Note: Descriptions are shown in the official language in which they were submitted.
3~63
S _ ch1~ evic
The inventicn relates to a switching device for
opening and closing electrical circuits~ in which, paral-
lel to each contact, located in the main circuit to be
switched~ o~ a magnet-controlled switchgear~ an elec~
tronic switch and a contact~ ser~in~ as an isolator~ o~
a flrther magne-t-controlled auxiliary switchgear are con
nected in series, and there is a central con-trol device
which connects through the electronic switch before each
change in switching state of the magnet-con-trolled switch~
gear located in the main circuit and which locks it again
therea~ter; -the contacts of the auxiliary switchgear
.
which are in series wi-th the electronic switch being
closed.
A switching device of thîs type became known, for
example~ ~rom U.S. Patent Specification 49251~845. In
this known devicc~ the three switching elements are sel-
ected via a series o:E auxiliary relays t the switching
sequence o~ which iS prede-tarmined by contacts inser-ted
in their selection circuits~ Here~ this selection is
inPluenced, apart from by a switching-on or switching-
off command, solely by an auxiliary corltact of ~the
: ma~net--controlled swit~hgear located in the main circuit~
; ,. .
~9~3~L~
-this auxilia:ry contact allowing the fur-ther progress of
the switching sequence during both switching-on and
swi-tching-off.
I~e disadvantage of this device is -that the
switching-on time of the electronic switch has to be
made relatively long because o~ -the tolerances o~ the
opera-ting and releasing -times of the auxiliary relays,
with the result that the electronic switch has to absorb
a correspondingly large power loss and has to be chosen
accordin~ly. Moreover, in the known case, when -the
main circuit is opened -t~e switching sequence depends on
releasing delays produced by capacitors cormected in
parallel to the colls of auxillary relays, with the res~
ult that because of ch~lges in capacitance of -the
capacitors during the operating -time there can arise
f~ult~ switching operations which can lead to destruc-
tion, especially of the electronic.switch.
The object of the invention is to propose a
switching device of the type mentioned in the introduc-
tion, in which faulty selection of the three switching
elements is safely prevented.
This is achieved~ according to the invention9 due
ta the fact that -there is a central con-trol unit which
has for each of the switching elements a separate selec-
tion circui-t~ ~md -these selection circui-ts comprise test
loops connec-te~l to sensors monitoring the switching state
of the switching elements and/or -their selection ~rld are
linked to one another pre~erabl~ in dependence on the
command transmitted from the central control unit.
~ ~9~ 3~ ~
It is thereby possible to proceed further in the
switching sequerlce only as soon as the preceding sw.itch-
ing command has been made. This also makes it pos-
sible, however? to do away with safety in~tervals bet~een
the individual switching steps~ such as are required in
the kno~l case9 with the result that despite increased
safety a reduction in the switching-on ti~e of the elec
tronic switch is achieved~
It is especially appropria-te if, in order -to moni~
tor the position of the contacts of the magnet-contro.lled
switchgear which are located in the main circuit, ~there
is an auxiliary contact which ensures that the switching
sequence is continued only when the contacts loca-ted in
the main circuit are actually closed.
According to a further feature of -the invention,
the switching state of the elect~onic switch is monitored
by a sensor responding -to its control current) and the
selection of the electronic switch is preferabl~ linked
to that o~ the magnet-controlled auxiliary switchgear,
and when the selection of the electron.ic switchgear has
ended a signal is triggered, this signal ~triggering via
a delay element a command -to open ~the contacts of the
auxiliary switchgear~ This ensures tha-t~ as distinct
.from the known solution according to U S. Patent Speci-
fication 4,251,845, the elec-tronic switch .is isolated
~rom the main circuit at the mains~ In thi~ way9 the
electronlc switch is very largely protected on the load
side against t:he effect of surges or shor-t-circuits
which can result in the contacts ~eing torn open because
)3~ ~ .
of the current forces in -the region of the con-trac-tions
of the current paths caused by the contact poînts, and
under certain circumstances the arcs whic~ are formed
may be extinguished and high induction vol~tages may con-
sequen~tly arise.
The inven-tion is expla,ined in more detail with
re~erence to the drawing, In this, Fi~lres 1 and 2
show diagrammatically -two different embodiments o~ a
swîtching device according to the inven~tion ~or connect-
ing a load to or diconnecting from a network with a phase
sequence which is always the samey Figure 3 shows a
switching device for co~necting or disconnecting a load
wi-th a selective phase sequence~ Figure 4 shows a block
diagram of a control unit for a switching device accord-
ing, to Fi~ures 1 or 2, and Figure 5 shows a block
diagram of a control unit for a switching device accord-
ing the Figure 30
The magnetically controlled switchgear 1, 1I has
contacts 4 ~hich are located in th~ main circuit and
which control the connection of ~the mains terminals Llg
L2, L3 -to the load 5~ Connec-ted in parallel to each
of the contac-ts 4, 4' is a series connec-t.ion consisting
o~ a contact 6~ 6'7 ac-ting as an isolator, of an auxili-
ary switchgea:r 2~ 2', and an electronic switch 3
According to Figures 2 and 3, there are, ~o~
moni-toring the switching ~unction of the switchgears 1
1' or auxilia~y switchgears 2, 2' auxilia~y contacts 7,
7' and 8~ 8I respec-tively, which~ like the switchgear 1,
1~ and the auxiliary switchgears 2v 2' and the electronic
~ 3
swi-tch 3~ are connec~ted -to a cen-tral con-trol unit 9~
This control unit 9 is supplied from the mains
via a phase Ll and the neutral conductor and is wired -to
the conventional on-and-off but-tons 10, 10' and 11 res-
pectively~ A fault-warning device 12 is likewise
connected to the cen~tral control 9.
In the embodiment according to Figure 1, current
transformers 13~ 14 are provided ~or monitoring ~the
swi-tching .function of the switchgear 1 or the auxiliary
swi-tchgear 2 and the elec~tronic switch 3~ and o.~ course
current transformers can also be arranged in each phase
to achieve more precise monitoring~
When, in the switching device according -to Fig-
ures 1 or 2, a switching-on co~mand is transmitted to
the central control unit 9 by pressing -the ON button 10,
then after a tes-t 1QP has been passed through the selec-
tion circuit for the auxiliary switchgear 2 is ac-tivated
and the contacts 6 of the la-tter are closed. A~ter
the return signal has arrived via the closin~ o~ ~the
contacts ~ by means of the a~iliary con-tact 89 -the selec-
tion circuit o~ the electronic switch 3 is ac-tivated and
the latter is cor~ected throughO In -this way, the
load 5 is connected -to the malns Ll, L2, L3 via the
parallel current pa-th~ After tha~t, the selec~tion cir-
cuit of the magnet-controlled switchgear 1 is activated,
so tha-t the latter closes its contacts 4~
A~ter the return signal has arrived via the
closing o~ ~the contacts 4 of the switchgear 1 by means
o~ the auxilia~y contac-t 7 or the current-trans~ormer
13> -the electronic swi-tch 3 is blocked9 and thereafter
the selection circuit of the auxiliary switchgear 2 is
reset again so as to open the contac-ts 6 of -the au~
ary switchgear 2 again. Of course, instead of only
one phase, all three phases can be monitored by current
transformers 14.
When the OFF bu-tton co~lected in front oE the ON
bu-tton 10 is pressed, with the result that a swi-tching-
off command triggered by pressing the OFF button has
priorlty over a switching-on command~ then the selection
circuit o~ the auxiliary switchgear 2 is activated and
the contacts 6 are closed. After the return signal
has been transmitted via the closure of the contacts 6,
but at the latest after -the expiry of a speci~ic ~time~
-the selection circuit of the electronic switch 3 is activ-
ated so that the latter passes into its conductive state.
As soon as ~he re~n s~gnal corre.sponding to ~e built
through-connection of the electronic switch 3, arrives,but ~t
the latest at the expiry of a specific time~ the selec-
tion circuit of the swi-tchgear 1 is reset so as to open
the contac~s 4~ When this has taken place~ the selec-
tion circuit of the electronic switch 3 is reset, and
the electronic switch 3 passes into its blocked state,
the selection circuit o~ the electronic swi~ch 3 being
reset at the la-test after the expiry of a specific time~
After the selection circuit of the electronic
switch 3 has been reset, the selection circuit of the
auxiliary switchgear 2 is then reset, so that its con-
tacts 6 open and -the switching-of~ cycle is completed.
~g~31~
-- 7 ~
In the embodiment accordi.rlg to Figure 3? the
switching-on and switch.ing-of~ cycle takes place in the
same way. Here, depending on whether t~e ON button
10 or 10' is pressed, the auxi-Liary swi~tchgear 2 or 2'
is selected, as a further sequence of the switchgear 1
or 1', with closure of the con~tacts 6 or 6' and 4' or
4' respectively~
Be~ore the appropriate selection of ~the auxili-
ary switchgear 2 or 2'~ however, a test is conducted in
the test circuit as to whether none o~ the colls of the
swi~chgears 1~ 1' and auxiliar~ switchgears 2, 2' is
energised and none o~ the contacts 4, 4~ and 6', 6' is
closedO Moreover, the selection circuits of -the
au~iliary switchgears 2, 2' and the switchgears 1~ 1'
are mu-tually locked, so that as soon as a switching-on
signal arrives at the selection circuit of, for example,
the auxiliary switchgear 2 a blocking signal is trans-
mitted to the selection circuits of the auxiliary
swi-tchgear 2' and the switchgear 1~, w.ith the result -that
these can be activated only after a switching-of~ com
mand and a subsequent switching-on command trigger~d by
pressing the ON but-ton 10'.
~ y arranging the electronic switch 3 on the load
.side of the auxiliar~ switchgears 2, 2' connected in
parallelt it i.s possible.to make do with a single elec-
tronic switch 3 for both parallel circuits to the
~tacts 4g 4' of the swi.tchgears 1, 11.
A block diagram o~ a central control unit 9 for
a switching device according to Figures 1 or 2 is sho~
. - 8 -
in Figure 4, a representa-tion of the vol-tage supply
having been omi-tted.
The commands entered in the central con-trol unit
via -the ON and OFF but-tons 10, 11 are s~tored in -the mem-
ory 15, the output of which is connected to each of the
selec-tion circu.its 16, 17, 18 which are each assigned
to one o~ the switching elements of ~the switchgear9
specifically to the auxiliar~ switchgear 2, the electronic,
switch 3 and the switchgear 1. Fur-thermore~ ~the out-
put of the memory 15 is also connected to a test circuit
l9o ' :. ,
The test circuit 19 is also connected, moreover,
to a sensor ZO responding to a current flow through the
coil o~ the magnet controlled switchgear 19 a sensor
monitoring -the posi-tion of the contacts 4 of the switch-
gear 1~ for example a sensor 79 13 connected to an
a~xiliary contact 7 or a current-trans~ormer 13, and a
sensor 21 which monitors ~the switching state o~ the elec~
tronic switc.h 3 and which responds, for example, to -the
supply of the igniti.on electrode o~ the electronic switch
~ and/or also to a current flow through the parallel
-circuit. The test circuit 19 also receives signals
from the sensor 22 responding to -the curren-t flow through
~he coil o~ the auxil.iary swi-tchgear 2 and from a sensor
23 moni-toring the switching state of the contac-ts 6.
When a switching-on command reaches the test
circuit 19, the latter transmits a switching command to
the selection circuit 16 of the auxiliary switchgear 2,
i~ no current flows through the coils of the switchgear
- 9 -
1 or the auxiliary switchgear 2 and their contacts 4 or
6 repsectively are in the open position and the elec-
tronic switch 3 is also in its blocked state.
If this is not so, the switching-on command to
the selection circuit 16 of the auxiliary switchgear 2
is disconnected, and a signal for activating the fault
warning circuit 24 is transmitted.
The switching-on command to the selection cir-
cuit 16 is simultaneously applied to a resettable timing
element 25 which is connected to a resetting input of the
selection circuit 16 and which, after the end of its
operating time, transmits a signal to the resetting input
of the selection circuit 16 so as to reset this again.
At the same time, this signal also activates the fault
warning circuit 24 which controls, for example, the
lamp 12.
However, operation of the timing element 25,
which is also connected to the sensor 23 monitoring the
contacts 6 of the auxiliary switchgear 2, is discontin-
ued if the closing of the contacts 6 is signalled within
the operating time of the timing element 25.
As soon as the closing of the contacts 6 of the
auxiliary switchgear 2 is signalled to the selection
circuit 16 connected to the sensor 23, this selection
circuit transmits a switching-on command to the selec-
tion circuit 17 controlling the electronic switch 3,
this switching-on command being delayed via a timing
element 26 so as to prevent through-connection of the
electronic switch 3 during any rebound of the contacts
3~L~
-- 10 ~
6. When the switching-on command from the selec-tion
circuit 16 arrives at the selection circuit 17 connected
to the sensors 7, 13 and 21 as well as 23, this tests
whether the contacts 4 are still open? bu-t the contac-ts
6 are closed I~ this is -the case9 the control elec-
trode o~ the electronic switch 3 is subjected to igni-
tion pulses or a continuous signal and is thus kept in
-the connected-through sta-te~ If the above condi-tions
are not satisfiedt the control electrodes o~ the elec-
tronic switch 3 cease to be so subjected, and ~the fault
warning circuit 24 is activated. At the same time, a
command to open the contacts 6 is given to the selection
circui-t 16 of the auxiliary switchgear 2.
The fault-warning circuit 24 is activated and
the command to open the contacts 6 is transmitted to
the selection circuit 16 even when signals do not arrive
at the con-trol electrode of -the electronic switch 3
within a specific time a~ter the arrival of ~the switching-
on signal in the selection circui-t 17 or even when no
current flows in the parallel circuit, this being mo~it-
ored by the sensor 21 connected to the selection circuit
17. In this case, resetting o~ the selection circuit
17 also takes place~
I.*, on the other hand, a sign~l corresponding to
the proper through-connection~of the electronic switch
3 arrives ~rom the sensor 21, the selection circuit 17
transmits a switching signal to the selectio~ circuit 18
which is assi~led to -the switchge~r 1, the swi-tchgear 1
being s-tressed towards closure of the contacts ~ as a
~f~ 3~ ~
result o~ the switchin@-on signal coming from the memory
15. At the same time, this signal arrives at a rese-t-
table timing element 27 3 -the output of which is connected
to a resetting input of the se~Lection circuit 18 and the
fault-warning circuit 24. ~len a signal correspond
ing to the closed contacts 4 of the switchgear 1 reaches
the timing el~men-t 27 within the operating time o~ the
timing element 27, the la-tter is reset and ~there is no
transmission o~ a resetting signal to the selection cir-
cuit 18 and a signal ~or activating the ~aul~t warning
circuit 24.
In the opposlte case, resetting of the select;ion
circui-t 18 and activation of the ~a~lt-warning circuit
24 take place and, via the timing element Z8 which i.s
connec-ted to the output o~ the timing element 2~ and -to
a resettin~ input o~ the selection circuit 17~ resetting
of the selection circui-t 17, with the result that the
electronic switch ~ passes into the blocked state~
I~, however, a signal corr~sponding t:o the closed
con~acts 4 arrives at the timing element 27 and the selec-
-tion circuit 18 in due time, the latter transmits to the
selec-tion circui~ 17 a command to block the elec-tronic
swi-~ch 3.~ .
As soon as the retu~ signal ~rom -the sensor 21
arrives, via the blocking o~ the electronic switch 3~ at
the control circuit 17 7 the latter transmits to th~
selec-tion circ:uit 16, ~ia the timing elemenJ; ~6, a sig
nal to o~en the contacts 6 of the auxiliary switchgear
2~ I~ no return signal o~ this type arrives wi-thin a
- 12 -
specific time~ the fault-warning circuit 24 is activa~ted
and the signal for opening the con-tacts 6 is transmi-tted
-to the selectlon circuit 16.
The latter passes -the command to open the contacts
6 on to the auxiliary switchgear 2`and checks whether a
signal corresponding to the opened contacts 6 arri~es
~rom the sensor 23 within a specific -time. I~ this
does not happen, the selec-tion circui t 16 transmi ts a
signal ac-tivating the ~ault-warning circuit 241 but the
command to open the contacts 6 is main-tained and 7`S not
reset~
. When a swi-tching-off command reaches the central
control-unit because the OFF button 11 has been pressed,
this command is stored in -the memory 15~ and the latter
transmi~s at its output a corresponding si~nal which
reaches the test circuit 19 and the selection circuits
16, 17 and.l8 again~
The test circuit 19 checks whether the contacts
4 of ~he switchgear l are cIosed and the electronic
switch 3 is blocked If this is not so or if this
does not occur wlthin a specific -time9 the ~ault-warning
circuit 24 is ac~i~ated. In either case9 however, a
command to close the contac$s 6 of the auxiliary switch-
gear 2 is transmîtted to the selection circuit 16, and
the resetting input connec-ted to the timing element 25
is inacti~ated b~ the switching-o~ signal coming from
the memory 15. Fhrthermore) when there is a switchi~-
off signal coming from the memoryj after a specific time
the transmission of a switching-on co~mand to the
- 13 -
selection circui-t 17 is triggered~ irrespective o~
whether the SenSQr 23 supplies or does not supply
within a prede-termined time a signal corresponding to
-the closed contacts 6~ However, should a signal o~
this type not arrive, the fault-warning circuit 24 is
activated after the operdting -time o~ the timing ele-
ment 25.
The switching-off si~nal coming from -the memory
15 also ensures that~ even when there is no signal cor-
responding to the closed contacts 6, at -the arrival o~
the switching-on command from the selec-tion circuit 16
the selection circuit 17 brings the electronic switch 3
into ~he connected-through.state and -transmits a switch-
ing signal to the selec-tion circuit 18 which controls
the switchgear 1 by opening the contacts 4 as a result
of the switching-o~ signal coming from the memory.
When a signal corresponding to the open contac~s
4 is supplled from the sensor-7, 13, the selection cir-
cuit 18 transmits to -the se].ection circuit 17 of the
electronic switch 3 a signal -to block the latter.
However~ if this signal does not appear~ the timing ele-
ment 27 operates, and -the ~ault-warning circui-t is
acti~ated and after the operating time of the timin~
element 28 a blocking signal arri~es at the selection
circuit 17.
The electronic switch 3 is consequently blocked,
and after the arri~al from the sensor 21 o~ a signal
corresponding to the proper blocking of the electronic
switch 3 or after the e~pir~ of a predetermined time a
\
- 14 -
signal to open the contacts 6 of the auxilia~y switchgear
2 is transmitted from the selectlon circui-t 17 to the
selection circuit 16g in the ]atter case the fault-
warning circuit 24 also being activated.
~ he selection circuit 16 controls the auxiliary
swltchgear 2 for opening o~ the contacts 6 and checks
whether a signal corresponding to the open contac-ts 6
arrives *rom the sensor 23 within a.specific ~tlmes
I~ this lS not sog the fault-warning circuit 24 which
can be formed, for example~ by an OR ga-te is activatedy
but con-trol of the auxiliary swi~tchgear 2 for opening
of the contacts 6 is maintained.
This ensures that the swi-tching-of~ command is
: executed in any case, even when faults arise in ~the
switching operations.
In the block diagram accordlng to Figure.5~ there
is ~ memory 15 with two outputs which are interlocked as
regards a swltching-on command and whi¢h are each
assig~ed to one of the two ON buttons lO~ lO'~ but both
assume the same switching sta-te when a swi-tching-o~
command arrives~ mus~ onl~ one o~ the two outpu-ts
o~ the memory 15 can ever transmit a swi-tching-on sig-
nal, and this signal. is maintained un-til -the OFF button
ll is pressed9 irrespec-tive of whether one or both ON
buttons lO, 10' are pressed.
The test circuit l9 is connected not only to -the
sensors 20y 79 22 and 23 moni-toring the switchgear l and
the auxiliary switchgear 2 or their contacts 4 and 69
. .
. but also to the sensors 20', 7', 22' and 23' monitoring
~ 3
- 15 -
the swi-tchgear 1' and the auxlliary switchgear 2' and to
the sensor 21 monitoring the electronic switch 30
~rthermore~ the test circuit is also connected to the
two outputs of the memory 15 via an OR gate ~O. When
a switching-on command arrives at the test circuit 19
via this OR gate 309 it checks whet:her no current flows
-through any of the coils o~ the swi-tchgears 1 and 1l and
the au~iliary switchgears 2 and 2' and no con-tacts 4 or
4' and 6 or 6~ are closed and whether -the electronic
switch ~ is also in its locked state~ If -these con-
dltions are satis~ied9 the -test circuit 19 transmi-ts a
switching command which is fedt via one of the ~~wo AND
gates 31, ~2 each making a link wi-th one o~ the two ou-t-
pu-ts of the memory 15, to one of the two selec~tion cir-
cuits 16g 159 which are assigned to the auxiliary switch-
gear 2 and 2' respectively. At the same time, the
two selection clrcuits are interlocked, since the out-
puts of the ~D gates 31 and 32 respec~tively are
connected not only to the setting input of one selection
circuit 16 and 16' respectively, but also~ vi.a an OR
gate 3~y 34 respectively, to the resetting input o~ the
other selection circuit 16 and 16' respectively. The
two inputs are connectecl -to the output o~ the timing
elemen-t Z5 whi.ch is connected -to the sensors 7 and 7Y
monitoring -the positions o~ the contacts 6 ~nd 6 t of the
auxiliary swi~t;chgears 2, 2' and which can be rese~t dur-
ing its operating time by signals from one o~ the -~wo
sensors which correspond -to the closed position of these
contacts
3~
In the embodimen-t according -to Fi~ure 5, the
switching-on and swi-tching-off operation basically takes
place in exactly the same way as according to Figure 4,
and the fault~warning circui-t 24 is also activated
accordingly under -the same conditions.
Like the tes-t circuit 19, the selection circui-t
17 o~ the electronic switch 3 is connected to the -two
outputs o$ the memor~ 15 via the OR gate 30~ Further-
more, the selection circuit 17 is connected to sensors
7 and 7' monitoring the position of the contacts 4 and
4' and to sensors 23 and 23' monitoring the contacts 6
and 6?. When a switching-on command arrives from the
selection circult 16 or 16' via the -timing element 26,
the selection circuit 17 checks whether the contacts 4
and 4' are still open and whether the contacts 6 or 6'~
but not both contact groups 6 and 6'~ are closed and
only then selects the control electrode o~ -the electronic
switch 23 so that the latter is connected through.
When a signal corresponding to the connected-
through electronic switch 3 arrives from the sensor 21
at the selection circuit 17 3 the latter transmits a
switc~ng signal which is fed~ via one o~ -the AND gates
~5, 36, second i~puts o~ which are connec-ted -to the out-
pu-ts o~ -the memory 15, to one of -the two selection cir-
cuits 18J 18~ which are assigned to the switchgears 1 and
1' respec-tive:Ly. At the same -time~ the timlng element
~7 which can be reset by a signal corresponding to the
closed contacts 4 or L~- is also started.
The outputs o~ the AND gates 35 9 36 are
-- 17 ~
connected no-t only -to the set~ting inpu-ts of -the selec-
tion circuits 1~, 18l~ but also to OR gates 38 and 37
respect-vely, outputs of which are connec~ted to the
resetting inputs of the selection circuits 18 and 18'
respectively and seconds inputs of w~ich are connected
to the output of the timing element 27.
Interlocking of the selection circuits 18 and
1~' is provided again as a result.
As soon as a signal corresponding to -the closed
contacts 4 and 4' respectively arrives from the cor-
responding sensor 7 and 7' respectively at the selection
circuit 18 and 18' respectively, the la-tter transmits
to the selection circuit 17 a command to block the elec-
tronic switch 3.
The further course of the swi-tching-on cycle
takes place as in the exemplary embodiment according to
Figure 49 although signals c~using the contacts 6 and 6'
to open are ~ed to both selection circuits 16 and 16'
respect.ively.
When the two outputs of the memory 15 supply the
same.signals9 this represents a swi-tching-off signal~
and the test circuit 19 checks whether the contacts 4 or
4' of a switchgear are closed and whether the electronic
switch i5 blockedO In any case~ a swi-tching command
is transmitted from the test circuit 19 to ~the -two AN~
gates 39, 40~ the negated input o~ which is connected to
the ou.~put o~ the OR gate 30 and can therefore connect
throug;~ only in the even~t of a switching o~ commandO
The third inputs o~ these gates 39~ 40 are connected to
~3~93
` 18 ~
the sens~rs 7 and 7' respectively7 so that only -that of
the two gates ~9, 40 can co~nect through which is con~
nectel to the sensors 7 or 7' respectiYel~ which supplies
a si~nal corresponding to the closed contacts 4 or 4'
respectively.
Up to the transmission of the switching signal
from the selection circui~ 17 to one of the selection
circui-ts 18 and 18'; the furt,her cour~e of the switching-
of~ cycle is iden-tical to the cycle describ2d in the
explanation o~ Figure 40
When a switching~off command appears at the two
outputs of the memory 15~ the switching signal is trans-
,~erred via the AND gate 41, the inverting input o~ which
is connected -to the ou~put of the OR gate 30 and can
therefore connect through only in the event of a switching~
off command. me output of this AND gate 41 is con-
nected via decoupling elements 42, 43, for example
diodes, tQ the setting inpu-ts o~ the selection circuits
18J 18', so that both control the associated switchgears
1, 1' *or opening o~ the contacts 4, 4' as a resul-t of
the switching-off command which appears~
I~e further steps o~ the switching~off cycle
are the same'as those described in relation to Figure 4
