Simcenter Testing Solutions Simcenter Testlab Pass-by Noise Testing

Simcenter SCADAS Simcenter Testlab



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In many countries, there are legislated noise limits on vehicles (passenger cars, heavy trucks, motorcycles, construction equipment, …). These limits are used to reduce noise exposure in populated areas.  With the advent of electric vehicles, there are additional minimal noise level requirements to ensure pedestrian safety.

Simcenter Testlab Pass-by Noise Testing systems are used to measure the noise emissions of vehicles to ensure they meet regulatory requirements. 

The pass-by testing system has two functions:
  • Noise Measurement: The system measures the noise level as the vehicle passes by microphones at a prescribed distance.
  • Correct Test Procedure: Ensures the vehicle is driven in the manner prescribed by the standards including vehicle speeds or accelerations, as well as appropriate weather or track conditions.

A pass-by noise test is shown in Figure 1:
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Figure 1: Vehicle moving past microphones during a pass-by noise test.

The features and functions of Simcenter Testlab Pass-by Noise Testing system are described in this article.

1.    Introduction to Pass-by Noise
    1.1 Pass-by Noise Limits
    1.2 Standards (ISO 362, ISO 6395)
     1.3 Pass-by Noise Setup
2.    Hardware
    2.1 Acquisition System
    2.2 Wireless Microphones
    2.3 Weather Station
    2.4 Light Barriers
    2.5 Optical Sensors: Kickdown and RPM 
    2.6 Radar and GPS
    2.7 Driver Aid
3.    Software
    3.1 Parameters Workbook
    3.2 Validation Workbook
4.    Configurations
    4.1 Trackside versus In-Vehicle
    4.2 Exterior versus Interior 

1. Introduction

Pass-by noise testing is done to ensure vehicles meet legislated noise emission requirements.

1.1    Pass-by Noise Limits

Pass-by noise requirements have become more challenging over time (Figure 2):
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Figure 2: European noise limit requirements have been reduced over time.

This is a challenge for any global manufacturer.  Even if the pass-by noise limits in one country are higher and therefore easy to meet, if selling the same products in a countries with lower limits, the product needs to be designed accordingly.

Not only are the noise level requirements becoming lower and therefore harder to meet, but the execution to the standards has also become more complicated.  Test considerations include:
  • Outdoor pavement of the track must have a certain sound absorbency
  • Some requirements depend on the vehicle mass to power ratio which must be documented
  • Acceleration of the vehicle must be tightly controlled
  • More tests can be required (every or multiple gears tested, production samples tested, etc.)
  • Every country in which a product is sold may have a different pass-by procedure or limits
  • And more…

1.2 Standards, Governing Bodies, Regulations

Several entities are involved in managing the procedures and requirements for performing pass-by noise tests:
  • Governing Bodies: United Nations (UN), Economic Commission for Europe (ECE), and Environmental Protection Agency (EPA).
  • Regulations:  Federal Motor Vehicle Safety Standards (United States), UN/ECE Regulations (Europe), Type Approval Test Procedure (Japan).
  • Standards Organizations: Standards for the execution of pass-by noise tests are maintained by the International Standards Organization (ISO) and Society of Automotive Engineers (SAE).
A partial list is shown in Figure 3:
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Figure 3: Partial list of vehicle pass-by noise standards.

A partial list of pass-by noise regulations:
  • ISO 362: Measurement of Noise Emitted by Accelerating Road Vehicles.
  • SAE J986: Sound Level for Passenger Cars and Light Trucks.
  • SAE J366: Exterior Sound Level for Heavy Trucks and Buses.
  • SAE J1470: Measurement of Noise Emitted by Accelerating Highway Vehicles.
  • ISO 6394 and ISO 6395: Determination of Sound Power level of Earth-moving Machinery. 
  • ISO 5130: Measurements of Sound Pressure Level Emitted by Stationary Road Vehicles.
  • FMVSS 141: Minimum Sound Requirements for Hybrid and Electric Vehicles.
  • TRAIS 20: Noise Test Procedure for Motor Vehicles. 
  • UN/ECE Regulation 51.3: Exterior Noise Emission. 
  • UN/ECE Regulation 138: Regulation on the Approval of Quiet Road Transport Vehicles (QRTV) or minimal noise requirement for vehicles.
  • ASEP: “Additional Sound Emission Provisions” to show production vehicles do not differ from ISO Pass-by results.

1.3 Pass-by Noise Setup

The basic setup of a pass-by noise test has an outdoor track with microphones set at fixed positions as shown in Figure 4.
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Figure 4: An ISO 362 pass-by noise test (left) and an ISO 6395 pass-by noise test (right).

The vehicle is driven past the microphones at a specific speed.  Light barriers at the beginning and end of the track start and stop the acquisition when the light beam is crossed. 

2. Hardware

Several pieces of hardware are typically used in a pass-by noise test as shown in Figure 5.
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Figure 5: Equipment used in vehicle pass-by noise testing.

The function and purpose of the equipment is described in the next sections:

2.1 Acquisition System

The Simcenter SCADAS hardware (Figure 6) is used to record all data (microphones, vehicle speed, vehicle position, vehicle entry, vehicle exit, …) simultaneously.
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Figure 6: Simcenter SCADAS data acquisition systems for pass-by noise testing.

There can be two data acquisition systems in use during a test – one in the vehicle, one at the trackside. Depending on the exact setup, one acquisition unit or the other might be used alone.  In other configurations, two acquisition units might be used in conjunction with each other.

The two SCADAS hardware units will communicate via a specific card [product code SC-PBN-MOD].  This card has wireless capabilities (Figure 7):
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Figure 7: The Simcenter SCADAS pass-by noise (SC-PBN) card.

The card helps synchronize data from multiple sources, including any wireless data (from microphones, etc.) that is gathered. 

Pass-by noise testing involves a moving vehicle.  Some data is readily available from the vehicle (acceleration, kick down status, etc.) while other data is readily available trackside (microphones, light barriers, etc.). The SC-PBN card synchronizes data between the trackside and in-vehicle units with its wireless capabilities.

For example, wireless microphones can be used directly with the SCADAS PBN card.

2.2 Wireless Microphones

It is desirable to have single user operation to reduce the manpower requirements to perform a test.  One way to do this is to send all trackside data in real-time to an acquisition unit in the vehicle.  Wireless microphones [product code SCM-PBN-WMC] allow this to be done.  Microphones are shown in Figure 8.
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Figure 8: Wireless microphones used in pass-by noise testing help enable single user operation.

These microphones transmit a wireless digital audio signal based on the Sony/Philips Digital Interface (SPDIF).

2.3 Weather Station

Noise tests must be performed within a certain range of environmental conditions. A weather station [product code SC-PBN-WS] is used to monitor wind speed, temperature, humidity, and track surface temperature during the test to ensure consistent measurements.  Weather station shown in Figure 9.
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Figure 9: Weather station for Simcenter Testlab pass-by noise system.
Temperature and wind speed affect pass-by noise levels:
  • Temperature: When it is colder, sound levels increase for the same object.
  • Wind Speed: Gusts of wind blowing across microphones cause increases in sound levels.
If the appropriate weather conditions are not met, then the test results are invalid.  A weather station ensures this is documented.

2.4 Light Barriers

As a vehicle travels past the microphones, the test is started at a specified distance before (entry) and after (exit) the microphone location.  Light barriers [product code SC-PBN-LBR] on tripods are placed at the entry and exit locations that shoot beams of light across the path of the vehicle (Figure 10).  
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Figure 10: Light barriers and reflectors are used to create beams of light that generate a trigger pulse when a vehicle crosses.

When the light beams are broken, a voltage pulse is created.  With the light barriers of the Siemens pass-by noise test system, the pulse signal is carried on a single wire to the SCADAS data acquisition unit.  Each barrier generates a different amplitude pulse level.  The amplitude is used to determine the direction of travel.

2.5 Optical Sensors: Kickdown and RPM 

Optical sensors [product code SC-PBN-OTS] are useful in pass-by noise tests:
  • Kickdown: The vehicle must be accelerated (by pushing the accelerator) at a specific position on the track. A kick-down device can be used to determine the exact moment the accelerator is engaged.
  • Engine RPM: Engine speed must also be measured in many pass-by tests.  
These sensors are shown in Figure 11.
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Figure 11: Optical RPM and kickdown sensors.

These sensors use a light beam with reflective material:
  • In the case of kickdown. the sensor creates a trigger when the pedal reaches a specific position. 
  • For engine speed, reflective tape on the crank pulley in conjunction with the sensor is used. As the pulley rotates, pulses are created.  The time between pulses is used to determine how many revolutions occur each minute.
Both kickdown and engine speed can also be acquired using a CAN bus.

2.6 Speed Radar and GPS

The vehicle speed needs to be monitored during the test. Pass-by tests often require specific speeds for the testing. This can be done with either a Global Positioning Service (GPS) device [product code SC-PBN-GPS] or Radar [product code SC-PBN-RAD] as shown in Figure 12.
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Figure 12: Vehicle speed devices – GPS (left) and radar (right).

Either device, GPS or radar, could be used:
  • Radar: If permanently installed, no additional effort to measure vehicle speed.  Speed is automatically measured. Easy to connect to trackside setup. 
  • GPS: Must be moved between each test vehicle.   Easy to measure in-vehicle.

2.7 Driver’s Aid

A small tablet that works in conjunction with the pass-by noise testing will indicate speed, position, and when acceleration should occur in real-time for the driver (Figure 13).
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Figure 13: The driver’s aid tablet (middle) helps the vehicle operator focus on executing the maneuvers according to the standard. 
Not only does a sound play to indicate when the driver should accelerate, the tablet also indicates if the run or pass was performed properly and according to the standard being executed.

This feedback is given in both real-time (while the test is being performed) and post test (Figure 14).
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Figure 14: Tablet software indicates via sound and visual indicators if the test was performed properly. Top row of pictures is live feedback during test, bottom row is posttest display.

The driver’s aid tells the vehicle operator:
  • Approach Speed: Tells the operator to slow down or speed up to be at correct speed upon entry into the track.
  • Kick-down: Driver’s aid tells (via sound and visual) when to accelerate.
  • Valid versus Invalid: Immediately after test, validity of the results is indicated (green or red) based on speed, acceleration, weather conditions, etc.

The product codes for the driver’s aid include:
  • SCX-TAB: Hardware tablet
  • SM-PBN.01: Pass-by noise app
  • SC-XS-CK1: Car kit – Windshield mount, cable, DC adapter
  • TL-ACT.64.3: Pass-by Noise Advanced Driver’s Aid Software (requires SM-PBN.01)

3. Software

Simcenter Testlab Exterior Pass-by Noise testing is part of the Acoustics testing program group. If using token licensing, 92 tokens are required to run the software.  Optional licenses include the Advanced Driver’s Aid (36 tokens), Minimum Noise Analysis (19 tokens), and Vehicle/CAN bus Support (22 tokens).

The exterior pass-by noise interface is very similar to Simcenter Testlab Signature Acquisition.  There is a workbook called “Parameters” that is unique to pass-by noise testing where users make a selection from a pull-down list of standards (Figure 15).
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Figure 15: Simcenter Testlab Pass-by Noise contains a pull-down list of standards.

The parameters workbook also allows the creation of customized standards.  Settings can be changed for the layout of a track, vehicle definition, and more.

The track layout definition page is shown in Figure 16.
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Figure 16: Simcenter Testlab Pass-by Noise track layout definition.

The Validate workbook of the Exterior Pass-by Noise application is used to interrogate the data, compare runs, and calculate the regulatory sound level value(s) (Figure 17).
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Figure 17: Simcenter Testlab Pass-by Noise post processing includes using cursors to view the octave spectrum at any position of the test.

Pass-by processing options include viewing the list of runs (with valid/invalid status), statistics, checks, interactive octave viewing, reporting, and more.

4. Configurations

A Simcenter Testlab Pass-by Noise testing system can be configured several different ways (Figure 18).
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Figure 18: Trackside configuration of Pass-by Noise setup.

The configurations can have important implications for the personnel required to run the test.

4.1 Trackside versus In-Vehicle

An exterior pass-by noise test can be run with the acquisition system in-vehicle or with the main acquisition system trackside. These configurations are shown side-by-side in Figure 19 below:
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Figure 19: Two different exterior pass-by noise configurations, in-vehicle pass-by noise system (left) and trackside system (right).

For an in-vehicle configuration:
  • Trackside wireless microphones, weather, and light barrier information transmitted via telemetry in realtime to Simcenter SCADAS in vehicle.
  • Operator has a laptop and optionally a driver’s aid unit in vehicle.
  • Kick-down, speed (via GPS), and rpm sensor is measured directly or via CANBUS.
  • Ideal for a single operator.

For a trackside configuration:
  • Microphones and light barriers measured directly on trackside.
  • Computer and SCADAS located on trackside.
  • In-vehicle speed and kick-down transmitted wireless to trackside acquisition unit.
  • Driver’s aid in-vehicle enables single-operator mode.

4.2 Exterior versus Interior 

It is also possible to measure (usually for development purposes) pass-by noise in a large anechoic chamber (Figure 20).  Unlike an exterior outdoor track, an indoor pass-by noise facility can be run 24 hours a day.  There is no weather (rain, windy conditions, extreme temperature, etc.) that prevent testing taking place.
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Figure 20: Interior pass-by anechoic noise chamber.

In an interior pass-by noise test, the vehicle is stationary and runs on a dynamometer.  The speed and acceleration can be precisely controlled.

An array of microphones is positioned along the chamber on both sides of the vehicle as shown in Figure 21.
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Figure 21: Microphone array for interior pass-by noise test.

There microphones are weighted and combined based on the theoretical track position of the vehicle on the dyno.  The output is identical in format to an exterior pass-by test: overall levels are calculated versus position, etc.

On a dyno roll, the tire/road interaction of an interior pass-by test are not the same as an exterior test.  Because of this, it is not possible to certify a vehicle for pass-by noise using a interior pass-by noise test in most circumstances.
Room dimensions are very important. The microphones should be placed a minimum of 5 meters from the centerline of the vehicle (the noise is predicted at 7.5 meters away).  The microphone must also be a minimum of 1 meter away from the tips of the anechoic wedges.

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