Sensor Circuit - Covidien ForceTriad Service Manual

RF PCBA Principles of Operation
between the two. If this voltage exceeds a limit, the RF is folded back to prevent excess
leakage current.

Sensor Circuit

The sensor circuit provides RF output voltage and current monitoring to software in order
to deliver the correct energy dosage during a surgical procedure. Two identical sensory
circuit paths, composed of a primary and backup, are implemented to provide fail-safe
mitigation in the event of circuit failure.
Because each primary and backup sensor circuit mirrors the other, the sensed output
voltages, which are monitored by software, are equal when the sensory system maintains
proper operation. In the event of a failure of the primary or backup sense circuit,
dissimilar outputs are present and software detection stops delivery of RF. The user is
notified with an error message displayed on the front panel of the ForceTriad energy
platform.
Each primary and backup sensory circuit consists of four processing elements to ensure
that the correct RF is delivered. In the description that follows, the primary sensory path is
identified for the voltage-sense circuitry, with reference designation only provided to the
backup circuit.
Backup-circuit operation is identical to the primary circuit that is described here. RF
current-sense circuit process is symmetrical to the voltage-sense description in that it also
uses four processing elements. The only notable difference between voltage and current
sensing is the different transfer gains required to adequately address the dynamic range
of individual system operating modes.
First: Transformer T6, along with resistors R110 and R119, provide RF output voltage
monitoring by generating a proportionately scaled, secondary-sense voltage, which is
correlated to the delivered RF output voltage. Backup referenced components are T1,
R95, and R111.
Second: Coupled to the secondary of transformer T6, a software-controlled switched-
pad network is implemented to provide proper impedance scaling to address the
dynamic sensory range required for all operating modes of the system.
This pad-impedance switched network is used to develop the proportionately scaled
secondary sense voltage of T6. Resistors R103 and R107 provide the initial impedance
termination, paralleled by resistor-paired components R104 and R105, R94 and R106,
and R85 and R100, which are switched independent on the selected system cut, blend,
and coag operating modes respectively.
Paired-resistor switching is accomplished by electronic-switch components RL12, RL11,
and RL10 respectively. Backup referenced-terminating components are R89 and R93;
paired components are R90 and R91, R88 and R92, and R81 and R84; and switch
components are RL9, RL8, and RL7, which are used respectively.
Third: The Pad network output of T6 is then differentially fed to a gain control module,
U18, which provides continuous gain control to normalize the sensed voltage output,
independent of system operating modes and delivered RF power levels.
Amplifier, U19, buffers the signal received from software which is used to precisely
control the gain of U18, while amplifier U17 provides a scaled differential-output voltage,
ForceTriad Energy Platform Service Manual 3-7