Valleylab SurgiStat II, Руководство по обслуживанию, Страница: 49 / 82

Theory Of Operation
SurgiStat II Service Manual 4-3
DC Supply Check Circuit
System logic uses the DC supply check circuit to monitor the high voltage DC
supply. If the voltage increases by 30%, the system displays error code E4 and
disables the RF output.
For isolation purposes, the high voltage sense voltage is measured from the 15-
volt DC power supply.
Temperature Sensing Circuit
System logic uses the temperature sensing circuit to monitor the internal
temperature of the unit. If the temperature rises above 85° C (185° F), the system
displays error code E7 and disables the RF output.
Four Request Activation Sensing Circuits
System logic uses the activation request sensing circuit to detect both hand-
controlled and foot-controlled activation requests. This circuit consists of a
Colpitts Oscillator (operating at approximately 50 kHz) and a level detection
circuit.
In a nonactivation status, the Colpitts oscillator operates at its set operating
frequency and presents a sine wave to the level detection circuit. The level
detection circuit converts the sine wave into a square wave. Activation will not
occur as long as a square wave is present.
When a resistance (approximately 200
Ω
or less) is presented to the transformer’s
secondary winding by a hand-control or foot-control, the sense transformer is
essentially shorted. The “short” is felt on the transformer’s primary winding,
causing the Colpitts oscillator to temporarily shut down.
When the oscillator shuts down, the sense signal b5 VDC (logic “1”).
This informs the system logic that a handswitch or footswitch activation request
has been made.
If the square wave (from any of the request sense circuits) is not present at the
system logic when the unit is initially turned on, the system displays an error
code, sounds an alarm, and disables RF output.
Speaker Circuit
System logic uses the audio circuit to generate activation tones and alarm tones.
You can adjust volume for the activation tones from the back panel of the unit.
Notice
You cannot adjust alarm volume up or down.