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SC10 Signal Conditioner
When the computer of other process controls are specified instead of standard electronic controls, the signal conditioner provides compatibility with modulator / modulator-regulator valves.
This system requires a customer supplied 4 to 20 milliamp or 0 to 10 DC voltage signal from a building control system.
UNIT COMPONENTS
M4RT1 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 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. This is done by removing the FSC cover and 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 is also wired into an airflow switch, which tells it whether there is proper airflow through the unit (not just any airflow, but proper airflow).
Proper airflow occurs when there is a .15 in. w.c. to .95 in. w.c.
Flame Safety Controller
differential pressure drop across the burner . When the airflow through the heater produces a pressure drop in this range, the FSC indicates so by illuminating the AIRFLOW LED. The FSC controls the opening of the redundant solenoid 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.
DC Flame Signal
DC Voltage
0 to 5 VDC
6 to 11 VDC
Flame Status
No Flame
Weak Flame
Third, the unit will pause to purge any gasses or combustible vapors before attempting flame ignition. Then, there is a Pilot Trial For Ignition
12 to 18 VDC Strong Flame
(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 flame rod sensor detects the flame, it turns on the FLAME LED, turns off the PTFI
LED, and powers the modulating gas system. This is the normal operating mode. The FSC continues to monitor the flame and airflow. Once this occurs, the unit is in a main flame cycle and thus powers the main gas valve and the modulating gas system. This is the normal operating mode. The FSC continues to monitor the flame and airflow. 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 begin troubleshooting, or to reset the FSC, shut down power to the heater and restart the heater. This will clear the alarm from the flame safety.
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