High frequency power measurement

A high frequency power monitoring circuit for an electrosurgical generator applied to a load to achieve an electrosurgical effect comprising:

• a source of high frequency electrosurgical energy including an electrosurgical generator and its active and return conductors connected to the output thereof;
• an inductive pick up for voltage connected between the conductors of the electrosurgical generator;
• an inductive pick up for current flowing through at least one of the conductors of the output from the electrosurgical generator is located along the active conductor or the return conductor;
• an inductive pick up for the inverse of current flowing through the one conductor of the electrosurgical generator output is located along the active or return conductors;
• a first adder circuit for computing the instantaneous inductively picked up voltage with the instantaneously inductively picked up current to provide a sum indicative instantaneously thereof;
• a second adder circuit for computing the inductively picked up voltage and the inverse of the instantaneously derived current providing a differential value thereof;
• a root mean square to direct current converter for the summation value to provide a signal of the instantaneous value of the summation as a root mean square summation value;
• a root mean square to direct current converter for the differential value to provide a signal of the instantaneous value of the differential as a root mean square differential value;
• a microcontroller with band limited signal processing capabilities so the root mean square to direct current converter for the summation value and the root mean square to direct current converter for the differential value are each inputs to the microcontroller;
• a microprocessor to periodically receive the root mean square summation and root mean square differential values and square those instantaneous root mean square summation and differential values for application to a formula wherein the squared root mean square summation values have subtracted therefrom the squared root mean square differential values so the result therefrom can be divided by four to provide the root mean square value of the actual power applied to the load;
• a tissue load responsive regulator is connected to the electrosurgical generator output to in response to impedance shut off output when the impedance is at a level preset in the microprocessor;
• an internal diagnostic circuit which relates impedance load and output response during operation to a look up table or an algorithm programmed in the microprocessor for obtaining a correction to automatically calibrate the response and operation of the high frequency power monitoring circuit, and
• a feedback circuit connected to the electrosurgical generator for modifying the output thereof and the first and second adders determining the root mean square value of the actual power applied to the load in real time so the microprocessor can periodically receive the root mean square summation and root means square differential values and square those values for calculation in the formula for the result therefrom to be divided by four to provide an indication of load for use in the feedback circuit to control the output of the electrosurgical generator so the length and impedance of the active and return conductors are insignificant to the determination of the root mean square value of the actual power applied to the load.

A method for monitoring high frequency power from an electrosurgical generator applied to a load to achieve an electrosurgical effect with the following steps:

• connecting an electrosurgical generator output to active and return conductors;
• connecting an inductive pick up for voltage between the conductors of the electrosurgical generator;
• connecting an inductive pick up for current flowing through at least one of the conductors of the output from the electrosurgical generator;
• connecting an inductive pick up for the inverse of current flowing through the one conductor of the electrosurgical generator output;
• computing with a first adder circuit the instantaneous inductively picked up voltage with the instantaneously inductively picked up current to provide a sum indicative instantaneously thereof;
• computing with a second adder circuit the inductively picked up voltage and the inverse of the instantaneously derived current providing a differential value thereof;
• converting a root mean square to direct current for the summation value to provide a signal of the instantaneous value of the summation as a root mean square summation value;
• converting a root mean square to direct current for the differential value to provide a signal of the instantaneous value of the differential as a root mean square differential value, and
• receiving in a microprocessor periodically the root mean square summation and root mean square differential values;
• squaring those instantaneous root mean square summation and differential values for application to a formula wherein the squared root mean square summation values have subtracted therefrom the squared root mean square differential values, and then
• dividing the result therefrom by four to provide the root mean square value of the actual power applied to the load.