Method of providing a remote power feed to a terminal in a local area network, and corresponding remote power feed unit, concentrator, repeator, and terminal

Abstract

A method for sending a remote power feed to a terminal in a local area network. A repeater of the local area network produces a detection test signal in a line to which a remote terminal is connected, and the signal has an energy level that will not damage the terminal. The presence of a remote terminal adapted to receive a remote power feed via the repeater is detected by detecting the presence of a predetermined impedance in the terminal, and power is supplied to the terminal via the repeater in response to detection of the presence of the terminal.

What is claimed is: 
     
       1. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least one detection an alternating current test signal on at least two conductors of a line for connecting the local area network to a remote terminal, that the test signal having an energy such that the terminal cannot be damaged under any circumstances, 
 detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of predetermined impedance in the remote terminal on the basis of a current created by the test signal in that said line, and 
 sending a power supply current in that said line when the presence of a terminal adapted to receive a remote power feed is detected. 
 
     
     
       2. A remote power feed method according to  claim 1 , wherein, to detect a predetermined impedance in the remote terminal, the method detects the presence of a capacitor in the remote terminal. 
     
     
       3. A remote power feed method according to  claim 2 , wherein, to detect the presence of a capacitor in the remote terminal:
 ansaid alternating current test signal is applied to the line and it is verified that the remote terminal does not behave like an open circuit for thatthe alternating current test signal, 
 a direct current test signal is applied to the line and it is verified that the remote terminal behaves like an open circuit for that the direct current test signal, and 
 the method concludes that a terminal adapted to receive a remote power feed is present if the results of both tests are positive. 
 
     
     
       4. A remote power feed method according to  claim 1 , wherein, to detect a predetermined impedance in the remote terminal, the method detects the presence of a short-circuit in the remote terminal. 
     
     
       5. A remote power feed method according to  claim 1 , suited to a line including two pairs for sending/receiving data and each enabling the transmission of a remote power feed current in common mode and other conductors which can also be used for a remote power feed, wherein detecting a remote terminal adapted to receive a remote power feed comprises:
 performing a first test to detect if the terminal is adapted to receive a remote power feed via the two pairs for sending/receiving data, 
 performing a second test to detect if the terminal is adapted to receive a remote power feed via the other conductors that can also be used for a remote power feed, 
 sending a remote power feed current in the two pairs for sending/receiving data only if the first test shows that the terminal is adapted to receive a remote power feed via those two pairs, and 
 sending a remote power feed current in the other conductors that can also be used for a remote power feed only if the second test shows that the terminal is adapted to receive a remote power feed via those other conductors. 
 
     
     
       6. A remote power feed method according to  claim 5 , wherein the first test comprises of detecting the presence of a first predetermined impedance in the terminal on the basis of a current created by a first test signal in the two pairs for sending/receiving data and the second test comprises of detecting the presence of a second predetermined impedance in the terminal on the basis of a current created by a second test signal in the other conductors. 
     
     
       7. A remote power feed method according to  claim 6 , wherein one of the two predetermined impedances is a short-circuit and the other predetermined impedance is a capacitance. 
     
     
       8. A remote power feed unit for implementing the method according to  claim 1 , wherein the unit includes:
 means for producing at least one detection said alternating current test signal on at least two conductors of a line for connecting the local area network to a remote terminal, that the test signal having an energy such that the terminal cannot be damaged under any circumstance, 
 means for detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of a predetermined impedance in the remote terminal on the basis of a current created by the test signal in that connection said line, and 
 means for sending a power supply current in the said line when the presence of a terminal adapted to receive a remote power feed is detected. 
 
     
     
       9. A system remote power feed unit according to  claim 8 , wherein the means for detecting a predetermined impedance in the remote terminal include means for detecting the presence of a capacitor in the remote terminal. 
     
     
       10. A system remote power feed unit according to  claim 8 , wherein the means for detecting a predetermined impedance in the remote terminal include means for detecting the presence of a direct current short-circuit in the remote terminal. 
     
     
       11. A system remote power feed unit according to  claim 9 , wherein the means for detecting the presence of a capacitor in the remote terminal include:
 means for applying an said alternating current test signal to the line and verifying that the remote terminal does not behave like an open circuit for that the alternating current test signal, 
 means for applying a direct current test signal to the line and verifying that the remote terminal behaves like an open circuit for that the direct current test signal, and 
 logic means for concluding that a terminal adapted to receive a remote power feed is present if the results of both tests are positive. 
 
     
     
       12. A system remote power feed unit according to  claim 10 , wherein the means for detecting the presence of a short-circuit in the remote terminal include:
 means for applying a direct current test signal to the line, and 
 means for detecting if the remote terminal behaves like a short-circuit for that the direct current test signal and concluding that a terminal adapted to receive a remote power feed is present if the result of the test is positive. 
 
     
     
       13. A system remote power feed unit according to  claim 8 , further including:
 means for detecting disconnection of the terminal adapted to receive a remote power feed, and 
 means for interrupting the remote power feed current in response to detection of disconnection of the terminal. 
 
     
     
       14. A system remote power feed unit according to claim  8  13, wherein means for detecting disconnection of a terminal adapted to receive a remote power feed include:
 means for applying an alternating current test signal to the line, and 
 means for verifying if the terminal behaves like an open circuit for that the alternating current test signal. 
 
     
     
       15. A system remote power feed unit according to  claim 8 , further including:
 means for detecting a short-circuit for the remote power feed direct supply current on the line after sending the remote power feed supply current, and 
 means for interrupting the sending of the remote power feed supply current for a predetermined time and then sending a remote power feed supply current again if a short-circuit is detected for the power supply direct current. 
 
     
     
       16. A system remote power feed unit according to  claim 8 , further including:
 means for concluding that a terminal that is not adapted to receive a remote power feed or a direct current short-circuit is present if the remote terminal does not behave like an open circuit for the alternating current test signal and does not behave like an open circuit for the a direct current test signal, 
 means for then applying a further direct current test signal to the line to verify that the remote terminal or the short-circuit is still connected, and 
 means for concluding that the terminal that is not adapted to receive a remote power feed or the short-circuit has been disconnected and if the result of the direct current test is negative, then the means for concluding:
 applies an a further alternating current test signal to the line and verifies that the remote terminal does not behave like an open circuit for that the further alternating current test signal, 
 applies a further direct current test signal to the line and verifies that the remote terminal behaves like an open circuit for that the further direct current test signal, and 
 concludes that a terminal adapted to receive a remote power feed is present if the results of both tests are positive. 
 
 
     
     
       17. A system remote power feed unit according to  claim 8 , suitable for a line including two pairs for sending/receiving data each enabling the common mode transmission of a remote power feed current, and other conductors that can also be used for a remote power feed, wherein the means for detecting a remote terminal adapted to receive a remote power feed include:
 means for performing a first test to detect if the terminal is adapted to receive a remote power feed via the two pairs for sending/receiving data, 
 means for performing a second test to detect if the terminal is adapted to receive a remote power feed via the other conductors that can also be used for a remote power feed, 
 means for sending a remote power feed current in the two pairs for sending/receiving data only if the first test shows that the terminal is adapted to receive a remote power feed via those two pairs, and 
 means for sending a remote power feed current in the other conductors that can also be used for a remote power feed only if the second test shows that the terminal is adapted to receive a remote power feed via those other conductors. 
 
     
     
       18. A system remote power feed unit according to  claim 17 , wherein:
 the means for performing the first test include means for detecting the presence of a first predetermined impedance in the terminal on the basis of a current created by a test signal in the two pairs for sending/receiving data, and 
 the means for performing the second test including means for detecting the presence of a second predetermined impedance in the terminal on the basis of a current created by a test signal in the other conductors. 
 
     
     
       19. A system remote power feed unit according to  claim 18 , wherein one of the two predetermined impedances is a short-circuit and the other predetermined impedance is a capacitance. 
     
     
       20. A system remote power feed unit according to  claim 10 , wherein the means for detecting the presence of a direct current short-circuit in the remote terminal include means for limiting the duration of the test signal so that the energy dissipated in the terminal cannot damage it the terminal under any circumstances. 
     
     
       21. A remote power feed unit according to  claim 8 , wherein the means for sending a power supply current in the line include a direct current supply in series with a circuit for blocking an alternating current. 
     
     
       22. A remote power feed unit according to  claim 21 , wherein the circuit for blocking an alternating current includes at least one semiconductor diode which is conducting in the direction of the remote power feed direct current. 
     
     
       23. A remote power feed unit according to  claim 21 , wherein the circuit for blocking an alternating current includes at least one transistor behaving like a direct current generator. 
     
     
       24. A remote power feed unit according to  claim 8 , wherein the means for sending a power supply current in the line include a DC voltage supply in series with at least one electronic switching circuit including an active component and:
 means for turning it on and off to active activate or deactivate the remote power feed current, and 
 means for controlling it so as to limit the remote power feed current. 
 
     
     
       25. A remote power feed unit according to  claim 24 , further including means for controlling the active component so that it has a negligible conductance for the test alternating current. 
     
     
       26. A terminal adapted to be connected to a local area network and to receive a remote power feed via a line, wherein the terminal includes at least one predetermined impedance connected to at least two conductors of the line and which identifies terminals adapted to receive a remote power feed, wherein the predetermined impedance is a very much higher capacitance than that of terminations routinely connected to the ends of the lines in terminals that are not adapted to receive a remote power feed but are adapted to be connected to the local area network. 
     
     
       27. A repeater adapted to receive a remote power feed and adapted to be included in a line between a network equipment unit including a remote power feed unit and another network equipment unit in a local area network,
 the repeater including a power supply unit powered by a remote power feed and whose input is connected in parallel with the power supply input of the other network equipment unit to the conductors of the line that provide the remote power feed, and 
 the power supply unit having an input impedance whose modulus is very much higher than the modulus of the input impedance of the power supply unit which is characteristic of equipment units adapted to receive a remote power feed likely to be connected downstream of that repeater. 
 
     
     
       28. A concentrator adapted to be inserted into a line between a network equipment unit including a remote power feed unit and at least one other network equipment unit in a local area network,
 the concentrator including, for each of its ports adapted to be connected to another network equipment unit, a remote power feed unit which includes:
 means for producing at least one detection an alternating current test signal on at least two conductors of a line for connecting the concentrator to another network equipment unit, that the test signal having an energy such that the other network equipment unit cannot be damaged under any circumstances, 
 means for detecting the presence of another equipment unit adapted to receive a remote power feed by detecting the presence of a predetermined impedance in that other equipment unit on the basis of a current created by the test signal in the line, and 
 means for sending a power supply current in the line when the presence of another equipment unit adapted to receive a remote power feed is detected. 
 
 
     
     
       29. A concentrator according to  claim 28 , adapted to receive a remote power feed, the concentrator including at least one predetermined impedance which is connected to at least two conductors of the line and is characteristic of network equipment units adapted to receive a remote power feed. 
     
     
       30. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least first and second test signals on at least two conductors of a line for connecting the local area network to a remote terminal, the test signals having an energy such that the terminal cannot be damaged under any circumstances,   detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of predetermined impedance in the remote terminal in compliance with a predetermined impedance threshold, on the basis of a current created by at least one of the test signals in said line, and   sending a power supply current in said line when the presence of a terminal adapted to receive a remote power feed is detected.   
     
     
       31. A remote power feed method according to claim 30, wherein the first and second test signals are different electrical signals. 
     
     
       32. A remote power feed method according to claim 31, wherein one of said first and second test signals is an AC signal. 
     
     
       33. A remote power feed method according to claim 31, wherein one of said first and second test signals is a DC signal. 
     
     
       34. A remote power feed method according to claim 32, wherein the other of said first and second test signals is a DC signal. 
     
     
       35. A remote power feed method according to claim 30, wherein said step of detecting the presence of a remote terminal adapted to receive a remote power feed further comprises detecting the presence of predetermined impedances in the remote terminal on the basis of currents created by each of said first and second test signals. 
     
     
       36. A remote power feed method according to claim 35, wherein the first and second predetermined impedances are different types of impedance. 
     
     
       37. A remote power feed method according to claim 35, wherein said predetermined impedances comprise a low impedance to one of said first and second test signals and a higher impedance to the other of said first and second test signals. 
     
     
       38. A remote power feed method according to claim 37, wherein said one of said first and second test signals is an AC test signal and the other of said first and second test signals is a DC test signal. 
     
     
       39. A remote power feed method according to claim 35, wherein said predetermined impedances comprise an impedance in a first range detected on the basis of a current created by said first test signal and an impedance in a second range detected on the basis of a current created by said second test signal. 
     
     
       40. A remote power feed method according to claim 39, wherein said first and second ranges of impedances comprise impedances below and above respective impedance level thresholds. 
     
     
       41. A remote power feed method according to claim 40, wherein said impedance level thresholds are different from one another. 
     
     
       42. A remote power feed method according to claim 36, wherein one of the first and second predetermined impedances is capacitive impedance and the other is a resistive impedance. 
     
     
       43. A remote power feed method according to claim 35, wherein each of said predetermined impedances is a resistance. 
     
     
       44. A remote power feed method according to claim 43, wherein said first test signal is an AC test signal and said second test signal is a DC test signal. 
     
     
       45. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least one test signal on at least two conductors of a line for connecting the local area network to a remote terminal, the test signal having an energy such that the terminal cannot be damaged under any circumstances,   detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of predetermined impedance in the remote terminal on the basis of a current created by the test signal in said line, and   sending a power supply current in said line when the presence of a terminal adapted to receive a remote power feed is detected;   said method further comprising the step of subsequently producing a disconnect test signal superimposed on the power supply current provided over said line to detect the removal of said remote terminal adapted to receive a remote power feed.   
     
     
       46. A method of providing a remote power feed according to claim 45, wherein the disconnect test signal is an AC signal and the said step of detecting the removal of said remote terminal includes detecting an impedance in response to the AC disconnect signal. 
     
     
       47. A method of providing a remote power feed according to claim 45, wherein said step of producing at least one test signal comprises producing first and second test signals on said at least two conductors, and said step of detecting the presence of a remote terminal adapted to receive a remote power feed comprises detecting the presence of first and second impedances in response to said first and second test signals. 
     
     
       48. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least one test signal on at least two conductors of a line for connecting the local area network to a remote terminal, the test signal having an energy such that the terminal cannot be damaged under any circumstances,   detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of predetermined impedance in the remote terminal on the basis of a current created by the test signal in said line, and   sending a power supply current in said line when the presence of a terminal adapted to receive a remote power feed is detected;   wherein the step of detecting the presence of predetermined impedance includes detecting predetermined capacitive impedance.   
     
     
       49. A method of providing a remote power feed according to claim 48, wherein said step of detecting the presence of predetermined impedance further includes detecting predetermined resistive impedance. 
     
     
       50. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least first and second test signals on at least two conductors of a line for connecting the local area network to a remote terminal, the test signals having an energy such that the terminal cannot be damaged under any circumstances,   detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of first predetermined impedance and second predetermined impedance in the remote terminal on the basis of a current created by at least one of the test signals in said line, and   sending a power supply current in said line when the presence of a terminal adapted to receive a remote power feed is detected.   
     
     
       51. A method of providing a remote power feed according to claim 50, wherein one of said first predetermined impedance and second predetermined impedance is a capacitive impedance. 
     
     
       52. A method of providing a remote power feed according to claim 50, wherein one of said first predetermined impedance and second predetermined impedance is a resistive impedance. 
     
     
       53. A method of providing a remote power feed according to claim 51, wherein the other of said first predetermined impedance and second predetermined impedance is a resistive impedance. 
     
     
       54. A method of providing a remote power feed according to claim 50, wherein one of said first and second test signals is a DC signal. 
     
     
       55. A method of providing a remote power feed according to claim 54, wherein the other of said first and second test signals is an AC signal. 
     
     
       56. A method of providing a remote power feed according to claim 53, wherein one of said first and second test signals is a DC signal. 
     
     
       57. A method of providing a remote power feed to a terminal in a local area network, the method comprising:
 producing at least one test signal on at least two conductors of a line for connecting the local area network to a remote terminal, the test signal having an energy such that the terminal cannot be damaged under any circumstances,   detecting the presence of a remote terminal adapted to receive a remote power feed by (i) detecting the presence of first predetermined impedance in the remote terminal on the basis of a current created by the test signal in said line, and (ii) detecting the presence of a second predetermined impedance, and   sending a power supply current in said line when the presence of a terminal adapted to receive a remote power feed is detected.   
     
     
       58. A remote power feed method according to claim 57, wherein one of said first and second predetermined impedances is a resistive impedance. 
     
     
       59. A remote power feed method according to claim 58, wherein the other of said first and second predetermined impedances is a capacitive impedance. 
     
     
       60. A remote power feed method according to claim 58, wherein said resistive impedance is a resistance in a range of resistance values. 
     
     
       61. A remote power feed method according to claim 60, wherein said range of resistance values is resistance values below a threshold resistance value. 
     
     
       62. A remote power feed method according to claim 59, wherein said capacitive impedance reflects a capacitance in a range of capacitance values. 
     
     
       63. A remote power feed method according to claim 62, wherein said range of capacitance values is capacitance values above a threshold capacitance value.