A device with controllable voltage between switch contacts, comprising: a switch signal unit, wherein the switch signal unit comprises a first transistor (Q 51, Q 71, Q 91, Q 101), a switch (K 51, K 71, K 91, K 101, K 111) is coupled between the first transistor (Q 51, Q 71, Q 91, Q 101) and an output of a power supply (U 51, U 71, U 91, U 101) for controlling the close-open of the current path between the first transistor (Q 51, Q 71, Q 91, Q 101) and the power supply (U 51, U 71, U 91, U 101); a biasing circuit coupled to the switch signal unit, characterized in that the switch signal unit is adapted to output a corresponding switch signal according to the state of the switch, wherein the biasing circuit comprising two resistor parts (R 51 and R 52, R 71 and R 72, R 91 and R 92, R 101 and R 102) in series and with fixed resistance values, the resistor parts are coupled to the output of the power supply (U 51, U 71, U 91, U 101) and the switch signal unit respectively, the resistor part coupled to a positive pole of the power supply is an upper bias part, while the resistor part coupled to a negative pole of the power supply is a lower bias part, for providing a bias voltage to the control terminal of the first transistor (Q 51, Q 71, Q 91, Q 101) of the switch signal unit, so as to control the voltage (U K51, U K71, U K91, U K101) between contacts of the switch (K 51, K 71, K 91, K 101, K 111) and the current flowing through the switch, when the switch (K 51, K 71, K 91, K 101, K 111) is opened, if a conductive liquid and/or the stream of a conductive liquid exist(s) inside the switch, the first transistor (Q 51, Q 71, Q 91, Q 101) is in a turn-on state; if the inside of the switch is dry, the first transistor (Q 51, Q 71, Q 91, Q 101) is in a turn-off state. a switch signal unit, wherein the switch signal unit comprises a first transistor (Q 51, Q 71, Q 91, Q 101), a switch (K 51, K 71, K 91, K 101, K 111) is coupled between the first transistor (Q 51, Q 71, Q 91, Q 101) and an output of a power supply (U 51, U 71, U 91, U 101) for controlling the close-open of the current path between the first transistor (Q 51, Q 71, Q 91, Q 101) and the power supply (U 51, U 71, U 91, U 101); a biasing circuit coupled to the switch signal unit, characterized in that the switch signal unit is adapted to output a corresponding switch signal according to the state of the switch, wherein the biasing circuit comprising two resistor parts (R 51 and R 52, R 71 and R 72, R 91 and R 92, R 101 and R 102) in series and with fixed resistance values, the resistor parts are coupled to the output of the power supply (U 51, U 71, U 91, U 101) and the switch signal unit respectively, the resistor part coupled to a positive pole of the power supply is an upper bias part, while the resistor part coupled to a negative pole of the power supply is a lower bias part, for providing a bias voltage to the control terminal of the first transistor (Q 51, Q 71, Q 91, Q 101) of the switch signal unit, so as to control the voltage (U K51, U K71, U K91, U K101) between contacts of the switch (K 51, K 71, K 91, K 101, K 111) and the current flowing through the switch, when the switch (K 51, K 71, K 91, K 101, K 111) is opened, if a conductive liquid and/or the stream of a conductive liquid exist(s) inside the switch, the first transistor (Q 51, Q 71, Q 91, Q 101) is in a turn-on state; if the inside of the switch is dry, the first transistor (Q 51, Q 71, Q 91, Q 101) is in a turn-off state.