Interface unit for coupling a probe to a measuring system

An interface unit comprising:

• an input configured and adapted to receive an input current having an input voltage (VIN), from an electrochemical measuring probe for use in contact with a process material, the electrochemical measuring probe having an electrode (EL) provided with a sensing element arranged so as to generate a sensor voltage (VSENSOR) as an electrode voltage related to at least one property of the process material when the electrode is in contact with the process material;
• an output configured and adapted to be coupled to an input of an evaluating device, the interface unit being configured to deliver, on the output, an output current having an output voltage (VOUT) essentially equal to the input voltage (VIN);
• a first transistor provided with a first insulated gate terminal coupled to the input, a first source terminal coupled to a first terminal of a first resistor, and a first drain terminal coupled to a first terminal of a second resistor, a second terminal of the second resistor being coupled to a point where a constant voltage (VC) is maintained to a constant value, the first transistor being configured and arranged to generate in the second resistor a second resistor voltage (VR2), according to the input voltage (VIN);
• a first operational amplifier provided with a first non-inverting input coupled to a circuit point where a reference voltage (Vref) is maintained to a constant value, with a first inverting input coupled to a first drain terminal of the first transistor, and with a first output coupled to a second terminal of the first resistor;
• a second transistor provided with a second source terminal coupled to a second terminal of a third resistor, and a second drain terminal coupled to a first terminal of a fourth resistor, a first terminal of the third resistor being coupled to the second terminal of the first resistor, a second terminal of the fourth resistor being coupled to a point where the constant voltage (VC) is maintained;
• and
• a second operational amplifier provided with a second non-inverting input coupled to the second drain terminal of the second transistor, and with a second inverting input coupled to the first inverting input of the first operational amplifier, and with a second output coupled a second insulated gate terminal of the second transistor and to the output of the interface unit;
• wherein the first operational amplifier is configured and arranged to provide a variable tension to the first source terminal of the first transistor in accordance with a comparison between the reference voltage (Vref) and the second resistor voltage (VR2), in order to control an operating point of the first transistor.