Light Shock Test

According to MIL-DTL-901E, Light Shock Machine (LWSM) Test is a military specification covering shock testing requirements for ship machinery, equipment, systems and structures. Anyone who produces a product for military use in any of these ship categories will need to complete this test.

The purpose of this test is to verify the ship board setup's ability to withstand shock loads that may occur during wartime service due to the effects of conventional or nuclear weapons. These requirements are the Navy's II. It originated from experiences during World War II and subsequent underwater explosion (UNDEX) experiments. In many cases, it has been found that critical ship systems can be disabled due to the shock effects of nearby weapon explosions that do not hit the ship directly.

The current "D" revision of MIL-S-901 was published on March 17, 1989, and was later issued in the form of a directive from the Naval Naval Systems Command (NAVSEA). The most recent letter was titled “Cost Avoidance and Clarification of MIL-S-21D Shock Test Requirements for Shock Qualification of Equipment in Light Shock Machine” dated 2012 November 901. A similar directive also covers tests on a medium-weight shock machine. The following information is based on the above mentioned documents. The MIL-S-901 specification defines not only test methods, but also equipment required to perform the test. The equipment defined by this specification consists of three machines (or platforms) covering test categories by equipment weight (see Categories below). Since the majority of tests for small equipment are performed on the Light Shock Machine (LWSM), the following issues are intended for the use of LWSM equipment.

When testing is required per MIL-S-901, the test equipment must be classified according to the four criteria specified in the specification. These are Category, Degree, Class and Type.

There are three test categories (criterion 1 above), depending on the size and weight of the equipment to be tested:

• Light - Tested on LWSM. The weight of the test item, including the fixture installed in the machine, must be less than 550 lbs. This usually means that the equipment and any related fixtures should be less than 300 lbs. There are also restrictions on maximum size and flexible mounting deflection limits. These will be discussed in more detail later.
• Medium Weight - The test was carried out on the Medium Weight Shock Machine (MWSM). MWSM tests Simulate Body level inputs and the weight of the test item, including the fixture, will be less than 7.400 lbs. Superior size and flexible mounting deviation limits also apply.
• Heavy weight - Testing is performed on a standard or large Floating Shock Platform (FSP). FSP tests simulate hull or deck entrances and the weight of the test item is usually> 4.500 lbs. This test is used for both shell and wetted surface mounted products and requires a specific test procedure written and approved by NAVSEA prior to testing. NTS performs the heavy shock test MIL-S-901 at our Rustburg, VA facility.

The equipment is classified according to its intended use into one of the following classes:

• Class A - Items required for the ship's safety and constant combat capability.
• Class B - Items not required for the safety or combat capability of the ship, but as a result of shock exposure personnel, Class A equipment or substances that may pose a hazard to the ship itself.

The equipment is then classified according to the mounting configuration according to one of the following three classes:

• Class I - Equipment required to meet shock requirements without using flexible fittings mounted between equipment and ship structures.
• Class II - Equipment required to meet shock requirements by using flexible connections between equipment and ship structures.
• Class III - Unless otherwise specified in section 901 of MIL-S-3.1.6.3, this equipment class is defined because it has ship applications where flexible joints are used and not used, and therefore must meet both Class I and Class II. Requirements.

The tests are then classified according to the level of equipment installation according to the following types:

• Type A - Test of the main unit. This is the preferred test type. The main units are products supported by the ship structure or a foundation directly connected to the ship structure. This includes elements installed in pipe systems, duct systems and similar systems supported by the ship's structure.
• Type B - Testing of an auxiliary component. Auxiliary components are items that make up the main parts of the main unit. The shock response of these components is significantly affected by the relevant base unit and all associated auxiliary components. The shock responses of the associated master unit and all associated accessory components are significantly affected by that of the accessory component.
• Type C - Test of a subassembly. Subassemblies are items that are part of the base unit or an auxiliary component. The shock response of the subassembly is significantly affected by the response of the respective base unit or auxiliary component, but the shock response of the base unit or auxiliary component is not significantly affected by the subassembly.

Once the equipment has been classified by Category, Grade, Class and Type, it must meet a number of other criteria in order to be successfully tested in LWSM. The equipment must be installed by one of the standard luminaires installed in the LWSM and defined by MIL-S-901 specification drawings. There are a total of six standard fixtures defined as follows:

• Armature 4A - Standard mounting armature (Type A) for Partition Apparatus equipment
• Armature 4C - Standard mounting armature (Type A) for Base-Mounted equipment
• Armature 6D-1 - Standard mounting armature for Power Station Meters and other panel mounted equipment (Type C)
• Armature 6D-2 - Standard mounting armature for Electrical Indicator measuring devices and other panel mounted equipment. (Type C)
• Luminaire 6E - Standard mounting fixture (contactors, relays, resistors, etc.) for Controller Components (Type C)
• Armature 11C - Standard mounting armature for Floor Mounted equipment