Abstract: A method and apparatus for controlling the transmission of data, via a telephone network (20), between a first location (2,14,16) where data is collected and a central station (22).

Abstract: A system for transmitting data via a telephone line by means of a data communications device (4) connected to the telephone line, at least one other communications device being connected to the telephone line and each device being switchable between an inactive state, in which the device is not in use and presents a high impedance to the telephone line, and an active state, in which the device reduces the telephone line voltage and signals can be transferred between the device and the telephone line, the system including a telephone line state detection unit (10) associated with the data communications device (4) and connected to the telephone line for electrically monitoring the telephone line to provide an indication of the state of another communications device connected to the telephone line.

Abstract: A power line carrier communication system for monitoring refrigerated containers which includes a master monitoring unit and a first power line interface which interchange messages in a first format. The first power line interface translates the first format to a second format suitable for power line environment, and messages in the second format are applied to a power line. Remote monitoring units receive the messages from the power line, and they return messages to the power line containing status data relative to refrigerated containers. The second format includes a message starting preamble having a duration and logic level which is not duplicated by normal operation of the apparatus, enhancing the probability of proper message synchronization and reception over noisy power line environments.

Abstract: A microprocessor based system monitors and controls a transport refrigeration system having a two speed compressor coupled to a condenser and an evaporator and further having two speed condenser and evaporator fans, a refrigerant modulating valve, and heater means to cool or heat a served space. A keypad is provided for operator entry of the temperature setpoint and for display selections. Return air and discharge air temperature sensors provide signals to the microprocessor for temperature control. The microprocessor is programmed to sequence or control the compressor, the fans, the modulating valve and the heater means for temperature control in accordance with one of four stored algorithms. One of the temperature sensors is used for control, and if it is detected to have failed automatic switchover is made to use of the other temperature sensor for temperature control.