Tradition and Innovation
OCTOPUS 300 Service Manual
Page 13 / 64
5.2.1
Current Control
Two current reference values (operating points) are ascertained during the stimulus calibration procedure:
Operating point OP1:
0dB
(max. stimulus intensity)
Operating point OP2:
20dB
(max. stimulus intensity/100)
Thus the entire dynamic range is divided into two segments:
Segment 1 / operating point OP1:
20dB ... 0dB
Segment 2 / operating point OP2:
40dB ... 20dB
I (LED) OP1
I (LED) OP2
I (LED)
L (asb)
L
min
= 40dB L
max
/100 = 20dB L
max
= 0dB
Operating point 1
Operating point 2
Figure 5-3:
Stimulus LED current control
5.2.2
Pulse-width Modulation
A typical stimulus of 100ms duration is formed by a burst of 20 5ms pulses. The width (ratio LED switch-on/LED switch-off time) of
the 20 pulses can be increased or decreased by processor control in steps of 0.4
s (12'500 steps for 5ms). With a longer switch-on
time the LED is emitting light for a longer time period, resulting to the human eye, which has an integrating characteristic, in an
impact of higher brightness. Pulse-width and light emission are proportional. Pulse-width modulation and stimulus duration are
controlled by the microprocessor software through logic timer signals.
darker
darker
darker
brighter
brighter
brighter
P
u
ls
e
1
P
u
ls
e
2
0
P
u
ls
e
2
OP2
OP1
I (LED)
S (MOD) = on
S (MOD) = off
Pulse of 5ms
Stimulus duration = 100ms (20 pulses)
t
