RF303_RS Electrosurgical Analyzer

The load resistors typically used in ESU analyzers are not "ideal". They possess some reactive components that are frequency dependent. The RF303RS derives applied power by measuring the voltage across the set load and calculating the power (V2/R). Most other ESU analyzers on the market derive the applied power by measuring the current flowing through a set load and calculating the power (I2*R). At fundamental frequencies below 500 kHz and regardless of the load setting, the two methods of measurement are comparable. Above 500 kHz, and at the extremes of the loads, the readings displayed by the two methods will differ on opposite sides of the expected value.

As an example, when testing the Conmed Excalibur Electrosurgical Unit in the monopolar output with the RF303RS load set to 50 ?, the set value on the Conmed will correlate with the displayed value on the RF303. When in the Bipolar mode, the RF303RS will display higher than expected values - up to 35% higher. The same test performed on some current measuring analyzers will produce lower than expected values. This is due to the difference in fundamental frequencies between the monopolar and bipolar modes. In this case, the Conmed operates at 500 kHz in monopolar mode and 1 MHz in bipolar mode. When comparing readings measured with a V2/R device to readings measured with an I2*R device, total measurement difference will likely be larger than 35%, due to different methods of deriving power.

This does not mean that the RF303RS is malfunctioning or in error. Rather, it reflects the different results the two measurement techniques will produce when the load deviates from the nominal value used in the power calculations. It should be noted that most ESU manufacturers use the current measuring technique to calibrate production units.

This characteristic does not affect Electrosurgical Units that operate with a fundamental frequency less than 500 kHz, such as ValleyLab electrosurgical units.