| 摘要 |
A level detecting resistor (Rd) is inserted into a liquid (5) and has a length immersed in the liquid. The level detecting resistor (Rd) is supplied a constant current (Id) from a constant current source (1). The voltage drop (Vd) developed across the level detecting resistor (Rd) is supplied to a non-inverting input terminal of a differential input amplifier (OP1, R1-R4). The output (Vo) of the differential input amplifier is then divided by a series-circuit of a temperature compensating resistor (Rc) and a resistor (R5). The divided voltage (Va) across the resistor (R5) is fed back via a voltage follower (OP2) to the non-inverting input terminal of the differential input amplifier.
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