Wayne HSG400 Specifications download pdf (Page 12)

PAGE 11

FLAME SENSING

The Honeywell S89 series primary ignition controls

utilize the flame current rectification principal for main

burner flame sensing.

The flame rectification phenomenon occurs as follows.

The ignited gas flame causes the immediate

atmosphere around the flame to become ionized (gas

atoms become electrically charged). The ionization

causes the atmosphere around the flame to become

electrically conductive. An AC voltage output from the

control sensing circuit is routed through the flame

sensor probe. When the sensor probe and the burner

head are both in contact with a properly adjusted flame,

the burner head with its larger surface attracts more free

electrons, thus becoming negatively charged. The

sensor probe with its small surface area gives up free

electrons, thus becoming positively charged. The free

electrons from the AC voltage in the sensor probe flow

through the ionized gas flame to the grounded burner

head. As the AC current passes through the gas flame,

it is rectified into a DC current flowing back to the

grounded side of the sensing circuit. The flame in

actuality is a switch. When the flame is present, the

switch is closed allowing current to flow through the

sensing circuit of the control. When no flame is present,

the switch is open with no current flowing through the

sensing circuit of the control.

The DC current flow is measured in units called DC

microamperers. A steady DC microamp current of .8

minimum (and steady) or higher through the sensing

circuit of the primary ignition control is sufficient to keep

the burner running without a safety lockout. See Figure

13 for sensor probe and electrode dimensional settings,

Figure 14 for flame current measurement.

Figure 13

Figure 14

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Wayne HSG400 Specifications Page 12