A fluid ejection system, comprising: a fluid ejection device (100, 200, 500) including: a fluid supply chamber to store fluid; a plurality of ejection chambers including nozzles and corresponding ejection members to selectively eject the fluid through the respective nozzles; a channel to establish fluid communication between the fluid supply chamber and the ejection members; a temperature adjustment module configured to establish at least one temperature of the fluid of the fluid ejection device (100, 200, 500); and a sensor unit (15, 25) having a sensor plate, the sensor unit (15, 25) configured to detect at least one impedance in the fluid at the at least one temperature to obtain at least one detected impedance value; and a fluid identification module configured to identify a characteristic of the fluid based on the at least one detected impedance value to obtain an identified fluid characteristic; and a) a generator unit configured to supply a multi-frequency excitation signal to the sensor unit (15, 25), the sensor unit (15, 25) configured to transmit the multi-frequency excitation signal from the sensor plate through the fluid to a grounding member to obtain one of a range of voltage values and a range of current values on the sensor plate, or b) wherein the temperature adjustment module is configured to selectively adjust the temperature of the fluid to a plurality of temperatures, and the sensor unit (15, 25) is configured to selectively detect a first impedance of the fluid corresponding to a first temperature of the plurality of temperatures and a second impedance of the fluid corresponding to a second temperature of the plurality of temperatures different than the first temperature. a fluid ejection device (100, 200, 500) including: a fluid supply chamber to store fluid; a plurality of ejection chambers including nozzles and corresponding ejection members to selectively eject the fluid through the respective nozzles; a channel to establish fluid communication between the fluid supply chamber and the ejection members; a temperature adjustment module configured to establish at least one temperature of the fluid of the fluid ejection device (100, 200, 500); and a sensor unit (15, 25) having a sensor plate, the sensor unit (15, 25) configured to detect at least one impedance in the fluid at the at least one temperature to obtain at least one detected impedance value; and a fluid supply chamber to store fluid; a plurality of ejection chambers including nozzles and corresponding ejection members to selectively eject the fluid through the respective nozzles; a channel to establish fluid communication between the fluid supply chamber and the ejection members; a temperature adjustment module configured to establish at least one temperature of the fluid of the fluid ejection device (100, 200, 500); and a sensor unit (15, 25) having a sensor plate, the sensor unit (15, 25) configured to detect at least one impedance in the fluid at the at least one temperature to obtain at least one detected impedance value; and a fluid identification module configured to identify a characteristic of the fluid based on the at least one detected impedance value to obtain an identified fluid characteristic; and a) a generator unit configured to supply a multi-frequency excitation signal to the sensor unit (15, 25), the sensor unit (15, 25) configured to transmit the multi-frequency excitation signal from the sensor plate through the fluid to a grounding member to obtain one of a range of voltage values and a range of current values on the sensor plate, or b) wherein the temperature adjustment module is configured to selectively adjust the temperature of the fluid to a plurality of temperatures, and the sensor unit (15, 25) is configured to selectively detect a first impedance of the fluid corresponding to a first temperature of the plurality of temperatures and a second impedance of the fluid corresponding to a second temperature of the plurality of temperatures different than the first temperature. a) a generator unit configured to supply a multi-frequency excitation signal to the sensor unit (15, 25), the sensor unit (15, 25) configured to transmit the multi-frequency excitation signal from the sensor plate through the fluid to a grounding member to obtain one of a range of voltage values and a range of current values on the sensor plate, or b) wherein the temperature adjustment module is configured to selectively adjust the temperature of the fluid to a plurality of temperatures, and the sensor unit (15, 25) is configured to selectively detect a first impedance of the fluid corresponding to a first temperature of the plurality of temperatures and a second impedance of the fluid corresponding to a second temperature of the plurality of temperatures different than the first temperature.