Functional requirements for electric motor sirens, Part 1: ac 3 phase 50 Hz, 415 volts type

Scope of IS 1941 Part 1 (1976)

• Covers: Construction and performance of electric motor sirens up to 3.75 kW, 3-phase, 50 Hz, 415 V AC supply.
• Excludes: Sirens of other types such as 240 V single-phase, universal motors, and battery-operated (6/12 V) sirens (covered separately).

Key Performance Specification (Clause 7.1):

• Siren must produce acoustic power ≥ 200 W.
• Corresponds to a sound power level of 143 dB referenced to (10^{-12} W).

Rounding Off (Clause 0.3):

• Final test values must be rounded per IS 2-1960.
• Retain the same number of significant figures as the specified value.

Summary Table

flowchart LR
    A[IS 1941 Part 1 Scope] --> B[Electric Motor Sirens]
    B --> C[Power ≤ 3.75 kW]
    B --> D[Voltage: 415 V, 3-phase]
    B --> E[Frequency: 50 Hz]
    B --> F[Acoustic Power ≥ 200 W]
    F --> G[Sound Level 143 dB]

This concise scope defines the siren's electrical and acoustic performance requirements under IS 1941 Part 1.

IS 1941 (Part 1) - General Requirements Summary

• Scope: Covers electric motor sirens up to 3.75 kW, 3-phase, 50 Hz, 415 V AC motors.
• Rounding Off: Final test results must be rounded per IS 2-1960, retaining the same significant figures as specified.

Key Specification (Clause 7.1)

• Minimum Acoustic Power:
  [ P_{acoustic} \geq 200 \text{ W} ]
• Corresponding Sound Power Level:
  [ L_w = 143 \text{ dB re } 10^{-12} \text{ W} ]

Notes

• The acoustic power level corresponds to the siren's minimum sound output.
• Other siren types (240 V, battery operated) are covered in separate drafts.

Rounding Off Rule (IS 2-1960)

• Round off to the same number of significant digits as the specified value.

flowchart LR
    A[Electric Motor Siren] --> B[Power ≤ 3.75 kW]
    B --> C[3-phase, 50 Hz, 415 V]
    C --> D[Produces ≥ 200 W Acoustic Power]
    D --> E[Sound Level ≥ 143 dB (ref 10⁻¹² W)]

This ensures sirens meet minimum acoustic performance for safety and compliance.

Key Specifications for Electric Motor (IS 1941 Part 1):

• Supply System:

  • 3-phase, 415 V, 50 Hz AC
  • Number of poles: Two

• Motor Construction:

  • Totally enclosed type with greased sealed ball bearings
  • Conforms to IS 325:1970 (3-phase induction motors)
  • Temperature rise after 15 minutes continuous operation shall not exceed specified limits
  • Windings insulated and impregnated for damp/moist climates (monsoon conditions)

• Accessories:

  • Small lock-up box for spare carbon brushes, springs, etc. (Clause 2.6)
  • Starter relay and wailing switch motor may operate on single-phase 240 V for remote control

Important Notes:

Reference Formula for Temperature Rise (from IS 325):

[ \Delta T = T_{final} - T_{ambient} \leq \text{Specified limit (usually 80°C max)} ]

flowchart TD
    A[Electric Motor] --> B[3-phase, 415 V, 50 Hz]
    A --> C[Two Poles]
    A --> D[Totally Enclosed]
    A --> E[Greased Sealed Ball Bearings]
    A --> F[Insulated Windings for Moist Climate]
    A --> G[Lock-up for Spare Brushes]
    A --> H[Starter Relay on 240 V Single Phase]

This summary ensures compliance with IS 1941 Part 1 for electric motors used in siren units or similar applications.

IS 1941 Part 1 Key Points: Blower Heads & Acoustic Frequency

Blower Heads (Clause 4.1)

• Two blower heads fitted on motor shaft (same or opposite side).
• Must have unequal number of slots on stators.
• Produce a basic acoustic frequency between 400 Hz and 1000 Hz.
• Stator and rotors made of aluminium alloy or similar material.
• Blower heads should be properly balanced.

Acoustic Power Formulas for Sirens

1. Reverberant Room Method (Clause 7.1.1)

[ 10 \log_{10} W = 20 \log_{10} P_m - 10 \log_{10} T + 10 \log_{10} V - 14 ]

Where:

• ( W ) = Acoustic power output (watts)
• ( P_m ) = Mean sound pressure level due to siren (Pa)
• ( T ) = Reverberation time (seconds)
• ( V ) = Volume of reverberant room (m³)
• Reference power ( W_0 = 10^{-12} ) W

2. Reference Source Method (Clause 7.1.2)

[ 10 \log_{10} W = 10 \log_{10} W_r + 20 \log_{10} P_o - 20 \log_{10} P_r ]

Where:

• ( W ) = Acoustic power of siren under test (W)
• ( W_r ) = Acoustic power of reference siren (W)
• ( P_o ) = Mean sound pressure level due to siren under test (Pa)
• ( P_r ) = Mean sound pressure level due to reference siren (Pa)

Simplified:
Acoustic power level (dB) of test siren = Acoustic power level of reference + (Sound pressure level of test siren - Sound pressure level of reference)

Specification Summary

• Sirens must produce ≥ 200 W acoustic power (143 dB ref. (10^{-12}) W).
• Motor blower heads designed for frequency range 400–1000 Hz.

flowchart LR
    A[Motor

Automatic Equipment for Producing a Warbling Note (IS 1941 Part 1)

Key Specifications:

• Motor & Blower Heads (Clause 4.1):

  • Two blower heads, balanced, mounted on the same or opposite motor shaft side.
  • Unequal number of slots on stators.
  • Basic frequency range: 400 to 1000 Hz.
  • Stator and rotor material: Aluminium alloy or similar.

• Warbling Note Operation (Clause 5.1):

  • Controlled by motor-driven cam or equivalent.
  • Power supply: 240 V, single phase, 50 Hz AC.
  • Warbling cycle: 4 seconds ON, 4 seconds OFF.
  • Frequency drop during OFF cycle: 10-15% of basic frequency.
  • Durability: 20,000 cycles without failure.
  • Motors comply with IS: 996-1964.

• Acoustic Power Output (Clause 7.1):

  • Minimum acoustic power: 200 W.
  • Corresponding sound power level: 143 dB (ref. 10⁻¹² W).

Acoustic Power Calculation (Clause 7.1.2):

[ 10 \log_{10} W = 10 \log_{10} W_r + 20 \log_{10} P - 20 \log_{10} P_r ]

Where:

• (W) = Acoustic power of siren under test (W)
• (W_r) = Acoustic power of reference source (W)
• (P) = Mean sound pressure level of siren (Pa)
• (P_r) = Mean sound pressure level of reference source (Pa)

Simplified:
Siren dB Level = Reference Source dB + (Siren Pressure dB - Reference Pressure dB)

Summary Table

IS 1941 Part 1 - Motor Starter and Finishing Key Points

Motor Starter (Clause 6.1)

• Must comply with IS 1822-1967 (Specification for motor starters).
• Suitable for 3-phase, 415 V, 50 Hz supply.
• Relay and wailing switch motors can operate on single-phase 240 V for remote control.

Electric Motor (Clause 3)

• Type: Totally enclosed, with greased sealed ball bearings (IS 325-1970).
• Poles: Two poles.
• Temperature rise: Shall not exceed limits after 15 minutes continuous operation.
• Insulation: Windings insulated and impregnated for damp/moist climates.
• Spare parts storage: Lock-up box for brushes, springs, etc. (Clause 2.6).

Typical Motor Starter Selection Parameters:

Formula for Motor Full Load Current (approximate):

[ I = \frac{P}{\sqrt{3} \times V \times \eta \times \cos \phi} ]

• (P) = motor power (W)
• (V) = line voltage (V)
• (\eta) = efficiency (decimal)
• (\cos \phi) = power factor

flowchart LR
    A[Power Supply 415V, 3-Phase] --> B[Motor Starter (IS 1822)]
    B --> C[Electric Motor (IS 325)]
    C --> D[Load]
    B -. Remote Control (240V Single Phase) .-> E[Starter Relay & Wailing Switch]

This summarizes the key compliance and technical specs for motor starters and finishing per IS 1941 Part 1.

IS 1941 Part 1 - Acoustic Power of Sirens

Key Formulas:

1. Direct Measurement in Reverberant Room (Clause 7.1.1):

[ 10 \log_{10} W = 20 \log_{10} P_m - 10 \log_{10} T + 10 \log_{10} V - 14 ]

• (W) = Acoustic power output (watts)
• (P_m) = Mean sound pressure level due to siren (N/m²)
• (T) = Reverberation time (seconds)
• (V) = Volume of reverberant room (m³)
• Reference power (W_0 = 10^{-12} W)

2. Comparison Method Using Reference Source (Clause 7.1.2):

[ 10 \log_{10} W = 10 \log_{10} W_r + 20 \log_{10} P_m - 20 \log_{10} P_r ]

• (W) = Acoustic power of siren under test
• (W_r) = Acoustic power of reference siren (known)
• (P_m) = Mean sound pressure level of siren under test
• (P_r) = Mean sound pressure level of reference siren

Specification:

• Minimum acoustic power: 200 W (143 dB re (10^{-12}) W) (Clause 7.1)
• Paint finish: Steel grey, with corrosion protection by nickel plating, galvanizing, or painting (Clause 6.3)

Notes:

• Sound pressure levels are measured in a reverberant room to ensure diffuse field conditions.
• Reverberation time (T) and room volume (V) are critical for accurate power calculation.

flowchart LR
    A[Siren] --> B[Sound Pressure Level \(P_m\)]
    B --> C[Reverberant Room]
    C --> D[Measure Reverberation Time \(T\) & Volume \(V\)]
    D --> E[Calculate Acoustic Power \(W\) using formula]

This provides a reliable method to quantify siren acoustic power per IS 1941 Part 1.

IS 1941 Part 1 - Marking: Key Points & Specifications

Marking Requirements:

• Rounding Off Values:
  As per IS:2-1960, test results must be rounded off to the same number of significant figures as specified in the standard.

• Acoustic Power for Sirens (Clause 7.1):

  • Minimum acoustic power: 200 W
  • Corresponding sound power level: 143 dB (reference 10⁻¹² W)

Important Notes:

• The sound power level (Lw) in decibels is calculated by:
  [ L_w = 10 \log_{10} \left(\frac{P}{P_0}\right) ]
  where:

  • (P) = acoustic power (W)
  • (P_0 = 10^{-12} , W) (reference power)

• For 200 W,
  [ L_w = 10 \log_{10} \left(\frac{200}{10^{-12}}\right) = 143 , dB ]

Summary Table:

flowchart LR
    A[Test Result] --> B[Rounding off]
    B --> C[Same significant figures as specified]
    D[Siren Acoustic Power] --> E[≥ 200 W]
    E --> F[Sound Power Level ≥ 143 dB]

For detailed marking and labeling, always refer to the exact clauses of IS 1941 Part 1 and IS 2-1960 for rounding rules.