1-12
1.5.4.4 150 PSIA Pressure Transducer (T3)
Reference Drawing 91S25912
The 0-150 PSIA Pressure Transducer is of the piezoresistive type. This transducer is used to
measure saturation pressures above 50 PSIA. The output voltage is connected to channel 6 of
the ATB for measurement by the STD-A/D circuit board. The output of the transducer is 0 to
5 VDC for 0 to 150 PSIA (refer to 4.2.3 for calibration).
1.5.5 Control Logic
All control is performed digitally at a logic level of 5 VDC. Activation of all devices is
accomplished by applying a logic low to the control input of the associated solid state relay or
other coupling device.
1.5.5.1 Air Supply Solenoid Valve (SOL1)
Reference Drawing 91S25907
The Air Supply Solenoid Valve is activated (air on) by applying a low from the STD-CPU
(monitored at TIB terminal C5) to the optical input (-) side of SSR5 on the Solid State Relay
Board (SSRB). Valve actuation voltage is 24 VAC.
1.5.5.2 Refrigerant Solenoid Valve (SOL2)
Reference Drawing 91S25907
The Refrigerant Solenoid Valve, when activated, allows refrigerant to be injected into the
refrigeration evaporator to remove heat from the heat transfer fluid. This valve is activated
by applying a low from the STD-CPU (monitored at TIB terminal C0) to the optical input (-)
side of SSR0 on the Solid State Relay Board (SSRB). Evaporator temperature is controlled
through fixed frequency pulse width modulation of the refrigerant solenoid valve. Valve
actuation voltage is 24 VAC.
1.5.5.3 Pressure Bleed Solenoid Valve (SOL3)
Reference Drawing 91S25907
The Pressure Bleed Solenoid Valve, when deactivated (normally open), vents system pressure
during all SHUTDOWN procedures and when electrical power is OFF. This valve is
activated by applying a low from the STD-CPU (monitored at TIB terminal C3) to the optical
input (-) side of SSR3 on the Solid State Relay Board (SSRB). Valve actuation voltage is 24
VAC.
