Introduction

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System Diagram

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Vibration tests conducted in the vertical direction are quite common and normally demand nothing more than a shaker system of the proper size. Specifications that require the DUT to be qualified in two or three mutually perpendicular directions can be executed in sequence, rotating the specimen between runs. Alternatively, special fixtures may be used to test 3 (or a multiple of 3) examples simultaneously with one facing X, a second facing Y and the third facing Z. In some instances, the size of the fixture may be too large to fit on your shaker. This problem can be solved (at the cost of increased non-DUT mass) with a head expander, a larger platform that is bolted to the shaker’s load table. Sentek Dynamics can provide both custom fixtures (Cube, L-type and T-type) and head expanders for new or existing systems.

Horizontal testing is best addressed with a slip table. The table is driven by a shaker rotated on its trunnion to the horizontal and connected by a driver bar. We offer these tables in a variety of standard (square) sizes from 300 mm (12 in) to 1500 mm (60 in). We can also provide custom sizes. Two families of Sentek Dynamics slip tables are offered. The cost-effective LST Series features a magnesium slip plate guided by V-groove bearings gliding on a low-pressure oil film over a precision-ground granite slab. They are compact, having an integral hydraulic pump, reservoir and filter. LST slip-plates are very suitable for testing light objects with their center-of-gravity (CG) close to the plate; a lawn mower deck, for example.

The more capable (and more expensive) HST Series use T-slot bearings and high-pressure oil provided by an external hydraulic power supply and oil cooler. They offer far greater resistance to over-turning moments and are thus suitable for testing heavier specimens with a CG well above the slip plate; think telecommunication equipment racks.

Both the LST and HST Series can be delivered as independent components that can be driven by any vertical shaker in your laboratory. Leveling feet on the steel support platform simplify alignment. This arrangement offers excellent equipment flexibility and allows the use of a legacy shaker from any manufacturer. A more convenient solution is to order your shaker and slip table in a mono-base. In this configuration, the shaker and slip table share a common steel base that enables rapid conversion between horizontal and vertical operation. Exact alignment of the shaker to slip table is guaranteed – just flip the shaker 90° and everything slips smoothly together. This is the right answer for a new facility purchase.

Now there is only one matter to be resolved. Which Sentek Dynamics shaker is right for you? This is never a simple question to answer, but one catch phrase will serve you well: “Bigger is better!” Whether you are talking about the maximum force rating, the maximum acceleration rating, the stroke, the load-table (armature) diameter, the maximum payload, usable frequency range or your facility budget, more is always better. Tomorrow’s testing specifications will demand more from your shaker than yesterdays. There is nothing less comfortable than being a “can do” guy with a “must do” mission and a “can’t quite make the spec” facility. 

We currently catalog 24 standard electromagnetic shakers grouped into six series. The fundamental performance metrics are summarized in the following table. Use it to home in on the system that’s the right size for your needs.

When first approached, selecting a shaker for a particular test or set of tests can be a daunting task. You may also need to spend precious facility dollars for upgraded electrical service, air-conditioning, lift-and-transport facilities, improved lighting or high-quality shop air. Planning a new laboratory is an old problem. We can help you with both issues – please contact us for more information.