FloAire FAV - Manual (Page 24)

24
Flame Safety Controller
High Temperature Limit
DC Flame Signal
DC Voltage Flame Status
0 to 5 VDC No Flame
6 to 11 VDC Weak Flame
12 to 18 VDC Strong Flame
Signal Conditioner
•
When computer of other process controls are specified, the signal conditioner provides
compatibility with modulator / modulator-regulator valves.
•
This system requires a field supplied 4 to 20 milliamp or 0 to 10 DC voltage signal.
OTHER UNIT COMPONENTS
Flame Safety Control
The first system to understand is the Flame Safety Control. The FSC is
there only to monitor the flame, NOT to control temperature. The FSC
uses a flame rectification sensor (flame rod) mounted on the pilot
assembly to detect the presence of flame in the burner. Flame strength
and presence can be measured at the FSC by reading the rectified flame
signal using a DC voltage meter in the test jacks. Flame is present when
the DC voltage reads between 6 and 18 VDC. Ideal flame intensity
produces a signal of 12 VDC or greater. The FSC controls the opening of
the main and pilot gas valves and the operation of the spark igniter to
initiate a pilot flame upon start-up.
The OPR CTRL LED indicates that there is power to the FSC. Next, the
AIRFLOW LED will come on if there is proper airflow through the unit.
Third, the unit will pause to purge any gasses or combustible vapors
before attempting flame ignition. Then, there is a Pilot Trial For Ignition
(PTFI) and the PTFI LED comes on. During PTFI, the FSC opens the pilot
gas valve and allows gas to flow to the pilot assembly. At the same
moment, the spark igniter is started, causing the spark to ignite the pilot
gas. When the flamerod sensor detects the flame, it turns on the FLAME
LED, turns off the PTFI LED. This is the normal operating mode. The last
LED on the FSC is the ALARM LED. This will turn on when the FSC determines an unsafe condition has
occurred, and will not allow the unit to recycle for heat until it has been properly reset. Anytime the FSC
has gone into “Alarm” mode, the problem must be diagnosed and corrected to avoid future lockouts after
resetting. To reset the FSC, cycle power to the control. This will clear the alarm from the flame safety.
High Temperature Limit
One of the safety device is the high temperature limit switch. This switch is a
mechanical thermostat that measures the temperature inside the unit downstream of the
burner. If the factory-set temperature is exceeded, it will disable the burner. This
requires a manual reset of the high temperature limit.
Electric Cabinet Heater
On units shipped with an optional electric cabinet heater, ensure that the heater is wired to a separate
120V, 15 amp input, the thermostat sensing bulb is mounted correctly in the control vestibule where the
heater is located, and the thermostat set to 0 Degrees Fahrenheit.