A pulse signal output circuit, comprising: a signal-receiving module, a photoelectrical coupler, a signal conversion module and an external power acquiring module; wherein the signal-receiving module is connected to the photoelectrical coupler, and the photoelectrical coupler is connected to the signal conversion module; the signal-receiving module is configured to receive a source pulse signal acquired by a flowmeter and send the source pulse signal to the photoelectrical coupler; the photoelectrical coupler is configured to perform electrical-optical-electrical conversion processing on the received source pulse signal to obtain an electrical signal, and send the electrical signal to the signal conversion module; and the signal conversion module is configured to perform conversion processing on the received electrical signal, to obtain and output an output pulse signal corresponding to the source pulse signal; characterized in that an external power acquiring module is connected between an external power supply and a control unit of a processor; the external power acquiring module is configured to send a first reference signal to the processor when the external power supply supplies power, and send a second reference signal to the processor when the external power supply does not supply power; wherein the external power supply is configured to supply power to the photoelectrical coupler and the signal conversion module, the external power acquiring module comprises an external acquiring photoelectrical coupler and a second voltage-dividing sub-module; the external power supply is connected to the second voltage-dividing sub-module, the second voltage-dividing sub-module is connected to the external acquiring photoelectrical coupler, and the external acquiring photoelectrical coupler is connected to the processor; the external power supply is further configured to send a power signal to the second voltage-dividing sub-module; the second voltage-dividing sub-module is configured to perform voltage-dividing processing on the power signal, to obtain and send to the external acquiring photoelectrical coupler, a voltage-dividing signal; and the external acquiring photoelectrical coupler is configured to process the received voltage-dividing signal to generate an optical signal, and then send the first reference signal or the second reference signal to the processor according to the optical signal. wherein the signal-receiving module is connected to the photoelectrical coupler, and the photoelectrical coupler is connected to the signal conversion module; the signal-receiving module is configured to receive a source pulse signal acquired by a flowmeter and send the source pulse signal to the photoelectrical coupler; the photoelectrical coupler is configured to perform electrical-optical-electrical conversion processing on the received source pulse signal to obtain an electrical signal, and send the electrical signal to the signal conversion module; and the signal conversion module is configured to perform conversion processing on the received electrical signal, to obtain and output an output pulse signal corresponding to the source pulse signal; characterized in that an external power acquiring module is connected between an external power supply and a control unit of a processor; the external power acquiring module is configured to send a first reference signal to the processor when the external power supply supplies power, and send a second reference signal to the processor when the external power supply does not supply power; wherein the external power supply is configured to supply power to the photoelectrical coupler and the signal conversion module, the external power acquiring module comprises an external acquiring photoelectrical coupler and a second voltage-dividing sub-module; the external power supply is connected to the second voltage-dividing sub-module, the second voltage-dividing sub-module is connected to the external acquiring photoelectrical coupler, and the external acquiring photoelectrical coupler is connected to the processor; the external power supply is further configured to send a power signal to the second voltage-dividing sub-module; the second voltage-dividing sub-module is configured to perform voltage-dividing processing on the power signal, to obtain and send to the external acquiring photoelectrical coupler, a voltage-dividing signal; and the external acquiring photoelectrical coupler is configured to process the received voltage-dividing signal to generate an optical signal, and then send the first reference signal or the second reference signal to the processor according to the optical signal.