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. <EOS>