Patent ID: 6930956

Claim:
A time of flight ranging system coupled to a receiver at a remote location through a two-conductor loop carrying a current signal, and the two-conductor loop providing a signal path and a supply current at a supply voltage for the time of flight ranging system to transmit measurements to the remote receiver, said time of flight ranging system comprising: (a) a process variable measurement stage comprising, a transducer for emitting energy pulses and coupling reflected energy pulses; a controller having a receiver stage and a transmitter stage; said transducer having an input port operatively coupled to said transmitter stage and being responsive to said transmitter stage for emitting said energy pulses, and said transducer including an output port operatively coupled to said receiver component for outputting reflected energy pulses coupled by said transducer; said receiver stage converting said reflected energy pulses into corresponding electrical signals for output to said controller, and said controller including a program component for processing said electrical signals and generating measurement readings; (b) a current control circuit comprising, an input port having first and second terminals for connecting to respective conductors of the two-conductor loop, and said input port receiving the current signal from the two-conductor loop; an output port for coupling to a process variable measurement component for measuring a process variable, said output port providing said process variable measurement component with a power supply derived from the current signal in the two-conductor loop, and said process variable measurement component generating an output corresponding to the process variable being measured; a current controller having a current source for outputting a current signal level in the two-conductor loop, and said current signal level being a function of the state of the process variable output and said current signal level serving to transmit the process variable output to the remote receiver; an adjustable current controller having an input coupled to said input port for receiving the current signal from the two-conductor loop, and an output coupled to said current source, and said adjustable current controller including a control input for adjusting the level of the current signal received from the two-conductor loop and passed to said current source; a control component coupled to the control input of said adjustable current controller, said control component being responsive to the supply current being used by the process variable measurement device, and said control component generating a control output for said adjustable current controller to adjust the received current signal to a level to provide an optimal voltage level for the process variable measurement device.