System & method for monitoring & diagnosing faults in environmentally controlled containers, such system and method being especially adapted for remote computer controlled monitoring of numerous transportable containers over existing on-site power wiring

• US 4,234,926 A
• Filed: 12/05/1978
• Issued: 11/18/1980
• Est. Priority Date: 12/05/1978
• Status: Expired due to Term

• Current Assignee: Sealand Service, Inc.
• Original Assignee: Sealand Service, Inc.
• Inventors: Bryant, Robert T., Chun, Michael D., von Isenburg, Carl, Holmberg, Kenneth G., Wallace, Clifford G.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US05/966,785
• Time in Patent Office: 714 Days
• Field of Search: 364/550, 364/551, 364/418, 364/101, 364/102, 364/103, 364/11, 364/436, 364/492, 364/493, 364/900 MS File
• US Class Current: 702/188
• CPC Class Codes: G01D 9/007 Data loggers attached to transport containers for perishable products, e.g. food or medicines

Abstract

An environmentally controlled transportable container monitoring system including a data acquisition unit mounted to each container monitorable by the system, and a central microcomputer system located at a container storage site, e.g. a container ship or land based terminal, which communicates over existing on-site power wiring with the data acquisition unit of all containers plugged into the on-site power. The container data acquistion unit includes electronics forming a microcomputer adapted to store current container parameters, prepare a history of the container'"'"'s past condition, and alert a system operator or other persons of an "out of limit" condition, a possible container malfunction, and to diagnose the source of the malfunction. A signal transfer circuit is provided in the data acquisition unit and a separate signal transfer unit is provided in proximity to the central monitoring microcomputer system wherein serial data outputs from the system'"'"'s microcomputers can be conditioned for transmission over the existing on-site wiring to permit bidirectional communication over such wiring. The system provides for minimizing noise induced operating problems and for detecting those problems when they occur; it also preferably generates information for identifying the precise location of each container within a particular storage area by means of a location transmitter provided at each defined on-site container storage location.

Claims

1. A system for monitoring the condition of a controlled area over existing on-site wiring, said system comprising

sensor means disposed for detecting predetermined parameters representative of the condition of said controlled area.

a data acquisition unit located proximate said controlled area, said data acquisition unit comprising electronic means forming a first digital computer having input/output interface means including serial input/output interface means, and further comprising means for inputting to said first digital computer container parameter data generated by said sensor means, and a first bidirectional data transfer means for transferring serial digital data between said first digital computer and on-site power wiring,

a second digital computer and input/output means therefore, said second digital computer and input/output means being suitably located to provide for the remote monitoring of said controlled area, and

a second bidirectional data transfer means for transferring serial digital data between said second digital computer and said on-site wiring whereby a serial digital data stream can be transmitted in either direction between the monitoring second digital computer and the first digital computer of the data acquisition units.

2. The system of claim 1 wherein said data acquisition unit includes means under the control of said first digital computer for repetitively scanning said sensor means for providing a current record of the controlled area'"'"'s condition.

15. The system of claim 1 or 3 wherein said first and second bidirectional means for serial data transfer include, respectively, first and second cooperating modulation/demodulation means for suitably modulating and demodulating a carrier signal for transmitting and receiving serial data over said on-site wiring between said second bidirectional data transfer means and the first bidirectional data transfer means of the data acquisition units of on-line containers.

16. The system of claim 15 wherein said carrier signal is frequency modulated and demodulated by said first and second cooperating modulation/demodulation means.

17. The system of claim 16 wherein at least one of said first and second frequency modulation/demodulation means is operated in a tone detection mode whereby "1" and "0" bit representations of said transmitted signal are characterized by the presence of absence of a signal frequency.

3. A system for monitoring environmentally controlled transportable containers, over existing on-site power wiring into which said container'"'"'s environmental control unit is electrically connected, said system comprising

sensor means on each container capable of being monitored by said system, said sensor means being disposed for detecting predetermined parameters representative of the condition of said containers,

a data acquisition unit mounted to each monitorable container and having means for identifying the particular container to which it is mounted, said data acquisition unit comprising electronic means forming a first digital computer having input/output interface means including serial input/output interface means, and futher comprising means for inputting to said first digital computer container parameter data generated by said sensor means, and a first bidirectional data transfer means for transferring serial digital data between said first digital computer and the power line of said container to provide for external communication with said first digital computer whereby, when the container is placed on-line by electrically connecting said container power line to a power receptacle for said on-site power wiring, a bidirectional communication link will be established between said on-site power wiring and said first digital computer,

a second digital computer and input/output means therefore, said second digital computer and input/output means being suitably located to provide for the monitoring of on-line containers equipped with one of said data acquisition units,

a second bidirectional data transfer means for transferring serial digital data between said second digital computer and said on-site power wiring wherein a bidirectional communication link is established therebetween and whereby a serial digital data stream can be transmitted in either direction between said monitoring second digital computer and the first digital computer fo the data acquisition units of any on-line container,

said second digital computer being adapted to send out predetermined commmand sequences for communicating with the first digital computer of the data acquisition unit of on-line containers and also being adapted to identify individual on-line containers for selective communication therewith whereby numerous on-line containers can be remotely monitored by said second digital computer when said containers are connected into existing on-site power wiring.

4. The system of claim 3 wherein said data acquisition unit includes means under the control of said first digital computer for repetitively scanning said sensor means for providing a current record of the container'"'"'s condition.

5. The system of claim 4 wherein said sensor scanning means is interrupted by a command sequence inputted to said data acquisition unit, such as from said second digital computer over said on-site wiring, whereupon the first digital computer of said data acquisition unit determines if its container is being addressed, and, if it is, permits external communication through said bidirectional data transfer means, such as communication between said first and second digital computers.

6. The system of claim 5 wherein scanning of said sensor means automatically resumes either when said first digital computer determines that its container is not being addressed, or, if it is being addressed when external communication therewith terminates.

7. The system of claim 6 wherien said data acquisition unit includes means for aborting the transmission of a serial digital data stream from said first digital computer after a predetermined length of transmission whereby unintended continuous transmission, such as may be caused by a noise induced continuous computer program loop, will be prevented thereby preventing the date acquisition unit of an on-line container from tying up communications of said system.

8. The system of claim 7 wherein said transmission abort means comprised of a time out circuit connected in line with said first bidirectional means for transferring serial digital data wherein all serial data transmissions from said first digital computer over said bidirectional serial data transfer means is terminated after a predetermined time interval.

9. The system of claim 8 wherein said predetermined time interval of said time out circuit is approximately 10 milliseconds.

10. The system of claim 4 wherein said first digital computer includes

memory, and

means for storing in said memory the digital representation of container parameter data which is substantially continuously generated during the scanning of said sensor means whereby there is stored a current record of the container'"'"'s condition which can be outputted, such as to said second digital computer in response to suitable command therefrom.

11. The system of claim 10 wherein predetermined parameter limit values are stored in memory of said first digital computer and means are provided for comparing said limit values to the digital representation of said container parameter data for producing a container status indication and wherein means are further provided for outputting said container status indication, such as to said second digital computer in response to suitable command therefrom.

12. The system of claim 10 wherein an external alarm means is provided and wherein means are further provided for actuating said alarm when the sensed inputs for at least one selected sensor means reaches a predetermined out of limit value whereby a person in the vicinity of said alarm can be immediately alerted to a preselected out of limit condition.

13. The system of claim 10 wherein current container parameter data, when stored in memory of said first digital computer, substantially replaces previously stored non-current parameter data to provide a current but only temporarily stored record of the container'"'"'s condition.

14. The system of claim 13 wherein said first digital computer includes means for periodically setting aside temporarily stored container parameter data into separate memory locations for making a substantially permanent record thereof, and means for outputting said substantially permanent record of container parameter data whereby a history of said container'"'"'s condition, as opposed to a current condition check, can be obtained.

18. A system for monitoring environmentally controlled transportable containers over existing on-site power wiring into which said containers'"'"' environmental control unit is electrically connected, comprising

sensor means on each container capable of being monitored by the system, said sensor means being disposed for detecting predetermined parameters representative of the condition of said containers,

a data acquisition unit mounted to each of said monitorable containers, said data acquisition unit comprising

(a) means for identifying the particular container to which said data acquisition unit is mounted,

(b) electronic means forming a first digital computer having memory, input/output interface means including serial input/output interface means, and means for storing in a preallocated portion of said memory the digital representation of container parameter data currently generated by said sensor means wherein current parameter data substantially continuously replace previously stored non-current data to provide a current stored record of the container'"'"'s condition,

(c) means under the control of said first digital computer, including analog to digital conversion means, for repetitively scanning said sensor means for inputting current container parameter data to said first digital computer, and

(d) a first bidirectional means for transferring serial digital data between said first digital computer and a power line of said container to provide for external communication with said first digital computer whereby placing said container on-line by electrically connecting said container power connector means to a power receptacle means for said on-site power wiring will establish a first bidirectional communication link between said on-site power wiring and the digital computer of said data acquisition unit over which a serial data stream can be transmitted, said first bidirectional serial data transfer means including frequency modulation/demodulation means for frequency modulating and demodulating a carrier signal for transmitting and receiving serial data over said on-site wiring,

a second digital computer and input/output means thereofre, said second computer and input/output means forming a central monitoring station for on-line containers equipped with one of said data acquisition units,

a second bidirectional means for transferring serial digital data between said second digital computer and said on-site power wiring wherein a bidirectional communication link is established therebetween, said second bidirectional serial data transfer means including frequency modulation/demodulation means for frequency modulating and demodulating a carrier signal for transmitting and receiving serial data over said on-site wiring, said frequency modulation/demodulation means of said second bidirectional serial data transfer means being cooperative with said frequency modulation/demodulation means of the first bidirectional serial data transfer means of said data acquisition units whereby a serial digital data stream can be transmitted in either direction between the monitoring second digital computer and the first digital computer of the data acquisition units of any one-line container,

said second digital computer being adapted for sending predetermined command sequences, such as a form of container condition request command, to the first digital computer of the data acquisition unit of on-line container, with each command sequence including means for identifying which container or containers are being addressed by said command sequence, and

said first digital computer having means responsive to said predetermined command sequence, such as might be received from said second digital computer, and for acting in accordance with said commands, and futher having means for recognizing and acting only on those command sequences which are addressed to the container to which the data acquisition unit is mounted including means for testing an incoming command sequence against the data acquisition unit'"'"'s means for identifying the particular container to which the data acquisition unit is mounted, whereby said second digital computer can selectively communicate with the date acquisition units of numerous on-line containers.

19. The system of claims 3 or 18 wherein the operating voltages of said data acquisition unit are provided by at least one existing battery secured within said container.

20. The system of claims 3 or 18 wherein means are provided for automatically resetting said first digital computer to an initialized condition if the operating program of said computer falls into a disabling continuous loop such as might be caused by a burst of electro-magnetic noise generated by an external source proximate the container.

21. The system of claim 20 wherein said automatic reset means is comprised of means for generating a reset signal after a predetermined program running time unless said automatic reset means is first disabled by a control signal generated by said first digital computer.

22. The system of claim 21 wherein said reset signal generating means is comprised of a one shot circuit having a control signal input from said first digital computer.

23. The system of claim 20 further including a manual reset means which can be independently actuated from outside said container.

24. The system of claims 3 or 18 further comprising location transmitter means operatively responsive to the electrical connection of a container'"'"'s environmental control unit into a container storage area'"'"'s on-site power, said location transmitter means being adapted to transmit a location code which identifies the location in said storage area where said container has been electrically connected whereby said container'"'"'s location can be identified to said second computer.

25. The system of claim 24 wherein said location transmitter means is comprised of

means for setting a binary location code corresponding to a particular storage area location,

digital multiplex means for sequencing each digital bit of said binary location code for outputting therefrom said location code as a serial data stream,

means for pulsing said digital multiplexer at a predetermined rate for serial data transmission,

a serial data output adapted to communicate with said on-site power wiring for transmitting said location code thereover, and

means for enabling the transmission of serial data through said serial data output after a container is electrically connected to a power receptacle associated with the storage area location identified by said location transmitter, but inhibiting further transmissions therefrom some finite time after such transmission has commenced.

26. The system of claim 25 wherein said on-site power wiring comprises at least two wires with a first wire being used for transmitting a serial data stream to said data acquisition unit and a second wire used for transmitting a serial data stream from said data acquisition unit, and wherein the serial data output of said location transmitter means is connected to the first wire of said power wiring whereby said location code is transmitted to said data acquisition unit for storage therein such that it is available for subsequent transmission to said second digital computer when said data acquisition unit receives a suitable command therefrom.

27. The system of claim 26 in which each storage area power receptacle into which a container might be connected is actuated by a circuit breaker means and wherein said means for enabling and inhibiting transmission of said data through said serial data output includes having said serial data output connected to said on-site power wiring between said circuit breaker means and said on-site power receptacle, and further having a feedback circuit means from said power wiring for inhibiting transmission through said serial data output when high voltage appears at the connection between said location transmitter and on-site power, whereby said location transmitter means will be free to transmit its location code to the data acquisition unit of said container between the time when electrical connection is made with said power receptacle and the time when said circuit breaker means is switched from a power off position to a power on position.

28. The system of claim 26 wherein the computer of said data acquisition unit has an unknown location status flag means adapted to be set when the container is disconnected from on-site power whereby the presence of an unknown location status flag can be detected by said second computer by a suitable command therefrom to determine if the container'"'"'s location within a storage area is known whereby newly arrived containers can be detected and also their locations determined by retrieval of their stored location code.

29. A system for monitoring environmentally controlled containers over existing on-site power wiring wherein the environmental control unit of said containers electrically connect into said power wiring through on-site power receptacles, each of which is electrically actuated by a circuit breaker means, said system comprising

sensor means in each container capable of being monitored by said system, said sensor means being disposed for detecting predetermined parameters representative of the condition of said containers,

a data acquisition unit mounted to each monitorable container, said data acquisition unit having electronic means forming a first digital computer, said data acquisition unit, under the control of said first digital computer, being adapted to read and store container parameter data generated by said container sensor means, and further being adapted for external serial input/output data communication through the power line of said container whereby, when said container is placed on-line by electrically connecting said container power line to said power receptacle and actuating said circuit breaker means to supply power to said container, a bidirectional communications link will be established between said on-site power wiring and said first digital computer, said bidirectional communications link permitting the first digital computer of said data acquisition unit to communicate over said on-site power wiring with a second digital computer which is suitably located to provide substantially central monitoring of all on-line containers equipped with one of said data acquisition units, and

a location transmitter means associated with each on-site power receptacle which is to be adapted for a location transmission capability, said location transmitter having a serial data output and being adapted to transmit therefrom a location code which identifies where in a container storage area said power receptacle means is located,

the serial data output of said location transmitter means being connected to the wire of the on-site power wiring used to transmit serial digital data to said data acquisition unit, and having a feedback circuit means from said power wiring for inhibiting transmission of serial data through said serial data output when a high voltage appears at said serial data output, said serial data output connection being between said power receptacle means and said circuit breaker means whereby said location transmitter transmits its location code to the data acquisition unit of a container electrically connected to said power receptacle between the time such receptacle connection is made and said circuit breaker means is actuated to supply power to said container, said location code being stored by said first digital computer of said data acquisition unit for later access by said central monitoring second digital computer.

30. The system of claim 29 wherein said location transmitter means comprises

means for setting a binary location code corresponding to a particular storage area location,

digital multiplex means for sequencing each digital bit of said binary location code for outputting therefrom the location code as a serial data stream, and

means for pulsing said digital multiplexer at a predetermined rate for serial data transmission.

31. A data acquisition unit adapted to be mounted to an environmentally controlled transportable container having sensors disposed therein for detecting container parameters representative of the containers condition, said data acquisition unit comprising

electronic means forming a first digital computer having input/output interface means including serial input/output interface means,

means for inputting to said first digital computer container parameter data generated by said sensor means,

a bidirectional data transfer means for transferring serial digital data between said first digital computer and the power line of said container to provide for external communication with said first digital computer whereby, when said container is placed on-line by electrically connecting said container'"'"'s power line to a power receptacle means for said on-site power wiring, a bidirectional communication link will be established between said on-site power wiring and said first digital computer,

said first digital computer having means responsive to predetermined command sequences whereby said command sequences can be inputted as a serial data stream through said bidirectional data transfer means whereby remote external communication with said data acquisition unit relative to the container'"'"'s condition can be effected over said on-site power wiring by a known available set of commands transmitted by a second digital computer, and

said first digital computer further having means for recognizing and acting on only those command sequences which are addressed to the container to which the data acquisition unit is mounted whereby said second digital computer is permitted to selectively communicate with the data acquisition units of numerous on-line containers.

32. The data acquisition unit of claim 31 including means under the control of said first digital computer for repetitively scanning said sensor means for providing a current record of the container'"'"'s condition.

33. The data acquisition unit of claim 32 wherein said sensor scanning means is interrupted by a command sequence inputted to said data acquisition unit, such as from said second digital computer over said on-site wiring, whereupon the first digital computer of said data acquisition unit determines if its container is being addressed, and, if it is, permits external communication through said bidirectional data transfer means, such as communication between said first and second digital computers.

34. The data acquisition unit of claim 33 wherein scanning of said sensor means automatically resumes either when said first digital computer determines that its container is not being addressed, or, if it is being addressed, when external communication therewith terminates.

35. The data acquisition unit of claim 34 wherein said data acquisition unit includes means for aborting the transmission of a serial digital data stream from said first digital computer after a predetermined length of transmission whereby unintended continuous transmission, such as may be caused by a noise induced continuous computer program loop, will be prevented thereby preventing the data acquisition unit of an on-line cargo container from tying up communications of said system.

36. The data acquisition unit of claim 35 wherein said transmission abort means is comprised of a time out circuit connected in line with said first bidirectional means for transferring serial digital data wherein all serial data transmissions from said first digital computer over said bidirectional serial data transfer means is terminated after a predetermined time interval.

37. The data acquisition unit of claim 32 wherein said first digital computer includes

memory, and

means for storing in said memory the digital representation of container parameter data which is substantially continuously generated during the scanning of said sensor means whereby there is stored a current record of the container'"'"'s condition which can be outputted such as to said second digital computer in response to suitable command therefrom.

38. The data acquisition unit of claim 37 wherein predetermined parameter limit values are stored in memory of said first digital computer and means are provided from comparing said limit values to the digital representation of said container parameter data for producing a container status indication and wherein means are further provided for outputting said container status indication, such as to said second digital computer in response to suitable command therefrom.

39. The data acquisition unit of claim 38 wherein an external alarm means is provided and wherein means are further provided for actuating said alarm when said container status indication shows an out of limit condition for said container whereby a person in the vicinity of said alarm can be immediately alerted to an out of limit condition.

40. The data acquisition unit of claim 37 wherein current container parameter data which is stored in memory of said first digital computer continuously replaces previously stored non-current parameter data to provide a current but only temporarily stored record of the container'"'"'s condition.

41. The data acquisition unit of claim 38 wherein said first digital computer includes means for periodically setting aside temporarily stored container parameter data into separate memory locations for making a substantially permanent record thereof, and means for outputting said substantially permanent record of container parameter data, such as to said second digital computer in response to a suitable command therefrom, whereby a history of said container'"'"'s condition, as opposed to a current condition check, can be obtained.

42. The data acquisition unit of claim 31 wherein said bidirectional means for serial data transfer includes modulation/demodulation means for suitably modulating and demodulating a carrier signal for transmitting and receiving serial data over said on-site wiring between said second bidirectional data transfer means and the first bidirectional data transfer means of the data acquisition units of on-line containers.

43. The data acquisition unit of claim 42 wherein said carrier signal is frequency modulated and demodulated by said first and second cooperating modulation/demodulation means.

45. The data acquisition unit of claim 31 or 44 wherein the operating voltages of said data acquisition unit are provided by at least one existing battery secured within said container.

46. The data acquisition unit of claims 31 or 44 wherein means are provided for automatically resetting said first digital computer to an initialized condition if the operating program of said computer falls into a disabling continuous loop such as might be caused by a burst of electromagnetic noise generated by an external source proximate the container.

47. The data acquisition unit of claim 46 wherein said automatic reset means is comprised of means for generating a reset signal after a predetermined program running time unless said automatic reset means is first disabled by a control signal generated by said first digital computer.

48. The data acquisition unit of claim 47 wherein said reset signal generating means is comprised of a one shot circuit having a control signal input from said first digital computer.

49. The data acquisition unit of claim 46 further including a manual reset means which can be independently actuated from outside said container.

44. A data acquisition unit adapted to be mounted to an environmentally controlled container having sensors disposed therein for detecting container parameters representative of the containers condition, said data acquisition unit comprising

means for identifying a particular container to which said data acquisition unit can be mounted,

electronic means forming a first digital computer having

(a) memory,

(b) input/output interface means including serial input/output interface means, and

(c) means for storing in a preallocated portion of said memory the digital representation of container parameter data currently generated by said sensor means wherein current parameter data substantially continuously replaces previously stored non-current data to provide a current stored record of the container'"'"'s condition, means under the control of said first digital computer including analog to digital conversion means for repetitively scanning said sensor means for inputting the container parameter data to said first digital computer, and

a first bidirectional means for transferring serial digital data between said first digital computer and a power line of said container to provide for external communication with said first digital computer whereby placing said container on-line by electrically connecting said container power connector means to a power receptacle means for said on-site wiring will establish a first bidirectional communications link between said on-site power wiring and said first digital computer over which a serial data stream can be transmitted, said first bidirectional serial data transfer means including frequency modulation/demodulation means for frequency modulating and demodulating a carrier signal for transmitting and receiving serial data over said on-site wiring,

said first digital computer having means responsive to predetermined command sequences, such as a form of container condition request command, whereby said command sequences can be inputted as a serial data stream through said bidirectional data transfer means whereby remote external communication with said data acquisition unit relative to the container'"'"'s condition can be effected over said on-site power wiring by a known available set of commands transmitted by a second digital computer, and

said first digital computer further having means for recognizing and acting on only those command sequences which are addressed to the container to which the data acquisition unit is mounted whereby said second digital computer is permitted to selectively communicate with the data acquisition units of numerous on-line containers.

50. A location transmitter adapted to be used in connection with a power receptacle of a container storage area for transmitting a location code to an environmentally controlled container equipped with a computer controlled data acquisition unit wherein said data acquisition unit is adapted to transmit and receive serial digital data over existing on-site power wiring by transmitting and receiving such data over the power line of the container'"'"'s environmental control unit which electrically connects into said power receptacle, said location transmitter comprising

means for setting a binary location code corresponding to a particular storage area location,

digital multiplex means for sequencing each digital bit of said binary location code for outputting therefrom the location code as a serial data stream,

means for pulsing said digital multiplexer at a predetermined rate for serial data transmission,

a serial data output adapted to communicate with said on-site power wiring for transmitting said location code thereover, and

means for enabling the transmission of serial data through said serial data output after a container is electrically connected to the power receptacle associated with the storage area location identified by said location code, but inhibiting further transmissions therefrom some finite time after such transmissions have commenced.

51. The location transmitter of claim 50 in which the container data acquisition unit transmits and receives serial data over different wires of said on-site power wiring, and wherein the serial data output of said location transmitter means is connected to the data acquisition unit data receive wire of said wire of said on-site power wiring whereby said location code is received by said data acquisition unit for storage therein and whereby said location code will thereafter be available for subsequent transmission from said data acquisition unit to an externally monitoring digital computer when said data acquisition unit receives a suitable command therefrom.

52. The location transmitter of claim 51 in which each power receptacle at a storage area into which a container might be connected is actuated by a circuit breaker means and wherein said means for enabling and inhibiting transmission of said data through said serial data output includes having said serial data output connected to said one-site power wiring between said circuit breaker means and said one-site power receptacle, and having a feedback circuit means from said power wiring for inhibiting transmission through said serial data output when high voltage appears at said connection, whereby said location transmitter means will be free to transmit its location code to the data acquisition unit of said container between the time when electrical connection is made with said power receptacle and said circuit breaker means is switched from a power off position to a power on position.

54. The location transmitter of claims 52 or 53 including means for frequency modulating the serial data location code outputtted from said location transmitter.

55. The location transmitter of claim 54 wherein said frequency modulation means includes gating means for gating the serial data outputtted from said digital multiplexer and a suitable frequency signal derived from said digital multiplexer pulsing means whereby the "0" and "1" bit representations of the transmitted serial data location code will be characterized by the present or absence of the frequency signal gated therewith.

53. A location transmitter adapted to be used in connection with a power receptacle of a container storage area for transmitting a location code over existing on-site power wiring wherein said location transmitter identifies where in said storage area said power receptacle is located, said location transmitter comprising

means for setting a binary location code corresponding to a particular storage area location,

digital multiplex means for sequencing each digital bit of said binary location code for outputtting therefrom the location code as a serial data stream,

means for pulsing said digital multiplexer at a predetermined rate for serial data transmission,

a serial data output adapted to communicate with said on-site power wiring for transmitting said location code thereover, and

means for enabling the transmission of serial data through said serial data output after a cargo container is electrically connected to the power receptacle associated with the storage area location identified by said location code, but inhibiting further transmissions therefrom some finite time after such transmissions have commenced.

56. A method for monitoring the condition in a controlled area having a plurality of sensors disposed for detecting area condition parameters wherein said monitoring is under the control of a parameter data acquisition digital computer having data storage memory, said method being comprised essentially of the steps of

substantially continuously scanning the analog signals generated by said sensors,

converting the scanned analog signals to computer readable digital parameter data,

storing said digital parameter data in a preallocated portion of said data storage memory,

transmitting digital data over existing on-site wiring to a remote data processing digital computer for remote monitoring of said controlled area.

57. The method of claim 56 further comprising the steps of

comparing parameter data stored in the memory of said parameter data acquisition digital computer with parameter limit values also stored in said memory, and

generating a signal indicative of the condition status of said controlled area based on the comparison between said parameter data and said limit values, and

transmitting said condition status signal over said existing on-site power wiring to said remote data processing digital computer.

58. The method of claim 56 wherein parameter data newly stored in said data acquisition computer memory substantially replaces previously stored parameter data such that the continuously stored parameter data only temporarily resides in and utilizes a relatively small amount of memory space, and wherein there is provided the steps of

sampling such temporarily stored data at a predetermined sampling rate, and

setting aside such sampled data in separate memory locations so as to prepare a retrievable history of the controlled area'"'"'s condition.

59. A method for monitoring an environmentally controlled transportable container having a plurality of sensors disposed for detecting parameters relating to the operation of said container'"'"'s environmental control means, wherein said monitoring is under the control of a parameter data acquisition digital computer, said method being comprised essentially of the steps of

substantially continuously scanning the analog signals generated by said container sensors,

converting the scanned analog signals to computer readable digital parameter data,

storing said digital parameter data in a preallocated portion of the data acquisition computer memory,

comparing parameter data with parameter limit values stored in said computer memory for detecting a normal or out of limit condition status for said container, and

transmittig data storred in said computer memory, including data indicative of the container condition status, to an external monitoring computer in response to a command therefrom, said data being transmitted as a modulated serial data stream over existing on-site power wiring whereby numerous computers can be monitored from a central location over said existing on-site wiring.

60. The method of claim 59 wherein parameter data newly stored is said data acquisition computer memory substantially replaces previously stored parameter data such that the continuously stored parameter data only temporarily resides in and utilizes a relatively small amount of memory space, and wherein there is provided the steps of

sampling such temporarily stored data at a predetermined sampling rate, and

setting aside such sampled data in separate memory location so as to prepare a retrievable history of the container'"'"'s condition.

61. A method for monitoring, under the control of digital computers, transportable environmentally controlled containers equipped with sensors for detecting parameters relating to the container'"'"'s operating condition, and also equipped with a parameter data acquisition unit which is adapted for data communication over the electrical path provided by the power line of the container'"'"'s environmental control means whereby, when said container is placed on-line at a container storage area by electrically connecting its power line to one of the power receptacles for the storage area'"'"'a on-site power wiring, a data communication link is established between said on-site wiring and said data acquisition unit, said method being comprised essentially of the steps of

substantially continuously collecting parameter data generated by said parameter sensors and storing same in said container data acquisition unit,

selectively interrogating the data acquisition units of on-line containers over said on-site power wiring to provide from said parameter data a record of the condition of said on-line containers including an indication of a possible malfunction with respect to any one of said containers, and

displaying said container record at a monitoring station with said container storage area whereby a large number of on-line containers can be readily monitored.

62. The method of claim 61 further including the steps of

storing in said data acquisition unit limit values for said stored parameter data,

comparing said parameter data with said parameter limit values to determine whether there exists a normal or out of limit condition status for said container, said condition status being capable of being transmitted over said one-site power wiring for display in said central monitoring station.

63. The method of claim 62 further including the steps of

diagnosing the cause of an out of limit condition which is detected by an interrogation of a container, said diagnosis being achieved by calling up a predetermined diagnostic program which selects probable causes for out-of-limit conditions for given parameters, and

displaying said diagnostics at said central monitoring station.

64. The method of claim 61 further including the steps of

automatically inputting a location code to said data acquisition unit for storage therein when the power line of the container carrying said data acquisition unit is electrically connected to one of the storage area'"'"'s power receptacles, wherein said stored location code will identify where in said storage area said container is located, and

periodically requesting, by an interrogation over said on-site power wiring, that all on-line containers, the locations of which are unknown, to identify themselves to said central monitoring station whereby there will be provided an updated record as to which containers are present in said storage area.