temperature bridge results in a dc error voltage.
error voltage to go to the modulator circuit. The
This voltage is ac modulated by the modulator
resulting amplified signal regulates the cabin
circuit, amplified, and goes to the suit temperature
control valve to return the duct air to its original
control valve, altering suit air temperatures.
temperature. Error voltages caused by cabin
Rate-of-change voltage from the feedback
temperature bridge or cabin duct limit bridge
imbalance override the cabin duct anticipator
potentiometer in the ventilated suit temperature
control valve is capacitance-coupled to the
bridge, provided the duct air temperature error
modulator circuit. As in the cabin temperature
is gradual or small.
channel, this voltage is present only when the valve
One additional error voltage is capacitor
is operating. It reduces the initial starting voltage
coupled to the modulator circuit. The voltage
to the valve once actuator rotation has started,
change is proportional to the rate of change of
thus slowing actuator rotation.
the feedback potentiometer of the cabin dual
temperature control valve. This voltage change
ANTI-ICING AND DEICING
is applicable only when the valve is being
EQUIPMENTS
regulated (the feedback potentiometer is rotating).
Therefore, the error feedback voltage seen at the
control input is proportional to the feedback
The anti-ice and defrost system on some
aircraft having the air-conditioning and pressuri-
potentiometer rate of change. Once regulation of
zation system described in this chapter use the air
the valve starts, the potentiometer rate-of-change
cycle systems as an air source. The anti-ice and
voltage reduces initial starting voltage to the
defrost equipment consists of the windshield anti-
control valve actuator motor, slowing valve
ice system (fig. 4-30.) and the windshield defrost
actuator rotation.
system. Each receives its hot air supply from the
The vent suit channel (fig. 4-29) of the
same manifold. The anti-icing switch is on the
temperature controller uses one bridge circuit to
pilot's temperature control panel.
maintain suit temperature. Operation of this
In a typical system, a windshield overheat
bridge is similar to that of the cabin temperature
thermostat and a shutoff valve in the windshield
bridge. The suit temperature selector resistance
defrosting duct operate together to prevent
in one leg balances against the suit duct
windshield overheating. The thermostat opens
temperature sensor resistance in the opposite
the valve automatically when the temperature
leg. Imbalance between these legs of the suit
Figure 4-29.-Vent suit channel.
