Process for transferring information and system for carrying out the process

An arrangement for transferring both power and information on one or more common AC power lines in which a first type of information is transmitted by terminating the current from the power supply in periods which constitute a fraction of a halfwave cycle. The transmission of this first type of information is dependent upon the frequency of the AC power supply. A second type of information is transmitted during the periods in which the current from the power supply is terminated, and the second type of information is transmitted at a higher frequency independent of that of the AC power supply.

The invention relates to a process for transferring information between 
electrical devices interconnected via at least two power supply lines 
through which an alternating supply current flows, said lines being also 
used for transferring information between the electrical devices. 
The German Offenlegungsschrift No. 2 428 173 discloses a technique by means 
of which the supply current to a plurality of electrical devices is 
essentially cut off in one or more subsequent halfwave intervals to 
thereby transfer information to the electrical devices which have means 
for detecting one or more missing halfwaves. 
This technique suffers from the drawback that certain forms of loads do not 
function satisfactorily when the supply current is cut off for the 
duration of a halfwave interval. For example, lamps show an inconvenient 
flicker in this technique. This drawback is particularly pronounced when a 
high rate of information is desired which implies cutting away many 
halfwaves in a predetermined, relatively dense pattern. Another 
disadvantage of said technique is that the maximum rate of information is 
limited by the frequency of the supply current. 
The object of the invention is to provide a process making it possible to 
transfer information on the power supply lines without said drawbacks. 
This object is achieved in that, depending upon a first type of information 
to be transferred, current flow through the power supply lines is blocked 
fully or partially in positionally determined periods constituting a 
fraction of a halfwave interval, and in that one or more of the devices 
transmit a second type of information on the power supply lines at least 
in some respective ones of said periods in which, as opposed to the first 
type of information, the second type of information is not dependent upon 
the frequency of the current supply. 
By cutting-off current only for a fraction of a halfwave interval and 
preferably adjacent a current zero-crossing, the reduction in power supply 
during the transfer of the first type of information will be significantly 
smaller than the reduction in power caused by the prior art. The rate of 
information of the second type of information is not limited by the 
frequency of the current supply, so information may be transferred at a 
great velocity on the power supply lines themselves, i.e. without the use 
of special data lines, because the second type of information is 
transmitted during the periods in which the current supply source is 
disconnected. The current supply source will accordingly not act as a load 
on the transmission of the second type of information which may therefore 
be effected with a significantly lower consumption of power than would 
normally be required. 
Blocking of a power supply line is normally initiated at a time which is 
synchronized with the zero-crossing of the supply current, and as 
allowance must be made for the possibility of a certain phase displacement 
between current and voltage on the power supply lines, the periods in 
which the power supply lines are disconnected may become unnecessarily 
long if blocking is ended a predetermined time after the zero-crossing of 
the supply voltage. Ending of said blocking a predetermined time after the 
zero-crossing of the supply current allows a necessary and sufficient 
duration of the periods to be achieved in which the power supply line is 
disconnected. Another advantage is that the duration of said periods is 
well-defined which means that the second type of information may be 
transmitted during the entire period mentioned. 
The invention also relates to a system for carrying out the process, said 
system being characterized by the fact that it comprises change-over means 
arranged to cut off, in response to a first type of information, current 
flow in positionally determined periods which constitute a fraction of a 
halfwave interval, and that at least some of the devices have detector 
means for positional determination of said periods and have control means 
and transmission means arranged to transmit a second type of information 
on the power supply lines during said periods, at least one of the devices 
having means for receiving the second type of information. 
The system of the invention allows the second type of information to be 
transmitted on the power supply lines when said lines are essentially 
disconnected from the current supply source, the devices capable of 
transmitting the second type of information having means for determining 
when the current supply source is disconnected and transmitting the second 
type of information in a state where the current supply source does not 
act as a load on the transmission. As change-over means is preferably used 
a triac (two controlled rectifiers of opposite polarity) which possesses 
the property that it carries current in both directions when a control 
signal is applied, while without this control signal it exhibits great 
resistance to current flow in both directions when the current becomes 
zero the first time. 
The time when the power supply line is initially disconnected is perferably 
controlled synchronously with the zero-crossing of the supply voltage, and 
the features set forth in claim 4 permit a well-defined duration of the 
periods in which the current supply cource is disconnected, as has 
previously been mentioned. 
Claim 5 defines a particularly expedient construction of the detector means 
for positional determination of said periods. At a first time constant for 
said resistor and capacitor, the detector means may be made independent of 
the variations in voltage occuring at the beginning of said period, and at 
a second time constant for the resistor and capacitor the detector means 
may be made sensititive to the variations in voltage occurring at the end 
of said period. A diode is coupled over the resistor so that the capacitor 
is rapidly re-charged in the direction opposite the conduction direction 
of the light diode. 
Thus, it will be understood that the system according to the invention is 
generally applicable for transfer of information via power supply lines. 
In adverse circumstances, there is a remote risk of transients disturbing 
the various detector circuits. However, the system of the invention may be 
made extremely insensitive to such disturbances by building the controller 
together with logic circuits capable of performing error detecting and 
error correcting operations. The combination, as provided by the 
invention, of said circuits is excellently suitable for being constructed 
as a single, integrated circuit, as is stated in claim 6. The integrated 
circuit is arranged to process all direct current signals and is 
preferably galvanically separated from the power supply lines, e.g. by 
means of optical couplers. 
The integrated circuit may e.g. be incorporated in a microcomputer so that 
the system of the invention may serve both as power supply for and mutual 
communication between several data units.

In FIG. 1 there is shown an information transmitter 1 which is arranged to 
introduce information into power supply lines 4 and 5 for a plurality of 
devices connected thereto. The individual devices comprise each a receiver 
2, 2A . . . and a power consuming unit 3, 3A . . . , which parts will be 
described later. 
The transmitter 1 is connected to for example an ordinary 220 volts 
alternating voltage network having a zero and a phase line, O and F 
respectively. The zero-conductor is passed directly through the 
transmitter 1, while a change-over means with a converter 9 is inserted in 
series with the phase line, said converter being arranged to connect a 
large and a small resistor respectively (R1 and R2). The converter 9 is 
controlled by a controller 8 receiving activation signals from circuits 10 
and 11, respectively. Ideally, the resistance of one of said resistors is 
zero, while that of the other resistor is infinite, but to obtain rapid 
connection/disconnection a semi-conductor device is, in practice, used as 
converter, permitting the achievement of a sufficiently large difference 
between the resistances in practice. A preferred semi-conductor device may 
be a triac comprising two controlled rectifiers of opposite polarity, and 
in the following the invention will be explained with a triac. 
The system of the invention is arranged to transmit and receive information 
of a first type as well as to transmit and receive information of a second 
type. The first type of information comprises information transferred by 
briefly disconnecting a power supply line, the second type of information 
comprising information which is transmitted via a power supply line while 
said line is disconnected from a current supply source. Below, the mode of 
operation with respect to the first type of information will be described 
first with reference to FIGS. 2A-C, while the mode of operation with 
respect to the second type of information will be described later with 
reference to FIG. 4. FIG. 2A shows the output voltage V and the output 
current I from the transmitter 1 when the change-over means is 
substantially short-circuited, apart from the period between T4 and T5. In 
the latter period, current passage through the change-over means, that is 
the triac, is essentially cut-off, leading to the drop in voltage V shown 
in the drawing. The connected units 2, 2A . . . are arranged to detect 
this irregularity in voltage so that information may be transferred from 
the transmitter 1 to the other units by cutting-off the current through 
the triac momentarily within a halfwave. According to the invention there 
may be several interruptions of a short duration within each halfwave, but 
for the sake of clarity only the interruption shown in FIG. 2A will be 
explained. To reduce transient noise current interruption is preferably 
initiated in the zero-crossing (T4) of the current, which may be obtained 
merely be removing the control signal from the triac whereby it 
automatically cuts off the current in the zero-crossing. When the 
controller 8 has been signalled to emit an impulse on the power supply 
lines 4 and 5, the control signal is taken in time from the triac before 
the time T4, for example at the time T3, when the voltage passes zero. 
This voltage zero crossing is detected by means of the circuit 10 shown in 
FIG. 1. At the time T5 a control signal is again applied to the triac so 
that the phase line is connected to the supply network. The time T5 may be 
determined by a predetermined delay from the time T3, but this involves 
the drawback of an unnecessarily long interruption of current when the 
phase difference T2 less T1 is small. To obtain the necessary, but 
shortest possible current interruption of a well-defined duration, the 
circuit 11 shown in FIG. 1, is arranged to determine the time T4 by 
detecting the voltage V, permitting the determination of the time T5 as a 
fixed delay with respect to the time T4. Thus, provision is made for a 
detectable change in voltage within such a short period that the devices 
connected to the power supply lines 4 and 5 are not affected noticeably by 
said current interruption. Said interruption of current is moreover 
effected so as to minimize transient noise and, as explained above, is 
initiated and ended at a well-defined time independent of the phase and 
frequency concerned. 
The circuit 10 shown in FIG. 1 may be a commercially available 
zero-crossing circuit preferably optically connected to the zero and phase 
line and emits a synchronization signal to the controller 8. 
FIG. 3 illustrates an embodiment of the circuit 11 shown in FIG. 1. This 
detector circuit comprises two uniform halves of opposite polarity, and 
for this reason only one half will be described. The circuit is partly 
connected to the zero and phase line as shown in the figure and is 
provided with a connection to the controller 8 via an optical coupler 12, 
13 for each half. FIG. 2B shows the current 11 and 12, respectively, 
through the respective light diodes 14, 15 of the optical couplers. FIG. 
2B is shown such that the resistor 17 gives rise to no essential phase 
shift away from the phase shift caused by the capacitor 16, and the light 
diode 14 is connected over the resistor 17 such that the dash-and-dot line 
shown in FIG. 2B indicates the transitional area between on (above the 
line) and off below the line) states of the light diode. The curve on FIG. 
2B will then be readily understood, the change in the differential 
coefficient (at the time T4 on FIG. 2A) of the voltage having the effect 
that current through the light diode 14 stops flowing simultaneously with 
an initial discharge of the capacitor 16 through the diode 18. When at the 
time T5 voltage V increases rapidly, a relatively strong current impulse 
is generated through the light diode 14 which then immediately begins 
lighting again. It will be understood that the moment when the light diode 
14 goes out, indicates when current I (FIG. 2A) passes through zero, and 
this state is detected in the controller 8 in that the light sensitive 
transistor of the optical coupler changes from an on to an off state. 
It should be noted that the shown detector circuit has the dead zones 
indicated by hatching on FIG. 2B which require that the controller 8 must 
be able to establish whether the disconnected state of the light sensitive 
transistor occurs outside these dead zones depending upon the position of 
the potentiometer 17. When the dead zones are located as shown in FIG. 2B, 
that is symmetrically around the maximum values of the voltage, the 
detector will be equally suitable for inductive as well as capacitive load 
on the power supply lines, but it may be preferred to adjust the resistor 
17 with respect to the capacitor 16 so as to obtain a phase displacement 
of the signal shown in FIG. 2B. 
FIG. 2C shows the same signals as those described above in connection with 
FIG. 2B, but where the values of the components 16 and 17 are changed so 
that the transistion between the on and off state of the light diode is 
located completely outside the maximum current through the light diode 
when no signals are transmitted on the power supply lines. It will then be 
readily understood that the detector circuit shown in FIG. 3 may also be 
employed for detecting the time T5 (FIG. 2A) when the light diode of the 
optical coupler begins lighting, which is tantamount to the associated 
light sensitive transistor becoming conductive. The detector circuit shown 
in FIG. 3 may thus be used for detecting time T4 as well as time T5, and 
reacts of course to irregularities both in the positive and negative 
voltage shifts owing to the two uniform halves of opposite polarity. 
FIG. 1 shows the units 2 comprising a circuit 6 and a circuit 7, where the 
circuit 6 may correspond to the circuit shown in FIG. 3 which is adjusted 
to the function shown in FIG. 2C, while circuit 7 corresponds to the 
change-over means, i.e. preferably a triac, which is already described. 
FIG. 4 shows a block diagram of a general embodiment of a device for the 
system of the invention. This circuit is arranged to receive information 
and power supply via the phase line F1, the circuits 6, 7A and 8 being 
active during reception. The circuit may also emit information and power, 
and in this case the circuits 7B, 8, 10 and 11 are active. The two 
functions may readily be understood by means of the above explanation of 
said active circuits. Thus, the general circuit shown in FIG. 4 permits 
the construction of a branch structure or hierarchy of such general 
circuits, opening many opportunities of transfer of combined power and 
information. In addition to its ability to transmit and receive 
information of the first type, viz. the one previously explained where the 
rate of transmission is restricted by the frequency of the current supply, 
the device shown in FIG. 4 can according to the invention also transmit 
and receive information of a second type which is not restricted by the 
frequency of the current supply. This is effected via the connections 22 
and 23 shown in FIG. 4 under the control of the control circuit 8 which 
via a data connection D communicates with a data processing unit for the 
first as well as the second type of information. 
According to the invention, information of the second type is transmitted 
in the periods in which the phase line it is desired to use for the 
transmission is cut off from the current supply source so that said source 
does not act as a load on the transmission. 
When information of the second type is to be transmitted from the device 
shown in FIG. 4 to the line F1, the circuit 8 transmits information via 
the connection 22 when it receives a signal from the detector circuit 6 
which tells it when the line F1 is disconnected from the current supply 
source. Transmission of the second type of information must thus wait 
until such brief interruption occurs. If it is desired to transmit 
information of the second type on the line F2 from the device shown in 
FIG. 4, the device itself may optionally disconnect the line F2 from the 
current supply source by means of the change-over means 7B which is 
controlled from the control circuit 8. For the duration of the 
interruption, information of the second type may be transmitted from the 
control circuit 8 via the connection 23 to the line F2. 
The transmission itself of the second type of information may e.g. be 
brought about with a plurality of capacitors which are connected to the 
power supply lines via respective cut-off means. The cut-off means may be 
controlled so that the capacitors are first charged to the supply voltage 
and then discharged at subsequent, predetermined moments when the power 
supply lines are disconnected from the power supply source, and carry 
impulses representing the second type of information on the power supply 
lines. 
Transmission of the second type of information may of course also be 
brought about in a manner known per se by means of known transmission 
circuits. Likewise, the control circuit 8 may contain means known per se 
for receiving the second type of information via the connections 22 and/or 
23, the detector means, already described, being capable of activating the 
receiver means in the positionally determined periods in which information 
of the second type may occur on a current supply line. 
FIG. 5 shows an integrated circuit 20 for performing the operations 
explained in connection with FIG. 4, among others. The shown circuit 19 
may be a triac like the one designated 21 which connects the power 
consuming unit 3 to the line F1 and disconnects it therefrom. In this case 
power (from F1) and information may be transmitted to units connected to 
the line F2 (in FIG. 5 below the circuit 19). However, the circuit 19 may 
also be a generator capable of emitting impulses on the line F2 when said 
line is not connected to other voltage sources. Transfer of the second 
type of information is preferably brought about via an adapter circuit T 
which is galvanically separated from the circuit 20 by means of optical 
couplers as shown at 22A and 22B (corresponding couplings for the 
connection 23 in FIG. 4 are not shown in FIG. 5). 
Apart from the high voltage circuits designated H and T, such as the one 
shown in FIG. 3, the circuit 20 may comprise all the other, previously 
described circuits which are separated from the high voltage lines for 
example by means of optical couplers. The connections, indicated in FIG. 
5, to the circuit 20 have relation to the circuits shown in FIG. 4 where 
two sets of connections are present at 6 and 11, cf. FIG. 3. It will be 
understood that the optical couplers and the high voltage units may also 
be integrated into the circuit 20 which may comprise the triac 21 and the 
circuit 19 when relatively low power is transmitted. 
The circuit 20 may, however, be a microcomputer capable of performing logic 
operations, for example the control of the dead zones of the detector 
circuits as mentioned above. The circuit 20 is also able to detect and 
correct errors in the data which are transferred on the power supply 
lines, making the system of the invention very immune to errors if now and 
then disturbing transients occur on the phase lines. Thus there is 
provided an inexpensive and reliable system for remote control of power 
consuming devices, such as lamps, motors, data units, etc., and which 
makes it possible to transmit information on power supply lines in both 
directions, i.e. both upstream and downstream transmission.