Mixed Mode Vibration Testing is less common than Sinusoidal and Random Vibration Testing.  However, it does have a special purpose for simulating specialized helicopter vibration or vibration from tracked vehicles such as tanks.

The three mixed modes of vibration testing are:

• Sine-on-Random (SoR)
• Random-on-Random (RoR)
• Sine-on-Random-on-Random (SoRoR)

Some common test standards that have specifications for Mixed Mode Vibration Testing are:

• MIL-STD-810 Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests
• RTCA DO-160 Environmental Conditions and Test Procedures for Airborne Equipment

Sine-on-Random (SoR) Vibration Testing

Sine-on-Random (SoR) vibration testing contains sine tones that are superimposed on a low level of broadband random vibration.  The sine tones can be fixed frequency or sweeping.  If they are sweeping, they are normally very narrow frequency bands.  Some examples of SoR vibration are from helicopters, propeller driven airplanes and aircraft rapid gun-fire events.

All aircraft have some levels of random vibration.  In helicopters and propeller driven airplanes, the sine tones are produced by the main rotary components.  In addition, sine tones can come from rapid gun fire events.  Figure 1 shows a typical SoR helicopter vibration test profile from MIL-STD-810G.

Random-on-Random (RoR) Vibration Testing

Random-on-Random (RoR) vibration testing has narrow band random peaks that are superimposed on a low level of broadband random vibration.  Typical applications that contain RoR vibration are tracked vehicles such as tanks or a truck changing speed while driving over a rough road.  For example, the pitch of the tracks produces rhythmic random vibration peaks at specific frequencies versus speed of the vehicle.  Figure 2 shows a typical tracked vehicle vibration test profile from MIL-STD-810G.

Sine-on-Random-on-Random (SoRoR) Vibration Testing

Sine-on-Random-on-Random (SoRoR) vibration testing contains both sine tones and narrow band random peaks superimposed on broadband random vibration.  Applications that contain SoRoR vibration could be a rapid gun-fire event on a tracked vehicle or components mounted near a turbine engine with various rotating machinery elements and background random vibration produced by air turbulence.

Whether your vibration testing needs are complex or simple, DES has the experience and knowledge to perform your test.  For more information on Vibration Testing or other testing services contact DES or call 610.253.6637.

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Components sealed with internal fluid such as batteries or capacitors may fail or leak during altitude testing because an internal pressure results at rising altitudes as the external pressure is reduced.  It is also possible to power a product during the test to verify that it remains operational during the altitude test. The lower pressure at higher altitudes can reduce the cooling of components which can lead to possible failures. For this type of testing, it is necessary to have power and signal wires that can be fed into the altitude chamber without causing vacuum leaks. DES can provide a generic feed through that can be used for most testing. A custom feed through can also be fabricated if the component to be tested has specialized power or signal cables. It will be necessary to seal these cables to maintain the low pressure.

Altitude testing is normally conducted at room temperature. It is also possible to perform altitude testing at hot and cold temperatures. This will increase the test time as additional time will be required to heat up or cool down the altitude chamber.

Delserro Engineering Solutions, Inc. (DES) has many years of experience performing altitude testing and can assist customers in setting up a test using the proper test conditions. So if you do not know what test conditions that you should use, what specification to choose then we will help you because we are altitude testing experts!

Examples of common altitude testing specifications:

• IEC 60068-2-13, Low Air Pressure
• MIL-STD-202, Method 105, Barometric Pressure (Reduced)
• MIL-STD-810, Method 500, Low Pressure (Altitude)
• MIL-STD-883, Method 1001, Barometric Pressure, Reduced (Altitude Operation)
• RTCA/DO-160, Section 4, Temperature and Altitude

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