Multiplex system for automatic meter reading

• US 4,710,919 A
• Filed: 10/21/1983
• Issued: 12/01/1987
• Est. Priority Date: 10/21/1983
• Status: Expired due to Fees

• Current Assignee: David W. Rose, Firstpoint Energy Corporation NA, Michael A. Cherry, Orion Investment Corporation
• Original Assignee: International TEL Data Corporation
• Inventors: Cosgrove, John, Oliver, Stewart W.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): KUNTZ, CURTIS A
• Application Number:
  US06/544,110
• Time in Patent Office: 1,502 Days
• Field of Search: 370/90, 370/79, 370/96, 370/110.2, 340/825.63, 340/870.13, 340/870.03, 340/870.02, 340/825.02, 340/825.03, 340/310 A, 340/310 R, 340/870.07, 179/2 AM
• US Class Current: 370/242
• CPC Class Codes: H04M 11/002 with telemetering systems telemetering in general G08C

Abstract

A remote meter reading system employing a plurality of multiplexers coupled between the telephone central office and remote interrogatable utility data sources. A number of lines are connected to a single data channel through a plurality of multiplexers. An interrogation signal source is connected to the multiplexer for sending controllable level interrogation signals to the data sources under the control of a microprocessor. The level of interrogation signal which produces a response from each different data source is stored. Upon failure to evoke a response from the highest level of interrogation signal causes that line to be recorded in memory as defective. The number of OFF-HOOK conditions encountered in a predetermined period is recorded and any excess of a predetermined value deleted as a line trouble condition. Signalling in the preferred embodiment is via pulse width modulated signals. In the alternate embodiment, dual tone signalling is employed.

Claims

1. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising:

a multiplexer means for coupling said multiplexer to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone line from each of the plurality of interrogatable data transmitters via said multiplexer; and

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

including means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

in which the alternating current representation from each of the interrogatable data transmitters is a series of pulses of a single audio tone, the pulses having at least two different pulse periods, and, the means for converting the alternating current representation into the digital representation comprises;

means for substantially filtering out all but the series of pulses of the single audio tone received at the single input line;

means for deriving a series of positive voltage pulses which are proportional in pulse period duration to the pulse period duration of the series of pulses of the single audio tone; and

,

means for deriving a series of zero voltage transitions which are proportional in duration to the duration of the transition periods between the pulse periods of the series of pulses of the single audio tone.

2. The multiplexer system in accordance with claim 1 further including a means for disregarding positive voltage pulses received from the telephone lines during any of the transition periods when the positive voltage pulses have a duration corresponding to a predetermined positive noise pulse period so that positive noise pulses on the telephone lines do not destroy the ability of the converted digital representations to reflect the proportional pulse periods of the series of pulses of the single audio tone.

3. The multiplexer system in accordance with claim 2 further including a means for disregarding losses in continuity of the positive voltage pulses derived from the series of pulses of the single audio tone during any of the positive voltage pulse periods when the losses in continuity of positive voltage pulses have a duration corresponding to a predetermined negative noise pulse period so that negative going noise pulses on the telephone lines do not destroy the ability of the converted digital representations to reflect the proportional pulse periods of the series of pulses of the single audio tone.

5. The multiplexer system in accordance with claim 1 in which the data from each of the interrogatable data transmitters is a utility usage figure, meter identification figure, and at least one sentinel figure, and the converting of the alternating current representation to digital representations further includes:

means for determining the relative pulse periods of the series of pulses of the single audio tone;

means for determining the series of pulse periods which represent a sentinel character from the relative pulse codes of the series of pulses of the single audio tone;

means for comparing the relative pulse periods found in least one of the distinguishable sentinel characters to the other relative pulse periods of the series of pulse periods of the single audio tone, and, thus defining the plurality of character periods for the series of pulses of the single audio tone;

means for producing digital value signals for each of the character values in the utility usage figure and meter identification figure by comparing the relative pulse periods of the series of pulses of the single audio tone during each of the character periods with a plurality of predetermined patterns of relative pulse periods corresponding to the possible digit values found in a single character period; and

,

means for storing at least a portion of the digital value signals in a digital value signal storage system.

4. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

in which the means for coupling the multiplexer system to the plurality of telephone lines comprises;

means for continuously coupling each of the telephone lines to the multiplexer system by at least one coupling device, the coupling device comprising;

means for providing a low impedance path for alternating current signal from between 300 and 20,000 Hertz in frequency from at least one of the telephone lines to the multiplexer system;

means for providing a low impedance path for alternating current signals from between 300 and 20,000 Hertz in frequency from the multiplexer system to at least one of the telephone lines;

means for leaking a direct current voltage from at least one of the telephone lines to the multiplexer system;

means for substantially preventing damage to the multiplexer system caused by high voltage conditions on at least one of the telephone lines.

6. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising:

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

means responsive to trouble-shooting commands from an external digital interfacing device for selecting a particular, non-default voltage level of any of the multiplexer system;

means for providing a low impedance path for alternating current signals from between 300 and 20,000 Hertz in frequency from the multiplexer system to at least one of the telephone lines;

means for leaking a direct current voltage from at least one of the telephone lines to the multiplexer system;

means for substantially preventing damage to the multiplexer system caused by high voltage conditions on at least one of the telephone lines.

7. The multiplexer system in accordance with claim 6 further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default interrogation signal duration of any of the interrogation signals.

10. The multiplexer system in accordance with claim 6 further including means responsive to receiving the trouble-shooting command to select the interrogation signal voltage level for communicating the voltage level which activated a non-responsive interrogatable data transmitter selected by the voltage level trouble-shooting command from the external digital interface device.

8. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

further including a means responsive to trouble-shooting commands from an external digital interfacing device for selecting a particular, non-default voltage level of any of the interrogation signals;

further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default frequency of the interrogation signal sent over any of the telephone lines coupled to the multiplexer system.

9. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

further including a means responsive to trouble-shooting commands from an external digital interfacing device for selecting a particular, non-default voltage level of any of the interrogation signals;

further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default no-response drop-out time period for any of the telephone lines coupled to the multiplexer system, the no-response drop out time period beinghe period that the multiplexer system will wait for data from a non-responsive interrogatable data transmitter after sending an interrogation signal.

11. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

further including a means responsive to trouble-shooting commands from an external digital interfacing device for selecting a particular, non-default voltage level of any of the interrogation signals;

further including means responsive to receiving the trouble-shooting command to select the interrogation signal voltage level for communicating the voltage level which activated a non-responsive interrogatable data transmitter selected by the voltage level trouble-shooting command from the external digital interface device;

in which at least one of the following conditions is communicated to the external digital interfacing device responsive to receiving at least one trouble-shooting command, a current voltage level being used to activate the particular interrogatable data transmitter selected by the trouble-shooting command from the external digital interface device, a voltage level which activated the selected non-responsive interrogatable data transmitter, a non-decodable response has been received from the selected interrogatable data transmitter, no response has been received from the selected interrogatable data transmitter and an OFF-HOOK condition as been found on the telephone line coupled to the selected interrogatable data transmitter.

12. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising;

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations; and

means for counting the number of occasions when a particular telephone line coupled to the multiplexer system has been in the OFF HOOK condition during a predetermined period.

13. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

in which the means for coupling the multiplexer system to the plurality of telephone lines comprises;

means for continuously coupling each of the telephone lines to the multiplexer system by at least one coupling device, the coupling device comprising;

means for providing a low impedance path for alternating current signal from between 300 and 20,000 Hertz in frequency from at least one of the telephone lines to the multiplexer system;

means for providing a low impedance path for alternating current signals from between 300 and 20,000 Hertz in frequency from the multiplexer system to at least one of the telephone lines;

means for leaking a direct current voltage from at least one of the telephone lines to the multiplexer system;

means for substantially preventing damage to the multiplexer system caused by high voltage conditions on at least one of the telephone lines;

in which the means for continuously coupling each of the plurality of telephone lines to the multiplexer system when the plurality of telephone lines are single-ended telephone lines including a RING conductor comprises;

a first resistor for each telephone line having its first lead connected to the RING conductor of the telephone lines, and, the central office BATTERY conductor of the telephone line connected to an internal ground for the multiplexer system;

a second resistor for each telephone line having its first lead connected to the second lead of the first resistor;

a capacitor for each telephone line having its first lead connected to the second lead of the first resistor and its second lead connected to second lead of the second resistor;

a third resistor for each telephone line having its first lead connected to the internal ground of the multiplexer system and having its second lead connected to the second lead of the second resistor;

a first diode for each telephone line having its anode lead connected to the second lead of the second resistor;

a first zener diode having its cathode lead connected to the cathode leads of the first diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a second diode for each telephone line having its cathode lead connected to the second lead of the second resistor; and

,

a second zener diode having its anode lead connected to the anode leads of the second diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negative voltage source relative to the internal ground;

the path from the multiplexer system to each of the telephone lines being a combination of the second leads of the second resistors and the internal ground;

the path from each of the telephone lines to the multiplexer system being a combination of first leads of the first resistors and the internal ground which is connected to the central office GROUND conductor of each telephone line.

14. The multiplexer system in accordance with claim 13 in which each of the first resistors has a value of approximately 10 thousand ohms, each of the second resistors has a value of approximately one megaohm, each of the third resistors has a value of approximately 100 thousand ohms, and each of the capacitors has a value of approximately 0.47 microfarads.

15. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

in which the means for coupling the multiplexer system to the plurality of telephone lines comprises;

means for continuously coupling each of the telephone lines to the multiplexer system by at least one coupling device, the coupling device comprising;

means for providing a low impedance path for alternating current signal from between 300 and 20,000 Hertz in frequency from at least one of the telephone lines to the multiplexer system;

means for providing a low impedance path for alternating current signals from between 300 and 20,000 Hertz in frequency from the multiplexer system to at least one of the telephone lines;

means for leaking a direct current voltage from at least one of the telephone lines to the multiplexer system;

means for substantially preventing damage to the multiplexer system caused by high voltage conditions on at least one of the telephone lines;

in which the means for continuously coupling each of the plurality of telephone lines to the multiplexer system when the plurality of telephone lines are double-ended telephone lines including TIP and RING conductors comprises;

a first resistor for each telephone line having its first lead connected to the RING conductor of the telephone line;

a second resistor for each telephone line having its first lead connected to the second lead of the first resistor;

a first capacitor for each telephone line having its first lead connected to the second lead to the first resistor and its second lead connected to second lead of the second resistor;

a third resistor for each telephone line having its first lead connected to an internal ground of the multiplexer system and having its second lead connected to the second lead of the second resistor;

a first diode for each telephone line having its anode lead connected to the second lead of the second resistor;

a first zener diode having its cathode lead connected to the cathode lead of each of the first diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a second diode for each of the telephone lines having its cathode lead connected to the second lead of the second resistor;

a second zener diode having its anode lead connected to the anode leads of each of the second diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negative voltage source relative to the internal ground;

a fourth resistor for each telephone line having its first lead connected to the TIP conductor of one telephone line;

a fifth resistor for each telephone line having its first lead connected to the second lead of the fourth resistor;

a second capacitor for each telephone line having its first lead connected to the second lead of the fourth resistor ad its second lead connected to the second lead of the fifth resistor;

a sixth resistor having its first lead connected to the internal ground and having its second lead connected to the second lead of the fifth resistor;

a third diode for each telephone line having its anode lead connected to the second lead of the fifth resistor;

a first zener diode having its cathode lead connected to the cathode leads of the third diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a fourth diode for each telephone line having its cathode lead connected to the second lead of the fifth resistor; and

,

a second zener diode having its anode lead connected to the anode leads of the fourth diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negative voltage source relative to the internal ground;

the path from the multiplexer system to each of the telephone lines is the combination of the second leads of the fifth resistors and the second leads of the second resistors;

the path from each of the telephone lines to the multiplexer system being the combination of the first leads of the first resistors and the first leads of the fourth resistors.

16. The multiplexer system in accordance with claim 15 in which each of the first and sixth resistors have values of approximately 10 thousand ohms, each of the second and fifth resistors have values of approximately one megaohm and each of the third, sixth resistors have values of approximately 100 thousand ohms and each of the first and second capacitors have values of approximately 0.47 microfarads.

17. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

a multiplexer;

means for coupling said multiplexer to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines to respective interrogatable data transmitters via said multiplexer;

means including said multiplexer for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters,

said interrogatable data transmitters responsive to an interrogation signal on its respective telephone line for generating and transmitting the alternating current representation as a series of dual-tone signals, and

means for converting each of the alternating current representations of the data into digital representations.

18. The multiplexer system in accordance with claim 17 further including means for storing at least one of the digital representations in a digital representation storage system.

19. The multiplexer system in accordance with claim 17 wherein said multiplexer is operative for conducting each of the distinct interrogation signals from a single output circuit to a particular one of the plurality of telephone lines.

20. The multiplexer system in accordance with claim 17 further including means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit.

21. The multiplexer system in accordance with claim 17 in which the series of dual-tone alternating current representations from the interrogatable data transmitters represent a utility usage figure and a meter identification figure from a utility usage monitor coupled to each the meter interface devices, there being at least twelve distinct dual-tone alternating current representations, the dual-tone alternating current representations representing the following:

a digit value between and including 0 to 9, a first framing sentinel and a second framing sentinel.

23. The multiplexer system in accordance with claim 17 further including a means responsive to trouble-shooting commands from an external digital interfacing device for selecting a particular, non-default voltage level of any of the interrogation signals.

24. The multiplexer system in accordance with claim 23 further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default interrogation signal duration of any of the interrogation signals.

25. The multiplexer system in accordance with claim 24 further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default frequency of the interrogation signal sent over any of the telephone lines coupled to the multiplexer system.

26. The multiplexer system in accordance with claim 25 further including a means responsive to trouble-shooting commands from the external digital interfacing device for selecting a particular, non-default no-response drop-out time period for any of the telephone lines coupled to the multiplexer system, the no-response drop-out time period being the period that the multiplexer system will wait for data from a non-responsive interrogatable data transmitter after sending an interrogation signal.

27. The multiplexer system in accordance with claim 26 further including means responsive to receiving the trouble-shooting command to select the interrogation signal voltage level for communicating the voltage level which activated a non-responsive interrogatable data transmitter selected by the voltage level trouble-shooting command from the external digital interface device.

28. The multiplexer system in accordance with claim 27 in which at least one of the following conditions is communicated to the external digital interfacing device responsive to receiving at least one trouble-shooting command, a current voltage level being used to activate the particular interrogatable data transmitter selected by the trouble-shooting command from the external digital interface device, a voltage level which activated the selected non-responsive interrogatable data transmitter, a non-decodable response has been received from the selected interrogatable data transmitter, no response has been received from the selected interrogatable data transmitter and an OFF-HOOK condition has been found on the telephone line coupled to the selected interrogatable data transmitter.

35. The multiplexer system in accordance with claim 21 further including means for communicating the digit values received to an external digital interfacing device responsive to a command therefrom.

22. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

a multiplexer;

means for coupling the multiplexer to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means including said multiplexer for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters, the alternating current representation being a series of dual-tone signals, and

means for converting each of the alternating current representation of the data into digital representation;

in which the means for coupling the multiplexer system to the plurality of telephone lines comprises;

means for continuously coupling each of the telephone lines to the multiplexer system by at least one coupling device, the coupling device comprising;

means for providing a low impedance path for alternating current signal from between 300 and 20,000 Hertz in frequency from at least one of the telephone lines to the multiplexer system;

means for providing a low impedance path for alternating current signals from between 300 and 20,000 Hertz in frequency from the multiplexer system to at least one of the telephone lines;

means for leaking a direct current voltage from at least one of the telephone lines to the multiplexer system; and

means for substantially preventing damage to the multiplexer system caused by high voltage conditions on at least one of the telephone lines.

29. The multiplexer system in accordance with claim 22 further including means for sensing when any of the plurality of telephone lines is in an OFF-HOOK condition responsive to a drop in the direct current voltage leaked to the tranceiver device relative to the direct current leaked to the multiplexer system when the telephone lines are in an ON-HOOK condition.

30. The multiplexer system in accordance with claim 29 further including means for counting the number of occasions when a particular telephone line coupled to the multiplexer system has been in the OFF-HOOK condition during a predetermined period.

31. The multiplexer system in accordance with claim 22 in which the means for continuously coupling each of the plurality of telephones lines to the multiplexer system when the plurality of telephone lines are single-ended telephone lines comprises:

a first resistor for each telephone line having its first lead connected to the ring wire of the telephone line, and, the central office battery wire of the telephone line connected to an internal ground of the multiplexer system;

a second resistor for each telephone line having its first lead connected to the second lead of the first resistor;

a capacitor for each telephone line having its first lead connected to the second lead of the first resistor and its second lead connected to second lead of the second resistor;

a third resistor for each telephone line having its first lead connected to the internal ground of the the multiplexer system and having its second lead connected to the second lead of the second resistor;

a first diode for each telephone line having its anode lead connected to the second lead of the second resistor;

a first zener diode having its cathode lead connected to the cathode leads of the first diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a second diode for each telephone line having its cathode lead connected to the second lead of the second resistor; and

,

a second zener diode having its anode lead connected to the anode leads of the second diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negative voltage source relative to the internal ground;

the path from the multiplexer system to each of the telephone lines being a combination of the second leads of the second resistors and the internal ground;

the path from each of the telephone lines to the multiplexer system being a combination of first leads of the first resistors and the internal ground which is connected to the central office ground of each of the telephone lines.

32. The multiplexer system in accordance with claim 31 in which each of the first resistors has a value of approximately 10 thousand ohms, each of the second resistors has a value of approximately one megaohm, each of the third resistors has a value of approximately 100 thousand ohms, and each of the capacitors has a value of approximately 0.47 microfarads.

33. The multiplexer system in accordance with claim 22 in which the means for continuously coupling each of the plurality of telephones lines to the multiplexer system when the plurality of telephone lines are double-ended telephone lines comprises:

a first resistor for each telephone line having its first lead connected to the ring wire of the telephone line;

a second resistor for each telephone line having its first lead connected to the second lead of the first resistor;

a first capacitor for each telephone line having its first lead connected to the second lead of the first resistor and its second lead connected to second lead of the second resistor;

a third resistor for each telephone line hawing its first lead connected to an internal ground of the the multiplexer system and having its second lead connected to the second lead of the second resistor;

a first diode for each telephone line having its anode lead connected to the second lead of the second resistor;

a first zener diode having its cathode lead connected to the cathode leads of the first diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a second diode for each telephone line having its cathode lead connected to the second lead of the second resistor;

a second zener diode having its anode lead connected to the anode leads of the second diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negatlve voltage source relative to the internal ground;

a fourth resistor for each telephone line having its first lead connected to the tip wire of one telephone line;

a fifth resistor for each telephone line having its first lead connected to the second lead of the fourth resistor;

a second capacitor for each telephone line having its first lead connected to the second lead of the fourth resistor and its second lead connected to the second lead of the fifth resistor;

a sixth resistor for each telephone line having its first lead connected to the internal ground and having its second lead connected to the second lead of the fifth resistor;

a third diode for each telephone line having its anode lead connected to the second lead of the fifth resistor;

the first zener diode having its cathode lead connected to the cathode leads of the third diodes and having its anode lead connected to the internal ground, the first zener diode having its cathode lead connected to a positive voltage source relative to the internal ground;

a fourth diode for each telephone line having its cathode lead connected to the second lead of the fifth resistor; and

,

the second zener diode having its anode lead connected to the anode leads of the fourth diodes and having its cathode lead connected to the internal ground, the second zener diode having its anode lead connected to a negative voltage source relative to the internal ground;

the path from the multiplexer system to the telephone lines is the combination of the second leads of the fifth resistors and the second leads of the second resistors;

the path from the telephone line to the multiplexer system being the combination of the first leads of the first resistors and the first leads of the fourth resistors.

34. The multiplexer system in accordance with claim 33 in which each of the first and sixth resistors have values of approximately 10 thousand ohms, each of the second and fifth resistors have values of approximately one megaohm and each of the third, sixth resistors have values of approximately 100 thousand ohms and each of the first and second capacitors have values of approximately 0.47 microfarads.

42. The combination in accordance with claim 22 including means for recording a faulty line if no usable data is detected after interrogation at the highest incremental step level of said interrogation signal.

36. A method for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising;

sending at least one distinct interrogation signal over each of the coupled telephone lines;

receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

converting each of the alternating current representations of the data into digital representations;

in which the alternating current representation from each of the interrogatable data transmitters is a series of pulses of a single audio tone, the pulses having at least two different pulse periods, and, the step of converting the alternating current representation into the digital representation comprises;

filtering the series of pulses of the single audio tone received at the single input line;

deriving a series of positive voltage pulses which are proportional in pulse period duration to the pulse period duration of the series of pulses of the single audio tone; and

,

deriving a series of zero voltage transitions which are preportional in duration to the duration of the transition periods between the pulse periods of the series of pulses of the single audio tone.

37. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations,

including means responsive to an unacceptable signal from an interrogated data transmitter for increasing the level of the interrogation signal for that data transmitter at the next interrogation thereof; and

means for registering the data transmitter as inoperative upon the failure to receive data therefrom in response to such subsequent interrogation.

38. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising;

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

wherein said increasing means increases the level of interrogation signal sequentially to higher levels.

39. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising;

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relay;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

means for setting the normal level for interrogation at the lowest level for which a usable response has been received from a data transmitter.

40. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising;

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines via said multiplexer;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

wherein said increasing means increases the level of interrogation signal in stepped increments.

41. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines connected to a telephone central office including line cutoff relays comprising:

a multiplexer means for coupling said multiplexer system to the plurality of telephone lines beyond the line cutoff relays;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines from each of the plurality of interrogatable data transmitters via said multiplexer;

means coupled to said multiplexer for converting each of the alternating current representations of the data into digital representations;

means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

means for storing line condition information as a function of the lowest step level at which usable data is received from each data transmitter.

43. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

further including means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit;

including means responsive to an unacceptable signal from an interrogated data transmitter for increasing the level of the interrogation signal for that data transmitter at the next interrogation thereof; and

means for registering the data transmitter as inoperative upon the failure to receive data therefrom in response to such subsequent interrogation.

44. A multiplexer system for receiving data from a plurality of interrogatable data transmitters coupled to a plurality of telephone lines comprising:

means for coupling the multiplexer system to the plurality of telephone lines;

means for sending at least one distinct interrogation signal over each of the coupled telephone lines;

means for receiving an alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representation of the data sent over the coupled telephone lines from each of the plurality of interrogatable data transmitters;

means for converting each of the alternating current representations of the data into digital representations;

further including means for demultiplexing the received alternating current representations from the plurality of coupled telephone lines to a single input circuit, including means responsive to an unacceptable signal from an interrogated data transmitter for increasing the level of the interrogation signal for that data transmitter at the next interrogation thereof; and

means for registering the data transmitter as inoperative upon the failure to receive data therefrom in response to such subsequent interrogation.