Flow volume measurement device and flow velocity measurement device

A flow volume measurement device comprising:

• a measurement cell including a main pipe with opposite ends being open and connectable to a flow channel through which fluid flows, an incident tube that is connected to the main pipe and formed with a window for allowing passage of light at an end opposite to a side connected to the main pipe, an emission tube that is connected to the main pipe and formed with a window for allowing passage of light at an end opposite to a side connected to the main pipe, and a first purge-fluid supply tube that is connected to the incident tube;
• a purge-fluid supply unit that supplies purge fluid into the first purge-fluid supply tube of the measurement cell;
• a light emitting unit that emits a laser beam to the incident tube;
• a light receiving unit that receives the laser beam having entered from the incident tube, passed through the measurement cell, and emitted from the emission tube, and outputs a received amount of light as a light reception signal;
• a calculation unit that calculates a flow volume of fluid flowing in the measurement cell, based on a light reception signal output from the light receiving unit;
• a flow-direction detection unit that detects a flow direction of fluid flowing in the measurement cell;
• a control unit that controls an operation of respective units, wherein the purge-fluid has a different temperature or characteristics from the fluid flowing in the measurement cell;
• the calculation unit calculates the flow volume of the fluid flowing in the measurement cell based on a relationship between a characteristics change of a light reception signal output from the light receiving unit and the flow volume of the fluid flowing in the measurement cell;
• and
• the calculation unit demodulates a light reception signal received by the light receiving unit by at least one frequency, and calculates the flow volume of the fluid flowing in the measurement cell based on a magnitude of the fluctuation in the demodulated signal in the at least one frequency.