FGP55 SERIES GAS RETHERMALIZERS
CHAPTER 1: SERVICE PROCEDURES
1-2
Electronic Ignition Configuration (cont.)
The module contains a 60-second time delay circuit and a coil that activates the gas valve. The
ignitor assembly consists of a spark plug, a pilot, and a flame sensor element.
At start-up the power switch is placed in the "ON" position, supplying 12 VDC to the heat control
circuitry in the computer. Current is supplied to the other leg of the heat relay coil which then closes
an electronic switch in the 24 VAC circuit to provide current to the ignition module.
Circuitry in the ignition module sends 24 VAC current to the gas valve via a normally closed high-
limit switch and a float switch. Simultaneously, the module causes the ignitor to spark for up to 60
seconds to light the pilot flame. A flame sensor verifies that the pilot is lit by measuring the flow of
microamps through the flame. If the pilot does not light (or is extinguished), current to the ignition
module is interrupted, preventing the main valve from opening, and the ignition module "locks out"
until the power switch is turned "OFF", then back "ON".
A temperature probe monitors the temperature in the cookpot. When the programmed setpoint
temperature is reached, resistance in the probe causes the heat cycle circuitry in the controller to
interrupt current flow through the heat relay. This in turn interrupts the 24 VAC current to the
ignition module, resulting in closure of the gas valve.
Control Options
FGP55 Series gas rethermalizers are equipped with computers. These are unique in that the
components are wired directly to the computer and do not require an interface board.
Temperature Probe
FGP55 rethermalizers equipped with computer controls have a
temperature probe
. In this
configuration, the probe resistance varies directly with the temperature. That is, as the temperature
rises, so does resistance at a rate of approximately 2 ohms for every 1° (°F or °C). Circuitry in the
computer monitors the probe resistance and controls burner firing when the resistance exceeds or
falls below programmed temperatures (setpoints). The temperatures are programmed by means of a
keypad on the face of the computer.
All FGP55 Series gas rethermalizers are equipped with a
high-limit thermostat
. In the event that the
rethermalizer fails to properly control the water temperature, the high-limit thermostat prevents the
rethermalizer from overheating. The high-limit thermostat acts as a normally closed power switch
that opens when exposed to temperatures above 250°F (121°C).
