AADS FUNCTIONAL DESCRIPTION

TM 9-1270-219-13&P

1-15.

AADS

Functional

Description. The

angle

Unit

contains

two

The

Pressure

Transducer

resolvers which measure the head movement in pitch and

e l e c t r i c a l f o r c e b a l a n c e t r a n s d u c e r s secured to a support

y a w are fed with a 400 Hz reference signal from the EPU

f r a m e by means of grommets and bolts, together with a

(fig.

1-13).

The

resolver

outputs

are

fed

the

EPU.

pneumatic connector, a printed circuit board assembly

containing the transducer control electronics and a 54-pin

connector.

Sampling

the

resolver

output

signals

p e r f o r m e d in the EPU, where the outputs give sine and

The

Analog

Interface

Unit

circuit

card

cosine values of the AADS yaw and pitch angles with

connected to the motherboard on the Chassis by a 54-pin

respect to the helicopter.

connector, and the Central Processor Unit circuit card is

c o n n e c t e d with a 90-pin connector.

b. Temperature measurements from the resistive ATS

are made in the EPU, where the constant current source

a n d differential amplifier circuits associated with the ATS

e. The Power Supply Unit consists of a machined

are located.

cast chassis which acts as a heat sink for all dissipating

components, and supports two printed circuit boards and

a 20-pin connector.

c . AADS monitoring is carried out by the EPU and

includes out-of-range tests and sine, cosine compatability

testing. AADS failures are displayed on the EPU front

panel by a ADS BITE indicator.

EPU Functional Description. Airflow pressure

1-17.

data

are

received

from

the

AADS,

and

converted

into

electronic

data

the

Pressure

Transducer

Unit.

Airflow

angle and temperature data are demodulated and monitored

1-16.

E P U P h y s i c a l D e s c r i p t i o n . The EPU (fig. 1-14)

the

Analog

Interface

Unit,

which

also

contains

the

contains seven Shop Replaceable Units, replaceable at

R a d a r Altitude input interface and the A to D converter.

AVIM level. The seven units are the Chassis, Front Panel

All

calculations

and

system

control

functions

are

carried

Assembly, Rear Cover, Pressure Transducer Unit (PTU),

out

the

Central

Processor

Unit,

which

Analog Interface Unit (AIU), Central Processor Unit (CPU)

microprocessor based computing system. Input power from

and Power Supply Unit (PSU). See figure 1-15.

t h e h e l i c o p t e r 28 V d c su p p l y is con v e r t e d a n d re g u l a t e d

into the system voltage requirements by the Power Supply

Unit. A block diagram of the EPU is shown in figure FO-1.

a . An exploded view of the EPU is shown in figure

1 - 1 5 and the dimensions of the unit are shown in figure

1-16.

The

chassis

and

front

and

rear

covers

are

a. P r e s s u r e

Transducer

Unit

(PTU). T h e

PTU

a l u m i n i u m and the unit is secured in the helicopter by

contains two Electrical Force Balance (EFB) transducers

f o u r bolts through cast metal feet. Removal of the rear

t o m e a s u r e t h e S t a t i c ( Ps )

and

Pitot-Static

( Pt- Ps )

cover gives accesss to the PTU, AIU, CPU and PSU. These

pressures. A typical transducer is shown in figure 1-17.

SRUs plug into the motherboard, which is part of the

With their associated control electronics they are capable

front panel assembly, using two part keyed connectors.

of measuring very low pressures with great accuracy. The

When these four SRUs have been removed, the front panel

transducers are temperature-sensitive, and each transducer

assembly, containing the BITE panel and connectors as

characteristic

stored

temperature

has

its

well as the motherboard, may be removed.

programmable read only memory (PROM) located on the

P T U printed circuit card.

b . All electrical and pneumatic connections are made

(1) Operation of EFB Transducer. The low mass beam

via the front panel. Static and pitot lines are connected to

of each transducer (figure 1-18) is supported by four

standard pneumatic connectors and electrical connections

flexible leaf springs which form a frictionless pivot, whose

are

made

66-pin

connector.

The

BITE

panel

axis is aligned with and attached to a rotary pick-off. The

l o c a t e d on the front panel and contains the LRU BITE

far end of the beam is connected to both a precision

indicators, SELF TEST indicator lamp and switch and

bellows and a forcer coil which sits centrally in a stable

RESET

switch.

1-14