THEORY OF OPERATION
4-11
Versapulse Select Service Manual
0621-499-01 01/94
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1 MSEC TIMER - At 1 millisecond intervals an interrupt request is asserted by the timer. The main
processor uses this interrupt to increment/decrement various registers used to time events, such as
the Inactivity and Main Program Dead Timers.
INTEGRATE - The INTEGRATE signal controls the operation of the three energy monitor circuits.
When this signal is low, the energy monitor circuits are activated to translate the energy measured by
the pyrodetector into a voltage, and then to hold that voltage until the microprocessor reads it. When
the INTEGRATE signal goes high the energy monitor circuits are turned off and reset to prepare
them for measuring the next pulse. The timer is used to provide a precise starting point for enabling
the energy monitor circuits approximately 100 µseconds after the fire pulse goes low.
Before a fire pulse, the INTEGRATE signal is high, and the TAI (timer A input) line is high. The /
FIREPULSE/ signal is a very short low pulse that will cause the flip flop formed by U59- 6 and U59-3
to change states, driving the TAI line low. The TAI line high to low transition is the input that
triggers the start of a timing cycle in the programmable timer TA channel. After the timed delay, the
TA timer TAO output goes high, driving the INTEGRATE line low through U59-11 to enable the
energy monitor circuits. After the main processor and safety processor have read the energy monitor
circuits, the main processor resets the TA timer, setting the INTEGRATE line back to a high.
COMMUNICATION TIMING - The SI and SO lines may be used in the future to provide timing
functions to an RS 232 port.
4.4.3 Shutter / Footswitch / Remote Interlock Circuits
The operation of the Shutter, Footswitch, and Remote Interlock circuits are related.
Remote Interlock refers to an external electrical jack that can be wired to a remote switch to disable
the laser. If this loop is opened the laser is disabled and a BRH OPEN message appears on the touch
screen. A dummy plug is supplied to directly connect across the loop if the customer does not wire
to a remote switch. The jack is located on the system back panel.
The Footswitch is a foot operated SPDT switch and 12 foot cable. The user depresses the footswitch
to fire the laser. The footswitch cable plugs into a jack on the back panel.
The Shutter is a solenoid operated mechanism that blocks the treatment beam path when the
solenoid is energized, directing the beam into a water cooled beam dump. The shutter moves out of
the beam path when the solenoid is energized. The main processor operates the shutter through one
of its digital I/O ports. The safety processor can force the shutter closed with its /NOFIRE/ signal.
The beam is blocked when the shutter solenoid is de-energized. Energizing the solenoid moves the
shutter out of the beam path. The position of the shutter is monitored by two slotted optical switches.
The switch outputs are monitored by the main processor digital I/O and by the safety processor.
Refer to the Shutter/Footswitch/Remote Interlock Circuits Simplified Diagram (Figure 4.2) and to the
associated schematics in Section 8. The footswitch is connected to the 24 VDC ground through J12-2 on the
Shutter PCB. When the footswitch is not depressed, the ground is applied to the N.C. return (J12-1) and the
N.O. line is open. Note that the N.C. and N.O. lines are both sensed by the main processor and safety proces-
sor as digital I/O inputs, through opto-isolators. In this manner the processors can monitor the footswitch
status.
12/95
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