An electrode-type liquid level detection method for detecting a liquid level by using an electrode unit including first and second liquid level measurement electrodes, which are used to detect the liquid level, and a calibration electrode, which is not used to detect the liquid level but is used to calibrate the first and second liquid level measurement electrodes by flowing electric current therethrough during calibration, the method comprising:
- supplying current to the first and second liquid level measurement electrodes and the to-be-measured object connected in series with and between the first and second liquid level measurement electrodes,
- recording a pre-use resistance value of each electrode of the electrode unit as initial resistance value;
- obtaining absolute resistance value of the to-be-measured object after use of the electrode unit based on the initial resistance value;
- controlling to adjust a threshold value for determining whether or not the to-be-measured object exists, based on a change in resistance values of the first and second liquid level measurement electrodes when in use, wherein
- the obtaining absolute resistance value includes:
- relatively moving the electrodes to change distances between the electrodes after usage of the electrode unit,
- supplying current to the first and second liquid level measurement electrodes and the to-be-measured object connected in series with and between the first and second liquid level measurement electrodes, before and after the moving,
- a first calibration of supplying current to the first liquid level measurement electrode and the calibration electrode, and the to-be-measured object connected in series with and between the first liquid level measurement electrode and the calibration electrode, before and after the moving,
- a second calibration of supplying current to the second liquid level measurement electrode and the calibration electrode, and the to-be-measured object connected in series with and between the second liquid level measurement electrode and the calibration electrode, before and after the moving,
- calculating, by a calculation unit, per-unit-length resistivity p of the to-be-measured object by following equation:
- ρ=(V12−V11)/(rI)
- wherein V11 represents a voltage over the first liquid level measurement electrode and the calibration electrode in the first calibration after initiation of usage of the liquid level detection device and before the moving, V12 represents a voltage over the first liquid level measurement electrode and the calibration electrode in the first calibration after the moving, r represents a distance of moving in the moving, and I represents current supplied by a power source;
- and
- calculating, by the calculation unit, an absolute resistance value of the to-be-measured object based on the per-unit-length resistivity, and absolute resistance values of the first and second liquid level measurement electrodes and the calibration electrode based on the absolute resistance value of the to-be-measured object;
- the controlling including:
- adjusting the threshold based on the absolute resistance values of the first and second liquid level measurement electrodes and the calibration electrode.