Fluid device

A fluid device including a flow path where a liquid flows, the fluid device comprising:

• as electrodes for measuring a degree of electrical conductivity between the liquid in the flow path on an inflow upstream side and the liquid in the flow path on an outflow downstream side, a first electrode electrically in contact with the liquid on the upstream side and a second electrode electrically in contact with the liquid on the downstream side;
• and
• a circuit which measures the degree of electrical conductivity using the first electrode and the second electrode to detect an amount of the liquid flowing through the flow path or detect whether the liquid is present or absent, wherein
• the circuit includes
• a signal generation part which applies, between the first electrode and the second electrode, a voltage of an alternating square-wave in which a voltage of a positive value and a voltage of a negative value are cyclically and alternately switched,
• a signal processing part which acquires a measurement value indicating a magnitude of a current between the first electrode and the second electrode, and
• a determination part which determines the amount of the liquid flowing through the flow path or determines whether the liquid is present or absent,
• the signal processing part acquires a first measurement value as the measurement value at a point in time shifted by a predetermined time with reference to a first point in time when the voltage to be applied by the signal generation part is switched from a negative value to a positive value, and acquires a second measurement value as the measurement value at a time shifted by the predetermined time with reference to a second point in time when the voltage applied by the signal generation part is switched from a positive value to a negative value, and
• the circuit measures a magnitude of a differential value between the first measurement value and the second measurement value as an index indicating the degree of electrical conductivity.