| 摘要 |
PURPOSE:To prevent the corrosion of an electrode bar to detect accurately a liquid level by providing a protecting diode to a circuit from the collector of a relay driving transistor TR to a long electrode bar or a short electrode bar. CONSTITUTION:When the liquid level goes to lower than a long electrode bar 2 and the liquid is not brought into contact with the long electrode bar 2, the circuit between electrode bar terminals 13 and 14 is opened, and therefore, the base voltage of an electrode current detecting TR9 is released from the voltage division state, and the TR9 is turned on, and simultaneously, a relay 5 is closed. Since a relay driving TR11 is turned off when the liquid level is between the lower end of a short electrode bar 1 and the lower end of the long electrode bar 2, a point 21 has a DC positive potential at this time, and a DC current is prevented from being flowed from an operating point improving resistance 35 to the long electrode bar 2 or the short electrode bar 1 through a base current limiting resistance 36 by a DC component preventing diode 22. Consequently, the corrosion of electrode bars is prevented to detect accurately the liquid level. |
