Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention
The present invention relates to electrical circuits for ring trip
detection in telephone exchanges.
Summary of the Invention
In accordance with the present invention there is provided an electrical
ring trip detection circuit comprising: a Hall effect device to couple ringing
current to a called subscriber's subset line and to generate at its output an
output voltage that is proportional to the current flow to the line; first meanscoupled to the device responsive to the output voltage to indicate whether or not
direct current is on the line superimposed on the ringing current; and second
means coupled to the first means and the device to disconnect the ringing current
and to complete the connection to the line for communication being a calling
party and a called party when the direct current ls detected; the Hall effect
device including three windings, one of the three windings and the ringing
current being coupled to the line during a ringing operation and being discon-
nected from the line when ring trip occurs with the other two of the three windings
being inserted in the circuit upon occurrence of ring trip, the other two of thethree windings being balanced windings each of which are included in a differentleg of the line when looped to enable monitoring off-hook and on-hook
condition of the line.
Brief Description of the Drawing
Above-mentioned and other features and objects of this invention will become
more apparent by reference to the following description taken in conjunction
with the accompanying drawing, in which:
Fig. 1 is a simplified block diagra~ of the ring trip detector in
accordance with the principles of the present invention;
Fig. 2 is a somewhat more detailed block diagram of a second ring trip
detector in accordance with the principles of the present invention; and
Figs. 3 and 4 are two block diagrams of a combined ring trip and loop
detection circuit in accordance with the principles of the present invention. -
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DH_ crip~lon of the Preferred El~boclim_nts
In a Hall efEect device as usecl herein, an electrical condition to
be monitored influcnces the current in the device's energLzing winding or
windings, and produces a magnetic field normal to the p~ane of the Hall
element. This element is loca~ed in an air gap in the magnetic circult,
which may be an E shaped magnetic material core with an I-shaped
magnetic material core fitted together to produce a three-legged core.
There is a small air gap in the central lec3 in which the Hall effect
element is located, e.g. by glueing. A control current flows across
the element ancl an output voltage is generated across the other dimension
oE the IIall element. Thus the output voltage, the control curr~nt a~d
th~ ma~ne~lc field are mutually at rlyht-arlgles to each other. The Hall
element is a single crystal slructure or a deposited thin film of a semi-
conductor material, preferabl~l wlth a temperature-independent aharacter~
istic. The ma~netic circuit may be a soft iron, a modern ferrite, or
any other suitahle magnetic material. In all of the accompanylng drawings
the Hall effect eIement HS is shown separated from its windings HFD, `
with an arrow interconnecting them to show that the element is part of
the Hall effect device.
Referring first to FigO 1, when a connection has been extended to an I
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outgoing line, a relay II (not shown) is operated, and contacts ~ nd
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H2 o~ the outgoing circuit for the alternatin~ current (AC) ringing
current. Ring current is applied to the called subscriber subset via the
~in~le winding HED of the Hall effect device, contacts RT1 and Hl,
the line, and contacts H2 and RT2. The control direct c~!rrent Is applied
from the source V~ to the Hall effect element via the collector-emitter
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R. KIT~JEWSKI - A.W. SWEET -
M.P. DYER - 13-7-2
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circui-t of a transistor T. This transistor is switched on
by a control input to its base ~rom the pulse source PS when
a call has been ex-tended as just mentioned. This control
current is a pulsed one to reduce power consumption.
Hence the output from the Hall elemen-t HS to the ampli-
fier and threshold switch A~S will be, during the pulse from
pulse source PS, an ~C voltage un-til the called subscriber
replies. When he does so, direct current (DC) flows in the
loop, and the output from Hall effect element HS to amplifier
and thresho~d switch ATS becomes AC superimposed on DC. The
output from amplifier and threshold switch ATS becomes logic
"1" when this DC is present, and this is applied to ring
trip and validation logic RV. This assesses whethex the
change o~ input is a true loop condition and not a transient
condition, e.g. by accepting it as a valid loop if it persists
for a pre-selected number of pu~ses from pulse source PS.
When the circuit RV decides that the loop condition is valid,
it operates the relay RT, which disconnects the ringin~ and
completes the loop to the called line. When in due course
the call ends, relay H releases to open the loop at contacts
H1 and H2 and it resets circuit RV at contact ~3.
The delay introduced by circuit RV in assessing the
validity of a loop condition can be provided by analog means,
e.g. by an integration technique, or digitally. In the latter
case an up-down counter can be used to count pulses from
source PS at which the line is looped. If a pulse from source
PS finds the line unlooped it counts down once. Only when
the coun~er has reached a preset condition is it assumed
that the line is looped, and ringing is tripped.
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128 R KITAJEWSKI - A W. SWEET~
(Revision)
Fig. 2 is in some respects similar to Fig. 1, and uses
standard operational amplifiers to perEorm an analog integrator
method of discrimination in conjunction with a micro-processor
MP, which is preferably a device such as described and claimed
in the U.S. Patent No. 4,001,789 of A.W. Sweet! issued January
4, 1977. The thresholds to which operational amplifiers OP1
and OP2 respond are fixed by the potential dividers connected
to their non-inverting inputs. When the line is to be rung,
the processor MP operates relay H, which at contacts Hl and
H2 completes the loop for supplying interrupted ringing to
the line. As in Fig. 1, this ringing flows in the single
winding HED of the Hall effect device. In addition, pro-
cessor MP switches on the sampling current through Hall r
effect element HS at the base o~ the transistor T. Of the
two operational amplifiers, amplifier OPl acts as an ampli-
fier while amplif1er OP2 acts as an integrator since it has
a capacitor Cl connected across it as shown. When the called
line replies and completes the loop for direct current, the
output of amplifier OP2 moves from 0 volts to ~5 volts, i.e.
from a logic "0" state to a logic "1" state. This change
in condition is detected by the processor MP, which thereupon
opexates relay RT to trip the ringing and completes the
talking loop. As before, relay H is released when the call
ends.
In the two circuits to be described with reference
to Figs. 3 and 4, the functions of loop detection and
ring trip are combined, using the analog circuitry as
used in Fig. 2, with~a micro-processor MP, which is pre-
ferably of the type described and claimed in the above-cited
R. KITAJEWSKI - A W. SWEET -
~ 8 ~Rev DYER)- 13-7-2 ;~
U.S. Patent. The changeover of Eunction between loop detection
and ring--trip detection is efEected by the programming of
the processor MP.
In Fig. 3 the Hall effec-t device has -two balanced windings
indicated at HED, which are identical to what is needed for
loop detection, and as in the case of Fig. 2, the second
operational amplifier OP2 has a feedback capacitor C1 to
- establish an analog integrator function. When ringing
current is to be applied to the line, processor MP operates
relay RG. The relay contacts RG1 and RG2 connect the windings
of the Hall effect device HED to the llne, and at contact ;~ ;
RG3 it connects -the ringing current generator to the Hall
effect device HED and, hence, to the line. In addition,
the processor MP applies a condition to the base ~f the
transistor T to switch on a continuous sampling current
through the Hall effect element HS.
As in the circuit of Fig. 2 the ring trip aondition
is indicated by a change in the logic level at the output
of amplifier OP2, and when this changes from logic level
"0" to "l", processor MP releases rela~ RG to trip the
ringing and operates relay CD to complete the speech con-
nection. Note that the windings HED of the Hall effect
device remain in the loop via contacts RG3, CD3, CD4, CD1
and CD2, so the device now performs a loop detection func-
tion. As long as -the direct current in the loop is that
fo~ a valid off-hook condltion, the output voltage of-the
Hall element HS after amplification by amplifier OP1 exceeds
the threshold set for amplifier OP2. Hence, its output
remains at the logic level "1". When the line resumes
the on-hook state the output of amplifier OP2 goes back
to logic level "0", and this is interpreted by the pro-
cessor MP as an indication that the speech connection
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is ~o be cle-lle(l. I-Iencc!, proccssor MP rcleasos the rclay CD to break i
tl~e conr-ectk~ll. Note that in l~igo 3 the connections to the reEerence .
voll:ages V`JhiCIl fi~; tlle thresl-lolcls of amplificr OPI and OP2 are lndicated ~ . .
at V and V , respectively. :
1'he anange.mellt oE Fi~ ~1 di.ffers from that of Fig. 3 in that the
Hall efEect device has three windings indicated at HED, ~vo of which ~:.
are balanced windings for loop detection while ths third is an additional :
winding for ring trip. This enables the line polarit~ to he reversed when
the change is made from the ringing to the speakinc~ condition. It enahles
an ir~terception circuit elsewhere in the system to pe~r~orm a ring trip
functlon wlthout causing tha loop detection to :Eunction so that a non-
metered ring l~ip can occur. This is efiectecl by placlny a ~50 volt
potential on the negative wire of the speech pair via a protective resistor.
~ An additional operational amplifier OP3 is now needed to establish the ~ j
loop detector threshold in the oppo~i~e sense to that of amplifier OP2, .
which acts as a combined threshold and integrator. . .
When ringing is to be applied to the line, rela~v RN is operated by
processor MP in use or tlle connection, which connects ringing current
to the line.via the upperrnost wind.ing of windings ~fED. In addition, .
processor MP caus~es a continuous control current to be applied to the ~:
Hall element HS hy switching on transistor T. When the called line . ~i
'off-hooks', t}hQ output of amplifier OP2 indicates this condition, as i~ ~ ~r,
the case of Fig. 3. The c'nanye of -the output -from amplifier OP2 from ~2,
"()" to "1" is responded to by processor MP, which changes over to a !.
~5 speaking condit.ion by relcasing relay RN, as a result of which rin~ing .
and the uppertnost windlng of the Hall effect device are disconnected. .
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The t-~o ba].clllce(1 v~.indin(Js oE the windinc1s iILD are now in circuit in
the called l;ne loop. The output from arnplifier C)P2 now reverts to zero, .
but that from amplifier OP3 to processor MP remains at logic "l" until .
the on-hoo1c condition returns. When this occurs, operations are slmilar
to -those oE Fi~o 3~
While we have described above the principles of our invention in
connectiorl with specific apparatus it is to be clearly understood that :;
this description is made only by way oE example and not as a limitation I
to the scope of our invention as set forth in the objects thereof and in . ;
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the accompanying claimsO .
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