Garland 200 - Manual (Page 35)

Part # MCOSM06 Rev 1 (11/03/08) Page 35
G76X DIRECT SPARK IGNITION CONTROLS
Application Requirements
Following are the application requirements of the
G76xcontrol.
• The G76x can be used on gas-fired equipment with a
maximum firing rate of 117 kW (400,000 Btu/hr). Any
application greater than117 kW (400,000 Btu/hr) must
have written approval in advance from the Johnson
Controls Heating Products Engineering Department.
• All G76x applications must use a redundant gas valve
system where the main valve seats are in series and open
simultaneous for direct spark burner ignition.
Operating Mode Definitions
The following definitions describe operating conditions:
• Prepurge: Initial time delay between thermostat contact
closure and trial for ignition.
• Trial for Ignition: Period during which the main valve and
spark are energized in an attempt to ignite gas at the main
burner. The control attempts to prove flame at the main
burner within the trial-for-ignition time.
• Run: Main gas valve remains energized and the spark is
turned off after successful ignition.
• 100% Shutoff: For controls with automatic recycle, main
gas did not ignite within the trial-for-ignition time. The
control de-energizes the spark circuit and main valve.
• Automatic Recycle: If 100% shutoff occurs, the control
delays for a specific recycle delay period before beginning
another trial for ignition. (Modelswith recycle only.)
• Interpurge: Period between trials for ignition when both
the gas valve and spark are deactivated to allow unburned
gas to escape before the next trial. Interpurge occurs
between unsuccessful trials on a multi-trial control or after
a loss of proven flame (flameout).
• Ignition Lockout: Main gas did not ignite within the final
trial-for-ignition time. Open the thermostat contacts for 30
seconds, then close to restart the sequence of operation.
(Models with an optional LED will flash the LED to indicate
ignition lockout.)
• Flameout: Loss of proven flame.
• Hard Lockout: The control detected a fault. Open the
thermostat contacts for 30 seconds, then close to restart
the sequence of operation. (Models with an optional LED
will turn off the LED to indicate a hard lockout.)
Sequence Of Operation
Figure 3 illustrates the sequence of operation of the G76x
control.
The control is energized on a call for heat from the system
thermostat. (Models with an optional LED will turn on the LED
[steady on] until the call for heat is satisfied.) If the control is
equipped with the optional prepurge, the control will delay
for the time selected before initiating a trial for ignition.
During the trial for ignition, the control attempts to light the
main burner by simultaneously energizing the main gas valve
and supplying a continuous spark at the igniter electrode.
If the optional prepurge is not selected, then the trial for
ignition begins within one second after the call for heat.
The spark is deactivated immediately following the trial for
ignition.
Under normal conditions, the main burner gas ignites within
the trial-for-ignition time. If the control senses main burner
flame by the end of the trial, the control proceeds to a run
condition. During the run state, the control energizes the
main valve until the call for heat ends, or until a flameout
occurs. If main burner flame is not sensed by the end of the
trial-for-ignition time, the control may:
• Proceed to a 30-second interpurge followed by another
trial (three trial models whose first two trials produced no
flame)
• Proceed to a lockout (no automatic recycle models whose
final trial produced no flame)
• Proceed to a recycle delay period followed by another trial
(automatic recycle models whose final trial produced no
flame)