AUTOFLAME Mk8 MM, Technical Manual

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2 Flame Safeguard
Page | 54
MM Application Possibilities
2.3.2 UV Self Adaptive Pulse Width Modulation
Figure 2.3.2.i UV Timing Diagram
Figure 2.3.2.i shows a timing diagram for the UV signal. After first safety time, voltage is reduced by 5
volts every 500ms. This is providing the flame signal is above the UV setpoint. If below the UV
threshold, voltage will remain at 330 volts. The voltage will not increase during main flame operation.
If 5 counts or less have been detected over any 730ms period, the system will invoke a lockout. A
short circuit between the two wires connected to the UV would produce 3 counts or less. This is the
reason for nominating 5 counts as the lockout level.
During normal operation, 300 volts would be applied for a 240ms period after the second safety time.
This is providing the UV signal is above the UV setpoint which is set at 25 counts. The setpoint cannot
be adjusted.
If the UV count is above 25 counts then the time voltage is applied to the UV sensor is decreased by
1ms every 500ms. This time is reduced until a maximum of 10ms has been reached. This helps
preserve the life of the UV scanner as the time that voltage is applied to the scanner is reduced
dramatically.
Every 500ms the recorded counts are averaged and displayed on the MM screen.
Note: When using a self-check scanner the timing reduction resets the minute when the paddle
operates.
Note: As the flame is increasing, the UV counts will stabilise at 5 times the UV threshold set in
option/parameter 120. As the flame is dereasing, the UV counts will stabilise at 3 times the UV
threshold set in option/parameter 120.