
B-70315EN/02 APPENDIX F.CONTROL SEQUENCES IN LASER OSCILLATOR
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[SQ291] When the discharge start switch (HVON) is turned on, a high voltage
is applied to the discharge tube, and voltage control is started. The
command induces discharge by changing the command value in a
ramp manner to the value set in PRM No. 15220 (discharge start
command value). The time required to reach the value set in PRM No.
15220 after the discharge start switch (HVON) is turned on is 6
seconds.
[SQ292] In this sequence, discharge is maintained at the discharge command
value set in PRM 15220 for the period of time set in PRM 15222
(discharge start wait time). Here all the tubes must be in discharge.
The state of discharge is checked by comparing tube voltage with
discharge start voltage (PRM 15221).
[SQ293] When discharge start is confirmed in SQ292, power command
changes to PRM 15223 (bias command).Here base discharge is
established for a while and the comparison between discharge tube
voltage and PRM 15270 (tube voltage in normal discharge) is done
using the following decision equation.
V
n-1
- V
n
< PRM.No.15272
V
n-1
: PRM.No.15270 (tube voltage in normal discharge)
V
n
: monitored voltage of the tube of the smallest number
(power supply)
PRM.No.15272 : Tube voltage decrease limit
The decision of normal state is given by the holding of the above
inequality. When normal, monitored voltage of Vn tube is set for
PRM15270. If PRM15000#4 is 0 (no power compensation) then, laser
enters oscillation preparation completion (LSTR) state.
[SQ294] When normal base discharge is confirmed and PRM15000#4 is 1, this
sequence begins to obtain power calibration coefficient. Power
calibration is to calibrate so that real and command powers become
equal. The equation used is as follows.
PRM.No.15204 = Pc / Pa ×1024
PRM.No.15204 : Power calibration coefficient
Pc : Command power
Pa : Actual power
The calibration coefficient is calculated by outputting the value
specified with PRM 15200 (when half of the discharge tubes are used)
or PRM 15201 (when all the discharge tubes are used) then assigning
that value to the above equation.
The value of Pa becomes an actual value measured after the time set in
PRM 15205 (compensation time setting) has elapsed.
The difference between the specified power and actual power is also
monitored. The laser is judged as being normal provided the
difference is less than the value specified with PRM 15271(power
decrease limit).The calibration coefficient is clamped to the value
specified for PRM 15203 (power calibration limit). Once the above
procedure has terminated normally, the laser enters the oscillation
preparation completion (LSTR) state.