Ventrac Tests Noise and Vibration of Compact Tractors with LabVIEW and NI CompactDAQ

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"We acquire data using NI 9234 dynamic signal acquisition modules in an NI cDAQ-9174 chassis because the modules are compact, DC powered, and able to provide excitation power to the microphones used in the array."

- Roscoe Lehman, VENTRAC by Venture Products Inc.

The Challenge:
Developing a noise emissions test facility to test compact tractors for the European market.

The Solution:
Using a portable data acquisition system based on LabVIEW and NI CompactDAQ modules to record the test parameters and generate a report based on the unit and configuration tested.

Author(s):
Roscoe Lehman - VENTRAC by Venture Products Inc.

Noise emissions need multiple kinds of tests, particularly for European directives on guaranteed sound power levels. Using LabVIEW software and NI CompactDAQ data acquisition (DAQ) hardware, we created a testing system that was portable, customizable, cost-effective, and capable of testing the parameters required.  

Venture Products designs and manufactures Ventrac tractors and attachments. These are commercial-duty all-wheel-drive compact tractors with more than 30 attachments that fall into numerous categories such as mower, snow blowers, front-end scoop, loader, and blade. National Instruments made it possible for us to develop a testing facility to test our own noise emissions for the equipment we manufacture.     

We chose a portable data acquisition system based on LabVIEW and the NI CompactDAQ modules that could easily be transported to our outdoor test facility. The system records the test parameters and generates a report based on the unit and configuration tested. Also, we can configure the system for other applications including measuring vibration.  

The graphical nature of programming in LabVIEW makes it easier and faster to learn, but the software has limitless options for customization. This gave us the ability to start with a program written by an NI software engineer, and heavily customize the inputs and outputs to generate reports with all the information needed for each specific test.

There are a variety of standards for tractor noise emissions as well as the exposure of operators to engine noise. For a tractor to be sold in Europe, one must demonstrate evidence of thorough testing to show that the equipment conforms to certain European standards and directives with an indication of the guaranteed sound power level among other tests. These rules were created to prevent potential hearing loss and fatigue and because exposure to prolonged loud noises or mechanical vibrations can negatively affect the human body.

Sound Power Measurements

The LabVIEW reference library VIs for sound power and the NI Sound and Vibration Measurement Suite allowed us to make sound power calculations from an array of microphones located around a sound source according to ISO-3744 standards. Sound power represents the amount of acoustic energy emitted by a source and is specified for most environmental noise emissions testing. We can take measurements by placing an array of microphones in a known geometric pattern around the source being measured. We average the sound pressure levels (dB ref 20 µPa) measured at the microphones over the surface area of the geometric pattern to obtain a sound power level (dB ref 1 pW). 

The standard typically explains the options for the size and shape of the microphones’ geometric pattern and how to handle background noise correction. Before calculating the total sound power level, we have to average the sound pressure levels over the surface area to obtain a surface averaged octave spectrum. After the surface averaged octave spectrum has been calculated, the total sound power level can be determined. The results of a sound power measurement can be presented as a total level or an octave spectrum displaying the sound power in each band. We used the reference library of built-in VIs to make a custom program to measure sound power using LabVIEW along with the assistance of a systems engineer at National Instruments. 

The Test Facility

We constructed an outdoor cement test site with a 13 m radius for these tests along with a grass test site. We used a six-microphone array with microphones mounted on tripod stands, including two that were approximately 17 ft tall. To set up for a test, we used our custom-designed container, which stores and protects all of the stands, cables, microphones, laptop computer, and table. We set up the six stands and microphones, ran cables from each microphone to the data acquisition chassis, took a reference measurement to verify the system calibration, and began testing. 

Figure 2. Test Facility with 3000 Series Tractor

Data Acquisition and Analysis

We acquire data using NI 9234 dynamic signal acquisition modules in an NI cDAQ-9174 chassis because the modules are compact, DC powered, and able to provide excitation power to the microphones used in the array. The modules provide an alias-free bandwidth up to 20 kHz. The microphones were half-inch type 1 measurement microphones and preamps from ACO Pacific fitted with wind screens that meet IEC and ANSI specifications for sound level measurements. The sound and vibration filters used in conjunction with the ACO Pacific type 1 measurement microphones created a system that was compliant with international standards for sound level measurements, weighting filters, octave analysis according to IEC 61260 (Electroacoustics - Octave-band and fractional-octave-band filters) and IEC 61672 (Electroacoustics - Sound Level Meters), which means the measurements should be accurate and repeatable.

Figure 3. Microphone and Preamp Mounted on Tripod and Fitted with a Wind Screen

Figure 4. Test Table with NI CompactDAQ Data Acquisition System

 

When making sound power measurements in a free-field environment, there is often background noise that we cannot control. To obtain a valid sound power measurement, we have to measure the background noise and turn on the device under test to measure the source noise. The background noise data is used to correct the sound power level of the source. Because our test site is relatively quiet, the noise correction has never been an issue. For louder test sites, the LabVIEW program will calculate a correction factor and automatically include the correction in the results. We perform stationary sound power tests and drive-through, or mobility noise tests.

Additional Noise and Vibration Testing

In addition, there are standards on noise emissions limits for the exposure of the driver to engine noise. Sound pressure levels at the operator’s position on the machine must be measured. We mounted measurement microphones on a special fixture, which is worn by a person sitting on the seat of the tractor. Standards call for specific placement of the microphone so the fixture can locate it at the right place.

Another type of testing performed is whole body/hand and arm vibration testing with a seat accelerometer and hand mounted triaxial accelerometer using the weighting filters that can be applied to human vibration signals in the Sound and Vibration Measurement Suite. Applying weight to human vibration signals can isolate the directional components and help further analyze different types of human vibration. Being able to accurately measure vibration amplitude and direction at the design stage makes it easier to find solutions to reduce the vibration.

Figure 5. Noise Testing at the Operator Position Inside a Cab

The “mobility test” is more complicated than a stationary test because it involves a background test, three runs forward and backward, and a lift test. The program we wrote shows the results for each direction as soon as the stop button is clicked. This test is not for mowers, but applies to certain other attachments.

Figure 6. Mobility Test Acquisition Screenshot

The flexibility of the LabVIEW reference library VIs for sound power allowed us to add and change things in the program, such as inputs we want to record at test time. Having the ability to use the microphones and accelerometer for additional tests on parts of the machine where we would like to reduce noise and vibration helps pinpoint problem areas significantly faster and increases the overall value of investing in a flexible, high-quality system.

Author Information:
Roscoe Lehman
VENTRAC by Venture Products Inc.
328 E. Water Street
Orrville, OH 44667
Tel: 330-683-0075
rlehman@ventrac.com

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