This invention relates to Frequency & Discrete Acquisition Module (FDAM) for
use in Data Acquisition System (DAS) of Flight Data Recorders and, more particularly,
to fight data acquisition systems for receiving fight data signals in a variety of signal
forms like Frequency & Discrete Signals.
BACKGROUND OF THE INVENTION
Flight data recorders are monitoring and recording instruments, carried aboard
an aircraft, which systematically monitor and store the instantaneous values of various
aircraft parameters. Early recorders were analog electromechanical devices which
periodically marked, in analog form, the value of a given airplane parameter on a
moving wire or other permanent storage medium. The time of occurrence of the
parameter was also suitably scribed into the medium opposite the mark for the sensed
parameter. Subsequently, digital flight data recorders have been developed which
operate by converting each analog aircraft parameter into a corresponding digital signal,
and storing the digital signals on a permanent storage medium such as magnetic tape.
The numerous mechanical parts employed in the analog and digital type
electromechanical flight data recorders have rendered such units expensive to construct
and bulky in design, requiring periodic maintenance of the mechanical parts. In addition,
extraction of the stored data from these data recorders requires physical removal of the
storage medium.
The development of solid state memory devices, such as electrically erasable
read-only memory, has led to the design of all solid state flight data recorders. The solid
state flight data recorders commonly employ a data acquisition system (DAS) which
receives and processes the various aircraft input signals to be monitored and stored
under the control of a central processing unit (CPU). The analog signals are converted
to digital signals by the DAS and, under CPU control, are passed over a data bus to the
solid state memory devices. Programming within the CPU controls the processing of
input airplane signals to corresponding digital signals through the DAS and the
subsequent transference of these digital signals to controlled locations in the solid state
memory.
Annexure‐II
The signals representative of monitored aircraft parameters are typically either
discrete level signals or frequency in the form of analog signals. Discrete signals are
typically switch positions and produce either a high or a low level output depending
upon the status of the particular switch. A typical example in an aircraft is a squat
switch, which indicates whether or not a load is being borne by the landing gear.
The analog signals may be DC ratio metric signals, Synchro signals or AC ratio
metric signals and frequency signals. The DC ratio metric signals are DC signals having
a ratio representative of the value of the parameter being sensed. A typical DC ratio
metric signal is that produced by a potentiometer having a DC voltage applied across its
resistive element, with the wiper position indicative of the level of the sensed parameter.
Frequency signals are generated from aircraft tacho generator coupled with engine
sensor and main gear box.
To accurately collect data from discrete sensor switch for discrete signals, engine
sensor & gear box for sensing RPM, therefore, the Frequency & Discrete Acquisition
Module (FDAM) of DAS should simultaneously collect and hold each signal associated
with the multi signal-type sensor. Further, it is desirable to minimize the overhead on
‘the CPU in its accessing of data as collected by the DAS. In prior art flight data
recorder designs, the CPU sends a request to the FDAM asking for the value of a given
aircraft parameter and this parameter is then selected, processed, and signal is digitally
converted by the DAS which then signals the CPU that the requested information is
available. Since a large number of air plane parameters may be monitored by the flight
data recorder, constant requests by the CPU on the DAS significantly increases CPU
overhead.
Further, it is desirable to conform the flight data recorder such that it is capable of
being conveniently modified to operate in any one of several different types of aircraft.
To this end, the FDAM of DAS is preferably configured such that its inputs may be
assigned by the CPU to handle no. of Frequency or Discrete input signals. Further, the
levels of the various signals at the inputs of the DAS must often be sealed for proper
processing within the DAS.
Annexure‐II
SUMMARY OF PRESENT INVENTION
The present invention, therefore, is directed to Frequency & Discrete Acquisition
Module (FDAM) of data acquisition system for use in a Flight data recorder.
An aspect of the present invention is the ability of the data acquisition system to
process a set of parameter sense signals in response to a single CPU request. In this
way, integrity of multiple signal sensor data is assured and overhead on CPU operation
is reduced.
The discrete part of the module accept separate isolated inputs and convert
them into a serial data stream with TTL (Digital) compatible level. The discrete
parameters of the aircraft are fed through opto-couplers, which maintain isolation
between the Flight Data Recorder (FDR) and aircraft sensors.
The differential frequency signals are fed to signal conditioning circuit and
convert it to single ended. These frequencies are multiplexed by analog multiplexer
(8x1). This single-ended signal is fed to voltage comparator (Schmitt Trigger), which
converts into TTL logic pulses. This signal then fed to the Flip-Flop that is used to gate
“Freq Clock” pulse to one of channel of Time Processing Unit (TPU) module of 32 – bit
microcontroller for one period of selected frequency signal.
Preferably, the processing means includes input impedance buffer for frequency
parameter, which are an integral part of the analog multiplexers & multiplex the signals
into a common data bus.
Frequency & Discrete Acquisition Module (FDAM) carries out the following functions:
• Decoding of address bus signals for control of the module & generation of
outputs.
• Period Measurement of one of four selectable differential frequency input signals.
• Multiplexing one of two frequency data onto serial data output.
• Generation of enable BUILT IN TEST (BIT) signal for opto-couplers.
• Performing BUILT-IN-TEST & Acquisition of discrete data.
• Parallel loading of output of Opto-Couplers into parallel in serial out (PISO) shift
register and them clocked out serially by discrete clock.
Annexure‐II
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention will become more apparent
and descriptive in the description when considered together with figures/flow charts
presented:
Figure 1: is a Block Diagram of Frequency & Discrete Module (FDAM) of FDAU
Figure 2(a): is a Block Diagram of Frequency Conditioning Circuit of FDAM
Figure 2(b): is a Block Diagram of Discrete Conditioning Circuit of FDAM
Figure 3: is a Block Diagram of Flight Data Acquisition Unit (FDAU) of FDR
DETAILED DESCRIPTION
This electronic module receives all the Frequency & Discrete parameters coming
to FDR unit. Module converts Frequency & Discrete inputs into Digital format to make
compatible for storage in Solid-state memory.
Further, for acquisition and digitization of frequency & discrete signals, two
conditioning circuits are used which converts the signal into digital form after
conditioning of the signal and send it to 32-bit microcontroller for further processing and
recording in solid state memory. Detail description of conditioning circuits are elaborated
in succeeding paragraph:
FREQUENCY CONDITIONING:
The required signal conditioning logic for the frequency inputs is provided using
operational amplifier devices. After signal conditioning the inputs are fed to the
Multiplexer which selects various frequency inputs based on its address select lines,
which are obtained from the hex latch. Then each selected frequency signals are
passed through the Schmitt trigger to convert into TTL pulse. These pulses are
interfaced to counters of the processor for measurement of frequency. Frequency
conditioning circuits is attached at Figure: 2(a)
The output of the de-multiplexer is used to clock the data lines into hex latch. The
Multiplexer selects various frequency inputs based on its address select lines, which are
obtained from the hex latch. The Operational amplifiers form an instrumentation
amplifier with high common mode rejection, which converts the selected differential
signal into a single ended signal and converts it into TTL logic levels using Schmitt
trigger. Output of the comparator is fed to the D-Flip-Flop to gate “FREQUENCY
Annexure‐II
CLOCK” pulse to TPU (Time Processing Unit) module of the microcontroller for one
period measurement of the selected frequency signals.
DISCRETE CONDITIONING:
The discrete signals of the aircraft are fed through the opt couplers which are
used to maintain isolation between the FDR and the Aircraft sensors. When data is
available at the output of these opt couplers then it is latched into PISO shift register
provided the clock pulse from the output of the Multi vibrator and mode select input is
HIGH. Once data is loaded into shift resister, it is clocked out serially from the shift
register when clock pulse is available and mode select input is LOW, which is then sent
to Queued ADC module of Microcontroller. Discrete Conditioning circuits is attached at
Figure: 2(b)
The de-multiplexer is used to decode the address bus lines when enabled
by “DISC_EN_BAR” signal. The Y0 output of the de-multiplexer U-10 are used for
triggering the gated active low going inputs of the Mono stable multi vibrator U-11. The
output Q1 of the Mono stable multi vibrator U-11 is used for the mode selection of the
shift resister U-8 & U-9. When mode signal will be HIGH then data will be entered to
shift resister U-8 & U-9 through P0-P15 & when mode signal will be LOW then data will
be out of shift resister through P0 output. The output Q2 of the Mono stable multi
vibrator U-11 is used to clock the shift resister. The discrete parameters are fed through
resistors to the input pins of opto-couplers. The each LED of these opto-couplers is
connected to ENBIT signal through a diode. When sufficient current is supplied to each
LED then it forces the voltage on each phototransistor collector below the CMOS
threshold so that data is read to each discrete input when it is active. When data is
available at the O/P of these opto-couplers then it is latched into PISO shift resister
provided the clock pulse from the Q2 output of the multi vibrator and mode select input
is HIGH. Once data is loaded into shift resister, it is clocked out serially from the shift
register when clock pulse is available and mode select input is LOW, which is then sent
to Queued ADC module of Microcontroller.

WE CLIAMS:-
Accordingly, the description of the present invention is to be considered as illustrative only and is for the purpose of teaching those skilled in the art of the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and exclusive use of all modifications which are within the scope of the appended claims is reserved. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A Frequency & Discrete Acquisition Module (FDAM) for an aircraft flight data recorder responsive to a central processor unit (CPU) for processing a plurality of frequency & discrete signals to provide a digitally encoded signal representative of a selected set of input signals each time the CPU provides a simple command signal, said digitally encoded signal being used by said CPU for generation of recorded flight data information, said data acquisition system comprising: multiplexing means for outputting said selected set of said input signals, each selected input signal set being output responsive to a corresponding address command signal; logic means responsive to said single command from said CPU for producing each address command signal; and processing means for processing each signal in a selected signal set to supply said digitally encoded signal representative of said selected set of input signals.

2. The FDAM of claim 1, wherein said processing means comprises: Voltage spike suppressor & overvoltage circuits for frequency signals & isolation of high voltage discrete signal from module using opto-coupler responsive to conditioning circuits.

3. The FDAM of claim 2, further comprising of input scaling circuit for frequency signal means for attenuating selected input signals by a predetermined scaling factor; and wherein said gain factors for said gain controlled amplifiers are selected such that each signal, after being attenuated in said input scaling circuit.

4. A FDAM as claimed in any of the preceding claims wherein means are provided for decoding of address bus signals for control of the module & generation of outputs.

5. A FDAM as claimed in any of the preceding claims wherein means are provided for period Measurement of one of four selectable differential frequency input signals through time processing unit(TPU) channel of 32-bit Micro controller.

6. A FDAM as claimed in any of the preceding claims wherein means are provided for multiplexing one of two frequency data onto serial data output.

7. A FDAM as claimed in any of the preceding claims wherein means are provided for generation of enable BUILT IN TEST (BIT) signal for opto-couplers. Performing BUILT-IN-TEST & Acquisition of discrete data.

8. A FDAM as claimed in any of the preceding claims wherein means are provided for parallel loading of output of Opto-Couplers into parallel in serial out (PISO) shift register and them clocked out serially by discrete clock. ,TagSPECI:As per Annexure-II