Table I. Integrated Absolute En-or for a Second-Order Servomechanism Subject to a
Step Input of Magnitude Ρ
Ιωο Ρ
0 . 1 6 . 3 8 4 0 . 2 3 . 3 4 1 0 . 3 2 . 3 6 4 0 . 4 1.924 0 . 5 1.712 0 . 6 1 .618 0 . 6 5 1.606 0 . 7 1 .608 0 . 8 1.631 0 . 9 1.804 1.0 2 . 0 0 0
integrated absolute error of a second-order system subjected to a step input becomes
— σθι
(6)
This form of the equation is particularly
useful when ζ approaches unity, where the other equation leads to an indeterminate form. For f = l , equation 6 of the discussion gives directly
ωο (7)
which can also be obtained by direct integration of the error for the critically damped case. For Γ > 1 , the integrated absolute error is the same as the integrated error and can be found ^ by adding the time constants of the closed-loop transfer function.
For purposes of comparison and to save future workers some labor, values computed from equation 6 are given in Table I of the di.scussion.
In some experimental studies similar to those described in the paper, we have been using a slightly different method for determining the integral of the error. In our case, a voltage proportional to the error was applied to an integrating amplifier in which the usual input resistor had been re
placed by a diode rectifier. With this arrangement, only errors of one sign are integrated; the diode characteristics determine whether the absolute or squared error, or some intermediate power of the error, is used. Part of the integral is found by application of a positive signal to the input of the simulated servomechanism, and the remainder is found by applying an equal negative input, which simply means removing the previous signal.
This technique, although less elegant than the procedure described in the paper, is useful when the time constants in the computer sinmlation are fairly large, and it eliminates the need for an absolute value unit.
R E F E R E N C E S 1. See reference 9 of t h e pape r .
R. R. Caldwell and V. C. Rideout: We wish to thank Mr. Stout for pointing out the simplifications possible in equation 2 of the paper.
Diesel-Electric Locomotive Ground
Relays
G . R. M C D o n a l d A S S O C I A T E M E M B E R AIEE
Synopsis: The following paper lists and describes the various protective functions of the ground relay as used on diesel-electric locomotives. The connections are described, and comments are made on the control features initiated by the operation of the relay.
General Functions
TH E USE of ground relays s tar ted in the early 1920's in au tomat ic substa
tions. These relays were primarily for the purpose of limiting the damage caused by armature breakdown. P rompt oi)era-tion of an instantaneous-type r d a y Hm-ited damage to conductors and ani ia ture stackings. The relay also furnished similar protection for commuta to r flash-overs.
The first use of a ground relay on a diesel-electric locomotive was about 1930. The first relays installed for this purpose were low-resistance high-current devices. In fact, some of these early relays did not have enough resistance to be self-protecting on the high currents imposed by flashovers, and as a consequence the relays were severely damaged by a flash-over. Higher resistance, higher voltage relays were, therefore, in order. Along
with the tendency in this direction, other miscellaneous functions were entrusted to the ground relay until now the list of protective features which i t provides is quite imposing. Any discussion of this relay, therefore, involves having a clear concept of these various functions and their interrelations.
The following list covers most of the protective functions now performed by the ground relay.
1. Armature grounds in either the main generator or in the traction motors. 2. Accidental power circuit grounds:
(a) On the positive power circuits. (b) On the power cables which are at one-half of the generator voltage during series-parallel operation. (c) On the negative power circuits.
3. High resistance creepage grounds, such as those caused by moisture and dirt:
(a) On the positive circuits. (b) On the half-voltage circuits.
P a p e r 53-77 , r e c o m m e n d e d b y t h e A I E E L a n d T r a n s p o r t a t i o n C o m m i t t e e a n d a p p r o v e d b y t h e A I E E C o m m i t t e e on Techn ica l O p e r a t i o n s for p r e s e n t a t i o n a t t h e A I E E W i n t e r Gene ra l M e e t i n g , N e w Y o r k , N . Y. , J a n u a r y 1 9 - 2 3 , 1953. M a n u scr ip t s u b m i t t e d O c t o b e r 20, 1952; m a d e ava i l ab l e for p r i n t i n g D e c e m b e r 3 , 1952.
G. R . M C D O N A L D is w i th t h e G e n e r a l E l e c t r i c C o m p a n y , E r i e , P a .
(c) On the negative circuits. (d) On the armatures of generator or motors.
4. Flashover protection: (a) Generator armature. (b) Motor armature with motors operating in parallel, (c) Motor armature on the positive side when operating in series parallel. (d) Motor armature on thenegative side when operating in series parallel. (e) Positive side contactor flashover. (f) Negative side contactor flashover. (g) Series contactor flashover (one-half generator voltage).
5. l^rotection during dynamic braking: (a) Motor flashover. (b) (jround in braking resistor. (c) Leakage or moisture ground. (d) Resistor blower motor groimd or flashover.
6. (jround protection during engine starting.
A short discussion of each of the preceding j)oints will help to clarify the functions of this relay. This discussion is based on an Alco-GE road locomotive. The .ground relay considered has a pickup
GR RELAY
Figure 1 . Ground relay connected on nega-tive side of generator
1 7 0 McDonald—Diesel-Electric Locomotive Ground Relays J U L Y 1 9 5 3
h
)
•c PI •c PI IP
) )
^ 1 0 2 Ό 3 0 4 K ) 5 0 6 0 7 0 6 K } 9 O K D O I 10 IS
GENERATOR F R E O U E N C Y - ( C P S . )
Figure 2. Ground relay pickup with generator armature grounded
of 38 volts with a coil current of 0.056 ampere. T h e coil resistance is 680 ohms. This relay is connected as shown in Figure 1.
ARMATURE GROUND
Consider a ground a t one point on a generator armatiu-e. As the a rma tu re rotates this ground will t ravel from one polarity to the other. A relay connected as shown by Figure 1 will have appHed to it an undulat ing voltage practically the equivalent of a completely displaced a-c wave. T h e relay pickup when operating on this voltage will be as shown by Figure 2. With this connection of the relay the drop through the generator commuta t ing field will modify the actual voltage required by a small amoun t resulting from the drop through this field.
Op^eration in detecting an a n n a t u r e ground for a parallel connected motor is identical with t h a t described for a generator, except for the slight modification caused by the commuta t ing field drop. If the a rma tu re ground were on a series-parallel connected motor operating on the positive side of the line, the voltage applied to the relay would be equal to one-half of the generator voltage plus the undulating voltage from this a rmature . The relay would pick up a t a slightly lower voltage t h a n indicated by Figure 2 because of the larger d-c component . If the ground were in the a rmature of a series-parallel ctmnected motor operat ing on the negative side of the line, conditions would
0 A L T E R N A T E Λ G R R E L A Y V
C O N N E C T I O N v -C . C O M M . C F I E L D
be the same as for a generator a rmature except t h a t this relay would be subjected to the voltage of this negative armature . This would be one-half of the generator voltage, and therefore, the pickup of the relay with respect to generator voltage would be double t h a t shown by Figure 2 .
These comments on a rmature grounds presupposed a zero resistance ground in an a rma t tue . If the a n n a t u r e ground actually has appreciable resistance as compared to the relay, then the voltage required to operate the relay will be correspondingly increased.
ACCIDENTAL POWER CIRCUIT GROUNDS
(a) If a ground takes place on the positive side of the power system, generator voltage would be applied directly to the ground relay. If this ground were of zero resistance, the relay would operate when the generator voltage reached 38 volts. If t he ground h a d appreciable resistance, the operat ing voltage would be correspondingly increased.
(b) If the ground took place in the connection between positive and negat ive motors when operating in the series-parallel connection, the same comments would apply except t h a t the relay pickup in terms of generator voltage would be doubled.
(c) If a ground took place on the negat ive of a system i t would appear , a t first thought , t h a t the ground relay coil would be short-circuited. Figure 3 illustrates this circuit. If t he ground took place on the lead B, the coil of the ground relay would be short-circuited. If, however, the ground took place on leads C or D, the series field would be intermediate between the ground location and the circuit through the ground relay. Ordinary s teady-state voltages developed across the series field would no t be sufficient to operate the relay; however, any fluctuations in current would create enough inductive voltage across the series field to provide operation if the ground were on either C or D. An improvement on this circuit is to move the ground relay connection from A to E. In this case the
transient inductive voltages of both the generator commuta t ing field and the motor series field are effective for producing relay operation with grounds on either C or D, and the generator commutat ing field inductive voltage is available for producing operation with a ground on B.
MOISTURE OR CREEPAGE GROUNDS
One place where the ground relay does, if anything, too good a job is in connection with moisttire or creepage grounds. These are always a mat te r of degree and most types of ground relays overprotect, causing unnecessarv^ interference with locomotive operation. However, this ma t t e r is, somewhat involved, particularly from the standpoint t h a t all of the leakage current does not necessarily pass through the relay coil.
(a) If leakage is taking place from the positive cable terminations and connections of the system, then conditions are identical with item (a) in the preceding section. Tak ing into account the equivalent resistance of the leakage path , the generator voltage with respect to relay pickup may readily be calculated.
(b) T h e same comments apply for leakage taking place on the cable terminat ions and connections between two or more series connected motors .
(c) vSimilar leakage from the negative does not tend to cause relay operation for the same reason as discussed under item (c) in the preceding section. The change in relay connections already mentioned would improve this situation, b u t the leakage resistance from the negative alone would have to be of a low value before relay operation could be expected.
(d) Leakage m a y be experienced from armatures because of the collection of dir t and moisture. This would usually be expected to occur a t the commutator string bands or a t the ends of the armature coils. If distr ibuted leakage of this
BRUSHI
! S E R I E S i F I E L D
" ^ R E V E R S E R
• G R R E L A Y
Figure 3 (left). Schematic diagram of negative
power circuits
Figure 4 (right). Paths of distributed leakage over commutator string
band
- BRUSHES
^ GR LEAKAGE ^ RELAY
lURFACE (string bond)
J U L Y 1 9 5 3 McDonald—Diesel-Electric Locomotive Ground Relays 1 7 1
1000 ,
h
§ (Τ
Ζ3
5
8 0 0
6 0 0
4 0 0
ω 200^
>
Fisure 5 (left). Ground relay pickup with distributed armature leakage
ARMATURE RESISTANCE TO G R O U N D - O H M S
Fisure 6 (lower leit). Equivalent circuits ior distributed cable leakase, parallel
connected motors
< 6R ^ R E L A Y ,
PCS. LEAKAGE RES.
Ϊ Ϊ r NE6. LEAKAGE RES. Fisure 7 (risht). Total leakase
current at s^ound relay operation
SOOr
40d
o) 300f
a:
I I 200 UJ
100
α I 0.2 0.3 0.4 0.5 0.6 0.7 TOTAL GENERATOR LEAKAGE CURRENT-AMPERES
type takes place, t he voltage apphed to the leakage pa ths varies between brushes or polarities around the a rmature . T h e leakage is in all directions even from one segment to the next, as shown by Figure 4 . T h e relay sees only a small pa r t of this total leakage current. Tests indicate tha t with uniform leakage around an armature , relay operation may be expected as shown by the curve of Figure 5. T h e armature insulation resistances used in plotting this curve are, of course, resistances taken a t standstill . T h e a rmature insulation resistance values shown are surprisingly low, ye t tests did not indicate any tracking or damage to the anna tu r e s as a result of these creepage grounds. This point is mentioned because ordinarily a rmature resistance to ground meas-lu-ements might be expected to be on the order of megohms. Obviously an armature having low leakage resistance is badly in need of maintenance. T h e im-phcationis t h a t in emergency cases motive power having low a n n a t u r e resistance to ground could be dispatched wi thout expecting damage to t he a rmature .
(e) Generalized moisture leakage condit ions: I n t he preceding text, moisture leakage from various par t s of the locomotive circuits ha s been considered on an individual basis. Usually such extreme leakage conditions would be expected to occur uniformly throughout a locomotive. On this basis the exposure on the negative side, with parallel connected motors, might be three tunes t h a t of the positive side of the system, as indicated by Figure 3. Equivalent drcui t s , neglecting the possibiHty of a rmature leakage and with motors operating in the parallel connec
tion, would be as indicated by Figure 6. To ta l leakage current supphed by the generator, as plot ted against generator voltage a t t h e point where ground relay operation is produced would be as shown in Figure 7 . Similar plots could be m a d e for the series-parallel connection. T h e point i l lustrated is t h a t the to ta l leakage current which is causing damage to the equipment m a y be very m a n y times the actual current t h a t goes through the ground relay.
FLASHOVER PROTECTION
One of the main duties of the ground relay is to detect generator or motor armature flashovers. A point which can be made in connection with the equipment under discussion is t h a t an a rmature flashover always involves ground in the circuit.
(a) Consider a generator a n n a t u r e flashover involving ground, as indicated by Figure 8. F rom the positive of the a rma tu re there is an anode drop, an arc s t ream drop, and a cathode drop where the connection is m a d e to ground. From ground back to the negative of the armature there are corresponding anode, arc s tream, and cathode drops. I t m a y be presumed, therefore, t h a t ground potential assumes a position approximately midway between the positive and negative of the a rmature . Oscillographic tests show t h a t this asstunption is substantially correct. I t mus t be apprecia ted t h a t dmring a flashover, arcing conditions va ry continuously and ground potential may , therefore, fluctuate considerably wi th respect to potential a t one side of the a rmature . T h e ground relay in
this case received half of the armature voltage. Experience has shown tha t with the type of relay here discussed, and the connections shown in Figure 1 or modified as suggested in Figure 3, the ground relay always received sufficient voltage to re-hably detect a generator flashover.
(b) T h e operation of the ground relay in detecting a parallel connected motor flashover is identical with t ha t of detecting a generator flashover. The current in a flashover of this type will be part ly generator current—which ser\'es as exciting current for the motor by returning to the generator via the motor field—and part ly current generated by the motor a rmature because the motor is being driven by train movement . A motor flashover wih very frequently result in a generator flashover.
(c) If the motors are operating in the series-parallel connections and a positive
Fisure 8. Generator flashover involvins a Sround
1 7 2 McDonald—DieseUElectrk Locomotive Ground Relays J U L Y 1 9 5 3
G R O U N D
Figure 9 (left). Flashover of positive connected motor in
series-parallel connection
ψ R E L A Y Figure 10 (right). Flashover of negative connected motor in
series-parallel connection
G R O U N D
connected motor flashes over the voltage across this motor will t end to collapse. The voltage across the negat ive motor connected in series will be increased as a result of the increase in generator current. T h e voltage available for operating the ground relay will be the sum of the voltage across the negat ive connected motor and half the voltage across the positive connected motor , see Figure 9.
(d) If in the series-parallel connection a negative connected moto r flashes over, the relay will be operated b y one-half of the voltage across this a rma tu re as indicated by Figure 10. In this case the inductance of the moto r field m a y also be considered as contr ibuting toward operating the relay and the ne t result is t h a t rehable indication of negative connected motors flashing while operating in the series-parallel connections is obtained.
(e) Positive side contactors flashover: A commonly used locomotive power circuit for a typical 4-motor locomotive using series-paraUel and parallel connections is shown in Fig 11 (A).
T h e restricted space available on a locomotive makes i t impossible to supply completely adequate arc distance for taking care of circuit interruptions of unusual severity on the main line contactors. Contactor flashover to ground although rare is always a possibility. A well-designed contactor tends to build up a fixed voltage across its contacts during circuit interruption and main ta ins this voltage unti l the arc is extinguished. This type of operation is indicated by Figure 11(B). Normally a contactor will mainta in about 150 per cent of the chrcuit voltage across its contacts during circuit opening. If the contactor arc goes to ground i t would be expected t h a t the ground voltage would be midway between the voltages across the contactor tips. For a flashover of contactor PI operation of the ground relay m a y be est imated from the assumed vector relationship of Figure 11(C).
(f) Negative side contactor flash-over: An analysis of the ability of the
ground relay to detect a flashover of the P2 contactor , which is on the negat ive side of t he system, m a y also be m a d e from Figure 11(B). Because of the induct ive voltages involved, i t will be observed t h a t no difficulty should be experienced with the operation of the ground relay on th is t ype of flashover.
(g) Series contactor flashover: A similar diagram m a y be drawn for a flash-over of the series contactor SI.
GROUND PROTECTION DURING DYNAMIC BREAKING
A dynamic braking circuit is shown in Figure 12. T h e motor a rmatures a n d braking resistors are located to i l lustrate the direction of their voltage depar ture from the positive of the generator. The actual voltage developed by the generator during dynamic braking is qui te small as compared to motor a rma tu re voltage. I t will be noted t h a t during dynamic braking all of the features previously discussed—armature grounds, creepage grounds, and flashovers—produce action of the ground relay. Hence i t affords full protection during this type of locomotiA^e operation.
ENGINE STARTING
While the generator is being used as a motor to s ta r t the diesel engine, the power
Figure 1 1 . Diagrams relating to power contactor
flashovers
A . Simplified schematic of cir
cuits B. Vol tage and current during contactor open
ing C. Vector diagram for flashover
of P1 D. Vector d iagram for flashover
of P2
circuits of the locomotive are connected to the control ba t te ry . T h e ground relay then responds to any ground tha t might exist on the control ba t te ry . If the ground relay is connected to the point Ε of Figure 3, i t will be noted t h a t when voltage is first applied to the generator, the armature drop is qui te small consequently the ground relay will, in effect, be connected to the positive side of the ba t te ry . Mos t of the voltage will be across the generator start ing field. As the generator comes u p to speed the a rmature develops back electromotive force, the current decreases and the ground relay, in effect, becomes connected to t he negative side of the ba t tery. T h e relay is thus responsive to a ground a t any location along the length of the control ba t t e ry and circuits.
Relay Connections
A ground relay connected as in Figure 1 has provided ver\ ' good protection on a large number of equipments . As discussed in connection with Figure 3, i t is considered bet ter to change the connections from point Λ to point Ε of Figure 3 in order to minimize the possibihty of making the relay inoperative by having a ground on a negative lead.
A resistance bridge connection has sometimes been used in order to provide
GEN. NEG.
' GEIt VOLTS M2
VOLTS M2
VOLTS P2 CONT
VOLTS Hi-
GEN. COMM. FLO VOLTS
GR RELAY
J U L Y 1 9 5 3 McDonald—Diesel-Electric Locomotive Ground Relays 1 7 3
Figure 12 (leit). Schematic diagram of dy
namic braking circuit
mid-point grounding of tbe generator voltage as indicated by Figtire 13. Referring to the preceding headings, i t would appear t h a t this type of connection will detect armatvue grounds of ei ther generators or motors . A relay so connected would recognize power circuit grounds except those during series-parallel operation which migh t occur on the cables operat ing a t potent ial between the positive and negat ive motors . A bridge-connected relay should provide successful protection in the case of a creepage ground on either the positive or negative of the power curcuits. I t would no t however respond to this type of ground on the cables connected between the positive and negative motors during series-parallel operation. Nei ther would i t t end to detect generalized a rma tu re leakage since such leakage would produce a ground potential midway between the terminals of the generator or motor on which i t existed. For generalized leakage conditions from the power cables the bridge-connected relay could give good operation on the basis t h a t there would be more leakage from the negative of the system than from . the positive. Theoretically this type of relay would no t be able to detect a generator or moto r flashover if the motors are operating in t he parallel
Figure 13 (right). Resistance bridge connec
tion for ground relay
connection since ground voltage should be midway of the system. Actual ly there are fluctuations in this voltage and these migh t produce operat ion of such a relay. T h e bridge-type relay should provide protection for a motor flashover if t he motors are being operated in the series-parallel connection and only one armatiu-e flashes over. For contactor flashovers i t migh t be expected t h a t this t ype relay would supply adequa te protection.
There has been some though t t h a t the bridge-connected relay relieves voltage stress on t he equipment b y grounding the mid-point of the system. Actually m a chine designers are most ly concerned with providing sufficient insulation and creep-age distances in series windings such as coimnutat ing fields and series fields. A negative connected ground relay will nonnal ly keep all of these field windings a t or near ground potent ial except in series parallel operation when some of the motor fields are raised to 50 per cent of system voltage above ground.
T h e functions performed by the ground relay should no t interfere with emergency plugging of a locomotive.
T h e ground relay is normally arranged to control a generator field contactor. Part icular ly in case of a flashover i t is necessar}^ t h a t the ground relay be fast in operation and t h a t it control circuits which will promptly remove the excitation from the generator. T h e equipment here
RES.
- Α Λ Α - | | | ι .
6R RELAY
RES,
discussed has a generator provided with a single shun t field winding. T h e ground relay operates a field contactor which inserts a field killing resistance in the field circuit having approximately 16 times the resistance of the field. T h e voltage of the generator is thus quickly reduced below the point which will sustain a flashover.
Wi th all ground relay systems it is cus tomary to provide a cu tout switch in series with the relay coil. This m a y be opened to permit emergency operation of the locomotive wi th a ground on the power circuit. Making the ground relay inoperat ive will, of course, eliminate its protect ive functions and such things as a flashover or a double ground on the system migh t cause considerable damage. T h e ground relay function should be retained during any load test since there is ordinarily no other way provided to clear a flashover.
T h e foregoing discussion illustrates the point t h a t the ground relay has a large number of functions to perform. In most cases the exact operat ing current or voltage of the relay is no t too critical; however, any changes made in the relay operat ing characteristics should be carefully considered with respect to all of the functions.
Considerable work is being done in connection with moisture groimds which, it is believed, will result in further improvements in locomotive operation.
Di iscussion
W. M. Hutchison (Westinghouse Electric Corporation, East Pittsburgh, Pa . ) : The importance of a ground relay to the protection of the electric equipment of a diesel-electric locomotive is well illustrated in Mr. McDonald's thorough paper on this interesting subject.
Our experience with several types of ground relay and with various ways of connecting them leads us to the following comments.
Mr. McDonald suggests that a ground on the negative system, by short-circuiting the relay coil, does not necessarily nullify the relay. He suggests tha t if the accidental ground occurs between the motor and the series field, fluctuations in current would create enough inductive voltage to operate the relay. Actually there is much more of the circuit at a potential which, if grounded, would short-circuit the relay coil (potential 5 , Figure 3 ) than there is between the motor armature and field (potential C or Z>, Figure 3) . Therefore, the probability of a ground which would nullify the relay is
correspondingly great. Even if the ground occius between the armature and field, only a violent change in generator or motor armature ciurent, such as a motor flashover to ground, will cause it to operate. These are the greatest objections to this type of ground protection.
Tests with a certain relay with one side grounded showed no response to a single armature ground and erratic response to flashover.
Several years ago ground relays connected equivalent to one side grounded were used. So many accidental grounds to the con-
1 7 4 McDonald—Diesel-Electric Locomotive Ground Relays J U L Y 1 9 5 3
ductor directly connected to the line side of the relay resulted in making the relay inoperative that it was necessary to reconnect the relay to another point which was not used in the locomotive wiring and which was at suiiicient difference in potential to all the locomotive circuits tha t any ground would be depended upon to trip the relay.
Since the protection offered by the relay depends on its operation on an induced
voltage supplied by either the generator commutating field or a motor series field, both of which have only a few turns, it appears tha t more data should be offered on the current surge required through these fields to develop the 38 volts required to operate the relay. I t appears unlikely tha t such voltages can be developed in normal operation.
The resistance bridge connection has
been found to be much more reliable. It is our practice, in our permanent series-parallel connection, to put the main fields all on the negative side and to use the resistance bridge ground relay.
Biasing the bridge-connected ground relay from a separate power supply with a suitable relay should give the best over-all response to grounds anywhere on the system from all causes.
Hydraulic Servos Incorporatins
a High-Speed Hydraulic-Amplifier
Actuated Valve
ROBERT L. SCRAFFORD A S S O C I A T E MEMBER A I E E
EL E C T R O H Y D R A U L I C systems have certain advantages over pure
electromechanical systems, which make them part icular ly suitable as an adjunct to electronic control for high-power level actuation. T h e main factor which has hmited the application of hydraul ic actuators unt i l recently has been the awkardness of the control systems required. However, developments in the technique of controlling hydraul ic flow electrically now permi t the flexibility of electronic control to be applied to the linear operat ion of hydraul ic valves a t high speeds.
The advantages of hydraul ic systems stem mainly from their abil i ty to provide large amoun t s of power from a "hydraul ic ba t t e ry" (accumulator) wi th minimtun of appa ra tus and storage volume, and with a small t ime cons tant . One-shot hydraulic systems have m a n y applications in guided missiles, where high-power output to opera te control surfaces is required for shor t period of flight. Another advantage of hydraul ic systems is the ease of obtaining either l inear or rota t ional motion.
Applications requiring cont inuous op-
P a p e r 53 -103 , r e c o m m e n d e d b y t h e A I E E F e e d back C o n t r o l S y s t e m s C o m m i t t e e a n d a p p r o v e d by t h e A I E E C o m m i t t e e on Techn i ca l O p e r a t i o n s for p r e s e n t a t i o n a t t h e A I E E W i n t e r Genera l Mee t ing , N e w Y o r k . N . Y. , J a n u a r y 1 9 - 2 3 , 1953. M a n u s c r i p t s u b m i t t e d S e p t e m b e r 29 , 1952; m a d e avai lab le for p r i n t i n g D e c e m b e r 19, 1952.
R O B E R T L . S C R A F P O R D is w i t h t h e Corne l l Aeronau t i ca l L a b o r a t o r y , I n c . , Buffalo, N . Y.
T h e d-c t r ans fe r v a l v e desc r ibed in th i s p a p e r was deve loped in t h e Corne l l Ae ronau t i ca l L a b o r a t o r y H y d r a u l i c L a b o r a t o r y u n d e r t h e d i rec t ion of W. C. M o o g .
eration m a y also benefit from the minim u m apparatus- to-horsepower rat io by providing a recharging system in a less restr icted location t h a n the ac tuator , and conveniently connected to i t by copper tubing.
I t is the purpose of this paper to describe a d-c transfer valve developed a t Cornell Aeronautical Laborator>% Inc. , and to call to the a t ten t ion of servo engineers, especially in industrial positions, the progress t h a t has been made in the field of hydraulic control , which m a y be familiar to engineers associated with the aircraft indus t ry .
This valve, operat ing in conjunction with a hydraul ic s t ru t or piston, has a combinat ion of gain, power ou tpu t , and torque-to-inert ia rat io which is difficult to obta in in an electrical ac tua tor . However, ra t ings are part icular ly difficult to apply to hydraul ic systems because of the inherent nonlinear relationships. I t is desirable, for the sake of simplicity, to m a k e a comparison on the basis of closed servo loops. These analyses indicate
superiori ty over o ther servo systems operat ing a t power levels of 1 to 10 horsepower, even when used in a control loop which does no t fully reahze the potentialities of the device.
Typical Hydraulic Control Systems
A typical control system is shown in block diagram form in Figure 1. In the case of a hydraulic system, the power source consists of a source of hydraulic fluid under pressure, and the power amplifier is a transfer or control valve. The ac tua to r m a y be ei ther of the linear or rotat ional-motion variety.
The General Servo Problem
We m a y divide all servomechanisms into two p a r t s :
1. Intelligence section, which includes voltage-amplifying and phase-compensating functions;
2. Power output and driver stages
The first pa r t contains devices which perform the various signaling and comput ing functions. These are shown as dot ted lines in Figure 1. They provide no power to the load and m a y accomplish intelhgence transmission by means of any. of the systems used by communications and telemetering engineers. The second pa r t contains the power-converting devices, in which power from some energy source is transferred to the load, in response to a signal from the intelhgence por t ion of the loop.
P O W E R
S U M P
/SFDL J S I G 1 J . 1 S I G N A L |
MfU.' I G A I N J I_ J ] _ A M P U F I E R
P O W E R A M P L I F I E R
- J
P I ^ K ) ) F F
I F E E D B A C K ! G A I N j
Figure 1 . Servo block diasram
S I G N A L P O W E R
S E C T I O N S S E C T I O N S
J U L Y 1 9 5 3 Scrafford—Hydraulic Servos Incorporalifig Actuated Valve 1 7 5
Top Related