A system for detecting a fluid type within a blood processing device includes a voltage source for electrical connection to a first electrode and to a second electrode, and a resistor in series between the voltage source and the first and/or second electrode. The voltage source may apply a voltage across the first and second electrodes. The system also includes a voltage detector that is electrically connected to the resistor and measures a voltage drop across the resistor. A circuit electrically connected to the voltage detector determines the type of fluid in contact with the first and second electrode based, at least in part, upon the measured voltage drop.
