Abstract:
The functionality and the mode of operation are evaluated in an electrosurgical generator by determining whether a patterned pulse signal that contributes to the generation of electrosurgical energy is as expected. A number of pulses in the patterned pulse signal is compared to an expected number of pulses, and an error condition is indicated when the two values are not the same or differ by more than a predetermined amount. The expected number of pulses depends on a mode of operation of the electrosurgical generator. The error condition may be used to as a basis to terminate the output power delivery.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This invention and application is related to an invention for an Electrosurgical Generator and Method for Cross-Checking Output Power, described in U.S. patent application Serial No. (24.345), and to an invention for Electrosurgical Generator and Method with Multiple Semi-Autonomously-Executable Functions, described in U.S. patent application Serial No. (24.346), which are filed concurrently herewith and assigned to the assignee of the present invention. The subject matter of these concurrently filed applications is incorporated herein by this reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention generally relates to electrosurgery. More specifically, the invention relates to a new and improved electrosurgical generator and method that checks the mode of operation of the electrosurgical generator to assure proper functionality of the electrosurgical generator and that the desired electrosurgical clinical effect is delivered during the surgical procedure.  
         BACKGROUND OF THE INVENTION  
         [0003]    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.  
           [0004]    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.  
           [0005]    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.  
           [0006]    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.  
           [0007]    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.  
           [0008]    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.  
           [0009]    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 monitoring processors.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention has evolved from a desire to achieve a high degree of reliability for monitoring purposes in a multiple-processor electrosurgical generator that delivers electrosurgical energy for surgical procedures. A control processor generates a patterned pulse signal that defines a pattern of pulses that is used to generate output electrosurgical energy. A monitor processor receives the patterned pulse signal and a mode signal indicative of activation of a selected mode of operation of the electrosurgical generator. To determine whether the electrosurgical generator is functioning in the proper selected mode, the monitor processor counts the number of pulses in the patterned pulse signal and compares it to an expected number of pulses for the selected mode. If the counted number of pulses is the same as, or within an acceptable range of, the expected number of pulses, then the monitor processor determines that the electrosurgical generator is functioning in the selected mode. If the counted number of pulses is not the same as, or not within the acceptable range of, the expected number of pulses, then the monitor processor may take appropriate action, such as issuing an error indication to the surgeon and/or causing the electrosurgical generator to terminate delivery of the electrosurgical energy or to shut down.  
           [0011]    In accordance with these improvements, the present invention involves a method of evaluating functionality of an electrosurgical generator. A patterned pulse signal is generated having a plurality of drive pulses. The patterned pulse signal is a signal with which the electrosurgical output power is generated. A number of the drive pulses in the patterned pulse signal is counted. The counted number of drive pulses is compared to an expected number of drive pulses. An error condition is indicated when the counted number of drive pulses and the expected number of drive pulses differ by a predetermined amount, which may preferably be one or more. Additionally, the electrosurgical output power is preferably controlled by adjusting a width of the drive pulses, for which a minimum width may be established. Furthermore, when the width of the drive pulses is about at the minimum width, the patterned pulse signal may preferably still be generated. Also, the method may preferably be combined with performing a power-related check on the electrosurgical output power, and indicating an error condition when a calculated power level is outside of a predetermined range.  
           [0012]    Alternatively, the present invention involves a method of evaluating functionality of an electrosurgical generator which delivers electrosurgical output power under a plurality of modes of operation. One of the modes of operation under which the electrosurgical generator is to deliver the electrosurgical output power is indicated. The electrosurgical output power is generated by generating a patterned pulse signal in accordance with the indicated mode of operation. The patterned pulse signal is detected. It is determined from the patterned pulse signal whether the electrosurgical output power is being generated according to the indicated mode of operation. An error condition is then indicated when it is determined that the electrosurgical output power is not being generated according to the indicated mode of operation.  
           [0013]    Additionally, the present invention involves an electrosurgical generator which delivers electrosurgical output power according to a selected mode signal. The electrosurgical generator includes a control processor and a monitor processor. The control processor generates a patterned pulse signal in accordance with the selected mode signal. The patterned pulse signal includes a series of drive pulses which contribute to generating the electrosurgical output power. The monitor processor is connected to the control processor and receives the patterned pulse signal, counts a number of the drive pulses in the patterned pulse signal, determines an expected number of drive pulses in accordance with the selected mode signal, compares the counted number of drive pulses with the expected number of drive pulses and indicates an error condition when the counted number of drive pulses and the expected number of drive pulses differ by a predetermined amount. The electrosurgical generator responds to the indication of the error condition by either issuing an error indication or terminating the delivery of output power.  
           [0014]    A more complete appreciation of the present invention and its scope, and the manner in which it achieves the above noted and other 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  
       [0015]    [0015]FIG. 1 is a block diagram of a multiple processor electrosurgical generator incorporating the present invention.  
         [0016]    [0016]FIGS. 2, 3 and  4  are waveforms generated in the electrosurgical generator shown in FIG. 1.  
         [0017]    [0017]FIG. 5 is a flow chart for a procedure for verifying a mode of operation of the electrosurgical generator shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0018]    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  20  is activated to deliver the electrosurgical output power at  22  by activation signals supplied at  26 . The activation signal at  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 at  26  may also be asserted from a conventional foot pedal switch (not shown) which is depressed by foot pressure from the surgeon.  
         [0019]    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 . 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 . Thus, the system processor  30  supplies a power supply enable signal  37  to the high voltage power supply  38  to enable the high voltage power supply  38 . The system processor  30  also supplies an output select signal at  39  to the RF output section  42 . The output select signal at  39  causes the RF output section  42  to output the desired electrosurgical energy at  22  to a selected handpiece (not shown) connected to an output connector (not shown) for monopolar or bipolar electrosurgery.  
         [0020]    The primary functionality of the control processor  32  is to establish and regulate the power delivered from the electrosurgical generator  20  at  22 . The control processor 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 control processor  32  sets the voltage level for the DC operating voltage at  46  by a voltage-set signal at  48  supplied to the high voltage power supply  38 . 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  20 .  
         [0021]    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 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 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 .  
         [0022]    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 .  
         [0023]    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 .  
         [0024]    The activation signals at  26  are applied from the finger and foot switches (not shown) to an activation port  62 . The system processor  30  reads the activation signals at  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 .  
         [0025]    To generate the electrosurgical energy at  22 , the control processor  32  sets the voltage level of the DC operating voltage output at  46  from the high voltage power supply  38  by the voltage set signal at  48 . The control processor  32  then generates a patterned pulse signal at  66  and sends it to an enable AND logic gate  68 , where the patterned pulse signal at  66  is logically ANDed with enable signals  70  and  72  supplied by the system processor  30  and the monitor processor  34 , respectively. The output of the enable logic gate  68  is supplied to a line driver  76  and a receiver  78  in series. The output of the line driver  76  and the receiver  78  forms a power driving signal at  80 . The power driving signal at  80  is supplied to the RF amplifier  40 . The RF amplifier  40  converts the DC operating voltage at  46  into the monopolar and bipolar drive signals at  50  and  52  according to the power driving signal at  80  formed from the patterned pulse signal at  66  output by the control processor  32 . The output select signal at  39  from the system processor  30  then causes the RF output section  42  to output either the monopolar or bipolar drive signal at  50  or  52  as the electrosurgical energy at  22  to the selected handpiece (not shown).  
         [0026]    The line driver  76  is preferably a conventional op amp. The line driver  76  and receiver  78  preferably isolate the high-voltage electronics of the RF amplifier  40  from the system, control and monitor processors  30 ,  32  and  34 .  
         [0027]    To shut down the electrosurgical generator  20  or to terminate the delivery of power from the electrosurgical generator  20 , the monitor processor  34  deasserts the monitor enable signal  72  and/or the system processor  30  deasserts the amplifier enable signal  70 . The assertion of both enable signals  70  and  72  to the enable logic gate  68  are required for the formation of the power driving signal at  80  from the patterned pulse signal at  66  through the enable logic gate  68 , the line driver  76  and the receiver  78 . Deasserting either one of the enable signals  70  or  72  prevents the enable logic gate  68  from conducting the patterned pulse signal at  66  through to the line driver  76  and the receiver  78  to form the power driving signal at  80  supplied to the RF amplifier  40 . Without the assertion of the power driving signal at  80 , the RF amplifier  40  will not deliver the monopolar or bipolar drive signals at  50  and  52  to the RF output section  42 , and the electrosurgical generator  20  will not deliver output power or will terminate the delivery of output power.  
         [0028]    The patterned pulse signal at  66  is generally a waveform (e.g.  92 ,  94  and  96 , shown in FIGS. 2, 3 and  4 ) formed of a patterned series of drive pulses  98  within a drive cycle  100  that repeats continuously during the selected mode of operation. The waveforms  92 ,  94  and  96  are examples for cut, coagulation and blend modes of operation, respectively. The pattern of the drive pulses  98 , including the time width of each drive cycle  100 , is fixed by the system processor  30  in accordance with the selected mode of operation. In most cases, the time width of each drive cycle  100  is approximately the same for the cut, coagulation and blend modes of operation, but the pattern of the drive pulses  98  within the drive cycles  100  are different, as shown in FIGS.  2 - 4 .  
         [0029]    A continuous uninterrupted sequence of the drive pulses  98  defines the cut pattern (waveform  92 ), as shown in FIG. 2. A repeating duty cycle application of the drive pulses  98  defines the coagulation pattern (waveform  94 ) and the blend pattern (waveform  96 ), as shown in FIGS. 3 and 4, respectively. In other words, no drive pulses  98  are delivered for an “off” time  102  during part of the drive cycle  100 . Other specialized modes of operation exist as subsets of these three basic modes, and the amounts of coagulation in the coagulation mode and of cutting and coagulation in the blend mode is varied by adjusting the duty cycle of the drive cycle  100 . Once the mode is selected, the pattern of drive pulses  98  defined by that selected mode remains unchanged until a different mode is selected. The width of the drive pulses  98 , however, may be changed longer or shorter throughout the surgical procedure in order to regulate the output power.  
         [0030]    The energy level in the output power at  22  (FIG. 1) is established by the width of the drive pulses  98  and the voltage of the high voltage power supply  38  (FIG. 1). The width of each drive pulse  98  is established by a number of equal-width steps dependent on the period of the clock (not shown) of the control processor  32  (FIG. 1). The number of equal-width steps is established by a pulse width count, which is initially set by the system processor  30  as representing the desired initial pulse width of the drive pulses  98 . The amount of power transferred by the RF amplifier  40  (FIG. 1) in response to each drive pulse  98  is directly related to the width of each drive pulse  98 . Thus, the width of the drive pulses  98  is increased and decreased in order to regulate the power output during each electrosurgical procedure.  
         [0031]    In order to monitor, or check, the mode of operation, as well as to achieve a high degree of reliability for monitoring purposes, the monitor processor  34  (FIG. 1) receives mode information, or a mode signal, from the system processor  30  (FIG. 1) through the system bus  36  (FIG. 1), and the patterned pulse signal at  66  (FIG. 1) from the control processor  32  (FIG. 1). The mode signal received by the monitor processor  34  includes information regarding the pattern of the drive pulses  98  (FIGS.  2 - 4 ) for the patterned pulse signal  66  generated by the control processor  32 . Thus, the monitor processor  34  has information regarding the expected number of pulses that should be in the patterned pulse signal at  66  in a given amount of time. The monitor processor  34  counts the drive pulses  98  (e.g. typically on the rising edge of each drive pulse  98 ) in the patterned pulse signal at  66  in the given amount of time and compares the number of drive pulses  98  counted with the number of drive pulses  98  expected. If the difference between the counted and expected number of drive pulses  98  is within an acceptable limit, then it is confirmed that the electrosurgical generator  20  is functioning in the proper mode of operation. Otherwise, if the difference is greater than the acceptable limit, then an error or failure condition is indicated and the monitor processor  34  takes appropriate action, such as causing the electrosurgical generator  20  to issue an error indication, to stop producing the electrosurgical energy and/or to shut down.  
         [0032]    The time period during which the monitor processor  34  (FIG. 1) counts the drive pulses  98  (FIGS.  2 - 4 ) is preferably longer than one drive cycle  100 . Additionally, the counting time period is preferably long enough to minimize potential counting errors that may result due to the lack of clock synchronization between the control processor  32  (FIG. 1), which generates the drive pulses  98 , and the monitor processor  34  (FIG. 1), which counts the drive pulses  98 . An acceptable counting time period is about two to three of the drive cycles  100  or more.  
         [0033]    The comparison of the counted and expected number of drive pulses  98  (FIGS.  2 - 4 ) allows the difference between the counted and expected number of drive pulses  98  to be within an acceptable limit, or range, since the monitor processor  34  (FIG. 1) may not be synchronized with the operation of the control processor  32  (FIG. 1), particularly since the control and monitor processors  32  and  34  may not operate at the same clock speed. Thus, some error between the counted and expected number of drive pulses  98  may be expected and taken into consideration.  
         [0034]    A procedure  104  performed by the monitor processor  34  (FIG. 1) for checking the mode of operation is shown in FIG. 5. The mode checking procedure  104  starts at  106  and waits for activation of the electrosurgical energy at  108 . Such activation is generally indicated to the monitor processor  34  by the system processor  30  (FIG. 1) in response to the activation signal at  26  being supplied to the system processor  30 . The selected mode of operation is then determined at  110  according to the mode information provided from the system processor  30  to the monitor processor  34 . Alternatively, the pattern or number of the drive pulses  98  (FIGS. 2, 3 and  4 ) is supplied to the monitor processor  34  in the mode information. The drive pulses  98 , or pulse edges, are then counted in the counting time period at  112 . Then it is determined at  114  whether the time length of the indicated activation is greater than the counting time period. If not, then it is assumed that the activation ended before the counting completed at  112 , so the count is invalid and cannot be used to verify the mode of operation. Therefore, the count is cleared at  116 , and the mode check procedure  104  returns to  108  to wait for the next activation. On the other hand, if the time length of the indicated activation is greater than the counting time period, as determined at  114 , then the count is valid. In this case, the difference between the number of counted drive pulses  98  and the number of expected pulses is calculated at  118 . The number of expected pulses depends on the selected mode determined at  110  or the pattern, or number, of pulses indicated in the mode information. It is then determined at  120  whether the absolute value of the difference calculated at  118  is greater than an acceptable limit. The acceptable limit is preferably determined empirically and depends on the selected mode. If the absolute value of the difference calculated is greater than the acceptable limit, as determined at  120 , then an error is declared at  122  and the mode check procedure  104  ends at  124 . On the other hand, if the absolute value of the difference calculated is not greater than the acceptable limit, as determined at  120 , then the count is cleared at  116  and the mode check procedure  104  returns to  108  to wait for the next activation.  
         [0035]    The control processor  32  (FIG. 1) is preferably programmed such that, to reduce the power output to almost zero, the width of the drive pulses  98  (FIGS.  2 - 4 ) of the patterned pulse signal at  66  (FIG. 1) is not decreased to zero, but to a minimum width. At the minimum width, attenuation properties of the line driver  76  and receiver  78  (FIG. 1) render them unable to pass the drive pulses  98  of the patterned pulse, signal applied at  66 , when received through the enable AND logic gate  68  (FIG. 1). Thus, the minimum width of the drive pulses  98  results in the delivery of no power driving signal at  80 , (FIG. 1), which results in no output power from the RF amplifier  40 . In this case, since the drive pulses  98  of the patterned pulse signal  66  have not been reduced to zero, but remain at minimally narrow widths, the mode check can still be performed. In other words, the minimum width of the drive pulses  98  enables the mode check performed by the monitor  15 , processor  34  (FIG. 1) to be able to determine that the electrosurgical generator  20  is operating in the proper mode, even when no power is being output.  
         [0036]    Additionally, rather than basing the mode check on an acceptable limit for the difference between the counted and expected number of drive pulses  98  (FIGS.  2 - 4 ), as determined at  120  (FIG. 5) of the mode check procedure  104  (FIG. 5), the mode check could require the counted and expected number of drive pulses  98  to be identical. Alternatively, the acceptable limit for the difference may be based on a percentage of the expected number of drive pulses, wherein the percentage is empirically determined for each mode of operation.  
         [0037]    The present invention is particularly advantageous in a situation where the monitor processor  34  (FIG. 1) also monitors the power output of the electrosurgical generator  20  (FIG. 1) using a power-related check. The first aforementioned patent application describes a power-related check, or monitoring function, incorporated in the electrosurgical generator  20 . The monitor processor  34  receives current and voltage feedback signals  126  and  128  (FIG. 1) from the RF output section  42  (FIG. 1) indicating the current and voltage of the output electrosurgical energy, from which the power level can be calculated. The control processor  32  (FIG. 1) also receives current and voltage feedback signals  130  and  132  (FIG. 1) from the RF output section  42  separately indicating the current and voltage of the output electrosurgical energy, from which the power level can be separately calculated. The power-related check may, thus, ensure that the electrosurgical generator is functioning with the proper power output level given the desired mode of operation and/or that the control processor  32  and the monitor processor  34  have both calculated about the same power output level, as described in the first aforementioned application. However, there are situations in which the power-related checks may not produce a correct failure or non-failure indication. For example, the power-related checks have no data on which to base the checks if the power output is at or near zero, which can occur often in normal non-failure electrosurgical situations, as well as in failure conditions. As described above, however, the minimum pulse width enables the mode check to confirm whether the electrosurgical generator is at least functioning in the proper mode, so that a failure condition can be avoided when one is not actually indicated.  
         [0038]    Additionally, given the large number and range of modes of operation in electrosurgery, and since there may be a considerable range of allowable power levels for each mode of operation, a proper power output for one mode may resemble a proper power output for a different mode. Thus, the power-related check may determine that the output power is proper for the intended mode of operation and that, no error has occurred, even when an error has, in fact, occurred that has caused the electrosurgical generator  20  to operate in the wrong mode. The mode check, though, would detect such a failure.  
         [0039]    Thus, the mode check performed by the present invention can detect an error condition that power-related checks cannot detect and can avoid an error condition when power-related checks cannot be performed. The mode check may serve as a backup check for power-related checks.  
         [0040]    On the other hand, the power-related check described in the first aforementioned application can detect errors that cannot be detected by the present invention. For instance, even if the mode check determines that electrosurgical generator  20  (FIG. 1) is delivering the electrosurgical energy in the selected mode of operation, it is still necessary to further determine whether the power level of the electrosurgical energy is within an acceptable range. Thus, the monitor processor  34  (FIG. 1) calculates the power output from the current and voltage feedback signals  126  and  128  (FIG. 1) from the RF output section  42  (FIG. 1) and determines whether the power output level is within the acceptable range, dependent on the mode of operation, as described in the first aforementioned application.  
         [0041]    The present invention offers the improvement and advantage of being able to determine whether a failure condition has occurred in many situations where other checks cannot. The electrosurgical generator can be prevented from operating under conditions which might possibly cause a risk to the patient and can be assured of operating under conditions where the output power and performance of the electrosurgical generator is more reliably delivered. 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.  
         [0042]    Presently preferred embodiments of the invention 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, and should not be unnecessarily limited by the detailed description of the preferred embodiments set forth above.