RETURN ELECTRODE CONTACT MONITOR
 Inventor: Michael R. Manes, Littleton, Colo.
 Assignee: Aspen Laboratories, Inc., Greenwood Village, Colo.
 Appl. No.: 156,540
 Filed: Feb. 16,1988
 Int. Q.* A61B 17/39
 U.S. a 128/303.13; 128/908
 Field of Search 128/303.13, 303.14,
 References Cited
U.S. PATENT DOCUMENTS
3,933,157 1/1976 Bjurwill et al 128/303.14
4.416.276 11/1983 Newton et al 128/303.13
4.416.277 11/1983 Newton et al 128/303.13
4,569,345 2/1986 Manes 128/303.14
4,574,801 3/1986 Manes 128/303.14
4,617,927 10/1986 Manes 128/303.14
FOREIGN PATENT DOCUMENTS
1139927 11/1962 Fed. Rep. of
2146534 4/1985 United Kingdom 128/303.13
Primary Examiner—Lee S. Cohen
Attorney, Agent, or Firm—Fields, Lewis, Pittenger &
Apparatus for monitoring the resistance of the return part of the patient circuit of either a dual foil or single foil return electrode according to a user's selection is disclosed. The apparatus measures the quality of the contact between the return electrode and the patient. A DC or AC converter provides a substantially DC voltage at its input that varies in relation to the resistance of the return part of the patient circuit at its AC output. Preferably, a constant current fed sinusoidal oscillator with a low pass filter at its DC output provides a substantially DC voltage related to the resistance at its AC input. An analog to digital converter converts the substantially DC voltage to a corresponding binary digital signal that is input to a programmed microprocessor. A manually operable set point switch coupled to the microprocessor is acatuated by the user which actuation establishes a resistance level with the pad (return electrode) in place on the patient. The microprocessor establishes preselected range between fixed maximum and minimum resistance values beyond which an alarm output is produced and establishes a threshold resistance value whereby upon a preselected fixed deviation, such as when the patient pad is partially detached, an alarm is produced and further an output so the RF power source will longer apply power to the active electrode.
17 Claims, 7 Drawing Sheets