Monitoring circuit for an RF surgical apparatus

Claim 1

A monitoring circuit for an RF surgical apparatus, said RF surgical apparatus having an RF power stage which generates an RF power output normally supplied to a patient via electrodes connected to an output of said RF power stage, and a control circuit for driving said RF power stage, said monitoring circuit comprising: adjustment means for connection to said control circuit for setting a rated value of the RF power output of said RF power stage; means for connection to the output of said RF power stage for continuously measuring the actual value of RF power output of said RF power stage by directly measuring the current and voltage at said output of said RF power stage; a load resistor having a predetermined resistance value; switching means for connecting said load resistor to the output of said RF power stage in place of said electrodes during a self-test of said monitoring circuit; a comparator having inputs respectively connected to said adjustment means and said means for measuring to which said rated value and said actual value are respectively continuously supplied, said comparator continuously determining deviation of said actual value from said rated value during supply of RF power to said patient and when said load resistor is connected to the output of said RF power stage during said self-test, said comparator having a threshold and generating an enable signal when said deviation exceeds said threshold; means for simultaneously actuating said switching means and supplying said rated value and said actual value to said inputs of said comparator to conduct said self-test; means for generating an alarm in response to said enable signal; and auxiliary circuit means connectable to said means for actuating for simulating a deviation in said comparator which exceeds said threshold.