Patent ID: 7533566

Claim:
A fluid measuring device, comprising: a logic operation unit with a switching signal output port for outputting a control signal; a capacitive sensor for generating a corresponding electrical signal in response to at least one physical property of a body of fluid; and a capacitance sensing circuit, comprising: a constant current source including a constant current source output electrical contact for outputting an electrical signal of the constant current source; a switch including a control terminal, a signal input port, and a signal output port; a voltage comparator including a high potential input port, a low potential input port, and signal output port, wherein the potential of the low potential input port is a reference voltage; and a time calculator for accumulating the time of the signal output from the voltage comparator, comprising: an electrical contact forming an electrical connection with the signal output port of the voltage comparator; another electrical contact forming another electrical connection with the switching signal output port of the logic operation unit; and a further electrical contact for outputting the accumulated time to the logic operation unit in the form of an electrical signal; wherein the constant current source is electrically connected to the signal input port of the switch, the capacitive sensor, and the high potential input port of the voltage comparator respectively through the constant current source output electrical contact; and the other terminals of the switch and the capacitive sensor are connected to ground, resulting in the electrical connection of the switch and the capacitive sensor in parallel.