GB Patent 401033 - Improvements in or relating to electrical signalling systems

Claims

according to Claim 1, 2 or 3 in which a 105

device comprises a three electrode thermionic rectifying valve in the anode circuit of which is connected a relay, the device which is rendered unresponsive to currents of a particular frequency being iio connected to the signalling circuit by way of a circuit having a great attenuation to the particular frequency.

5. Signal receiving arrangements according to any of the preceding claims F4b in which the occurrence for a short duration of current of signalling frequency is rendered ineffective by a delay device.

6. Signal receiving arrangements according to Claim 1, 2 or 3 in which the 120 devices control a normally operated slow releasing relay in such a manner that the relay is only released by the continued receipt for the duration of its releasing period of a current of pure signalling M25 frequency.

7. Signal receiving arrangements according to Claim 2 or 3 in which currents of the several signalling frequencies govern relays the relays being normally iA3 relay Q being open at contact 2 and the i circuit for this relay over contacts 10, 7 and 4 being open at contact 1 relay Q releases. Due to the release of relay Q i f relay R releases and a signal controlled I by further contacts of relays Q and R is given. Similarly in response to frequency y relays P and R are released and in 1 response to frequency z relays P and Q tO ale released and different signals may be given in response to signals of the different frequencies, the circuits for giving the signals being controlled by contacts of relays P, Q and, R. It will thus be seen that the relays P, Q and R are released in pairs by signalling currents. If current as received wbich does not include a signalling frequency relays X, Y and Z are all operated and relays P, Q and R are held over the front of contacts 1, 2 and 3 and serially connected contacts of the slow releasing relays.

All the siow releasing relays may be released by applying first one of the signalling frequencies, for example, the frequency x thereby releasing relays Q and R and then current of another frequency whilst maintaining the first applied frequency, allowing relay X to re-operate and holding relays Y and Z. Relay P now releases since its holding circuit is opened at 1 and the alternative circuit over 3 is open at contacts 6, 9 and 12.

Relays P, Q and R may be re-operated all together by simultaneously cutting off current from the line, releasing relays X, Y and Z or they may be re-operated in succession in different orders according to the order in which the several signalling frequencies are cut off from the line.

The relays P, Q and R may accordingly be operated and released in a variety of combinations and each combination may be made to give a signal by suitable contact arrangements. It will be appreciated that any number of signals within limits may be given by varying the number of signalling frequencies and providing a pair of relays such as X and P for each frequency. Other combinations may be had by making the relays X, Y and Z inoperative with signalling currents at more than one of the signalling frequencies.

Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I 0 claim is:1. In or for an electric signalling sysrem in which signal current within a narrow band of frequencies and currents of other frequencies within a range of frequencies including said narrow band 1 i L__ 401,033 operated and rendered slow to release, all the relays being released by the application to the signalling circuit of any two signalling frequencies in succession, the first application continuing during the second application.

8. Signal receiving arrangements according to Claim 7 in which while the devices rendered unresponsive to currents to of signalling frequency are operative the slow releasing relays are held over serially connected contacts of one another.

9. Signal receiving arrangements according to Claim 5 in which the grid circuit of the valve includes a condenser shunted by a pair of rectifiers arranged to permit a negative biassing of the grid, the junction point of the rectifiers being connected to the valve anode, the condenser being shunted by a resistance on the operation of the relay in the valve anode circuit.

10. In or for an electric signalling system according to Claim 2 or 3 in which each device includes a relay the relays of the devices controlling a like number of slow releasing relays the arrangement being such that after operation of the slow releasing relays operation and release of the relays of the devices in unison maintain the slow releasing relays operated.

11. Arrangements for discriminating between currents of a particular signalling frequency and currents of other frequencies substantially as described with reference to Fig. 1 of the drawings accompanying the Provisional Specification.

12. Arrangements for discriminating between currents of a plurality of signalling frequencies and currents of other frequencies substantially as described with reference to Figs. 1 and 2 of the drawings accompanying the Provisional Specification.

Dated this 9th day of June, 1933.

T. 11. FLOWERS.

Redhill: Printed for His Majesty's Stationery Office, by Love & Malcomson, Ltd.-.-1933 401,033

Description

PATENT SPECIFICATION

Appkication Date: June 9, 1932. No. 16,290/32.

Complete Left: June 9, 1933.

401,9033 . Complete Accepted: Nov. 9, 1933.

i: --- PROVISIONAL SPECIFICATION.

Improvements in or relating to Electyical Signalling Systems.

E, TtIOIomS HAROLD FioWoEnS, of 60, Winldsor Road, Palmers Green, London, N. 1:3, a British subject, do hereby declare khe nature of this invention to be as follows: The present invention relates to electrical signalling systems and is more particularly coneerned with systems which employ alternating currents, preferably within the voice frequency range, which are applied to the signalling circuit alone or in conibination. The invention is more particularly concerned with signalling circuits in which there may be present currents -which are not signalling currents, and to which the signalling apparatus must not respond.

According to the present invention, at a point where the signals are to be received, two or more devices which will respond to alternating currents, to actuate a relay for example, are provided.

It is arrangedl that signalling current at each of the signalling frequencies is prevented from operating at least one of the receiving devices, which are interconnected in such a manner that if the si-nalling circuit carries currents which are not signalling currents and which do not anopro::imiiate to sine wave form, the siganal receiving apparatus cannot function because all the receiving devices operate.

The invention will be better understood froin the following description of two methods of carrvingr it into effect which -hould be taklen in conjunction with the accompanying drawings comprising figs.

1 and 2. Each of the two modifications there shown represents an arrangement for signalling over a telephone line over which speech is to he transmitted while the signal receiving apparatus is still connected to the line.

Referring particularly to fig. 1 the modification there shewn is intended to respond to signals consisting of alternating current at a single frequency received over the telephone line. The signalling frequency for convenience will be called W cycles per second. The signalling current should preferably approximate closely to sine wave form.

[Price 1/-] The telephone line is represented by the conductors 1,1 and L2. The thermionic 55 valve V1, relay R, condensers Cl and 03 and rectifiers 7'1 and r9 together constitute a device which will respond to alternating, currents. The anode current.

of the valve is normally small or zero, 60 and increases to a value greater than the operating current of the relay when the potential between the grid and cathode is rhythmically varied sufficiently. This device is connected to the telephone 65 line at a receiving point by way of the transformer TI and the resistances RI. and R2. The primary of the transformer is shunted by a condenser C and an inductance L in series, the condenser and inductance together forming a circuit which is resonant at frequency W cycles per second. The impedance at resonance is designed in relation to the resistances RI and R2 to be such that signalling current 75 at frequency W does not operate relay R, but currents at frequencies not very close to WN c-ycles per second mayv operate relay H readily, In the same way, the thernlionic valve 80 V2, relay S, condensers C2 and C4, rectifiers rid and r4, transformer T2 and resistanices R3 and 1B4, together form a device which will operate with an alternating current inp)-uLt. No attempt is made, however, to make it less sensitive at one than at any other frequency.

Relay T is controlled by the coniacts i and 2 on relays R and S respectively The relay Sly is normally operated and g0 s'aould preferably have a slow releasing characteristic. It can be released only when contacts 1 and 2 are simultaneously O)pen for a time interval at least equal to its releasing lag. Signalling current ga operates relay S but not relay R and if applied to the line for a sufficiently lone timie, will release relay T to give a signal, for example by means of contact 3. The effect of speech currents received over the 100 line is to operate and release relays R and S arpproximately in unison, contacts I and 2 not then being simultaneously open for long enough periods for relay T to release. Ins The apparatus may b)e connected to the 1r1d CG< I 401,033 conductors Li and 12 by way of condensers 05 and C6 without adversely affecting the operation of the apparatus, if it is desirable that the apparatus should not form a direct current shunt on the telephone line. Earthing the centre point of the primaries of the transformers T1 and T2 tends to improve the electrical stability of the apparatus. A number of separate batteries are shewn in fig. 1, but the circuit may be arranged to work entirely from one battery, wrhiche may be the telephone exchange battery, or any suitable source of current may be used.

The invention may be applied to a signalling system emploving any number of signalling frequencies. Referring particularly to fig. 2 the modification there shiewn is suitable for a system which employs three different signalling frequencies, which will be referred to as X, Y, and Z cycles per second respectively.

In the same way that relay R in the modification of fig.] is prevented from being operated by signalling current at frequency W cycles per second, relay X in the modification shewn in fig. 2 is prevented from operating when signalling current at frequency X cycles per second is applied to the telephone line, but it operates readily with currents at frequencies not very close to X cycles per second. Similarly, relay Y is prevented from operating when s4gnallinla current 3;5 at frequency Y cycles per second is applied to the line, but it operates readily with feurrents at frequencies not, very close to Y cycles Der secowd. Relav Z behaves in a similar manner with respect 4(0 to signalling current at frequency Z cycles per second. The relays P. Q and P should preferably have slow releasing characteristics. In its normal position, contact 1 on relay X operates relay P.

Silarly, when relays Y and Z are normal, relays Q and R are held operated by contacts 2 and 3 respectively. It may be arranged that when speech currents are being carried by the line, relays X, Y and Z are normally released, relays P. Q and Ri then being operated. The speech currents will operate and release relays X, Y and Z approximately in unison and the relays 1P, Q and R, will be held operated.

For example, when relay X operates, 55 contact 1 will retain relay Q. the circuit for relay Q being completed by way of contacts J, 7, and 10, which will be closed.

Relay P will no longer be held operated by contact 1, but will be held operated 6o by a circuit completed through contacts 3, 6, 9 and 12, all in their operated positions.

For signalling, the relays P, Q and R may be released in pairs by applying 65 signalling current to the line one frequency at a time. Signalling current at frequency X, for example, operates relays Y and Z but not X, hence relays Q and R release, btit relay P remains operated. 70 Signalling current at frequency Y cycles per second in a similar manner releases relays P and R but not Q, and signalling current at frequency Z cycles per second releases relays P and Q but not R. All 75 the relays may be released by applying to the line signalling current at one frequency and after an appropriate time interval, applying, in addition to the first, signalling current at another frequency. 80 Havin.g released the relays P, Q and R, they ma.y be re-operated all together by si.ultaneoulsly cutting off all signalling curients from the line, or they may be re-operated in three dtifferent ways depending upon which signalling frequency is cut ofl first. In these ways the relays P, Q and R may be operated and released in a variety of combinations, and each combi)iiation. ma;- e a e to give a signal go if suitable contacts and connectionis are provided on the relays P, Q and R. Any number of signals mav be given by varying the number of signalling frequencies and providing a pair of relays such as X 95 and P for each frequency.

Comlbinations of operation and release of the relays P. Q and R, other than those already stated, can be obtained by making each of the relays X, Y and Z in- too operative with signalling current at more thani one of the signalling frequencies.

Dated the 9th. day of June, 1932.

T. HI. FLOWERS.

COMPLETE SPECIFICATION.

Improvements in or relating to Electrical Sig:31iing S-ystens.

I. TIHOMAS HAROLD FLOWERS, of 60, Windsor Road, Palmers Green, London, N. 1.3, a British subject, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention relates to elec- {lo trical signalling systems and is more particularly concerned with systems which employ alternating currents. It is especially applicable to telephone systems in which signalling over a circuit is carried jii5 out with alternating currents at frequen401,0333 cies l witng wthin the range of frequencies occurri in speech. The invention has mainly in view arrangements whereby signalling apparatus is rendered irnresponsive to currents of complex frequency which include a component at the signalling frequency. The arrangements of the invention are accordingly adapted to distinguislh between signal currents and 1O speech currents or " noise ".

According to the present invention at a point at which the signals are received two or more devices which will respond to alternating current are provided and it is arranged that received current of signalling frequency or lyino within a narrow band of frequencies is prevented from operating or maintaining operated at least one of the devices while currents of frequency other than that to which response is required or outside the narrow Dand operate or keep operated a pair of the devices. The arrangements are such that if the signalling circuit carries currents which are not of signalling frequency or which do not approximate to sine wave form the signal receiving apparatus is unaffected in the sense that no effective operation takes place as in the case of a signal.

It may he arranged that the two devices of a pair are prevented from operation by signallingr currents of different frequencies in which case both devices will le 3a operated if a signalling: frequency is not present and one or other will be operated if sisnalling current of one or other of the signalling frequencies be received, the sign-al given depending on the device operated or mnoperated.

A device includes a relay, contacts of the relays of the several devices provided at the receivingI end of a signalling circuit controlling the signal apparatus so that according to the relay combination operated different siiuals uiay be given.

A method of carrying out the invention will now be described by way of eample with reference to the drawings left with the Provisional Specification. Fig. 1 of the drawings showvs arrangements suitable for receiving signal currents of a single frequency over a telephone line and for discriminating between current of the signal frequency and currents at speech frequencies. Fig. 2 shows an arrangement of signal receiving relays for giving signals in response to three different signalling frequencies.

Reference will first be made to Fig. 1.

In this Figure the telephone line is represented by the conductors L1 and L2. The three electrode thermionic valve V1, the relay R, condensers 01 and 03 and rectifiers X1 and. r2 together constitute a device which will respond to alternating currents. The device is connected to the telephone line at a receiving point by way of the transformer T1 and the resistances RI. and 1)2. The primary of the transformer Ti is shunted by a condenser C and inductance L connected in series, the condenser C: and inductance L together.

forming a circuit resonant at the signalling frequency. The impedance at resonance is designed ini relation to the resistances RI and R2 to be such that current at the signalling frequency does not operate relay R but currents at frequencies not very close to the signalling frequency 80 operate relay R readily. In the same way the thermionic valve V2, the relay S, condenser 02 and C4, rectifiers r3 and r4 and transformer T2 and resistances R3 and R4 together form 85.

a device which will operate with an alternating current input. No attempt is made, however, to make it less sensitive at one frequency than at any other.

Relay T controls the signal apparatus gG by means of contact 3 and is itself controlled by contact 1 of relay R1 and contact 2 of relay S. Relay T is normally operated and is preferably of the slow releasing type. Incoming currents may 95 be amplified if required before being applied to the valves V1 and V2.

The mode of operation of the arrangements shown is as follows.

The grids of the v lves VI and V2 are 100l maintained at a negative value by means of the battery GB, such that the anode current is zero or only of a very small value and relays R and S are not operated.

On the arrival over the line Li L2 of cur- iO0 rent at any frequency the following action takes place in the device including valve V2. The received signal induces an e.m.f. in the secondary of the step up transformer T2 andl this e.m.f. is impressed on the grid of the valve V2. This e.m.f. produces a small change in anode current and the a.c. component of the anode current is fed back to the grid cireut by way of condenser C2 and rectifiers 115.

r3 and r4. Alternate half cycles of this component are rectified and decrease the negative potential on the grid which thereupon becomes more positive and a large increase in anode current results, 120 the current being now sufficient to operate the relay S. If the current includes a component at other than the signalling frequency a similar action takes place at valve V1 and relay R is operated. As a 125.

result of the operation of relay S contact 2 opens but since relay R is operated contact 1 closes and the circuit of relay T remains closed. If current at a pure signalling frequency is received relay S 130; i 1 Loperates as before but the valve V1 is bypassed by the oscillatory circuit CL no appreciable change in the potential of the grid of valve V1 taking place. Relay R accordingly remains unoperated and after an interval depending on its releasing period relay T releases and contact 3 opening the signal apparatus is operated.

In the reception of speech the signalling frequency may occur as a component of the complex speech currents and during the receipt of current of mixed frequencies including current at signalling frequency relay R is operated by the components of a frequency other than signalling frequency. Contact 1 closes and holds relay T.

The effect therefore of speech is to operate and release relays R and S in unison.

In a modification of this arrangemnent the primary of transformer T2 may be shunted by an oscillatory circuit similar to that shunting transformer Ti but resonant at a different frequency. A pair of slow releasing relays corresponding to relay T may be normally connected individually over back contacts of the anode circuit relays R and S or auxiliaries thereto, a circuit for the slow releasing relays also existing over series connected make contacts of the slow releasing relays and front contacts of the anode circuit relays, the anode circuit relay of one device controlling the slow releasing relay of the other device over its front contact, so that so long as the anode circuit relays = operate and release in unison as they will do u.nder speech conditions the slow releasing relays will remain held, their a release -ans covering any slight irregularity in the charing over of the anode circuit relay contacts. One or other of the slow releasin- relays will only be released on receint of current of pure signralel fr quency which will ef'ect i release of the appropriate anode circuit relayl while operating the other. Such an a arran-enment may be employed in con- r neclion with two wav signalling with voice frequency currents over a telephone r line, one of the devices being resonant at}i the incoming signalling frequency the 2 other being resonant at the locally applied d outgoing frequency. r The devices may be connected to the q line L! L2 by way of condensers C5 and a C6 without adversely affecting their q operation if it is desirable that the apparatus should not form a direct cur- o rent shunt on the telephone line. 1h Earthing the centre points of the o.

primaries of the transformers Tl and T2 r( tends to improve the electrical stability ci of the apparatus. Y An improved arrangement which per- rm mits the condenser C to be larger and therefore easier to manufacture for a specified capacity is to provide the transformer T1 with two secondary windings.

The primary and one of the secondary 7G windings are arranged as a step-dowsn transformer and are very tightly coupled, the secondary winding being shunted by the resonant circuit, and arranged to form an electrostatic screen between the '7.

primary winding and the other secondary winding, the centre point being eaithed as is the centre point of the primary winding. The other secondary winding which is arranged to step up the im- 81 pressed voltage is connected to the grid of the valve, the turns ratio being such as to operate the relay in the anode circuit with currents of the order of magnitude usually available on telephone circuits.

The input effecting operation of the anode circuit relay is greater than that which will cause the relay to release and the difference between the two input levels W varies in accordance with the frequency of the input current. By connecting a resistance across the condenser (C:3 or C4) in the grid circuit, conveniently by the operation of the anode circuit relay or 95 consequent thereon, the two levels are brought nearer together. With a comparatively low resistance, for example 100,000 ohlnls, the relay may be caused to release when the innut level over a J00 range of frequencies is higher than that which will effect the relay operation. The relay will then vibrate and this vibration may be turned to good effect in certain c-ases, as, for instance in maintaining 105 operated a slow releasing relay.

It rill Le appreciated that --ibration f the relay. u.vii h CesnOnD to received current ma"-.'e brounht about 1v other leans 3ui',abie to the type of rectifier emprovecd as, for ilistane. by increa.in. the attentation I et cen the line and the ectifier wbhe the relav operates.

In Fig. 2 is show n an arrangement for esponding to an; of three different sig- It5 m9llinag frequencies, the relays X, Y and corresponding to the relay R in three ifferent devices. It will be assumed that elay X is unresponsive to signals of frellenc('v 2 cycles per second, and relays Y 120 nd( Z are unresponsive respectively to freuencies of y and z cycles per second.

The relays X, Y and Z are normally unperated and consequently the slow reLasing relays P, Q and il are operated 125 ver the back contacts 1, 2 and 3 of the Alays X, Y and Z. If now signalling arrent of 2 frequency is received relays - and Z operate but not X. Relay P emains held but the direct circuit of 130 401,033 nay be transmitted or present an arrangeement for determining whether ignal current is being received comprisng a pair of devices responsive to alternating current one of which devices is 70 idapted to respond to currents of frequencies within the said range including those within said narrow band and the Alher of which is adapted to respond to currents of frequencies other than those 75 within said narrow band.

2. In or for an electric signalling system in which currents of signalling frequencies and currents of other frequencies within a range which includes the signalling frequencies may be transmitted or present discriminating signal receiving arrangements comprising a plurality of devices responsive to alternating current one of which devices is adapted to respond 85 to currents of different frequencies including the signalling frequencies and the other devices are rendered uinfesponsive individually to currents of pure signalling frequencies. 90 3. In or for an, electric signalling system in which for signalling purposes currents of frequencies lying within a plurality of narrow bands separated from one another in the frequency scale are transmitted and in which currents of other frequencies within a range including said narrow bands may be transmitted or present the provision at the end of a signalling circuit of a like plurality of devices 100 each of which is adapted to be unresponsive to currents of frequencies lying within one of the narrow bands.

4. Signal receiving arrangements