Valleylab Force FX-C - Instant Response Algorithm

Control Board
These tests detect stuck or aberrant sensors and improperly delivered
power in all modes. The dosage error firmware executes in less than one
second.
Instant Response Algorithm
This mode is a closed loop control algorithm implemented in
microcontroller firmware. It is applied to the bipolar modes and the cut
modes. It is not applied to the wag modes.
As tissue impedance increases from short circuit to open circuit, the
algorithm implements first constant current, then constant power, and
finally, constant voltage. The maximum output voltage is controlled to
reduce capacitive coupling, reduce video interference, and eliminate
sparking. At low impedances, constant current protects output circuitry.
At high impedances, constant voltage control limits arcing and
electromagnetic interference.
Constant current: output voltage is held at constant output current
according to
1= (p /R) A(1/2)
where I is the output current, P is the power set by the user, and R is the
cons1.:,nt current to constant power impedance switchpoint.
Constant power: the power set by the user is maintained.
Constant voltage: the output voltage is maintained according to
v = (P*R) A(ll2)
where V is the output voltage, P is the pmver set by the user, and R is the
constant power to constant voltage impedance switchpoint.
High Impedance Operation
The firmware algorithm clamps the output voltage to levels for
high impedance conditions. The clamp level is a function of the mode that
is activated. This helps prevent arcing and electromagnetic interference.
Analog to Digital Saturation
Analog to digital saturation works in conjunction with RF leakage current
limiting. If the analog to digital converter is saturated, the effect ulOdc
feedback loop reduces the output voltage to allow for an unsaturated
operating condition. The feedback loop switches the control function to
m<1intaining the cillalOg to digital converter in the linear operating range.
Force F)(TM-C Service Manual 4-11