High frequency power measurement

• US 5,422,567 A
• Filed: 12/27/1993
• Issued: 06/06/1995
• Est. Priority Date: 12/27/1993
• Status: Expired due to Term

• Current Assignee: Covidien AG (Medtronic Plc)
• Original Assignee: Valleylab Inc. (Medtronic Plc)
• Inventors: Matsunaga, Derek
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): WARDAS, MARK A
• Application Number:
  US08/174,593
• Time in Patent Office: 526 Days
• Field of Search: 606/38, 606/40, 364/483, 324/142
• US Class Current: 324/142
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 2017/00026 Conductivity or impedance, e.g. of tissue
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00678 upper
• CPC Class Codes: A61B 2018/00684 using lookup tables
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00708 switching the power on or off
• CPC Class Codes: A61B 2018/00755 Resistance or impedance
• CPC Class Codes: A61B 2018/00869 Phase
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/1273 including multiple generators in one device
• CPC Class Codes: G01R 21/133 by using digital technique

Abstract

A monitoring circuit for an electrosurgical generator has active and return output conductors. Voltage, current and the inverse of current picked up inductively are provided to a adder circuits for summing the picked up voltage and current and computing the difference of the picked up voltage and the current. Root mean square to direct current converters signal RMS average values of the sum and difference. A microprocessor squares the values and applies them to a formula wherein the sum signals have subtracted therefrom the difference signals; the results are divided by four to provide the root mean square of the power applied to the load. During desiccation the output is regulated in response to impedance to shut off output. A diagnostic circuit relates impedance load and output response during operation to a look up table or a microprocessor algorithm to calibrate. Feedback modifies the output when the adders determine the power applied to the load in real time. A method has generator output to active and return conductors and to inductive pick ups for voltage and current, computes sum and differential values, changes root mean square to direct currents, squares the values and subtracts the differential from the summation then divides the result finding the root mean square value of the power.

Claims

1. 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;

an inductive pick up for the inverse of current flowing through the one conductor of the electrosurgical generator output;

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, and

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.

2. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein 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 a microcontroller with band limited signal processing capabilities.

3. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein 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 so the result therefrom can be divided by four to provide an indication of load for use in the feedback circuit to control the output of the electrosurgical generator.

4. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein the 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.

5. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein the 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.

6. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein the electrosurgical generator has 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.

7. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein 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.

8. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein an inductive pick up for voltage between the active and return the conductors is connected to a root mean square to direct current converter for the voltage to provide a measure of the root mean square of the voltage and the microprocessor is programmed to find the phase angle between voltage and current.

9. The high frequency power monitoring circuit for an electrosurgical generator of claim 1 wherein an inductive pick up for voltage between the active and return the conductors is connected to a root mean square to direct current converter for the voltage to provide a measure of the root mean square of the voltage and the microprocessor is programmed to find the length of a controlled capacitance cable.

10. 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.

11. 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.

12. The method of claim 11 with the step of applying the root mean square to direct current converter for the summation and differential values to a microcontroller with band limited signal processing capabilities.

13. The method of claim 11 with the step of determining the root mean square value of the actual power applied to the load independently of the length and impedance of the active and return conductors.

14. The method of claim 11 with the steps of connecting a feedback circuit to the electrosurgical generator for modifying the output thereof and determining with the first and second adders 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 mean square differential values and square those values for subtracting the squared differential values from the squared summation values so the result therefrom can be divided by four to provide an indication of load for use in the feedback circuit to control the output of the electrosurgical generator.

15. The method of claim 11 with the step of locating the inductive pick up for current flowing through at least one of the conductors along the active conductor or the return conductor.

16. The method of claim 11 with the step of locating the inductive pick up for the inverse of current flowing through at least one of the conductors along the active conductor or the return conductor.

17. The method of claim 11 with the step of providing in the electrosurgical generator 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.

18. The method of claim 11 with the step of connecting a tissue load responsive regulator to the electrosurgical generator output to in response to impedance shut off output when the impedance is at a level preset in the microprocessor.

19. The method of claim 11 with the steps of connecting an inductive pick up for voltage between the active and return the conductors to a root mean square to direct current converter for the voltage and thereby providing a measure of the root mean square of the voltage and the microprocessor is programmed for finding the phase angle between voltage and current.

20. The method of claim 11 with the steps of connecting an inductive pick up for voltage between the active and return the conductors to a root mean square to direct current converter for the voltage and thereby providing a measure of the root mean square of the voltage and the microprocessor is programmed for finding the length of a controlled capacitance cable.