4000-SERIES INSTALLATION, OPERATION AND SERVICE MANUAL
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20.2 Direct Fired Burner Flame Proving (Flame
Rod)
The flame rod in the burner is constructed of a
material that produces a signal when heated. This
signal is measured as a direct current micro amp.
The path of the signal is from the flame rod to the
burner. From the burner, which is mechanically
grounded to the unit casing, the signal continues to
the grounded side of the flame rectification module in
the flame safeguard control. The signal continues out
of the module to the flame rod where it completes the
loop. The length the flame rod extends into the
burner is determined by, the insulator surrounding
the rod. This insulator must not be exposed more
than 1/8" into the burner and not recessed more than
1/8". At this setting the flame rod will be enveloped by
the pilot or main flame. It will be glowing bright red
along at least 50% of its length. See Page 115,
Figure 72.
NOTE: For the flame rod to produce this signal its
position in relation to the grounding rod, pilot and
main flame is critical.
The flame rectification module of the flame safeguard
control converts this signal to a D.C. voltage. This
v
oltage is the value that is used to monitor the pilot
and the main flame of the burner. For the flame
safeguard control to recognize this signal the value of
the voltage must be between 6 to 18 volts D.C. and it
must be steady. This signal is measured at the flame
relay, on the rectification module's test jacks; S1
(colored red) and S2 (colored black). Upon receiving
the correct signal, the flame relay will accept this as
proof that the burner is functioning correctly and will
proceed with its functions.
FIGURE 73: Maxon NPLE Burner
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