Ohmeda Giraffe Spot PT Lite Maintenance Service Manual

Contents

Ohmeda Giraffe Spot PT Lite Maintenance Service Manual Manual pdf 15 page image

Service5-1 6600-0361-000 08/10/02 5-1Functional DescriptionThe Giraffe Spot Phototherapy Lite consists of three printed circuit assemblies (PCA), several peripheralcomponents and an arc lamp. Power enters through an IEC320 receptacle line filter assembly. The line filter,along with a clamp-on ferrite bead that is located on the harness immediately after the line filter, providefiltering of both the phase and neutral lines for compliance with various agency approvals. The phase andneutral line then pass through circuit breakers for protection in the event of a device failure. After the circuitbreaker, the phase and neutral are connected to the power switch. The output of the power switch is con-nected to the power supply PCA. The power supply is a universal input (90-264 VAC 50/60 Hz) switchingpower supply. The supply outputs +12VDC + 5%. This voltage is not adjustable. The output of the powersupply is applied to the remaining two PCAs. The remaining two PCAs are the ballast and indicator board.These two boards work interactively to properly light and monitor the operation of the bulb. A description of theignition and operation of the lamp follows below.The bulb in this product is an arc lamp. To light the lamp a high voltage must be applied across the anode andcathode of the lamp. Once the arc has occurred a low voltage but higher current will fully sustain the arc. Theenergy input into the lamp causes the chemicals inside the lamp to excite causing them to emit a high intensitylight. The ballast converts the incoming 12 volts to a minimum 10.5 kilovolt pulses. The ballast s circuitrydetects the presence of an arc and then outputs 52 volts + 6 volts to the bulb. If no arc is detected, thecircuitry shuts down until power is cycled.The ballast takes in a remote on/off control signal that is sent from the indicator board and outputs a lampstatus signal to the indicator board. The indicator board utilizes the on/off control line to turn off the lamp in theevent of an over-temperature condition. A remote off-board thermostat is used to sense when an over-temperature condition occurs. The thermostat is normally closed and opens during an over-temperaturecondition. In normal operation, the thermostat is closed, the over-temperature LED is off and the ballastcontrol signal is low (<0.5 volts), which turns the ballast on. In an over-temperature condition, the thermostat isopen, and the over-temperature LED signal to the ballast control is high (>2.7 volts), which turns off the ballast.The lamp status signal from the ballast is converted to a 12 volt referenced signal to control the counting of thehour meter. If a fault is detected by the ballast, or if the ballast is turned off due to over-temperature condi-tions, the lamp status signal will go low, causing the hour meter to stop counting. A flashing hour glass on thedisplay of the hour meter indicates that the hour meter is counting. When in the stop counting mode, theelapsed hours will be displayed, but the flashing hour glass will not occur.Due to the large current (approximately 5 amperes) required by the ballast, the ballast and the indicator boardare connected in parallel to the power supply. The 12 volt supply for the hour meter and the two cooling fans ispassed directly through the indicator board. In addition the indicator board contains a power indicator LED.When power is applied to the device regardless of the lamp status the power indicator will light, the fans willoperate, and the hour meter display will light.