Patent Publication Number: US-2011049987-A1

Title: Power tap, terminal apparatus and communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-197706, filed on Aug. 28, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     A certain aspect of the embodiments discussed herein is related to a power tap, a terminal apparatus and a communication system. 
     BACKGROUND 
     A device that applies a power tap is developed. The power tap supplies an AC power (i.e., alternating current power) to an outside device. For example, there has been known a remote power controlling apparatus that controls the power tap from a remote place via a network, thereby controlling power supply to a device connected to the power tap. Such a power tap stores parameters for controlling operation of the power tap, and measured data thereinto. The power tap is provided with a communication connector, and communicates with an external terminal apparatus via the communication connector when the parameters are set to the power tap or data is acquired from the power tap. When there is no space for providing the communication connector in the power tap, or when there is not much amount of communication data, the power tap can communicate with the terminal apparatus according to communication using the AC power via an outlet provided on the power tap. As the communication using the AC power, for example, there has been known PLC (Power Line Communication) that can communicate a large mount of data with high speed. 
     A communication method using a current other than the PLC is proposed. For example, a document 1 (International publication No. WO 2005/109667) discloses a communication method utilizing a power line in which a load current is added to one wavelength of an AC waveform, and an AC (i.e., alternating current) including the processed waveform is transmitted as an information signal. A document 2 (Japanese Laid-Open Patent Application Publication No. 2004-502397) discloses a method of communicating over a power line, the method including a step of modulating a current component of an AC power signal present on the power line. 
     In the PLC, a circuit is complex and expensive. Further, in the PLC, communication data is superimposed with a power line, and hence a noise occurs to a shortwave radio or a wireless machine by an electric wave emitted from the superimposed signal. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a power tap that supplies an alternating-current power to an terminal apparatus, is connected to the terminal apparatus to configure a closed circuit, and transmits or receives data to/from the terminal apparatus, the power tap including: a plurality of routes including difference loads; a selecting portion that, when data is transmitted to the terminal apparatus, selects any one of the routes based on the transmitted data, in synchronism with timing in which amplitude of an alternating current flowing on the closed circuit becomes 0; and a first detecting portion that, when data is received from the terminal apparatus, detects change of the amplitude of the alternating current based on the received data. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a construction of a communication system according to an exemplary embodiment; 
         FIG. 2  is a diagram showing a construction of a power tap; 
         FIG. 3  is a diagram showing a construction of a terminal apparatus; 
         FIG. 4  is a diagram showing a construction of a circuit of the communication system; 
         FIG. 5  is a diagram showing a construction of a circuit of the communication system; 
         FIG. 6  is a diagram showing a relationship between on/off signals of triacs T 1  and T 2 , and an AC I 1 ; 
         FIG. 7  is a diagram showing a construction of a circuit of the communication system; 
         FIG. 8  is a diagram showing a relationship between an on/off signal of a triac T 3 , and an AC I 2 ; and 
         FIG. 9  is a diagram showing a construction of the circuit of the communication system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A description will now be given of an exemplary embodiment with reference to the accompanying drawings. 
     A description will now be given, with reference to  FIG. 1 , of a construction of a communication system  300  according to an exemplary embodiment.  FIG. 1  is a diagram showing a construction of the communication system  300  and surrounding devices. The communication system  300  includes a power tap  100  and a terminal apparatus  200 . The power tap  100  includes a power plug  10 , outlets  20   a ,  20   b ,  20   c , and  20   d , and a network port  22 . The terminal apparatus  200  includes a power plug  30 . For example, the power tap  100  receives power supply by connecting the power plug  10  to an outlet from which AC 100V is supplied. The terminal apparatus  200  receives power supply by connecting the power plug  30  to any one of the outlets  20   a  to  20   d  on the power tap  100 .  FIG. 1  illustrates an example of connecting the power plug  30  to the outlet  20   a . The power tap  100  and the terminal apparatus  200  transmit or receive data which is a bit sequence by utilizing the connection of the outlet  20   a  and the power plug  30 . The data which the power tap  100  transmits to the terminal apparatus  200  is a current value measured with each of the outlets. The terminal apparatus  200  calculates power consumption by using the received current value, for example. The data which the power tap  100  receives from the terminal apparatus  200  is commands and parameters for the terminal apparatus  200  to designate operation of the power tap  100 , for example. One of the commands designates a timer mode, for example. One of the parameter is time for switching on or off each outlet when the timer mode is set, for example. Internal operation of the power tap  100  and the terminal apparatus  200 , when data is transmitted or received between the power tap  100  and the terminal apparatus  200 , is described later. 
     As shown in  FIG. 1 , a headless server  202 , and routers  204  and  206  are connected to the outlets  20   b ,  20   c , and  20   d  of the power tap  100 , for example. The headless server  202  can be used without connecting input/output devices. The routers  204  and  206  relay between networks such as LANs (Local Area Networks). The network port  22  of the power tap  100  is connected to a remote management PC  400  via a network  500 . The remote management PC  400  is placed at a remote place far away from a server room at which the power tap  100 , the terminal apparatus  200 , the headless server  202 , and the routers  204  and  206  are placed. The remote management PC  400  instructs switching on or off the outlets  20   a ,  20   b ,  20   c , and  20   d  to the power tap  100  via the network  500 , thereby switching on or off the terminal apparatus  200 , the headless server  202 , and the routers  204  and  206 . 
     A description will now be given, with reference to  FIG. 2 , of a construction of the power tap  100  according to the exemplary embodiment.  FIG. 2  is a block diagram showing the construction of the power tap  100 . The power tap  100  includes the power plug  10 , the outlets  20   a ,  20   b ,  20   c  and  20   d , a power supply circuit  12 , a control circuit  14 , load selecting circuits  16   a ,  16   b ,  16   c  and  16   d , and current measurement circuits  18   a ,  18   b ,  18   c  and  18   d . The power supply circuit  12  converts an AC (Alternating Current) power supply supplied via the power plug  10  into a DC (Direct-Current) power supply. The converted DC power supply is supplied to the control circuit  14 . The control circuit  14  selects loads in the load selecting circuits  16   a ,  16   b ,  16   c , and  16   d , and measures amplitude of each of currents measured with the current measurement circuits  18   a ,  18   b ,  18   c , and  18   d.    
     A description will now be given, with reference to  FIG. 3 , of a construction of the terminal apparatus  200  according to the exemplary embodiment.  FIG. 3 . is a block diagram showing the construction of the terminal apparatus  200 . The terminal apparatus  200  includes a power supply circuit  32 , an internal main circuit  34 , a control circuit  36 , a switch  38 , a switching circuit  40  and a current measurement circuit  42 . The switch  38  is switched based on whether the terminal apparatus  200  communicates with the power tap  100 . When the terminal apparatus  200  communicates with the power tap  100 , the switch  38  is switched downward as shown by a solid line in  FIG. 3 , and hence the power plug  30  is connected to the switching circuit  40  and the current measurement circuit  42 . At this time, the control circuit  36  switches on or off a closed circuit via the switching circuit  40 , and measures amplitude of a current measured with the current measurement circuit  42 . When the terminal apparatus  200  does not communicate with the power tap  100 , the switch  38  is switched upward as shown by a broken line in  FIG. 3 , and hence the power plug  30  is connected to the power supply circuit  32 . The power supply circuit  32  converts an AC (Alternating-Current) power supply supplied via the power plug  30  into a DC (Direct-Current) power supply. The converted DC power supply is supplied to the internal main circuit  34 . The internal main circuit  34  includes a CPU (Central Processing Unit), a memory, and so on. The internal main circuit  34  generates data of control commands transmitted to the power tap  100 , and stores data of a measured value of the current received from the power tap  100 . 
     A description will now be given, with reference to  FIG. 4 , of a construction of the communication system  300  according to the exemplary embodiment.  FIG. 4  is a circuit diagram of the communication system  300 . In  FIG. 4 , a left side of terminals  60  and  62  corresponds to the power tap  100 , and a right side of the terminals  60  and  62  corresponds to the terminal apparatus  200 . Since the power tap  100  and the terminal apparatus  200  are connected by the outlet  20   a  and the power plug  30  as shown in  FIG. 1 , the terminals  60  and  62  indicate contact points of the outlet  20   a  and the power plug  30 . The power tap  100  and the terminal apparatus  200  constitute a closed circuit. 
     The power tap  100  includes an AC power supply  50 , the control circuit  14 , a current sensor  52 , triacs T 1  and T 2 , and a resistance R 1 . The AC power supply  50  corresponds to an AC power supply connected to the power plug  10  shown in  FIG. 2 . The current sensor  52  corresponds to the current measurement circuit  18   a  shown in  FIG. 2 . The triacs T 1  and T 2 , and the resistance R 1  correspond to the load selecting circuit  16   a  shown in  FIG. 2 . The triac T 1  is connected in series with the closed circuit, and the triac T 2  is connected in parallel with the triac T 1 . The triac T 2  is connected in series with the resistance R 1 . The current sensor  52  is connected in series with the closed circuit, measures amplitude of an alternating current (hereinafter referred to as “AC”) flowing on the closed circuit, and notifies the control circuit  14  of the measured amplitude. The control circuit  14  receives notification of the amplitude of the AC measured with the current sensor  52 . The control circuit  14  switches on or off the triacs T 1  and T 2 . 
     The terminal apparatus  200  includes the control circuit  36 , a current sensor  54 , a triac T 3 , and a resistance R 2 . The triac T 3  corresponds to the switching circuit  40  shown in  FIG. 3 . The current sensor  54  corresponds to the current measurement circuit  42  shown in  FIG. 3 . The current sensor  54 , the triac T 3 , and the resistance R 2  are connected in series with the closed circuit. The current sensor  54  measures amplitude of an AC flowing on the closed circuit, and notifies the control circuit  36  of the measured amplitude. The control circuit  36  receives notification of the amplitude of the AC measured with the current sensor  54 . The control circuit  36  switches on or off the triac T 3 . 
     A description will now be given, with reference to  FIG. 5 , of operation of the communication system  300  when the power tap  100  transmits data to the terminal apparatus  200 .  FIG. 5  is a circuit diagram showing only a construction relating to a case where the power tap  100  transmits the data to the terminal apparatus  200 , in the construction shown in  FIG. 4 . 
     The control circuit  14  of the power tap  100 , which is a transmission side of data, switches on any one of the triacs T 1  and T 2  and switches off the remaining one in synchronism with timing in which the amplitude of the AC becomes “0”, i.e., for each half-wave of the AC, based on whether each bit in the bit sequence transmitted to the terminal apparatus  200  is “0” or “1”. When a bit in the bit sequence is “1”, the control circuit  14  switches on the triac T 1  and switches off the triac T 2 . In this case, a route of the AC I 1  is a route  1 . When a bit in the bit sequence is “0”, the control circuit  14  switches off the triac T 1  and switches on the triac T 2 . In this case, a route of the AC I 1  is a route  2 . As shown in  FIG. 5 , the route  2  differs from the route  1  in including the resistance R 1 . Therefore, the amplitude of the AC I 1  flowing on the route  2  is smaller than that of the AC I 1  flowing on the route  1 . 
     In the terminal apparatus  200  which is a reception side of data, the triac T 3  is always switched on by the control circuit  36 . The amplitude of the AC I 1  measured with the current sensor  54  changes for each half-wave of the AC I 1 . The current sensor  54  measures the amplitude of the AC I 1 , and notifies the control circuit  36  of the measured amplitude, for each half-wave of the AC I 1 . The control circuit  36  detects a size of the notified amplitude for each half-wave of the AC I 1 . The control circuit  36  judges whether each bit transmitted from the power tap  100  is “0” or “1”, based on the size of the amplitude of the AC I 1 . Thereby, the control circuit  36  receives the bit sequence. 
     A description will now be given, with reference to  FIG. 6 , of a relationship between on/off signals of the triacs T 1  and T 2 , and the AC I 1  when the power tap  100  transmits data to the terminal apparatus  200 .  FIG. 6  is a diagram showing the relationship between the on/off signals of the triacs T 1  and T 2 , and the AC I 1 .  FIG. 6  illustrates, in order from the top downwards, the on/off signal of the triac T 1 , the on/off signal of the triac T 2 , and the AC I 1 . Lateral axes in  FIG. 6  indicate time t, and each interval from time tn to time t(n+1) (n=0 to 9) corresponds to a half-wave period of the AC I 1 . 
     It is assumed that, in  FIG. 6 , the data which the power tap  100  transmits to the terminal apparatus  200  is a bit sequence “01000001 (41 h of a hexadecimal form)” corresponding to “A” of an ASCII (American Standard Code for Information Interchange) character code. The bit sequence is sequentially transmitted from a least significant bit. In transmission of the bit sequence, “1” which is a start bit is added to a top of the bit sequence, and “0” which is a stop bit is added to an end of the bit sequence. 
     The control circuit  14  first switches on the triac T 1  and switches off the triac T 2  from time t 0  to time t 1 , and hence transmits “1” of the start bit to the terminal apparatus  200 . Next, the control circuit  14  sequentially transmits the bit sequence “01000001” from the least significant bit, from time t 1  to time t 9  for each half-wave period. That is, the control circuit  14  switches on the triac T 1  and switches off the triac T 2  from time t 1  to time t 2  and from time t 7  to time t 8 , and hence transmits “1” of a first bit and a seventh bit from the least significant bit to the terminal apparatus  200 . Further, the control circuit  14  switches off the triac T 1  and switches on the triac T 2  from time t 2  to time t 6  and from time t 8  to time t 9  for each half-wave period, and hence transmits “0” of second to sixth bits and an eighth bit from the least significant bit to the terminal apparatus  200 . The control circuit  14  finally switches off the triac T 1  and switches on the triac T 2  from time t 9  to time t 10 , and hence transmits “0” of the stop bit to the terminal apparatus  200 . 
     The AC I 1  flows on the route  1  from time t 0  to time t 2  and from time t 7  to time t 8 . The AC I 1  flows on the route  2  in which the resistance R 1  is serially connected, from time t 2  to time t 6  and from time t 8  to time t 10 . Therefore, as shown in  FIG. 6 , the amplitude of the AC I 1  flowing on the route  2  is smaller than that of the AC I 1  flowing on the route  1 . 
     A description will now be given, with reference to  FIG. 7 , of operation of the communication system  300  when the power tap  100  receives data from the terminal apparatus  200 .  FIG. 7  shows only a construction relating to a case where the power tap  100  receives the data from the terminal apparatus  200 , in the construction shown in  FIG. 4 . 
     The control circuit  36  of the terminal apparatus  200 , which is a transmission side of data, switches on or off the triac T 3  in synchronism with timing in which the amplitude of an AC  12  becomes “0”, i.e., for each half-wave of the AC I 2 , based on whether each bit in the bit sequence transmitted to the power tap  100  is “0” or “1”. When a bit in the bit sequence is “1”, the control circuit  36  switches on the triac T 3 . When a bit in the bit sequence is “0”, the control circuit  36  switches off the triac T 3 . Thereby, the AC I 2  flows on the closed circuit when the bit is “1”, and is 0 ampere without flowing on the closed circuit when the bit is “0”. 
     In the power tap  100  which is a reception side of data, the triac T 1  is always switched on by the control circuit  14 . The amplitude of the AC I 2  measured with the current sensor  52  changes for each half-wave of the AC I 2 . The current sensor  52  measures the amplitude of the AC I 2 , and notifies the control circuit  14  of the measured amplitude, for each half-wave of the AC I 2 . The control circuit  14  detects whether the notified amplitude is “0” for each half-wave of the AC I 2 . The control circuit  14  judges whether each bit transmitted from the terminal apparatus  200  is “0” or “1”, based on whether the notified amplitude is “0”. Thereby, the control circuit  14  receives the bit sequence. 
     A description will now be given, with reference to  FIG. 8 , of a relationship between an on/off signal of the triac T 3 , and the AC I 2  when the power tap  100  receives data from the terminal apparatus  200 .  FIG. 8  is a diagram showing the relationship between the on/off signal of the triac T 3 , and the AC I 2 .  FIG. 8  illustrates, in order from the top downwards, the on/off signal of the triac T 3 , and the AC I 2 . Lateral axes in  FIG. 8  are the same as those in  FIG. 6 . 
     It is assumed that, similarly to  FIG. 6 , the data which the power tap  100  receives from the terminal apparatus  200  in  FIG. 8  is a bit sequence “01000001” corresponding to “A” of the ASCII character code. The bit sequence is sequentially transmitted from a least significant bit. In transmission of the bit sequence, “1” which is a start bit is added to a top of the bit sequence, and “0” which is a stop bit is added to an end of the bit sequence. 
     The control circuit  36  first switches on the triac T 3  from time t 0  to time t 1 , and hence transmits “1” of the start bit to the power tap  100 . Next, the control circuit  36  sequentially transmits the bit sequence “01000001” from the least significant bit, from time t 1  to time t 9  for each half-wave period. That is, the control circuit  36  switches on the triac T 3  from time t 1  to time t 2  and from time t 7  to time t 8 , and hence transmits “1” of a first bit and a seventh bit from the least significant bit to the power tap  100 . Further, the control circuit  36  switches off the triac T 3  from time t 2  to time t 6  and from time t 8  to time t 9  for each half-wave period, and hence transmits “0” of second to sixth bits and an eighth bit from the least significant bit to the power tap  100 . The control circuit  36  finally switches off the triac T 3  from time t 9  to time t 10 , and hence transmits “0” of the stop bit to the power tap  100 . 
     The AC I 2  flows on the closed circuit from time t 0  to time t 2  and from time t 7  to time t 8 . The AC I 2  does not flow on the closed circuit from time t 2  to time t 6  and from time t 8  to time t 10 , so that the amplitude of the AC I 2  becomes “0”. 
     According to the exemplary embodiment, as shown in  FIGS. 5 and 6 , when the power tap  100  transmits data to the terminal apparatus  200 , the control circuit  14  and the triacs T 1  and T 2  select any one of the route  1  never including the resistance R 1 , and the route  2  including the resistance R 1 , based on the transmitted data, in synchronism with the timing in which the amplitude of the AC I 1  becomes “0”. As shown in  FIGS. 7 and 8 , when the power tap  100  receives data from the terminal apparatus  200 , the control circuit  14  and the current sensor  52  detect change of the amplitude of the AC I 2  based on the data. Thereby, a plurality of routes including different loads are switched, so that the data can be transmitted or received without stopping power supply. Further, since the amplitude of the ACs I 1  and I 2  is made to change with a simple arrangement, the data can be transmitted or received in synchronism with the timing in which the amplitude of the ACs I 1  and I 2  becomes “0”. Therefore, it is possible to reduce production costs of the power tap  100  and the terminal apparatus  200 , and to prevent a noise and a higher harmonic from occurring. 
     In the exemplary embodiment, the data which the power tap  100  transmits or receives to/from the terminal apparatus  200  is the bit sequence. The control circuit  14  and the triacs T 1  and T 2  select any one of the route  1  and the route  2  based on the value of each bit in the bit sequence. Thereby, the data can be transmitted or received with a simple arrangement. 
     In the exemplary embodiment, as shown in  FIGS. 7 and 8 , when the terminal apparatus  200  transmits data to the power tap  100 , the control circuit  36  and the triac T 3  switch on or off the closed circuit based on the data, in synchronism with the timing in which the amplitude of the AC I 2  flowing on the closed circuit becomes “0”. As shown in  FIGS. 5 and 6 , when the terminal apparatus  200  receives data from the power tap  100 , the current sensor  54  detects change of the amplitude of the AC I 1  based on the data. Since the terminal apparatus  200  need not supply a power supply like the power tap  100 , the terminal apparatus  200  can achieve transmission of data to the power tap  100  by switching on ore off the closed circuit, without switching the plural routes including different loads. Therefore, the terminal apparatus  200  can be configured more simply. Also, it is possible to switch on ore off the closed circuit in synchronism with the timing in which the amplitude of the AC I 2  becomes “0”. Therefore, it is possible to reduce production costs of the power tap  100  and the terminal apparatus  200 , and to prevent a noise and a higher harmonic from occurring. 
     In the exemplary embodiment, the route  1  and the route  2  are switched on or off with the triacs T 1  and T 2 . The closed circuit is switched on or off with the triac T 3 . Instead of the triacs T 1 , T 2  and T 3 , solid-state relays S 1 , S 2  and S 3  may be used as shown in  FIG. 9 . 
     In the exemplary embodiment, instead of the resistances R 1  and R 2  provided in the closed circuit, constant-current diodes may be used, for example. 
     In the exemplary embodiment, the ACs I 1  and I 2  are measured with the current sensors  52  and  54 , respectively. Instead of the current sensors  52  and  54 , low-resistances may be connected in series with the closed circuit, and voltage indicators may be connected to both ends of the respective low-resistances. The voltage indicators measures voltages of both ends of the respective low-resistances, and then the control circuit  14  and  36  may measure the ACs I 1  and I 2  from differences of the voltages, respectively. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various change, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.