edinburgh 1
Pergamon Press Inc., 44-01 21st Street, L o n g Island City, N e w Y o r k 11101
Pergamon of Canada, Ltd . , 6 Adelaide Street East, Toronto, Ontario
Pergamon Press (Aust . ) Pty. Ltd. , Rushcutters Bay, Sydney, N . S . W .
e
Pergamon Press S . A . R . L . , 24 rue des Écoles, Paris 5
Vieweg & Sohn G m b H , Burgplatz 1, Braunschweig
Copyright © 1968
Pergamon Press Ltd.
First English edition 1968
This is a translation of the Russian book
B o n p O C H Π Η Θ Β Μ Ο - H Γ Η ^ ρ θ - a B T O M a T H K H
(Voprosiy pnevmo- i gidro-avtomatiki)
published by A k a d . N a u k SSSR
Library of Congress Catalog Card N o . 66-19864
1103/68
TRANSLATOR'S FOREWORD
I N A collection of this kind, it is inevitable that some overlapping occurs be-
tween works on closely related subjects, particularly where the same author
is represented by a paper read at a conference, as well as by a magazine
article, which did not appear in the original book. As a rule, in such cases too
severe pruning is undesirable, because it would lead to untidy structure, un-
warranted deviations from the author's line of reasoning, and overburdening
by cross-references. Only in a few instances the considerations of economy
were allowed to prevail. The sequence of articles was changed in order to
bring together the related works, and it has been found that some further
rearrangements, authorized by the Editor of the Russian original, were needed
to improve the "balance" of the English edition.
P. L.
ix
TO ENGLISH READERS FROM THE EDITOR
OF THE RUSSIAN ORIGINAL
P E R G A M O N PRESS, in agreement with the International Book Society, has
decided to publish in English the collection of Russian works on the subject
of pneumatic and hydraulic automatic control. This collection includes the
papers presented to the "Symposium on Pneumo- and Hydro-automation"
in Moscow in 1957, and published by the Academy of Sciences U.S.S.R. in
1959, as well as works by several authors, printed in the magazine Avtomatika
i Tekmekhanika (Automation and Remote Control), in the years from 1947
to 1959.
Not long ago, it seemed to the majority of automatic control specialists
that remarkable successes of electronics have predetermined the main line of
development in automation techniques, and the importance of pneumatic
and hydraulic equipment is bound to decline from year to year. As often
happens, a rapid growth of one or another branch of engineering led to ex-
cessive enthusiasm and rash conclusions. N o w it is already certain that
pneumatic and hydraulic means of automation have held their ground
against the powerful onrush of new developments and new technological
ideas. In recent years, one hears more and more often the opinion that pneu-
matic and hydraulic automatic control has, and will continue to have, its own
domain of applications, which is still expanding. As a result, there is a rapidly
growing interest in scientific research and design investigations in the field of
pneumatics and hydraulics, as applied to automation.
In the light of these facts, the decision of Pergamon Press is undoubtedly
useful and timely, furthering the development of scientific contacts also in
this branch of engineering. It must be kept in view that the present collection
incorporates only a small part of Russian works on pneumatic and hydraulic
automatic control, and can provide but an incomplete picture of the develop-
ment of this branch of science and engineering in the U.S.S.R.
M . A . A I Z E R M A N
χ
PNEUMATIC EXTREMUM CONTROLLERS
I AT A N U.S.S.R.
Y u . I . O S T R O V S K I I
T H E O B J E C T O F E X T R E M U M C O N T R O L L E R S
Extremum controllers are required to find and maintain to a required ac-
curacy an extremum of a measured quantity, which varies with time in an
unspecified way. The location of the extremum is accomplished by an auto-
matic survey.
Extremum regulation is advantageous only when (a) optimum operation of
a process in a controlled system depends on an extremum (maximum or
minimum) of a certain characteristic parameter (for example, maximum ef-
ficiency, minimum fuel consumption, or consumption of a similar agent at a
given output of the plant, etc.) and (b) , when the magnitude of this charac-
teristic parameter, which has an extremum value under certain conditions, is
determined not by one but by several other parameters. These parameters
can be divided into two groups : the first group would comprise parameters
which cannot be influenced by a controller (e.g. the kind of fuel, the condition
of the surrounding atmosphere, the degree of wear of a plant, the load, etc.),
where the prediction of these parameters by calculations is either very dif-
ficult or impossible. The second group comprises parameters which are af-
fected by a controller. Their optimum values, which define the extremum,
depend on parameters of the first group.
Let us consider a concrete example. Figure 1 shows the block diagram of
a control system for a heating furnace. The temperature controller TC main-
tains the desired temperature t0 of the object Ο by acting on the control
valve ROx. This alters the fuel consumption Qf. The corresponding air
consumption Qa is established by a ratio controller RC, which maintains a
pre-set ratio QajQf = oc. The values of t0 and oc are determined by setting
controls SCt and SC2.
The controlled furnace can be considered as a series connection of two
elements—the flame chamber FC and the heated object O. The temperature
ίφ of the flame in the chamber depends on the regulated quantities Qf and
Qa, and also on unpredictable air leaks Q'a, the condition of fuel nozzles Φ
(their erosion, dirtiness, etc.) and on other factors. The temperature t0 of the
object at a steady state depends on the flame temperature, on the heat trans-
3
4 P N E U M A T I C A N D H Y D R A U L I C C O N T R O L
fer coefficients kt and k2 (from flame to object, and from object to its en-
vironment), and on the load L (e.g. on the discharge rate of the heated agent).
Obviously, the optimal running of the process from the viewpoint of
economy requires a desired temperature t0 with the minimum fuel consump-
tion.
The minimum fuel consumption, which may be attained at the optimum
value of oc = Qa/Qf (a parameter of the second group), depends on the load,
SC?
i
Air RC
Qa Φ ki ko
R02 Qg i i
^
FC 0
R01 Qf
in
Fuel
TC
F I G . 1. Block diagram of the furnace control without an extremum controller.
F I G . 2. Block diagram for the control of air-fuel ratio by an extremum controller EC
acting on the setting of the ratio controller RC. Minimum fuel consumption is main-
tained.
P N E U M A T I C E X T R E M U M C O N T R O L L E R S I A T A N U . S . S . R . 5
properties of the fuel, heat transfer coefficients k1 and k2, and the condition
of the nozzles. All these factors cannot be calculated accurately, and vary
with time. They can be considered as belonging to the second group of
parameters.
The optimum value of oc depends also on the properties of the fuel, and on
non-calculable, chance air leakage.
As can be seen, the two conditions given above which make the applica-
tion of extremum control advantageous are fully present here.
Figure 2 shows one of the possible layouts for this particular case. The
extremum controller EC acts continuously on the setting controls SC2 of the
ratio controller RC. The temperature controller TC suitably alters the fuel
w t o
fl° C?/ » maintain a given temperature 10. The extremum controller chooses
that setting of SC2 which ensures the minimum value of Qf. In fact, the
setting of SC2 oscillates with a relatively small amplitude about the deter-
mined optimum value.
If the object Ο has a substantial thermal capacity, the variation in SC2 set-
ting (searching the extremum) must be carried out relatively slowly; other-
wise the changes of fuel flow Qf would lag behind the changes of the SC2
setting, and the air flow would fluctuate with a large amplitude. As a result,
the economy of the plant would suffer. A low rate of searching the extremum,
however, is only possible if the parameters of the second group, which in-
fluence the optimum ratio, change infrequently and slowly. But if some of
them (e.g. load, or properties of fuel) are subject to frequent variations, the
scheme given above may prove to be impracticable. In this case the layout
shown in Fig. 3 may be used. Here the extremum controller acts on the
setting control of the ratio controller, in order to determine the maximum
flame temperature ί φ. With an increased flame temperature, the temperature
of the object will rise and the temperature controller TC will accordingly
reduce the fuel rate. If the response rate of the circuit RC—R02—FC—EC
is much greater than that of the circuit TC—RO^—FC—0, then, as a result
of simultaneous action of the controllers, the fuel consumption will take a
minimum value and will not oscillate appreciably, while the air consumption
will oscillate about the optimum value, and the temperature t0 will oscillate
about the maximum for a given fuel consumption.
The layout shown in Fig. 4 differs in having the extremum controller acting
not on the setting control of the ratio controller, but directly on the control
valve R02, which controls the air flow. This scheme is suitable when a high
searching rate can be used, in order to cope with drastic changes of the
working conditions (for example, with sudden changes of load).
Figure 5 shows the relationship between the flame temperature of a
metallurgical heating furnace and the air consumption at a constant rate
of consumption of fuel oil. The curves were obtained by A.Butkovskii of the
Steel Institute for one of the furnaces of the "Sickle and Hammer" Works.
The curves were taken at various times. They indicate that the actual setting
6 P N E U M A T I C A N D H Y D R A U L I C C O N T R O L
F I G . 3. Blockdiagram for the control of air-fuel ratio by an extremum controller EC
acting on the setting of the ratio controller RC M a x i m u m flame temperature is
maintained.
of the air-fuel ratio controller has not been at the optimum. At the optimum
setting, the flame temperature could have been increased, on the average, by
30°C, or the same flame temperature could have been obtained at a lower
rate of fuel consumption by the simultaneous use of a temperature controller
and an extremum controller.
ΤΓ
Fuei
TsCi
F I G . 4. Block diagram for the control of air-fuel ratio by an extremum controller
acting directly on the control valve.
P N E U M A T I C E X T R E M U M C O N T R O L L E R S I A T A N U . S . S . R . 7
1*50
Air consumplion per cent of max.
F I G . 5. Relationship between flame temperature and air consumption at a constant
rate of consumption of fuel oil. 181—conditions at the beginning of the measure-
ments.
T H E P R I N C I P L E OF T H E P N E U M A T I C E X T R E M U M
C O N T R O L L E R
The extremum controller described is based on the principle of "memorizing
of maximum". If the task is to find a minimum and not a maximum, then the
sign of a measured quantity is inverted in the transducer.
The measured quantity y (in the example given above—temperature) is
transformed into a proportional air pressure, which enters the input of the
extremum controller. The air pressure Px at the output of the extremum
controller determines the magnitude of the input of the system (on the
schemes of Figs. 2 and 3 this input is a particular setting of the control SC2
at the ratio controller, and in Fig. 4 the position of control valve R02).
An example of a static characteristic y = f(x) of a system is shown in
Fig. 6, a. Figure 6, c shows the change of pressure Px as a function of time, and
Fig.6,b corresponding changes of pressure Py. A t the instants tel the pres-
sure Py attains its maximum value Pyma x and with further changes of Px be-
gins to decrease. With an "inertial" system, the value of Pyma x will be smaller
than Pyina x corresponding to the static characteristic. The value of Pyma x at-
tained is registered by a special device, a "memory unit" (see Fig. 7).
8 P N E U M A T I C A N D H Y D R A U L I C C O N T R O L
F I G . 6. Operation of the pneumatic extremum controller.
The pressure Pm in the "memory chamber" of this unit follows the pressure
Py when Py increases, but when Py begins to diminish, the magnitude of Pm
remains constant (the dotted line in Fig. 6).
CPD
F I G . 7. Layout of the pneumatic extremum controller. M—memory unit; CU—com-
parison unit; RS—step switch; CPD—constant pressure drop unit; Ο—controlled
object; RO— control valve; T— transducer; PR—pressure reduction valve; Th—
controlable throttles; FR—fixed restrictors; N— nozzles; Β—bafles; S—springs;
V— seated valve; R—sealing ring; RV— rotary valve; Ρ—pressures.
