Notice that the sensor is modeled as a dc source in series with an internal resistance. Notice also due to the configuration, the output of the circuit increases as the sensor input decreases. Rheostat R3 is used to calibrate the sensor circuits so it has the output voltage for a given sensor input voltage as shown in Figure 2. Set the input voltage to 400 mV and R3 approximately in the middle of its range and simulate the circuit behavior, you should get 1.825 V at the output, if not readjust R3 to get that value output voltage Then sweep input voltage from -600 to 600 mV in step of 100 mV and record the output voltage Plot the graph of Vout vs pH for the measurement. Answer: If the output of the sensor circuit is 7 V, is the solution acidic, neutral, or basic (caustic)