Abstract:
The functionality and the output power delivered are evaluated in an electrosurgical generator by calculating first and second values related to the output power delivered by using separate first and second computations. The two calculated values are compared, and an error condition is indicated when the two values differ by a predetermined amount. The separate computations, coupled with the other separate activities of measuring, averaging and sampling the output current and voltage measurements, serve as an effective basis for detecting errors caused by malfunctions or equipment failure. The error condition may be used to as a basis to terminate the output power delivery or indicate the error.

Description:
CROSS REFERENCE TO RELATED INVENTION 
     This is a division of application Ser. No. 10/299,988, filed Nov. 19, 2002, which is now U.S. Pat. No. 6,948,503. This is also related to an invention for an Electrosurgical Generator and Method with Multiple Semi-Autonomously Executable Functions, described in U.S. patent application Ser. No. 10/299,953, now U.S. Pat. No. 6,942,660, and for an Electrosurgical Generator and Method for Cross Checking Mode Functionality, described in U.S. patent application Ser. No. 10/299,952, now U.S. Pat. No. 6,875,210, both of which were filed concurrently with application Ser. No. 10/299,988 and assigned to the assignee of the present invention. The subject matter of these previously filed applications is incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to electrosurgery. More specifically, the invention relates to a new and improved electrosurgical generator and method that cross-checks the amount of the electrosurgical power delivered to assure proper functionality of the electrosurgical generator and that the desired amount of electrosurgical power is delivered during the surgical procedure. 
     BACKGROUND OF THE INVENTION 
     Electrosurgery involves applying relatively high voltage, radio frequency (RF) electrical power to tissue of a patient undergoing surgery, for the purpose of cutting the tissue, coagulating or stopping blood or fluid flow from the tissue, or cutting or coagulating the tissue simultaneously. The high voltage, RF electrical power is created by an electrosurgical generator, and the electrical power from the generator is applied to the tissue from an active electrode manipulated by a surgeon during the surgical procedure. 
     The amount and characteristics of the electrosurgical energy delivered to the patient is determined by the surgeon and depends on the type of procedure, among other things. For example, cutting is achieved by delivering a continuous RF signal ranging up to relatively high power, for example 300 watts. Coagulation is achieved by rapidly switching the RF power on and off in a duty cycle. The coagulation duty cycle has a frequency considerably lower than the RF power delivered. However, during the on-time of each duty cycle, the electrical power is delivered at the RF frequency. The power delivered during coagulation is typically in the neighborhood of approximately 40-80 watts, although power delivery as low as 10 watts or as high as 110 watts may be required. Simultaneous cutting and coagulation, which is also known as a “blend” mode of operation, also involves a duty cycle delivery of RF energy, but the on-time of the duty cycle during blend is greater than the on-time of the duty cycle during coagulation. Power is delivered at the RF frequency because the frequency is high enough to avoid nerve stimulation, thereby allowing the tissue to remain somewhat stationary without contractions caused by the electrical energy. 
     The electrosurgical generator must also have the capability to deliver a relatively wide range of power. The resistance or impedance of the tissue may change radically from point-to-point during the procedure, thereby increasing the power regulation requirements for the electrosurgical generator. For example, a highly fluid-perfused tissue, such as the liver, may exhibit a resistance or impedance in the neighborhood of 40 ohms. Other tissue, such as the marrow of bone, may have an impedance in the neighborhood of 900 ohms. The fat or adipose content of the tissue will increase its impedance. The variable characteristics of the tissue require the electrosurgical generator to be able to deliver effective amounts of power into all types of these tissues, on virtually an instantaneously changing basis as the surgeon moves through and works with the different types of tissues at the surgical site. 
     These wide variations in power delivery encountered during electrosurgery impose severe performance constraints on the electrosurgical generator. Almost no other electrical amplifier is subject to such rapid response to such widely varying power delivery requirements. Failing to adequately regulate and control the output power may create unnecessary damage to the tissue or injury to the patient or surgical personnel. In a similar manner, failing to adequately establish the electrical characteristics for cutting, coagulating or performing both procedures simultaneously can also result in unnecessary tissue damage or injury. 
     Almost all electrosurgical generators involve some form of output power monitoring circuitry, used for the purpose of controlling the output power. The extent of power monitoring for regulation purposes varies depending upon the type of mode selected. For example, the coagulation mode of operation does not generally involve sensing the voltage and current delivered and using those measurements to calculate power for the purpose of regulating the output power. However, in the cut mode of operation, it is typical to sense the output current and power and use those values as feedback to regulate the power delivered. 
     In addition to power regulation capabilities, most electrosurgical generators have the capability of determining error conditions. The output power of the electrosurgical generator is monitored to ensure that electrosurgical energy of the proper power content and characteristics is delivered. An alarm is generated if an error is detected. The alarm may alert the surgeon to a problem and/or shut down or terminate power delivery from the electrosurgical generator. 
     Certain types of medical equipment controlled by microprocessors or microcontrollers utilize multiple processors for backup and monitoring purposes. Generally speaking, one of the processor serves as a control processor to primarily control the normal functionality of the equipment. Another one of the processors serves as a monitor processor which functions primarily to check the proper operation of the control processor and the other components of the medical equipment. Using one processor for primary control functionality and another processor for primary monitoring functionality has the advantage of achieving redundancy for monitoring purposes, because each processor has the independent capability to shut down or limit the functionality of the medical equipment under error conditions. Standards and recommendations even exist for multiple-processor medical equipment which delineates the responsibilities of the safety and monitoring processors. 
     SUMMARY OF THE INVENTION 
     The present invention has evolved from a desire to achieve a high degree of reliability for monitoring purposes in a multiple-processor electrosurgical generator. The present invention has also evolved from realizing that control and monitoring functionality, as well as the components used for monitoring conditions, need to be cross-checked on a continual and relatively frequently recurring basis to ensure proper functionality in the context of the rapidly and widely varying output requirements of an electrosurgical generator. In addition, the present invention advantageously monitors output power in an electrosurgical generator by using multiple processors not only for the purpose of controlling the electrosurgical generator from an output power regulation standpoint, but also for the purpose of checking proper functionality of the processors and their other associated equipment on a general basis. 
     In accordance with these improvements, the present invention involves a method of evaluating the functionality of an electrosurgical generator and the electrosurgical output power delivered by the generator. A first value related to the output power delivered is calculated using a first computation, and a second value related to the output power delivered is calculated using a second computation. The first and second values are compared, and an error condition is indicated when the first and second values differ by a predetermined amount. Preferably, separate measurements of the voltage and current of the power delivered are used in performing the first and second computations, the first and second values are average values calculated over different predetermined periods of time, and the two output current and the output voltage measurements are sampled at different sampling frequencies for calculating the first value with the first computation. The separate computations of the first and second values, coupled with the other preferable separate activities of measuring, averaging and sampling the output current and voltage measurements, contribute an effective basis for cross-checking the proper functionality and power output of the electrosurgical generator, and taking action to prevent risks to the patient from improper power delivery or other improper functionality of the generator under such error conditions. 
     Another method of evaluating the functionality and output power delivered, which also obtains the same benefits and improvements, involves activating the electrosurgical generator to deliver the output power, sensing the current and the voltage at first periodic intervals to obtain a first set of measurements of the current and voltage of the output power delivered, sensing the current and the voltage at second periodic intervals to obtain a second set of measurements of the current and voltage of the output power delivered, recording the first and second sets of measurements, deactivating the electrosurgical generator to terminate the delivery of the output power, calculating a first value related to the output power delivered from the first sets of recorded measurements by executing a first computation with the control processor, calculating a second value related to the output power delivered from the second sets of recorded measurements by executing a second computation with the monitor processor, comparing the calculated first and second values to determine whether the calculated first and second values differ by a predetermined amount, and executing an error response upon determining that the calculated first and second values differ by the predetermined amount. 
     The present invention also involves an improved electrosurgical generator having the capability of evaluating its own functionality and the output power delivered. A plurality of sensors sense current and voltage of the output power delivered and supply current and voltage measurement signals related to the amount of current and voltage sensed. A control processor receives the current and voltage measurement signals and performs a first computation based on the current and voltage measurement signals to derive power regulation feedback information and to derive a first value related to the output power delivered. A monitor processor receives the current and voltage measurement signals and performs a second computation separate from the first computation to derive a second value related to the output power delivered. A communication path connects the control and monitor processors by which to communicate information including the first and second values between the processors. One of the control or monitor processors functions as a comparison processor to execute a comparison procedure for comparing the first and second values and delivering an error condition signal when the first and second values differ by a predetermined amount. The electrosurgical generator responds to an assertion of the error condition signal by either issuing an error indication and/or terminating the delivery of output power. Preferable features of the electrosurgical generator include individual sensors for deriving independent current measurement and independent voltage measurement signals used in the two computations. Another preferable feature of the electrosurgical generator is a direct memory access (DMA) technique of reading digital forms of the current and voltage measurement signals into memory, and thereafter reading those signals from memory to perform the two computations. The separate computations, coupled with the other preferable individual measurements of the output current and voltage, permit the electrosurgical generator to cross-check its own functionality and power output, and to take appropriate action to prevent risks to the patient if a discrepancy is detected. 
     A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a multiple processor electrosurgical generator incorporating the present invention. 
         FIG. 2  is a block diagram of a portion of an RF output section of the electrosurgical generator shown in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating signal and information flow during a output power monitoring by one of the processors of the electrosurgical generator shown in  FIG. 1 . 
         FIG. 4  is a flow chart for a procedure for generating information used for monitoring power output and creating information, executed by the components shown in  FIGS. 2 and 3  of the electrosurgical generator shown in  FIG. 1 . 
         FIG. 5  is a flow chart for a procedure for communicating, analyzing and responding to the information generated by the procedure shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     An electrosurgical generator  20 , shown in  FIG. 1 , supplies electrosurgical output voltage and output current at  22 , which is conducted to an active electrode (not shown) for monopolar and bipolar electrosurgery. Current is returned at  24  to the electrosurgical generator  20  from a return electrode (not shown), after having been conducted through the tissue of the patient. The generator is activated to deliver the electrosurgical output power at  22  by an activation signal supplied at  26 . The activation signal  26  is asserted upon closing a switch on a handpiece (not shown) which supports the active electrode and is held by the surgeon. The activation signal  26  may also be asserted from a conventional foot switch (not shown) which is depressed by foot pressure from the surgeon. 
     The electrosurgical generator  20  includes a system processor  30 , a control processor  32 , and a monitor processor  34 . The system processor  30  generally controls the overall functionality of the electrosurgical generator  20 . The system processor  30  includes nonvolatile memory (not shown) containing programmed instructions to be downloaded to the other processors  32  and  34  to establish the functionality of the control and monitor processors  32  and  34 , as well as the entire functionality of the electrosurgical generator  20 . The processors  30 ,  32  and  34  communicate with each other over a system bus  36 . In general, the system processor  30  supervises and controls, at a high level, the entire electrosurgical generator  20 . 
     The primary functionality of the control processor  32  is to establish and regulate the power delivered from the electrosurgical generator at  22 . The control processor  32  is connected to a high voltage power supply  38 , an RF amplifier  40 , and an RF output section  42 . The high voltage power supply  38  generates a DC operating voltage by rectifying conventional alternating current (AC) power supplied by conventional mains power lines  44 , and delivers the DC operating voltage to the RF amplifier  40  at  46 . The RF amplifier  40  converts the DC operating voltage into monopolar drive signals  50  and bipolar drive signals  52  having an energy content and duty cycle appropriate for the amount of power and the mode of electrosurgical operation which have been selected by the surgeon. The RF output section  42  converts the monopolar and bipolar drive signals  50  and  52  into the RF voltage and current waveforms and supplies those waveforms to the active electrode at  22  as the output power from the electrosurgical generator. 
     The basic function of the monitor processor  34  is to monitor the functionality of the high voltage power supply  38  and the RF output section  42 , as well as to monitor the functions of the system processor  30  and the control processor  32 . If the monitor processor  34  detects a discrepancy in the output electrosurgical energy, or a discrepancy in the expected functionality of the system processor  30  or the control processor  32 , a failure mode is indicated and the monitor processor  34  terminates the delivery of output electrosurgical energy from the electrosurgical generator  20 . 
     The processors  30 ,  32  and  34  are conventional microprocessors, microcontrollers or digital signal processors, all of which are essentially general purpose computers that have been programmed to perform the specific functions of the electrosurgical generator  20 . 
     The electrosurgical generator  20  also includes user input devices  54  which allow the user to select the mode of electrosurgical operation (cut, coagulation or a blend of both) and the desired amount of output power. In general, the input devices  54  are dials and switches that the user manipulates to supply control, mode and other information to the electrosurgical generator. The electrosurgical generator  20  also includes information output displays  56  and indicators  58 . The displays  56  and indicators  58  provide feedback, menu options and performance information to the user. The input devices  54  and the output displays  56  and indicators  58  allow the user to set up and manage the operation of the electrosurgical generator  20 . 
     The activation signals at  26  are applied from the finger and foot switches to an activation port  62 . The system processor  30  reads the activation signals  26  from the port  62  to control the power delivery from the electrosurgical generator  20 . The components  54 ,  56 ,  58  and  62  are connected to and communicate with the system processor  30  by a conventional input/output (I/O) peripheral bus  64 , which is separate from the system bus  36 . 
     In order to continually monitor the power delivered, as well as to achieve a high degree of reliability and redundancy for safety monitoring purposes, the control processor  32  and the monitor processor  34  each independently calculate the power delivered from the RF output section  42 . The independent power calculations are thereafter compared, by at least one of the three processors  30 ,  32  and  34 , and if a discrepancy is noted, the comparing processor signals the system processor  30  of the discrepancy, and the power delivery from the electrosurgical generator  20  is shut down and/or an error is indicated. 
     The power calculations performed by the control processor  32  are part of the normal functionality of the control processor in regulating the output power. The control processor  32  receives an output current signal  70  and an output voltage  72  from the RF output section  42 . The control processor calculates the amount of output power by multiplying the current and voltage signals  70  and  72  to obtain the power output. The monitor processor  34  receives an output current signal  74  and an output voltage signal  76 . The output current and voltage signals  74  and  76  are derived independently of the output current and voltage signals  70  and  72 , by separate current and voltage sensors. The monitor processor  34  calculates the output power based on the output current and voltage signals  74  and  76 . The power-related calculations performed by the control processor  32  and by the monitor processor  34  are not necessarily performed at the same frequency or at exactly the same time, although the power calculations must be sufficiently related in time so as to be comparable to one another. 
     The separately-calculated power related information is periodically compared by one or more of the processors  30 ,  32  or  34 , preferably in either the system processor  30  or the monitor processor  34 . To make the comparison, the calculated power information is communicated over the system bus  36  to the processor which performs the comparison. If the comparison shows similar power calculations within acceptable limits, proper functionality of the electrosurgical generator  20  is indicated. If the comparison shows dissimilar power calculations outside of acceptable limits, safety related issues are indicated. Dissimilar power calculations may indicate that one of the control or monitor processors  32  or  34  is malfunctioning, or some of the components used in connection with the processors are malfunctioning, or a failure in one of the current and voltage sensors which supply the current and voltage signals  70 ,  72 ,  74  and  76 , among other things. In general, the response to an issue indicated by a power calculation discrepancy will result in indication of an error condition and/or the termination of power delivery from the electrosurgical generator  20 . Information will also be supplied to and presented at the displays  56  and indicators  58  describing the error condition. 
     Each of the processors  30 ,  32  and  34  has the capability to exercise control over the delivery of power from the electrosurgical generator. The monitor processor  34  and the system processor  30  assert enable signals  78  and  79  to an AND logic gate  82 . The control processor  30  asserts a drive-defining signal  80  to the logic gate  82 . The drive-defining signal  80  is passed through the logic gate  82  and becomes a drive signal  84  for the RF amplifier  40 , so long as the enable signals  79  and  80  are simultaneously presented to the logic gate  82 . If either the system processor  30  or the monitor processor  34  de-asserts its enable signal  79  or  78 , respectively, the logic gate  82  will terminate the delivery of the drive signal  84 , and the RF amplifier  80  will cease to deliver monopolar and bipolar drive signals  50  and  52 , resulting in terminating the delivery of electrosurgical power from the generator  20  at  22 . Because the control processor  32  develops the drive-defining signal  80  to control the output power of the electrosurgical generator, the control processor  82  can simply de-assert the drive-defining signal  80  to cause the electrosurgical generator to cease delivering output power. Thus, any of the processors  30 ,  32  or  34  as the capability to shut down or terminate the delivery of power from the electrosurgical generator under conditions of significant discrepancies in the independently-calculated power output by de-asserting the signals  79 ,  80  or  82 , respectively. 
     More details concerning the derivation of the output current and output voltage sense signals  70 ,  72 ,  74  and  76  are understood by reference to  FIG. 2 , which illustrates a portion of the RF output section  42  ( FIG. 1 ). The flow path for the monopolar electrosurgical current is through a delivery conductor  86 , through series-connected current sensors  88  and  90 , through relays  92  and to one or more plug connectors  94 ,  96  or  98  which are selected by the relays  92 . The monopolar electrosurgical current flows from the plug connectors  94 ,  96  and  98  to the active electrode at  22 . The return path for the monopolar electrosurgical current is from the electrical return electrode (not shown) at  24  to a return plug connector  100  to which the return electrode (sometimes referred to as a return pad) is connected. The return current flows through a return conductor  102 . Voltage sensors  104  and  106  are connected between the delivery conductor  86  and the return conductor  102  to sense the voltage at which the monopolar electrosurgical output power is delivered. 
     The current sensor  88  delivers the output current sense signal  70  to the control processor  32  ( FIG. 1 ), and the current sensor  90  delivers the output current sense signal  74  to the monitor processor  34  ( FIG. 1 ). In a similar manner, the voltage sensor  104  delivers the output voltage sense signal  72  to the control processor  32  ( FIG. 1 ), and the voltage sensor  106  delivers the output voltage sense signal  76  to the monitor processor  34  ( FIG. 1 ). Arranged in this manner, the current sensors  88  and  90 , and the voltage sensors  104  and  106  supply their own sense signals, independently of sense signals supplied by the other sensors. Any adverse functionality of one of the sensors will not therefore affect the functionality of the other sensors. 
     The flow path of the bipolar electrosurgical current is from a first bipolar delivery conductor  108 , through series-connected current sensors  110  and  112  and to a bipolar output plug connector  114 . The bipolar electrosurgical current flows from the plug connector  114  to the active electrode at  22  and returns from the return electrode at  24 . The return current flows from the bipolar output plug connector  114  through a second bipolar conductor  120 . Voltage sensors  116  and  118  are connected between the first and second bipolar delivery conductors  108  and  120  and therefore sense the voltage at which the bipolar electrosurgical output power is delivered. 
     The current sensor  110  delivers the output current sense signal  70  to the control processor  32  ( FIG. 1 ), and the current sensor  112  delivers the output current sense signal  74  to the monitor processor  34  ( FIG. 1 ). In a similar manner, the voltage sensor  116  delivers the output voltage sense signal  72  to the control processor  32  ( FIG. 1 ), and the voltage sensor  118  delivers the output voltage sense signal  76  to the monitor processor  34  ( FIG. 1 ). Arranged in this manner, the current sensors  110  and  112 , and the voltage sensors  116  and  118  supply their own sense signals, independently of sense signals supplied by the other sensors. Again, adverse functionality of one of the sensors will not therefore affect the functionality of the other sensors. 
     Only one set of the current sense signals  70  and  74  and only one set of the voltage sense signals  72  and  76  will be supplied when the electrosurgical generator is operating in either the monopolar or the bipolar mode. In other words, it is not possible for the electrosurgical generator to operate in both the monopolar and the bipolar mode simultaneously under normal operating conditions. Each of the sensors  116 ,  118 ,  104 ,  106 ,  110 ,  112 ,  88  and  90  is preferably a conventional transformer. 
     The current sense signals  70  and  74 , and the voltage sense signals  72  and  76  are applied to and dealt with by the control processor  32  and the monitor processor  34 , respectively, each in the similar manner shown in  FIG. 3 . The current and voltage sense signals  70  ( 74 ) and  72  ( 76 ) are supplied from the RF output section  42  ( FIGS. 2 and 1 ) to a conventional analog to digital converter (ADC)  122 . The ADC  122  converts the instantaneous values of the analog current and voltage sense signals  70  ( 74 ) and  72  ( 76 ) into sample values at sampling intervals established by control signals supplied by the microprocessor  32  ( 34 ). The sample values of the current and voltage sense signals  70  ( 74 ) and  72  ( 76 ) are stored in a conventional buffer memory  126  at sequential addresses established by a conventional direct memory access (DMA) controller  124 . The ADC  122  and the DMA controller  124  operate on semi-autonomous basis to store the sample values of the current and voltage sense signals in the buffer  126 . One exemplary sampling technique that may be effectively employed in the present invention is described in greater detail in the first above-identified U.S. patent application filed concurrently herewith. 
     After a predetermined number of sample values of the current and voltage sense signals  70  ( 74 ) and  72  ( 76 ) have been stored in the buffer  126 , the microprocessor  32  ( 34 ) reads those values and thereafter calculates power-related information. After reading the values of the current and voltage sense signals from the buffer  126 , the DMA controller  124  replaces those values in the buffer  126  with new values supplied by the ADC  122 . 
     The power-related information is preferably root mean square (RMS) output power or some value related to RMS output power. One preferred technique for calculating the power-related information is for the microprocessor  32  ( 34 ) to square each of the instantaneous sample values of the current and voltage sense signals  70  ( 74 ) and  72  ( 76 ), sum all of the squared current sample values, sum all of the squared voltage sample values, multiply together the sum of the squared voltage sample values and the sum of the squared current sample values, and take the square root of the product obtained from the multiplication. This example of a calculation is not true RMS power, because no step was performed to divide by the number of collected samples. However, the resulting power-related information is directly related to RMS power because the number of samples taken and used in the calculation is the same. Other types of mathematical calculations may be performed to obtain the power-related information in accordance with the present invention. One exemplary to calculation technique for determining power-related information is described in greater detail in the first above-identified U.S. patent application filed concurrently herewith. Other power-related information calculation algorithms can also be employed with the present invention. 
     Calculating power by obtaining a plurality of sample values over a predetermined time effectively integrates the power-related information. This is particularly advantageous in view of the typical manner in which an electrosurgical generator is activated by the surgeon. The typical activation procedure is for the surgeon to depress the finger control switch or step on the foot switch only for a few seconds at a time to perform a series of relatively short and continually repetitive surgical actions during the entire electrosurgical procedure. Collecting samples over a relatively long period of time permits integration and long-time digital filtering of the values resulting from each of these short activations as a type of filtering to eliminate anomalous effects. 
     With similar voltage and current sense signals, the control processor  32  and the monitor processor  34  should each calculate almost the same amount of power. Some small difference between the calculated values may occur due to timing considerations for each of the signals or slight differences in the sensors or in the signal paths for each of the signals. Thus, the comparison looks for the two results to be almost the same within an acceptable tolerance that may be determined empirically. 
     After performing the calculations, the results are stored in a memory  128  or held in the processor performing the calculation. The memory  128  is connected to the system bus  36  so that the results of the calculations stored in the memory  128  can be read by one or more of the other processors which are also connected to the system bus  36 . 
     To perform the comparison of the calculated power-related results, the calculated power-related results are communicated over the system bus  36  to the system processor  30  or to either the control processor  32  or the monitor processor  34  ( FIG. 1 ). Either the system processor  30  or the monitor processor  34  ( FIG. 1 ) should perform the comparison, to obtain a redundancy check on the operation of the control processor  32  ( FIG. 1 ) which must make the calculation to regulate the output power. However, depending upon the capability of the control processor  32 , it may perform the comparison of the power-related information. The processor which performs the comparison, hereinafter referred to as the “comparison processor,” receives the calculated power information from the memory  128  of the control processor  32  and the monitor processor  34  to perform the comparison. 
     An exemplary and more detailed explanation of the process flow or procedure  150  used by the control and monitor processors  32  and  34  to calculate the power-related information from the sampled current and voltage values is shown in  FIG. 4 . The procedure  150  starts at step  152 . At step  154  it is determined whether the electrosurgical generator has been activated, by the delivery of the activation signal  26  ( FIG. 1 ). Until activation, the procedure  150  waits at step  154 . Once activation occurs, either a timer is started or the current time (a start time) is recorded, and shown at step  156 . The processor is able to measure or calculate the duration of the activation. The sample values of the current and voltage signals are collected at step  158  until the electrosurgical generator is determined to be de-activated at step  160 . At step  158 , the ADC  122  converts the analog values of the current and voltage sense signals to their digital sampled values, and the DMA controller  124  stores the instantaneous sampled values generated by the ADC  122  in the buffer memory  126  ( FIG. 3 ). This occurs until the electrosurgical generator is de-activated at step  160  or until the buffer memory  126  is filled with samples. Upon deactivation at step  160 , the collection of the sampled values (data) is stopped at step  162 . Thereafter at step  164 , the timer is stopped or the current time (a stop time) is recorded. 
     If the time duration during which the electrosurgical generator was activated is not within a predetermined window of time, as determined at steps  166  and  168 , then the power-related information calculations are not performed. Instead, the procedure  150  returns to step  154  to wait for the next activation. In this manner, certain common events which typically do not involve the delivery of the electrosurgical power during an actual procedure will not result in an inadvertent, unnecessary shutdown of the electrosurgical generator. For example, some surgeons momentarily short-circuit the output power terminals of the electrosurgical generator to observe an arc as a technique for determining whether the electrosurgical generator is operating. While this is not recommended procedure, it does indicate to the surgeon that the electrosurgical generator is working. Since there is no tissue resistance or impedance, the current and voltage sense signals current and voltage sense signals  70  ( 74 ) and  72  ( 76 ) are anomalous. Such anomalies could cause such a large discrepancy in the calculated power-related information such that, when the comparison is made, an error is detected, when in fact, there was no actual error. Also, either the control processor  32  or the monitor processor  34  may miss part or all of a power delivery event that is too short. In a similar manner, the maximum time duration of the predetermined window of time determined at step  168  is used to obtain accurate samples during the activation time by preventing inordinately long activations of the electrosurgical generator from delivering so many sampled values of the sensed voltage and current to the buffer  126  ( FIG. 3 ) to cause it to overflow. 
     Thus, the predetermined window of time, established at steps  166  and  168 , enables the procedure  150  to prevent an inadvertent shutdown of the electrosurgical generator  20  in anomalous situations. The size of the window is selected based on an empirical data concerning of the typical duration of most electrosurgical procedures, which usually fall within a range of minimum and maximum times (e.g. 0.5-5.0 seconds, respectively). The size of the buffer  126  and the sampling rate of the ADC  122  ( FIG. 3 ) may also define the maximum time limit at step  168  over which data may be collected, although the results of filling numerous buffers may also be accumulated if information is collected over a longer time period. The predetermined window of time is fixed by a minimum time, established at step  166 , and a maximum time, established at step  168 , and these minimum and maximum times define the preferred time frame for which the power-related information is obtained. 
     If the duration of the electrosurgical procedure is within the predetermined window of time, as determined at steps  166  and  168 , then the various calculations for RMS voltage, current and power are performed at step  170 . The power-related results of the calculations are then sent, at step  172 , to the comparison processor to perform the comparison of the results. The procedure  150  then returns to step  154 . 
     As an alternative to determining whether the activation of the electrosurgical generator is within the predetermined window of time at steps  166  and  168 , the RMS calculations may be done by the control and monitor processors regardless of the duration of the activation. In this case, the comparison processor makes a determination of whether to eliminate the comparison if the duration is outside the window. 
     An exemplary and more detailed explanation of a process flow or procedure  200  for making the comparison between the calculated power-related information from the control and monitor processors, and responding, is shown in  FIG. 5 . The procedure  200  starts at step  202 . At step  204  a determination is made whether the electrosurgical generator has been de-activated. So long as deactivation exists, the procedure  200  waits at step  204 . Once activation occurs, the determination at  204  is affirmative, and the calculated power-related information is read from the memories  128  ( FIG. 3 ) of the control processor  32 , at step  206 , and from the memories  128  of the monitor processor  34 , at step  208 , or otherwise supplied by the two calculating processors. If either the control processor or the monitor processor is the comparison processor, it may or may not actually store the results of the power calculations in its associated memory  128 , while performing the procedure  200 . 
     At steps  210  and  212  respectively, it is determined whether the two calculated results are within an acceptable tolerance of each other. If the calculated result (C) from the control processor  32  is not greater than the calculated result (M) from the monitor processor  34  by a predetermined upper range limit, as determined at step  210 , and if the calculated result (C) is not less than the calculated result (M) by a predetermined lower range limit, as determined at step  212 , then the procedure  200  returns to step  204  to wait for the end of the next activation. Negative determination at steps  210  and  212  indicate acceptable functionality. On the other hand, if the two calculated results (C) and (M) are not within an acceptable tolerance of each other, as determined at steps  210  and  212 , then an appropriate error handling procedure is performed at step  214 . 
     The error handling procedure may log or count each occurrence of the error, alert the surgeon, shut down the electrosurgical generator and/or take any other appropriate responsive measures. Counting the occurrence of errors may enable other responsive measures after a certain number or threshold of errors occurs sequentially or some number of errors occurs within a larger number of activations or attempts to activate, for example, 5 errors out of 10 attempted activations. If the error response does not include shutting down the electrosurgical generator, as determined at step  216 , then the procedure  200  returns to step  204  to wait for the end of presently occurring activation. If, on the other hand, the response does include shutting down the electrosurgical generator, as determined at step  216 , then a command to shut down the electrosurgical generator is issued at step  218 , and the procedure  200  ends at step  220 . 
     The present invention offers the improvement and advantage of determining when a sensor fails. In such circumstances, the current or voltage sense signal from the failed sensor will result in a power-related calculation which does not compare favorably with the other power-related calculation, thereby indicating a safety-related issue with the electrosurgical generator. Additionally, the present invention can detect whether there is a failure in certain other components associated with the control and monitor microprocessors. Such a failure would also result in a discrepancy between the calculated results because the failed component will generally not properly pass or handle the value of the voltage and current signals which flow through that failed component. Moreover, should either of the controller or monitor processors fail to execute their programed functionality, such a failure is also likely to be reflected in erroneous calculations of the power-related information. 
     The present invention is particularly advantageous in combination when the monitor processor  34  monitors the mode functionality of the electrosurgical generator  20  ( FIG. 1 ). The second aforementioned patent application describes a mode functionality check incorporated in the electrosurgical generator  20 . In general terms, the mode functionality check involves observing the characteristics of the drive-defining signal  80  supplied by the control processor  32  to determine whether the control processor  32  is delivering the proper pattern of drive signals indicated by the selected mode of operation. If the characteristics of the drive-defining signal  80  are not consistent with the selected mode of operation, the monitor processor  34  terminates the delivery of electrosurgical power. For example, acceptable power calculations could be obtained even though the electrosurgical generator is operating in an incorrect mode. Since a malfunction could cause an error either in the power delivered or the pattern of drive signals relative to the selected mode of operation, checking both the power delivered and the mode information provides an very effective technique for determining the proper operation of the electrosurgical generator. 
     Many other benefits, advantages and improvements in monitoring the proper functionality of the electrosurgical generator will also be apparent upon gaining a full appreciation of the present invention. Thus, the electrosurgical generator can be prevented from operating under conditions which might possibly cause a risk to the patient and under conditions where the output power and performance of the electrosurgical generator is more reliably delivered. 
     Presently preferred embodiments of the invention and its improvements have been described with a degree of particularity. This description has been made by way of preferred example. It should be understood that the scope of the invention is defined by the following claims.