Indian Railways Telecom Manual - 2021: Equipment Installation

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Questions and Answers

What is the primary consideration for determining the height of the rack?

The size of the patch cords used

The number of equipment to be mounted and manual controls' ease of reach (correct)

The type of insulation required for the amplifier

The type of power supply available

Why should switches be provided for isolating faulty sections of the equipment?

To facilitate the operation of the equipment

To enable the remaining part of the equipment to be available for use (correct)

To ensure the safety of operating personnel

To avoid obstruction by patch cords

What should be done to avoid accidental contacts with high voltage points in the rack?

The amplifier should be able to withstand a dielectric strength test

The switches should be provided for isolating faulty sections

The patch cords should be tested and neatly arranged

Necessary safety measures should be adopted (correct)

What is the purpose of a voltage regulating device in the power supply?

To regulate the power supply to within ±5% Signup and view all the answers

What should be used when no mains supply is available?

A petrol or oil engine driven generating set Signup and view all the answers

What should be tested and neatly arranged to avoid obstruction?

The patch cords Signup and view all the answers

What is the minimum dielectric strength test voltage required for the amplifier and loudspeakers?

1000 AC rms for two seconds Signup and view all the answers

What is the normal operating voltage of the installation?

230 V single phase 50 Hz AC Signup and view all the answers

What is the recommended location for a generating set to avoid noise interference?

In another building at some distance from the hall Signup and view all the answers

What is the recommended power supply for amplifiers?

Both 230 V, 50 Hz AC supply and 12 V/24 VDC Car Battery Signup and view all the answers

Why are twisted pairs of conductors with sufficient insulation and screening used for microphone cables?

To reduce electrical interference Signup and view all the answers

What is the purpose of using separate ladders or ducts for microphone cables?

To isolate them from power, loudspeaker, and telephone cables Signup and view all the answers

Why should joints in microphone cables be avoided?

To minimize the risk of electrical interference Signup and view all the answers

What type of plugs and sockets should be used for microphone cables?

Strong, non-reversible contacts with sufficient pins Signup and view all the answers

Why should microphone cables be laid without sharp bends?

To minimize the risk of damage to the cables Signup and view all the answers

What type of cables should be used in 25 kV ac electrified areas?

Cables with their shields earthed Signup and view all the answers

What should be considered when using bare copper wire as an earthing connection lead?

It should be run insulated from other metallic objects. Signup and view all the answers

What is the maximum resistance allowed for the earthing of metal mounting of the cone type loudspeakers and the body of the horn type loudspeakers?

10 ohms Signup and view all the answers

What standard should amplifiers operating from mains supply conform to?

IS:9302 Signup and view all the answers

What should be avoided when installing a system in an area with a risk of explosion or inflammable atmosphere?

Vulnerability to fire explosion risks Signup and view all the answers

How often should the frequency response and the noise level of the amplifier be checked?

Annually Signup and view all the answers

How often should the earthing arrangement be inspected?

Quarterly Signup and view all the answers

What should be checked in addition to the earthing arrangement during inspection?

Alternating current induction hum at 50 Hz and its harmonics Signup and view all the answers

What is the recommended maintenance schedule for the general conditions of wiring and components of the entire system?

Annually Signup and view all the answers

What is the primary purpose of using matching transformers with loudspeakers in a public address system?

To enable the loudspeaker to take an input of predetermined value of audio load from the amplifier Signup and view all the answers

When connecting multiple loudspeakers to the same output circuit, what is the recommended connection method?

Parallel connection in phase across the output line Signup and view all the answers

What is the minimum frequency characteristic required for transformers used in a public address system?

The minimum frequency characteristic required of the public address system Signup and view all the answers

Why should the pair of wires from each loudspeaker group be terminated on the announcer's panel?

To enable isolation of the line from the output of the amplifier in case of a fault Signup and view all the answers

What is the minimum power handling capacity of the transformer used with a loudspeaker?

The power to be absorbed by the speaker Signup and view all the answers

What is the primary function of the taps on the primary and/or secondary of the transformer?

To provide multiple turns ratio for impedance matching Signup and view all the answers

When using a constant voltage output line from the amplifier, what limitation applies to the total wattage of the loudspeaker load?

It should not exceed the rated power of the amplifier Signup and view all the answers

What should be done when a single loudspeaker unit is to be connected to the amplifying system?

Its impedance should be matched to the source impedance to consume the rated power Signup and view all the answers

What is the recommended voltage range for constant voltage working in transformers?

70 to 100 volts Signup and view all the answers

What is the primary purpose of incorporating safeguard in high power amplifiers?

To protect against open circuit or short circuit conditions Signup and view all the answers

What is the advantage of having a seamless automatic changeover arrangement in standby amplifiers?

It reduces the need for technical staff Signup and view all the answers

Why is it essential to have convenient access to all sides of the equipment during installation?

To enable easy maintenance and repairs Signup and view all the answers

What is the primary reason for mounting equipment in racks?

To minimize the length of inter-connecting cables Signup and view all the answers

What is the benefit of having a provision for easy localisation and rectification of faults in any part of the installation?

It minimizes downtime and improves overall efficiency Signup and view all the answers

Why is it important to take precautions to keep dust away from the equipment during installation?

To reduce the risk of equipment failure Signup and view all the answers

What is the primary consideration when positioning equipment on a table or in racks?

Keeping the lengths of inter-connecting cables minimum Signup and view all the answers

In quiet places like waiting rooms and refreshment rooms, the sound level should be higher by how many decibels?

5 dB Signup and view all the answers

What should be provided during VVIP functions to avoid total interruption of service?

A standby battery operated audio system Signup and view all the answers

What is the advantage of using multi-contact microphone plugs and sockets?

To allow for easier connectivity and interchangeability Signup and view all the answers

What should be prepared and made available along with circuit diagrams for each equipment?

Block diagrams and schematic diagrams Signup and view all the answers

Why is it desirable to create the illusion that sound is being heard directly in a sound distribution system?

To minimize the effects of reverberation Signup and view all the answers

Where should the location of the central equipment, loudspeakers, and microphones be fixed?

By the engineer Signup and view all the answers

What should be indicated in the circuit diagrams for each equipment?

All of the above Signup and view all the answers

What is the primary function of a standby amplifier?

To enable seamless automatic changeover in case of failure Signup and view all the answers

What is the primary consideration for siting microphones and loudspeakers in a closed hall?

To reduce acoustic feedback Signup and view all the answers

Why should care be exercised in using the nomogram?

It is only applicable to halls with good acoustics Signup and view all the answers

What is the recommended way to mount equipment?

In racks of suitable dimensions Signup and view all the answers

Why should the microphone be sited normally in an acoustic shadow?

To reduce acoustic feedback Signup and view all the answers

What should be obtained from the competent authority?

Approval of plans for the proposed installation Signup and view all the answers

What is the primary consideration for equipment installation?

Robust construction and continuous operation Signup and view all the answers

What is the benefit of using a mixing system to combine the output from multiple microphones?

To allow for easier control and mixing of individual microphone inputs Signup and view all the answers

Why is it important to guard against unauthorised access to equipment?

To prevent equipment misuse Signup and view all the answers

Why is it important to predetermine the correct distance between the microphone and source?

To ensure consistent and optimal sound pickup Signup and view all the answers

In noisy places like railway platforms, the sound level should be higher by how many decibels?

10 dB Signup and view all the answers

What is the purpose of reducing the distance between the microphone and source in high-reverberation environments?

To compensate for high levels of reverberant sound Signup and view all the answers

What should be taken into consideration when installing equipment in an area with earth moving machines?

Dust accumulation Signup and view all the answers

Why should the microphone be placed behind the loudspeaker?

To minimize the risk of sound from the loudspeaker reaching the microphone Signup and view all the answers

What is the recommended voltage range for constant voltage working in transformers?

70-100 volts Signup and view all the answers

What is the primary purpose of incorporating safeguard in high power amplifiers?

To prevent excessive voltage or current rise Signup and view all the answers

What should be provided for easy rectification of faults in the installation?

A provision for easy localisation Signup and view all the answers

What is the primary purpose of earthing an entire installation?

To avoid danger from possible shocks to users and operating personnel Signup and view all the answers

Why is it inadvisable to use two or more separate earthing connections at different points on the system?

It increases the risk of trouble from circulating currents Signup and view all the answers

What should be done to avoid hum in the installation?

Connect the screening leads of a microphone to a separate insulated lead Signup and view all the answers

What should be followed for wiring loudspeaker installations?

Both A and B Signup and view all the answers

What is the recommended method of earthing an equipment or installation?

All of the above Signup and view all the answers

Why should the earthing connection from water supply mains or other earthed electrode be brought to an earth-busbar in the equipment room?

To make it easier to connect the earthing leads to the equipment Signup and view all the answers

What should be done to ensure safety and avoid obstruction in the normal functioning of the installation?

The layout and wiring of cables for loudspeakers should be done in a way that minimizes safety risks Signup and view all the answers

What should be followed to avoid danger from possible shocks to users and operating personnel?

Proper earthing of the entire installation Signup and view all the answers

Who should inspect and test the completed permanent installation?

ADSTE/DSTE Signup and view all the answers

How often should the routine inspection of the installation be carried out?

At intervals in accordance with the manufacturer's instructions Signup and view all the answers

What is the absorption coefficient of a brick wall with lime plaster at 512 Hz?

0.03 Signup and view all the answers

What should be kept in which details of all routine attention, faults and tests should be carefully recorded for scrutiny?

Log book Signup and view all the answers

What is the purpose of a log book in the installation?

To record the details of all routine attention, faults and tests Signup and view all the answers

Who should inspect and test the temporary installation?

SSE/JE Signup and view all the answers

What should be carried out in accordance with the manufacturer's instructions or as specified from time to time?

Routine inspection Signup and view all the answers

What is the absorption coefficient of a heavy curtain at 512 Hz?

0.35 to 0.5 Signup and view all the answers

Study Notes

Rack Installation

The height of the rack depends on the number of equipment to be mounted and available accommodation, ensuring all manual controls are within easy reach.
Switches should be provided to isolate faulty sections of equipment, allowing the remaining part to be available for use.
Patch cords should be tested, neatly arranged, and easily identifiable to avoid obstruction and accidental contacts with high voltage points.
Insulation is required in 25 kV ac electrified areas, with the amplifier, cable, and loudspeakers able to withstand a dielectric strength test voltage of 1000 AC rms for two seconds.

Power Supply

A reliable mains power supply should be available near the proposed location of the announcing equipment.
The installation should normally operate from 230 V single phase 50 Hz AC mains supply.
A voltage regulating device is required if the power supply regulation is poorer than ±5%.
If only DC supply is available, an inverter of required capacity should be provided to convert DC supply into AC supply.
If no mains supply is available, a petrol or oil engine driven generating set of required capacity giving 230 volts single phase 50 Hz, AC should be used.

Amplifier Installation

High power amplifiers should incorporate safeguards against excessive voltage or current rise in case of open circuit or short circuit conditions.
Standby amplifiers should be provided to ensure announcement is not held up due to defects in the working of amplifiers.
Seamless automatic changeover or easy changeover arrangement for switching from defective to standby amplifiers is preferable.
Provision should be available for easy localization and rectification of faults in any part of the installation.

Installation

All equipment should be robustly made and designed for continuous operation.
Equipment should be securely installed with convenient access to all sides and protection from unauthorized access.
Precautions should be taken to keep dust away from the equipment, especially in areas with earth moving machines or concrete mixers.
When the number of equipment is large, it is desirable to mount them in racks of suitable dimensions.
All amplifiers should preferably be capable of operating on 12 V/24 VDC Car Battery besides on 230 V, 50 Hz AC supply.

Wiring and Cabling

Microphone cables should carry low-level signal currents and be susceptible to electrical interference.
Twisted pairs of conductors with sufficient insulation, screened continuously with close mesh of tinned copper braid, should be used.
The copper braiding should be sheathed with an insulated covering, and microphone cables should be isolated from power, loudspeaker, and telephone cables.
Joints in the cables should be avoided as far as possible.
Plugs and sockets used for microphone cables should have strong self-cleaning contacts and be non-reversible with sufficient number of pins.
Microphone cables should be laid without sharp bends and may be laid on the floor along walls or under the carpet to avoid damage.

Earthing

Earthing leads should use a fairly heavy cable (such as 7/0.75 mm VIR in conduit) or bare copper wire (4.0 mm dia).
In electrified areas, the metal mounting of the cone type loudspeakers and the body of the horn type loudspeakers shall be earthed, with a resistance not exceeding 10 ohms.

Safety Requirements

Amplifiers operating from mains supply shall conform to the requirements specified in IS:9302 - Mains operated audio amplifiers.
The installation of the system in a situation where there may be a possibility of an explosion or in an inflammable atmosphere should be avoided, and fire extinguishers and smoke/fire detecting systems should be provided.

Maintenance

The general condition of wiring and components of the entire system should be checked once every year.
The frequency response and the noise level of the amplifier shall be checked annually and recorded.
The earthing arrangement shall be maintained properly and inspected once in a quarter, with alternating current induction hum at 50 Hz and its harmonics also checked.

Connecting Microphones

In large stages, multiple microphones may be necessary, and their outputs should be mixed in a mixing system before feeding into the amplifier.
Microphone plugs and sockets should be of multi-contact (three or more) type and freely interchangeable.

Siting of Microphone and Loudspeaker

Microphones and loudspeakers should be positioned to avoid acoustic feedback and ensure good sound distribution.
The microphone should be placed in an acoustic shadow to minimize feedback.
The correct distance between the microphone and source should be predetermined and maintained as constant as possible.
If the level of reverberant sound or surrounding noise near the microphone is high, the distance between the microphone and source should be reduced.

High Power Amplifiers

High power amplifiers should have safeguards against excessive voltage or current rise in case of open circuit or short circuit conditions.

Standby Amplifiers

Standby amplifiers should be provided to ensure continuous announcements in case of defects in the working amplifiers.
Seamless automatic changeover or easy changeover arrangements should be provided for switching from the defective amplifier to the standby amplifier.
Provision should be available for easy localization and rectification of faults in any part of the installation.

Installation

All equipment should be robustly made and designed for continuous operation.
Equipment should be securely installed with convenient access to all sides and protected from unauthorized access.
Precautions should be taken to keep dust away from the equipment, especially in areas with earth-moving machines or concrete mixers.
The positioning of equipment should be such that the lengths of inter-connecting cables are kept minimum.
In large installations, equipment should be mounted in racks of suitable dimensions.

Electrical Power Requirement

A nomogram can be used to determine the required electrical power output of the amplifying system based on the volume to be covered, required sound pressure level, reverberation time of the hall, and loudspeaker efficiency.
A standby suitable battery-operated audio system should be provided during VVIP functions to avoid total interruption of service.

Circuit Plans and Operating Instructions

Complete block diagrams and schematic diagrams should be prepared and made available along with circuit diagrams for each equipment.
The layout and sizes of wiring and cabling should be indicated, and the loudspeaker load connected to each output line and the particulars of the line transformer should be specified.
Operating instructions should be made available along with the rating of fuses to the operating staff.

Earthing and Other Safety Precautions

The layout and wiring of cables for loudspeakers should be done to ensure safety and avoid obstructions.
The Indian Electricity Rules 1956 and the Indian Standard Code of Practice for Electrical Wiring and Fittings in Buildings (IS:732-1958) should be followed.
Proper earthing of the entire installation is essential to avoid danger from possible shocks.
Earthing connections to the nearby water mains are usually of lower resistance than any form of buried earth electrode system.

Inspection and Testing

The completed permanent installation should be inspected and tested by the ADSTE/DSTE to ensure that the work is being carried out satisfactorily and that the materials and components used conform to standard practice.
Routine inspection of the installation should be carried out at intervals in accordance with the manufacturer's instructions or as specified from time to time.
A log book should be kept to record details of all routine attention, faults, and tests.

Annexe A: Absorption Coefficient

Absorption coefficients at 512 Hz for various materials:
- Brick wall-lime plaster: 0.03
- Brick wall opening: 0.02
- Woodwork: 0.05
- Concrete glasses tile: 0.015
- Carpet: 0.15 to 0.21
- Heavy curtain: 0.35 to 0.5
- Cellotex 1" thick: 0.8
- Acoustic plaster: 0.3
- Hair felt: 0.4
- Glazed windows: 0.027
- Gypsum plaster: 0.028
- Plywood chair: 0.03

Annexe C: Loudspeaker Cable Sizes and Lengths

Low impedance lines: 15% power loss

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Description

This quiz is about the installation guidelines for equipment in Indian Railways, focusing on the height of the rack, manual controls, and safety features.