A method of performing diagnostic of a flow transmitter system, comprising: obtaining, via a flow sensor, sensor measurements of flow characteristics of a moving medium being monitored; outputting, via at least one processor, a drive signal for driving a pulse output circuit to generate a pulse signal according to the sensor measurements from the flow sensor; generating, via a switching circuit of the pulse output circuit, a pulse signal according to the drive signal; monitoring, via a diagnostic circuit (142, 242) connected to the switching circuit, current corresponding to the pulse signal; and determining, via the at least one processor, whether the pulse output circuit is operating in a normal or abnormal state based on the drive signal from the at least one processor and a feedback signal corresponding to the monitored current from the diagnostic circuit (142, 242), wherein the pulse signal is outputted to or obtained by an external device with a power supply which supplies power to the pulse output circuit when connected to the flow transmitter system, the switching circuit of the pulse output circuit comprises at least one transistor which is powered by the power supply of the external device and driven according to the drive signal from the at least one processor, and the diagnostic circuit (142, 242) comprises a circuit of high gain bandwidth amplifier or amplifiers for providing the feedback signal to the at least one processor, the feedback signal corresponding to current drawn from the power supply of the external device when the at least one transistor is driven to turn or switch ON and OFF according to the drive signal from the at least one processor. obtaining, via a flow sensor, sensor measurements of flow characteristics of a moving medium being monitored; outputting, via at least one processor, a drive signal for driving a pulse output circuit to generate a pulse signal according to the sensor measurements from the flow sensor; generating, via a switching circuit of the pulse output circuit, a pulse signal according to the drive signal; monitoring, via a diagnostic circuit (142, 242) connected to the switching circuit, current corresponding to the pulse signal; and determining, via the at least one processor, whether the pulse output circuit is operating in a normal or abnormal state based on the drive signal from the at least one processor and a feedback signal corresponding to the monitored current from the diagnostic circuit (142, 242), wherein the pulse signal is outputted to or obtained by an external device with a power supply which supplies power to the pulse output circuit when connected to the flow transmitter system, the switching circuit of the pulse output circuit comprises at least one transistor which is powered by the power supply of the external device and driven according to the drive signal from the at least one processor, and the diagnostic circuit (142, 242) comprises a circuit of high gain bandwidth amplifier or amplifiers for providing the feedback signal to the at least one processor, the feedback signal corresponding to current drawn from the power supply of the external device when the at least one transistor is driven to turn or switch ON and OFF according to the drive signal from the at least one processor.