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Hindustan Aeronautics Limited (HAL)
Company Profile
Hindustan Aeronautics Limited (HAL) came into existence on 1st October 1964. The Company was formed by the merger of Hindustan Aircraft Limited with Aeronautics India Limited and Aircraft Manufacturing Depot, Kanpur. The Company traces its roots to the pioneering efforts of an industrialist with extraordinary vision, the late Seth Walchand Hirachand, who set up Hindustan Aircraft Limited at Bangalore in association with the erstwhile princely State of Mysore in December 1940. The Government of India became a shareholder in March 1941 and took over the Management in 1942. Today, HAL has 19 Production Units and 9 Research and Design Centers in 7 locations in India. The Company has an impressive product track record - 12 types of aircraft manufactured with in-house R & D and 14 types produced under license. HAL has manufactured over 3550 aircraft, 3600 engines and overhauled over 8150 aircraft and 27300 engines. HAL has been successful in numerous R & D programs developed for both Defense and Civil Aviation sectors. HAL has made substantial progress in its current projects: o
Dhruv, which is Advanced Light Helicopter (ALH)
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Tejas - Light Combat Aircraft (LCA)
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Intermediate Jet Trainer (IJT) 2
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Various military and civil upgrades.
HAL has played a significant role for India's space programs by participating in the manufacture of structures for Satellite Launch Vehicles like o
PSLV (Polar Satellite Launch Vehicle)
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GSLV (Geo-synchronous Satellite Launch Vehicle)
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IRS (Indian Remote Satellite)
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INSAT (Indian National Satellite)
HAL has formed the following Joint Ventures (JVs): o
BAeHAL Software Limited
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Indo-Russian Aviation Limited (IRAL)
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Snecma HAL Aerospace Pvt Ltd
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SAMTEL HAL Display System Limited
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HALBIT Avionics Pvt Ltd
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HAL-Edgewood Technologies Pvt Ltd
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INFOTECH HAL Ltd
Apart from these seven, other major diversification projects are Industrial Marine Gas Turbine and Airport Services. Several Co-production and Joint Ventures with international participation are under consideration. HAL's supplies / services are mainly to Indian Defense Services, Coast Guards and Border Security Forces. Transport Aircraft and Helicopters have also been supplied to Airlines as well as State Governments of India. The Company has
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also achieved a foothold in export in more than 30 countries, having demonstrated its quality and price competitiveness. HAL has won several International & National Awards for achievements in R&D, Technology, Managerial Performance, Exports, Energy Conservation, Quality and Fulfillment of Social Responsibilities.
o HAL was awarded the “INTERNATIONAL GOLD MEDAL AWARD” for Corporate Achievement in Quality and Efficiency at the International Summit (Global Rating Leaders 2003), London, UK by M/s Global Rating and UK in conjunction with IIMC o
HAL was presented the International - “ARCH OF EUROPE” Award in Gold Category in recognition for its commitment to Quality, Leadership, Technology and
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Innovation.
At the National level, HAL won the "GOLD TROPHY" for excellence in Public Sector Management, instituted by the Standing Conference of Public Enterprises (SCOPE).
The Company scaled new heights in the financial year 2006-07 with a turnover of Rs.7, 783.61 Crores
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HELICOPTER MRO DIVISION
OBJECTIVE To create a customer centric organization and provide focused impetus to the growing MRO activities on rotary wing aircrafts including ALH (DHRUV) & New Projects, a dedicated Helicopter MRO Division has been established within the Helicopter Complex. The Helicopter MRO Division is operational since Dec 06 with focus on robust customer support for the delivered helicopters.
NEED FOR MRO DIVISION: Airborne vehicles need to be continually maintained to ensure continued airworthiness of the product servicing: •
Safety of pilot and crew
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Safety of people on the ground
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Cost of the vehicle
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Strategic importance of the mission
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BACKGROUND
The Helicopter MRO Division is operational since Dec 06 providing end to end customer support for the delivered helicopters.
The Division is presently providing MRO support for ALH (conventional cockpit and IADS configurations) and Seaking projects. Future projects include variants of ALH like the ALH-WSI and LCH.
Strategies are put in place to sustain an optimum level of serviceability and minimum AOGs.
Effective LRU Management, Warranty management, Supply Chain Management, Reliability Improvement, Lifted Items and Obsolescence management, repair facilities for LRUs and RMSO support are some of the initiatives put in place to provide life cycle support.
The Division is ensuring continuous improvement by adopting lean culture, Kaizen and TWI approach to achieve customer delight. The Division is ISO 9001:2000 and AS 9100 Rev C certified.
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LINE REPLACEABLE UNIT( LRU’S)
A Line- replaceable unit is a complex component of an aircraft that is designed to be replaced quickly at the flight line or airport ramp area. An LRU is black box (scaled unit) radios or auxiliary equipment. LRU’s speed up repair, because they can be stocked and replaced quickly from inventory, restoring the larger system to services. They also reduce the cost of system, and increase the quality, by spreading development costs of systems and increase the quality, by spreading development costs, although an LRU is called a black box because its internal design is immaterial to the end user, the box itself is often painted grey in colour. LRU’s are designed to common specification ,which cannot plug input output interfaces specification also define the tools necessary to remove and replace the unit and the bulk and wait .There are also requirements for testing the LRU’s flammability, unwanted ,radio emission resistance to damage from fungus, static electricity, heat, pressure, humidity,vibration, radiation and other environmental measurements. Many LRU’s for commercial aircraft’s are designed according to ARNIC specification such as ARNIC 404 AND ARNIC 600. LRU’s are also defined by manufactures like airbus and bocing and by various military organisations. In the military, electronic LRU’s are typically designed to interface according to data bus standards such as MIL-STD1553. There are also about 340 LRU’s used in ALH(DHRUV).Among them 135 LRU’s are serviced and tested in HAL. 8
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INTERCOM SYSTEM (N200)
1. Introduction: The main purpose of the system is to provide the inter-communication among the flight crew. It also as the facility to communicate with ground crew through the external jack during maintenance operation whenever required. It is central control for all the communication equipment mounted on ALH. It interfaces with various radio channels, warnings and other audio outputs.
2. Basic principle: The Intercommunication is achieved through a microphone, station box, junction box and headphones. The speech from microphone will be passed through a station box to junction box. From the junction box this signal will be fed to other station boxes and headsets and vice versa as shown in fig 1.
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Junction Box:
It is a modular unit with five audio user junction box and
individually replaceable card for each user. It provides interface between station boxes, radio channels, intercom channels and other audio warning and voice warning channels. Junction box is located in nose cone region of the ALH.
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Fig : Junction Box
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Station Box: It is also a modular unit provides control for the operation of the intercom and radio channels .It interfaces with junction box, microphones and earphones. Station boxes for pilot and co-pilot is located in centre console of ALH and the third crew station box is fixed to centre of roof behind the co-pilot.
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Fig : Intercom system LRUs interconnection diagram and its interface with other systems.
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Fig : Intercom system LRUs location on ALH
Technical Features:
Normal operating condition
28 V DC
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Input current
3A max @ 27.5V DC
Input voltage
90Watts max (per junction box)
VOS Facility
It facilitates the intercommunication among the other flight crew without pressing any PTT.
Volume controls
There are 16 volume controls ,8 for receivers(ADF,SONIC ,ESM,SPARE3,SPARE-4,SPARE-5,ICS&VOS) 5 for transceivers (V/UHF-1,V/UHF-2,HFSSB,SPARE-1,SPARE2)
RAD PTT
RAD PTT is provided with each station box in parallel with cyclic stick and collective stick.
CALL Switch
It facilitates to call any station irrespective of their preset volume controls.
No. of station box
One for pilot ,one for co-pilot and one additional in cabin. Provision exits for 4th and 5th station box.
No. of interfaces
One receiver (ADF),provision exist for SONIC,ESM,2-SPARES receivers.
There transceiver (V/UHF-1,V/UHF2,HFSSB)provision exist for three transceiver.
Two audio warnings without volume control. •
Radio Altimeter
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Centralised warning panel(main 16
rotor high rpm,main rotor low rpm & engine failure)
One recorder interface(FDRCVR)
External jack
This provision is used by ground crew for communicating with flight crew while doing maintenance activites.
Press to Mute Switch
This provision exist in collective stick to mute the audio warnings to all the station boxes.
Radio Mute Switch
This switch is available in cyclic switch to mute the radio systems.
Audio warning signals
Radio altimeter warning: when the Helicopter comes below the pre-set decision height radio altimeter sends an audio warning of(400Hz in case of RAM-703A or 576(+/-)4Hzs signal in case of kra-405B) to the intercom headset for 3sec.
Main Rotor High rpm in case of main high rpm audio warning continues tone of 2400Hz with 500Hz ON/OFF will be heard in the headset.
Main Rotor low rpm in case of main high rpm audio warning continues tone of 800Hz with 100Hz ON/OFF will be heard in the headset.
Voice warning signals
The following voice warning signals are interfacing with intercom system 1.Main rotor high rpm 17
(In additional to audio tone) 2.Main rotor low rpm (In additional to audio tone) 3.Over torque 4.Torque 5.MCR 6.Power loss 7.Eng 1 fire 8.Eng 2 fire 9.Landing gear 10.Rotor brake 11.Mast Moment
Operating temperature
-45 c to +71 c
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Operating Instruction
Station Box: There are two CB’s for ICS i.e, ICS NORM which is connected to Emergency Bus Bar-1(EBB-1) and ICS STBY which is connected to EBB-2.These CB’s are located in overhead panel , which gives 28V DC to power to supply system .
Fig : Station box 19
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JUNCTION BOX
The N200 Intercom System provides intercom, transceiver, radio, alerting and control processing for up to five (5) Station Box crew positions, plus a simplified sixth ground crew position.
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N200-ALH4 Audio Junction Box It is a modular unit with five audio user junction box and individually replaceable card for each user. It provides interface between station boxes, radio channels, intercom channels and other audio warning and voice warning channels. Junction box is located in nose cone region of the ALH. All radio and alerting signals, and dual 28VDC power sources are connected to the Audio Junction Box. All the incoming and outgoing radio and alerting signals enter via the system connectors and are RF filtered for interference and transient suppression, and equalized and distributed through the internal Audio Junction Box buss to each Interface Card. Each Station Box connects to its respective Interface Card within the Junction Box to obtain power, and exchange control and signal data for each crew member. Within the Junction Box, the incoming dual 28VDC power lines are filtered and pre-regulated. Since either power bus (Normal or Standby) can fully power every respective 22
Interface Card and Station Box, failure in ether section or loss of power is easily overcome by transferring to the other buss. In addition, signal processing is duplicated within each Interface card, so that shifting from one mode to the other provides system redundancy.
The “cleaned” input DC voltage is then distributed to the six (6) individual Interface cards within the Junction Box (one for each Station Box and the ground crew position), where it is then converted via a switching power supply to dual channel, fully floating lower voltage DC supplies that power the interface sections and the remote Station Boxes. Secondary power supplies float (are ungrounded to the airframe) to avoid unwanted ground loop interaction and prevent noise injection with remote Station Boxes distributed through the airframe.
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DC power conditioning and distribution, and radio and airframe signal distribution take place within the Audio Junction Box, as well as individual signal mixing in each user’s interface card within the Audio Junction Box. Rotary volume controls produce a specially tailored DC level, which forms the control signal for remote level processing in the Audio Junction Box (N200ALH4). Raw source audio is not actually processed or selected in the Station Box itself, that set of functions takes place in the related Interface Card within the Audio Junction Box. The DC voltage controls the gain in the VCA (voltage controlled amplifier) stage, to provide the needed audio level control. Each user has this circuit for every adjustable source signal, in two parallel channels (normal/standby). These circuits are all on the user’s respective interface card within the ALH4 Audio Junction Box. All radio and alerting source and destination signals are routed to the interface cards in a parallel buss structure.
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STATION BOX
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Introduction •
It is a modular unit which provides controls for the operation of the intercom and radio channels. earphones.
It interfaces with junction box, microphone and
Station box for pilot and copilot is located in centre console
of the ALH and the third crew station box is fixed to centre of the roof behind copilot. •
The station box are single user audio controllers that are compatible with low and high impedance headsets.
They provide electrical and operational
interface between a single user and the N200-ALH4 audio junction box. The N200-ALH1, N200-ALH2 or N200-ALH3 is the interfaces to the user headset, receiving audio from the microphone and sending audio to the headphones. It allows user to control of receive and intercom volume via individual rotary knobs. It allows selection of one or more transceivers for transmit via frontpanel push button switches. •
Voice-activated intercom operation is also provided. All critical circuits have a secondary backup system that is selectable from the front panel
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.General description:
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Block Diagram Gives The General Description Of Station Box
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There are two major operational modes:
Normal and Standby.
Standby
mode provides duplicate circuits for certain critical functions. Standby mode can be activated either manually or automatically. The microphone input utilizes an automatic level control amplifier for maximum intelligibility without distortion. The ICS output is designed to provide a minimum output even when the ICS volume control is set to minimum, fully CCW(counter-clockwise) position. Radio levels may be fully turned off(de-selected) when rotated to the fully CCW position. The shift from “Normal” to “standby” operations occurs either by a front panel switch selection on the face of station box, or automatically from “normal” to “standby” operation if the normal dc input power bus is lost(which then illuminates a front panel annunciation for standby). The parallel normal/standby structure allows the N200 system to withstand many faults at the system and station level, and continue critical operation without interruption. Since each station box has its own interface card with its own power supplies(which are dual bus), and all signal processing is redundant, the N200 architecture is damage resistant and then continue full operation at every station even with extensive hardware failures. Transmit features A transceiver is selected for TX operation by pressing the appropriate rotary control in, selection is also indicated by an illuminated LED on the panel to the left of the rotary control. A radio is de-selected for transmit by pressing the control again, which returns it to the out/off position. The station box is in transmit mode when one or more transceivers are selected for transmit on that box and the radio PTT line is grounded, either via 28
external PTT switch, or via RAD PTT switch on the front panel. In this mode, VOS mic audio is passed to selected transceiver(s) and operates as if it were hot mic audio. Transmit sidetone for the selected transceiver(s) is not created by N200 system.
Sidetone level and creation is a function of selected
transceiver(s). TX active operation is annunciated by a front panel TX legend.
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All receive audio is muted during transmit. Side tone audio from the selected transceiver(s) and direct(warning) audio are not muted during transmit operation. Receive features
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Radio functions include independently selectable and adjustable receive level at each station box for up to 5 communication radios(transceivers). Additional receive audio selections include six front panel selectable individually adjustable sources, and six non-selectable direct/altering audio sources. Tranceiver and receiver audio is deselected by rotating the volume control to the fully CCW position. The dead zone of 25% of the shaft rotation in the CW direction is provided to ensure full audio OFF functionality can be achieved. The remaining 75% of the CW rotation provides 40dB of controlled audio level, with full output at the fully CW rotated position. All receive audio is muted during transmit. Sidetone audio from the selected transceiver(s) and direct(warning) audio are not muted during transmit operation. ICS features The microphone input utilizes an automatic level control amplifier for maximum intelligibility without distortion, and is active during all microphone operations, both transmit and ICS.
An adjustable VOS level control is
provided for “hot mic” or voice-controlled “VOX” ICS operation, and is adjusted for the local noise environment at each station box. The ICS output is designed to provide a minimum output even when ICS volume control is set to the minimum, fully CCW position, and also provides 40dB control range in CW direction for adjustment of intercom audio. A front panel ICS call switch on some panels is provided for system wide ICS calling in ”hot mic” mode. Lightning
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When the aircraft lightning bus is below a threshold voltage, the station box is in day time lightning mode. The front panel back lightning is off and all active annunciators are at full brightness. When the aircraft lightning bus is above threshold voltage, the station box is in night time lightning mode. When the threshold is exceeded, the front panel back lightning turns on at a minimum brightness and all active annunciators decreased to a minimum brightness. As the lightning bus voltage increases further, the brightness of the back lightning and active annunciators increases. Controls and indicators The station boxes are Dzus-rail mounted boxes with internally illuminated face plates. Each of the station box consists of 3 rows of controls. The top row are similar for each model, with the main differences occurring in the bottom row of controls. Each row will be described separately, and the differences between the units will be explained.
Fig: N200-ALH station box
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Transmit TX SEL(Transmission select)
The transceiver controls are illuminated, clear, locking, push-on/push-off rotary knobs. To select the transceiver for transmission, press the required TX SEL knob into the locked position. The relevant TX SEL indicator located below and to the left of the associated TX SEL knob, will illuminate green to indicate which control has been selected for transmission. Pressing the control again will release it from the locked position and the TX SEL indicator will go out to notify the operator that it has been de-selected. More than one transceivers may be selected for simultaneous transmit by pressing multiple TX SEL knobs at the same time. The rotary function of these knobs control volume. The volume at the operator’s headphones may be adjusted from full mute with the knob rotated fully CCW to maximum with the knob rotated fully CW. Receive volume is controlled when the transceiver is receiving audio and sidetone volume is controlled when the transceiver is transmitting audio. 33
TX SEL Indicators
The five TX selection indicators are green dead-front lights which are only visible when back lit. In day light, the indicators are illuminated at full brightness when activated. At night, the indicators are back lit when activated, and are dimmable with the reset of the panel backlighting. RAD PTT ( Radio push-to-talk)
The RADPTT button is a backlit momentary push button that operates ‘in parallel’ with the airframe TX key switch. when pressed , all selected transceivers will transmit , and the TX annunciator illuminates green. The RADPTT labeling is in white daylight-visible text. At night, the button text is backlit and dimmable with the rest of the panel backlighting.
Receive –Transceiver Level Adjustments
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The rotary function of these knobs control volume .the volume at the operator’s headphones may be adjusted from full mute with the knob rotated fully CCW and to maximum with the knob rotated CW .Receive volume is controlled when the transceiver is receiving audio and sidetone volume is controlled when the transceiver is transmitting audio. ICS- Level Adjustment
The ICS control is an illuminated ,clear knob . Rotating the knob in a CW direction increase the ICS volume and rotating CCW decreases the volume. Primary ICS (default )mode shares VOS mic audio between all station via the primary ICS audio bus .ICS volume control cannot be muted or reduced to zero.
VOX/VOS ICS
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The intercom MIC MODE control is clear illuminated knob that selects the mode of operation and sets the VOS(VOX) threshold of the intercom mic When the controls is in center of its range, the intercom is in the voice operated switch(VOS) mode. As the control is rotated CCW, the system becomes more sensitive, until in the fully CCW position it is in HOT mode (on constantly). As the control is rotated CW, the sensitivity decreases, until at the fully CW position it is in a keyed-only state (activated by cyclic or foot switch). Activation of ICS PTT switch will over ride the VOS setting .
Optional Features CALL Control
The CALL control is an illuminated push-on/push-off button labeled CALL in the white day light –visible text. At night, the button text is backlit , and is dimmable with the rest of panel back lighting. CALL ICS mode permits a single station to broadcast HOT mic audio to all other stations via a separate ICS audio bus. A control signal from the station box will cause HOT mic audio from the originating station box to pass to all other stations. This CALL ICS audio is distributed on a separate ICS audio bus at a higher than a typical level(50mW nominal, junction box trim pot adjustable ), by passing all station box switch settings and ICS volume controls. VOS mic audio from station originating the CALL function is muted. When the button is pressed, the associated ON annunciator above the button will illuminate green and all stations will hear the person who is talking independent of their preset volume controls. Other users can talk back by 36
pressing their own CALL button. To release the button, press it again. The ON annunciator will go out The ON annunciator text is dead –front type, which is only visible when backlit.
EMERGENCY OPERATION
Standby/Normal Operation The STANDBY/NORMAL control is a locking , two-position toggle switch, which will switch overall critical functions to duplicate circuits(standby). This transfer will also occur automatically if the normal power supply to the audio junction box fails. When STBY is selected (either manually or automatically), the green STBY annunciator will illuminate. The annunciator is dead-front type, which is only visible when backlit. In day light, the annunciator is illuminated at full brightness when activated. At night, the annunciator is back lit when activated and dimmable with the rest of panel backlighting.
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RX/VOS CARD
RX/VOS card consists of normal, stand by and volume control mode. The front panel volume controls are part of a DC level shifting circuit that is 39
used to control a VCA(Voltage Controlled Amplifier) stage in each user’s interface card within the Audio Junction Box. Volume control or muting for all radios can be achieved by sending the appropriate DC level for each radio source from each Station Box to the appropriate Interface Card in the Audio Junction box. Check the physical switch, to the command line going to the Audio Junction Box at J501 pin 18. This must function correctly for the manual transfer to operate. Loss of any internal power supply will prevent correct manual Normal/Standby transfer, and will force a shift to Standby if on the Normal busses. Open steering diodes or shorted bypass capacitors on any buss supply connection could also produce this effect by creating localized loss of a required power supply, giving the appearance of failed transfer operation. Subassembly N200-3 contains the VOS/VOX mic processor, which has both a normal and standby channel, each is enabled by the respective power supplies being active. U301A is a VCA (voltage controlled amplifier), and is used to provide automatic gain control for the microphone circuit, to prevent overdrive or clipping distortion. The incoming mic signal is sampled by U308, a log amplifier, which output is the comparator drive for the VOS circuit, and the start of the feedback compensation for the VCA. U309A, U309B and U305A form the DC amp portion of the feedback loop to drive the VCA control input. This provides a smooth gain compression curve to prevent excessive mic drive, and give maximum intelligibility in all mic modes. R308 provides the adjustment for the loop compensation. At this point, the hot mic signal is created, and buffered by the U303 mic driver, and output (via power supply switched U304A/B MOS circuits) as the hot mic signal for use in the Audio Junction Box. The input to the hot mic driver (U311) is logically switched by CMOS switches, and then (via power supply switched U316AB MOS circuits) exported to the Audio Junction Box. The output of the mic amp VCA is then further buffered by U302A, and followed by R307 (and buffered again by U302B). R307 provides common mic
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level adjustment for all functions. Note that this will affect EVERY mic signal originating from this station in the normal mode. Mis-adjustment here affects both TX and ICS operations. The U308 Log Amp output also feeds one side of the VOS trigger comparator, U310A, the DC level from the VOS front panel adjustment pot feeds the other side of the comparator after logic qualification (U306D) from TX keying operations. The output of the comparator triggers the U315 one shot, which provides delay for turn-off of the VOS circuit. This combination provides fast turn-on, and slow turn-off of the VOS ICS switch, which is important to avoid unwanted break up during speech. Turn off delay is set by R335. TOTAL HARMONIC DISTORTION Total harmonic distortion is defined as summation of all the voltage or current waveform compared again the fundamental component of voltage or current wave.
Total harmonic distortion is selected by pressing the function THD+N. It is available in both analog and digital modes. THD+N functions uses a notch 41
filter to eliminate the fundamental frequency and then measures the amplitude of signal remaining .This measurement is known as total harmonic distortion. THD+N reading on the top left of the display .The top left soft key selects the units for the measurement. In addition to the usual relative and absolute amplitude units % and dB are provided. The units measure the amplitude of the filtered signal relative to the amplitude of the unfiltered signal. The THD+N is measured using RMS detection except in the few of the filtering modes described below. Several types of filters may also erapplied to the measurement. The filter and the detector combination is selected by the lower left. Selection of the proper band limiting filters is of critical importance in THD+N measurements.
The dominant signal is often wideband noise when
measuring high-quality audio devices, so the specified band-limiting filter must be used if measurements are to correspond manufacture’s specifications. The 80KHz low pass filter is the most commonly used, since it eliminates wide band noise while passing the 2nd and 3rd harmonics of the frequencies within the audio band. Total harmonic distortion plus noise, is one of the most common and widely used measurements which are made on audio devices. Virtually, every type of device used to produce , transmit or process audio signal has THD+N specification. Fundamentally, THD+N is a measurement of sound that it not supposed to be there if your device is creating a sound, you want it to create that sound and nothing else. However, all devices create other sound as well.Unwanted sound breakdown into four basic categories.
Harmonic Distortion: unwanted sound that is related to the desired sound. Random Noise: unwanted sound caused by random fluctuation in eectronic components. 42
Interference: unwanted sound related to the frequency of the device or environment Hum: unwanted sound related to the frequency of the main supply voltage. Harmonic distortion is caused by the slight imperfections in the creation or recreation of the sound. These imperfections generally cause unwanted sounds to be generated at whole-number frequency multiplies of the desired sound. Random noise is created by almost every type of electronic components. Noise sounds generally sound like ‘fff… and are generated regardless of whether there is a desired sound being created or not some noise exist at every frequency. Hum is created by the main supply voltage leaking into the sound signals. Cross talk is a certain type of interference caused by the sound leaking in form other audio channels within the device. The THD+N measurement include all four types of unwanted sound if any of these are excessive ,ti will be noticeable ina THD+N reading .In the way,a single THD+N reading can be a good indication that a device is operating properly . To make a THD+N measurement, we begin having the device create or reproduce a single sine wave called the ‘fundamental tone’ ,which represents the desired sound. Some of the unwanted sounds will also be created ,so the frequency spectrum may look like this .
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The signal is measured with a voltmeter at this point. The measurement will be dominated by the amplitude of the fundamental tone, since it is at a high amplitude relative to the unwanted signals.
The fundamental tone has been reduced to a level where it will be insignificant. The filtered signal is then measured with another voltmeter and the reading is presented a ratio of the two voltmeter. Notice that the final measurement is ‘wideband’. It measure the total of all the noise sources within the frequency range of interest. It is not specific to the frequency of the fundamental tone while some devices many create more or less harmonic distortion for different fundamental frequencies ,the other source of the reading no matter what fundamental frequency is used. What is signal dominant? While all types of unwanted sounds are included in the THD+N measurement ,they may not contribute to the overall reading like all voltmeter
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reading on signals that include several frequency components ,the highest amplitude components will dominate the reading. When comparing two individual signal components such as interference tones or distortion products the limit is commonly considered to be 10Db. If one component is 10dB above the other, only the higher component will be significant to an amplitude reading. However ,when there are many lower components ,the combinations may become significant . For example , random noise can be significant contribution to a THD+N measurements even through its amplitude at any particular frequency is well below other products .since, noise exist at every frequency and each frequency has a tiny effect on the overall reading, noise may be quite significant . Often THD+N tests will be used in conjunction with noise only tests to be certain that a problem is not hiding underneath a more significant contributor.
Selecting Bandwidth Selection of a bandwidth limiting filter is often of critical importance in THD+N measurement. This is mainly for two reasons Noise exists at every frequency .The wider the bandwidth of the measurement the more noise is included. Limiting the bandwidth can eliminate other components, which you may or may not want include in the measurement. The amount of noise include in the measurement will be directly related to the bandwidth. If you are more concerned with distortion and interference products than noise, it is wise to set the upper band limit to allow the highest component of interest but reject noise above the frequency. Most mechanisms that create harmonic distortion concentrate most of the distortion in the second and third multiples (harmonics) of the fundamental . Therefore, foremost devices it is reasonable to limit the bandwidth to around four times the highest fundamental frequency of interest. Change with amplitude
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It is fairly common for the THD+N reading to apparently increases as the fundamental tone amplitude decreases, even if the device does not create more distortion or noise at lower amplitudes. This effects is due to the fact that the THD+N reading is the ratio of the amplitude before filtering to the amplitude after filtering is dominant by noise ,humour interference .it will be essentially constant regardless of the amplitude of the fundamental tone. Therefore as the amplitude of the fundamental tone increases there will be an apparent increases in the calculated ratio. Since all, devices create some noise, any devices has a ‘noise floor’. This is the level of noise that is always created by the devices. If the fundamental tone has a lower amplitude than the noise floor, there will be essentially no difference between the level of filtered and unfiltered signals and the THD+N will be 100%. In some devices, the unwanted signals may actually increases as signals amplitude decreases. If you suspect this, you may want to make an absolute THD+N measurement which does not include the amplitude before filtering in the measurement. This ia accomplished by selecting any unit besides % ordB . All devices also have a maximum allowable amplitude, if the fundamental tone is above this amplitude, the devices will generally ‘clip’ creating very high distortion. Almost any device will show very high distortion reading at maxi or near maximum amplitude.
Note that for some low- distortion devices, the flat area before clipping may shrink or not exist at all. The THD+N measurement may be noise dominated at all amplitude below the clipping threshold. THD+N at 100% (or dB)
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If the THD+N reads 100%(or dB) , the amplitude of the signal id the same before and after the filter. Even if a device is creating a huge amount of distortion or interference, the THD+N should be less than 100% because the signal before the filter should include the fundamental, whereas the signal after the filter should not. If the amplitude of the fundamental tone is below the noise floor, then both amplitude measurements ( before and after the notch filter )will be dominated by noise the amplitude will be the same, and the THD+N will read around 100%. Another common reason for a reading of 100% THD+N is that the notch filter is not correctly tuned to the fundamental frequency. In this case, the signals before and after the filter will be dominated by the fundamental tone, and the filter will be removing nothing except a ting, insignificant piece of the noise floor. If your distortion reading is 100%, check the filter tuning mode. AUTO-TUNE should tune correctly as long as there is sufficient signal amplitude for a valid frequency reading .FIX-TUNE will give 100% eading is unless the filter is tuned to the frequency of the incoming fundamental tone .GEN-TRACIC will give 100% reading if the frequency of the incoming fundamental tone is different from the generator frequency. Change with frequency Sometimes THD+N will be very consistent over the range of frequencies except that it will ‘drop out at one frequency ,giving a very low reading is dominated by significant hum or interference at that frequency. This is common when using a fundamental at 50 or 60 Hz in the presence of significant hum. The reason for this is that the notch filter tracks the fundamental tone when the fundamental tone is far away from the interfering in the signal. The interfering signal is included in the THD+N measurement. When the fundamental tone is at the same frequency as the interfering signal, the notch
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the notch filter removes the interfering signal as well as the fundamental tone. Therefore, the interfering tone is not included in the THD+N measurement at that frequency. This can be a useful technique for locating a source of interference. If you suspect interference at certain frequency, make the THD+N measurements with the fundamental at that frequency .If this measurement is much lower than measurement
made using other
fundamental frequencies ,then there is a interference at the frequency. In some cases, you may see an erroneous dropout in a THD+N frequency sweep because of phase cancellation .This is caused by one of the distortion products of the fundamental tone arriving out of phase with an interfering tone and cancelling it out .When the sweep in run again, the amount of cancellation will vary significantly. If you see an unexpected dropout in a THD+N .sweep, it is good idea to run it several times if it varies significantly with successive runs of the test, then it is probably a cancellation problem. In this case, the low THD+N reading is incorrect.
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TROUBLESHOOTING
There are three distinct levels of troubleshooting activity related to Intercom system. •
Initial Installation troubleshooting
•
In service Installation troubleshooting
•
Bench troubleshooting
7.1 Initial Installation troubleshooting The first step in troubleshooting is to check all the connections in the harness before any units are installed. The harness including the power and ground connections, shielded wires and signal pairs for reversal must be thoroughly tested before any intercom systems are installed. Do not connect the intercom systems components to wiring harness until and unless all wiring continuity has been checked and pin-to-pin, and all specified voltage/resistance checks have been performed, include tests for shorted shield to center conductors on shielded wires, and inverted high/low audio signals. If problem occurs with the initial installation, do not substitute boxes into a problemn location until all wiring has been re-checked between the station box and audio junction box. Incorrect wiring can result in damage to the equipment. 7.2 In-service installation troubleshooting Once the initial installation is proven, and units have been operational in the airframe, fault diagosis takes a different path, and additional tools become available to quickly localize the faulty item in the airframe. There are two general classes of problems in the airframe, System level problems, which will affect all users, and station box problems, which affect 50
only a single user. It is possible to recognise the fundamental difference between these issues. Following the flow of cause and effect, it is possible to arrive at a quick resolution of problems in a large percentage of causes. There can always be special causes unique to any installation that make fault isolation more troublesome, but you should look at the general causes first, and examine special causes only once you have ruled out the high probability faults. 7.2.1 Station box Problems One station is dead or forced into the Standby mode, or is unable to enter Standby mode: Check the DC power connections to the specific station(+/-11Vdc twin busses) at the mating connector. If voltage is not present or incorrect, it indicates a fault in the interface card within the Audio junction box. Disconnect the cable from the Audio junction box, and check for airframe shorts to ground or broken wires in the harness before substituting any new Audio junction box or using a spare interface card position. The intercom does not work at a specific box: Substitute a known good station box in the problem location and see if this corrects the problem. If not, then swap the cable at the audio junction box to a spare interface card in the Audio junction box. If the problem is resolved , replace the audio junction box, if not then check the wiring between the station box and the audio juction box, especially shield to signal shorts and open wiring related to the intercom lines. Transmit mode or ICS Special modes are always or never active at a specific station box: Check the external switches and associated wiring for shorts or opens for the TX or ICS key functions. If the wiring is ok, substitute a known station box in the problem location and see if this corrects the problem. If not, then swap the cable at the audio junction box to a spare interface card in the audio junction box. If the problem is resolved, replace the audio junction box, if not 51
then check the wiring between the station box and the audio junction box, especially shorts and open wiring related to the TX and ICS control lines.
7.3 Bench troubleshooting Because service of a removed line replaceable unit(LRU) isolates the unit from the original fault situation, the first and often most important step in effective troubleshooting a suspect component is to gather as much information about the reported problems as possible. This includes exact operating circumstances, what headset was used, who was involved and whether the problem occurred only once or was persistent. Troubleshooting •
Soldering is a procedure to connect ssemiconductor devices with the help of lead and flux.
•
Flux is used to remove the oxidation.
•
Lead is used as a connectivity material between the two intermediate semiconductor devices.
•
For a good solder joint 37% of lead and 63% of tin is best suitable.
•
Solder temperature required to melt lead is called eutic temperature.
•
Melting temperature of lead is 183 degree.
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Solder temperature required is 300-325 degree.
•
Conformal coating is done on the solder on PCB to avoid avoid conduction when foreign objects contacts with it.
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Isopropyle alcohol is used to remove flux.
•
ESD is one of the few things an individual can do to damage hardware components.
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•
Due to the friction present in the human body charges accumulate on the surface. These charges produces small amount of current and large amount of voltage. This current flows through track in the multilayer PCB which results in the reduction of durability of the components.
•
The best method of preventing ESD is to use an ESD wrist strap, grounding mat or grounding work bench. Include some steps to help reduce the chances of ESD as much as possible by providing zero potential etc.
The flow chart is a typical best practices path for reported “failed unit” unit correction.
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DESCRITION OF TESTKIT TESTKIT LAYOUT
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Test kit description The test kit is partitioned into 2 blocks, one block is for rx/vos placement and test point measurements for the rx/vos card . There are 12 test points for measurement and each point is a female banana socket of diameter 2mm. Another block is for power supply, signal control and power controls . The power supply slot is provided with 11V, 5A banana sockets for power supply to the power controls. Audio analyzer is used to generate 750microvolts , audio analyser is fed to the signal controls slot . 2 single pole 2 position toggle switch is used for power controls and each switch is indicated by its respective led’s Front view of test kit
Top view of test kit
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TEST SETUP
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Wiring Procedure 20,22 gauge cables are stripped using stripper As per the wiring diagram, the cables are soldered to the respective components The cables are crimped and spliced so that they are connected to the corresponding connectors Tools used for the wiring: •
Stripper
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Crimper
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•
Solder
•
Flux
•
Pins
•
Nose player
•
Multimeter
•
Lead
Mechanism Stripper: Removing the outer buffer layer of the cable to the core layer Crimper: technique used to fix the pins to the cables so that it can be further connected to the connectors. Splicing: Joining one cable to two or more cables using gold/steel pins to establish a continuous path
COMPONENTS REQUIRED
SL NO 1
COMPONENT Banana sockets 2mm
QUANTITY 12
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2
Banana sockets 4mm
3
3
BNC connectors
6
4
Led
7
5
SPDT toggle switch
5
6
Pogo pins
12
7
Co axial cables (0.25m)
5
8
Dual power supply
1
9
Audio analyser
1
10
Station box
1
11
D type 50pin connector
1
12
D type 15 pin connector
1
13
30 pin bus cable
1
14
30 pin bus male jack
1
15
BNC probes
3
16
4mm connecting probes
4
17
Mica insulating sheet
1
18
Epoxy glue
1
19
Prospect sheet
2
20
Connecting wires
WIRING DIAGRAM
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Fig: Powered test setup
Fig: Powered test kit
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TEST PROCEDURE Set TS-N200 switches to the following positions. •
LOCAL/REMOTE to LOCAL.
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LOAD to 600 OHM.
•
All other TS-N200 switches to the down position.
Connect TS-N200 connector J65 AND J66 using test cable . Set N200-ALH front panel controls to the following positions. •
TX SEL knobs fully ccw and to the out position.
•
RX SEL knobs fully ccw.
•
STBY/NORMAL to NORMAL.
Connect the left power supply to +11 and -11vdc power. Connect the audio analyzer input to TS-N200 CONTROLLED MIC and TS -N200 NORM phones connector. Connect the audio analyzer generator output to TS-N200 MIC connector and set the output to 750micro vrms @1khz with 50 Ohm BAL output impedance. Set TS-N200 NORM PWR to ON. The TS-N200 +VN LED will illuminate. PERFORMANCE TEST
MICROPHONE AUDIO The audio analyzer should read 2.0 to +/- 0.2Vrms. Set N200-ALH MIC MODE fully CW .The audio analyzer should read <2 mV rms. Set TS-N200 ICS to up position. The audio analyzer should read 2.0+/0.2 v rms. Set TS-N200 ICS to the down position. Set TS-N200 TX Switch to the up position. The audio analyser should read to 2.0+/-0.2V rms. Set TS-N200 TX Switch to the down position.
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Turn the audio analyser generator output OFF and set TS-N200 LOAD switch to the up position. Set N200-ALH MIC MODE fully CCW. Increase the audio analyser MONITOR volume until a tone is audible. Set N200-ALH MIC MODE to the 12 o’ clock position. Decrease the audio analyser generator output until the tone is no longer audible. The audio analyser generator output should be 100-500 micro V rms. Decrease the audio analyser MONITER volume.
PHONES AUDIO
Connect the audio analyzer input to TS-N200 STATION BOX PH connector. Connect
TS-N200 NORM PHONES connector to TS-N200
CONTROLLED MIC connector. Set N200-ALH MIC MODE fully CCW. ensure the N200-ALH is set for NORMAL mode operation. The audio analyzer should read 11.0+/- 0.5 Vrms with <10% THD+N. Set the audio analyzer generator output to 750micro vrms @ 200hz. The audio analyzer should read >7.7 vrms with 10%THD+N. Set the audio analyzer generator output to 750 micro Vrms @ 3500hz. The audio analyzer should read >7.7Vrms with <10% THD+N. Set the audio analyzer generator output 750 micro vrms @1khz. Remove the connection to TS-N200 NORM PHONES connector and connect it to TS-N200 STBY PHONES connector. Set TS-N200 NORMAL PWR switch to the down position and TS-N200 STBY PWR switch to the up position. The audio analyzer should read 11.0+/-0.5 vrms . Set the audio analyzer generator output to 750 micro vrms @ 200 hz the audio analyzer should read >7.7vrms with <10% THD+N. Set the audio analyzer generator output to 750micro vrms @3500 hz . the audio analyzer should read >7.7vrms with >10% THD+N. Set the audio analyzer generator output to 750 micro vrms @1khz.
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Set the audio analyzer generator output to 1mv @1khz.the audio analyzer should read 11.5+/-0.7 vrms. Remove the connection to TS-N200 STBY PHONES connector to connect it to TS-N200 NORM PHONES connector .set TS-N200 STBY PWR position to the down position and TS-N200 STBY PWR position to the down and TS-N200 NORMAL PWR switch to the up position. Set the audio analyzer generator output to 1 mv @ 1khz. The audio analyzer should read 11.5+/-0.7 vrms. VOS DELAY Set the audio analyzer generator output to 750micro vrms @ 1khz.increase the audio analyzer MONITOR volume until tone is heard. Quickly rotate N200-ALH MIC MODE fully cw. The audio analyzer MONITOR audio should mute between 0.5 and 1.5seconds.set N200ALH MIC MODE fully ccw.
Voltages at different test ponits are measured and are as follows.
At points E302(Normal) and E341(Stby)
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At points E305(Normal) and E344(Stby)
At points E303(Normal) and E342(Stby)
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At points E306(Normal) and E345(Stby)
At points E304(Normal) and E343(Stby)
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PERFORMANCE CHECKS
CONTROLS •
OBJECTIVE
MIC PHONE AUDIO
50 ohm Audio analyzer MIC MODE fully CW
2.0+.2 Vrms(N) 2.0+.2 Vrms(S) <2m Vrms(N) <2m Vrms(S)
ICS532-up
2.0+.2 Vrms(N) 2.0+.2 Vrms(S)
TXS30-up
2.0+.2 Vrms(N) 2.0+.2 Vrms(S)
S31-center MIC MODE fully CCw Audio analyzer generator output 750micrometer Audio analyzer GEN load
•
Audio with no unusual noise or Description (N) Audio with no unusual noise or Description (S) 2.0+.2 Vrms(N) 2.0+.2 Vrms(S) 7.5+/-7ohm
PHONE AUDIO
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MIC MODE fully CCW Normal Mode
11+/-5Vrms,40% THD
Audio Analyzer generator at 75 Vrms Audio Analyzer generator at 200Hz Audio Analyzer generator at 3500Hz MIC MODE fully CCW Standby Mode
>7.7Vrms,40%THD
Audio Analyzer generator at 75 Vrms Audio Analyzer generator at 200Hz Audio Analyzer generator at 3500Hz
>7.7Vrms,40%THD >7.7Vrms,40%THD VOS delay,.5+1.5sec 11+/-.5Vrms,40% THD >7.7Vrms,40%THD >7.7Vrms,40%THD >7.7Vrms,40%THD
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FUTURE SCOPE
To design a regulated dc power supply of +/-11V with a current rating of 1A/2A.
To utilize a DSP for analysing the audio signal and calculation of THD in the audio signal.
Using of embedded microcontroller to automise the testing of station box as per CMM.
To prepare a test jig for all the cards in the station box for component level testing.
CONCLUSION
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Incircuit tester for testing individual card is designed and tested.
Component level testing is done and is troubleshooted.
Overseas expenditure is minimized.
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