Patent GB-701447-A (GB)
Title: A device for ascertaining the phase of an alternating voltage
Inventor: OBERMAN ROELOF MAARTEN MARIE
IPC: H04Q1/18
Filed: 1950-11-07
Abstract: 701,447. Automatic exchange systems. STAATSBEDRIJF DER POSTERIJEN, TELEGRAFIE EN TELEFONIE. Nov. 7, 1950 [Nov. 11, 1949], No. 27237/50. Class 40 (4) [Also in Group XXXVI] A device for identifying the phase of an input voltage (which may be one of a number of phases separated by discrete intervals) by comparison in two stages with a range of reference voltages successively phase-displaced by similar intervals, and utilized, e.g. in an automatic telephone system for searching and identifying free lines of PBX subscribers, comprises a discriminator circuit embodying relayoperating gas-filled cold cathode discharge tubes to which the combined input and successive ieference voltages are applied, which is initially switched to operate within a wide discrimination limit when the input phase lies within a range of phase intervals distributed about the required phase and register the appropriate range upon a first relay chain, which then re-arranges the discriminator circuit to operate within a narrow discrimination limit only when the input phase corresponds with the phase of the appropriate successive reference voltage within the pre-determined range, register such phase on a second relay chain, and arrest the apparatus. In Fig. 1, a phase discriminator comprises transformers BT, PT energized by the input and reference signals having split cross connected secondaries in series with the anode supply and combining the two signals on the cathodes 1, 2 of a cold cathode gas discharge tube SVI through resistances R<SP>5</SP>, R6 preventing continuous discharge. When the resultant voltage (and thus the phase difference between input and comparison voltages) between the cathodes exceeds a critical value, the tube ionizes once per half-cycle and charges condenser C<SP>1</SP> negatively to bias one cathode of a similar tube SV<SP>2</SP>, which is prevented from ionizing, while when the resultant voltage falls below the critical value (as when the input and comparison voltages approach phase equality) the bias on SV<SP>2</SP> is removed, and it is ionised from its anode supply to operate relay WP. The input signal may have an amplitude of, e.g. 3 or 5 volts at one of 12 discrete phases differing by #/6, and on closure of start contact st relay A is operated over wp, c<SP>4</SP>, and the input is applied to tapping 3V on the primary of PT through a<SP>3</SP> and b<SP>1</SP>. If the input amplitude is less than 4 volts, SV1 is inoperative and SV2 ionizes to operate relay WP through a<SP>4</SP>, c<SP>3</SP>, h<SP>4</SP>, n<SP>3</SP>. Contact wp turns over and relay C operates through d<SP>2</SP>, a<SP>2</SP>, and relays A and C hold over c<SP>2</SP>, while relay B remains inoperative since WP turns over before B has time to operate over a<SP>1</SP>. If the input is greater than 4 volts, SV<SP>1</SP> ionizes and SV<SP>2</SP> is inoperative, so that relay B operates through a<SP>1</SP> to connect the input to tapping 5V on the primary of PT. The voltage on SV<SP>1</SP> is now insufficient to ionise the tube, so that SV<SP>2</SP> ionizes, operating relays WP, A and C. Relays A, C hold over c<SP>2</SP> and relay B over b<SP>2</SP>, so that if the input is 3 volts it is registered on relays A; C while if it is 5 volts it is registered on relays A, B, and C. Relay D now operates over st, wp, c<SP>4</SP>, and h<SP>2</SP>so that a reference voltage of phase 0 (which may successively assume 12 alternative discrete phases at #/6 intervals under control of relays E, F, G, L, M) is connected over d<SP>5</SP> to the primary of transformer BT. A portion of the primary of transformer PT is shunted out over c<SP>1</SP> and h<SP>5</SP> so that if the input phase lies outside a range of one discrete phase interval on either side of the coincident phase of the reference voltage, the intercathode voltage of SV is sufficient to ionize it, so that SV<SP>2</SP> is inoperative. Relay E then operates over st, wp, h<SP>2</SP>, d<SP>1</SP>, the comparison voltage phase is changed to #/2 over e', and if SV<SP>1</SP> is still ionized, relays F and G operate over e<SP>1</SP> and f<SP>1</SP> until the comparison voltage phase lies within the prescribed range, and SV<SP>1</SP> becomes inoperative. Then SV<SP>2</SP> ionizes to operate relay WP, and contact wp turns over to operate relay Hover d<SP>2</SP> and k<SP>2</SP>, and hold the operated relays of the E, F, G chain over d<SP>2</SP>, k<SP>2</SP>, e<SP>2</SP>, f<SP>2</SP>, or g<SP>2</SP>. The appropriate range within which the input signal phase lies is thus registered on the E, F, G chain and SV<SP>2</SP> is de-ionized by the opening of h' in the anode circuit while h<SP>3</SP>, h<SP>5</SP> respectively connect the reference signal to a tapping on the primary BT and shunt out a further section of the primary of PT, so that SV only ionizes if the reference and input phases are not coincident. The release of'relay WP operates relay K over wp, c<SP>4</SP>, h<SP>2</SP>, n<SP>2</SP> and if the phases are coincident the inter-cathode voltage on SV<SP>1</SP> is below the ionizing level, so that SV<SP>2</SP> ionizes and operates relay WP over a<SP>4</SP> d<SP>4</SP>, k<SP>3</SP>, n<SP>3</SP>. Contact wp then turns over to hold relay K and operate relay N over d<SP>2</SP>, k<SP>2</SP> and relay N then holds over n<SP>1</SP>. If on operation of relay K the phases are not coincident, SV1 ionizes and SV<SP>2</SP> is inoperative, so that relays L, M are successively operated over k<SP>1</SP> or l<SP>1</SP> to shift the comparison phase by steps of Œ#6 under control of contacts l<SP>3</SP>. . . l<SP>6</SP> or m<SP>3</SP>. . . m<SP>6</SP> until coincidence is reached, and SV<SP>2</SP> ionizes. Relay WP then operates to hold the operated relays of the K, L, M chain over wp, d<SP>2</SP>, k<SP>2</SP>, l<SP>2</SP> or m<SP>2</SP>, thus registering the exact input phase, and to operate relay N which holds over n<SP>1</SP>. SV<SP>2</SP> is then de-ionized by the opening-of n<SP>3</SP> in its anode circuit. The apparatus is applicable to the remote operation of selective devices by transmission of variable phase signals. The relay chain registers are replaceable by Stepping switches.