A loop powered distance transmitter, comprising: a laser emitter structured to output laser light toward a target; a light detector structured to receive the laser light reflected from the target; a processor coupled to the light detector and structured to output a first signal representing a distance of the target from the laser emitter and the light detector; a power converter being coupled to the laser emitter, the light detector and the processor, and the power converter being structured to provide power to the laser emitter, the light detector and the processor; and a signal converter coupled to the processor and structured to receive the first signal from the processor, the signal converter being structured to output a second signal to a two wire loop powered circuit, the second signal representing the distance of the target from the laser emitter and the light detector, and the second signal being compatible with a communication protocol of the two wire loop powered circuit, characterized in that the light detector comprises a single photon detector, the power converter is structured to receive electrical power from the two wire loop powered circuit, and the distance transmitter further comprises a voltage comparator coupled between the light detector and the processor, the voltage comparator structured to output a first signal when a pulse is received from the light detector and output a second signal when no pulse is received from the light detector, the voltage comparator is configured to use a threshold voltage to distinguish between a pulse and no pulse, wherein the threshold voltage is adjusted over a series of pulses to compensate for pulses of different amplitudes in response to different reflectivities of different targets. a laser emitter structured to output laser light toward a target; a light detector structured to receive the laser light reflected from the target; a processor coupled to the light detector and structured to output a first signal representing a distance of the target from the laser emitter and the light detector; a power converter being coupled to the laser emitter, the light detector and the processor, and the power converter being structured to provide power to the laser emitter, the light detector and the processor; and a signal converter coupled to the processor and structured to receive the first signal from the processor, the signal converter being structured to output a second signal to a two wire loop powered circuit, the second signal representing the distance of the target from the laser emitter and the light detector, and the second signal being compatible with a communication protocol of the two wire loop powered circuit, characterized in that the light detector comprises a single photon detector, the power converter is structured to receive electrical power from the two wire loop powered circuit, and the distance transmitter further comprises a voltage comparator coupled between the light detector and the processor, the voltage comparator structured to output a first signal when a pulse is received from the light detector and output a second signal when no pulse is received from the light detector, the voltage comparator is configured to use a threshold voltage to distinguish between a pulse and no pulse, wherein the threshold voltage is adjusted over a series of pulses to compensate for pulses of different amplitudes in response to different reflectivities of different targets.