CA1060128A - Ring trip detector with hall effect devices - Google Patents
Ring trip detector with hall effect devicesInfo
- Publication number
- CA1060128A CA1060128A CA253,765A CA253765A CA1060128A CA 1060128 A CA1060128 A CA 1060128A CA 253765 A CA253765 A CA 253765A CA 1060128 A CA1060128 A CA 1060128A
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- CA
- Canada
- Prior art keywords
- line
- amplifier
- coupled
- output
- current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Abstract
Abstract of the Disclosure A Hall effect device is employed in telephone exchange circuitry for detecting when a called subscriber goes off-hook. This is done by detecting when a DC current due to line looping is superimposed on the AC current due to ringing whereupon ring trip occurs. Also described are circuits in which after ring trip has taken place the Hall device con-tinues to supervise the called line loop.
Description
~ 6~Z~3 :
,: . .... ,.. ) , 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. -
,: . .... ,.. ) , 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. -
- 2 -?
lU~01~8 ~ 1~
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
:
outgoing line, a relay II (not shown) is operated, and contacts ~ nd - C ~n~P~e te . :
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 . . .
~3-~, . . .- . , R. KIT~JEWSKI - A.W. SWEET -M.P. DYER - 13-7-2 ~ 8 (Revision) 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.
: ' . . ~ ~ .. - .
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 . . , , , ~ , . . . . .
2~ ~ ~
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. .
~ 7 ~
1~3~
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 . ;
.
the accompanying claimsO .
'', ,,' . .' ~CH:vrn/g s l/2e/76 ., . i , .
" , , .. ,i, ' - a-
lU~01~8 ~ 1~
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
:
outgoing line, a relay II (not shown) is operated, and contacts ~ nd - C ~n~P~e te . :
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 . . .
~3-~, . . .- . , R. KIT~JEWSKI - A.W. SWEET -M.P. DYER - 13-7-2 ~ 8 (Revision) 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.
: ' . . ~ ~ .. - .
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 . . , , , ~ , . . . . .
2~ ~ ~
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. .
~ 7 ~
1~3~
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 . ;
.
the accompanying claimsO .
'', ,,' . .' ~CH:vrn/g s l/2e/76 ., . i , .
" , , .. ,i, ' - a-
Claims (6)
1. 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 said line, first means coupled to said device responsive to said output voltage to indicate whether or not direct current is on said line superimposed on said ringing current; and second means coupled to said first means and said device to disconnect said ringing current and to complete the connection to said line for communi-cation between a calling party and a called party when said direct current is detected;
said Hall effect device including three windings, one of said three windings and said ringing current being coupled to said line during a ringing operation and being disconnected from said line when ring trip occurs with the other two of said three windings being inserted in said circuit upon occurrence of ring trip, said other two of said three windings being balanced windings each of which are included in a different leg of said line when looped to enable monitoring off-hook and on-hook condition of said line.
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 said line, first means coupled to said device responsive to said output voltage to indicate whether or not direct current is on said line superimposed on said ringing current; and second means coupled to said first means and said device to disconnect said ringing current and to complete the connection to said line for communi-cation between a calling party and a called party when said direct current is detected;
said Hall effect device including three windings, one of said three windings and said ringing current being coupled to said line during a ringing operation and being disconnected from said line when ring trip occurs with the other two of said three windings being inserted in said circuit upon occurrence of ring trip, said other two of said three windings being balanced windings each of which are included in a different leg of said line when looped to enable monitoring off-hook and on-hook condition of said line.
2. A circuit according to claim 1, wherein said first means includes an amplifier and threshold circuit coupled to said Hall effect element to detect when said direct current in excess of a preset level is present in said line;
and said second means includes a validation circuit coupled to said amplifier and threshold circuit to check whether said direct current has persisted for a predetermined period of time before a looped condition is accepted as a valid one.
and said second means includes a validation circuit coupled to said amplifier and threshold circuit to check whether said direct current has persisted for a predetermined period of time before a looped condition is accepted as a valid one.
3. A circuit according to claim 2, wherein said validation circuit includes an up-down counter controlled by pulses from a pulse source, said pulses increasing the count of said counter by unity for each of said pulses which occur while said line is looped and decreasing the count of said counter by unity for each of said pulses which occur while said line is unlooped, where when the up-count has reached a preset value the looped condition is accepted as a valid one.
4. A circuit according to claim 1, wherein said second means includes a micro-processor coupled to the output of said first means which controls said ring current disconnection and said line con-nection in accordance with the output signal of said first means.
5. A circuit according to claim 1, wherein said second means includes a micro-processor to control the application and the removal of said ringing current and the completion of a speech path by suitable operation of relays.
6. A circuit according to claim 1, wherein said first means includes a first operational amplifier having its non-inverting input coupled to a first reference voltage and both its non-inverting and inverting inputs coupled to said Hall effect element, a second operational amplifier having a capacitor connected between its output and its inverting input so that said second amplifier operates as an integrator, its inverting input coupled to the output of said first amplifier and its non-inverting input coupled to a second reference voltage so that the output signal of said second amplifier indicates whether said line is looped or unlooped, and a third operational amplifier having its non-inverting input coupled to the output of said first amplifier and its inverting input coupled to a third reference voltage so that said third amplifier can be used for line loop supervision.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,765A CA1060128A (en) | 1976-05-31 | 1976-05-31 | Ring trip detector with hall effect devices |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,765A CA1060128A (en) | 1976-05-31 | 1976-05-31 | Ring trip detector with hall effect devices |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1060128A true CA1060128A (en) | 1979-08-07 |
Family
ID=4106089
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,765A Expired CA1060128A (en) | 1976-05-31 | 1976-05-31 | Ring trip detector with hall effect devices |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1060128A (en) |
-
1976
- 1976-05-31 CA CA253,765A patent/CA1060128A/en not_active Expired
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