The relationship between lighter temperature and pre-light time
On the Cerulean SM450 it is possible to set the pre-light time from the computer interface. This is
the time the voltage is applied to the lighter array before an audible signal is provided to raise the
lighter bar and so trigger the puff and lighting sequence. If the bar is not raised within 30 seconds
the lighting sequence is aborted.
Sometimes we are asked about the significance of the pre-light time.
Firstly realising that the lighters are powered by a constant voltage supply, the pre-light gives time
for the heaters to become hot and reach a nominal temperature before lighting. Due to the nature
of the coils and the power supply the surface temperature of the lighter increases with time until a
final temperature is reached many minutes after the voltage has been applied. See figure 1.
Average Temperature
700
600
temperature °C
500
400
30 sec
60 sec
300
200
100
1
5
9
13
17
21
25
29
33
37
41
45
49
53
57
61
65
69
73
77
81
85
89
93
97
101
105
109
113
117
121
0
Time seconds
Figure 1: Plot of temperature vs time for standard coils under standard lighting conditions
In figure 1 the surface temperature of a set of used lighting coils were monitored using an infra-red
video camera and the time temperature profile plotted. Typical images of the coil under test are
shown in figures 2 and using the thermal imaging
camera pseudocolour facility for analysis in figure
3.
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Figure 2: Thermal camera visible spectrum image
of coil test set up.
Selecting a nominal pre-light time is in practice
setting a lighting temperature for the cigarette.
The longer the pre-light time the higher will be
the temperature of lighting.
What is not often recognised is that the heaters
continue to rise in temperature after the prelight time is exceeded until the puff is taken and
the heaters turned off. This can be up to 30
seconds after the “light now” signal is provided,
the time interval being the time between the
signal being provided and the operator raising
the lighter bar. A 30 second delay between a pre-light time of 30 seconds and raising the lighter bar
could result in as much as 17% rise in lighting temperature. Clearly it is important that some
procedural rigor is adopted to eliminate a variable in lighting temperature.
Figure 3: Pseudocolour image of coil after 50
seconds prelight. Maximum and point
temperatures displayed.
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