Product User Manual
Page 17
EPRI Commercial Microwave Fabric Dryer
Gerling Applied Engineering, Inc.
Modesto, CA
by the microprocessor for control of the CMFD, but rather it is
provided only for data acquisition purposes.
Exhaust Gas Sensors
A series of four sensors monitor the exhaust air for the presence of
specific compounds commonly found in smoke or other products of
combustion. Each sensor is designed to detect a different set of
compounds as defined in the following chart:
Gas Sensor Compound Sensitivity
Sensor Number
Figaro Type
Compounds Detected
1
822
Toluene
2
825
Hydrogen Sulfide
3
842
Methane, Propane, Butane
4
882
Alcohol
The sensors operate by passing a current through a selective
adsorbent element whose resistance varies as compounds are
adsorbed. The output voltage varies with this resistance and
increases as compounds are adsorbed. The microprocessor
monitors the output voltage and triggers the gas sensor fault cycle
(see Basic Operation section) when its slope exceeds a preset
value.
The sensor elements operate most effectively at an elevated
temperature, thus a heater voltage (+5 VDC) is supplied in addition
to an instrument voltage (+10 VDC). These voltages are supplied
whenever line power is connected to the CMFD and the main circuit
breaker is turned on. A warm-up period of up to one hour is
required for stable and reliable operation of the sensors.
Magnetron Thermal Cutouts
Each magnetron is protected from overheating by a thermal cutout
switch device mounted to its side. Each thermal cutout is connected
in series with the coil of the contactor that turns on the respective
magnetron power supply. If a magnetron overheats then its
associated cutout opens and turns off only the power supply to that
magnetron. Since the blower continues to operate, the magnetron
will cool down until the thermal cutout resets and turns the power
supply back on.
Sensor Lint Screen Burn-off
To protect the exhaust gas sensors from fouling due to lint
accumulation, a lint screen separates the sensors from the flow of
air in the exhaust duct. But if lint is allowed to accumulate on this