We use a slip table for conducting many of our vibration tests. It is often unclear where we should position the control accelerometer. The slip plate has a 10-32 hole at the far end. Is this a good place for the control accelerometer?
The best location for the control accelerometer is somewhere on the fixture and as close to the UUT attachment point as possible. This positioning will ensure that the test profile is more accurately being applied to UUT. The 10-32 hole (at the end of the table) is usually used by the slip table manufacturer to test and qualify the table prior to shipment.
When using a small table (3 feet or less), mounting the control accelerometer on the slip plate's end is often adequate. Never mount a single control accelerometer at the shaker attachment end of the slip table, since this is often close to a node point.
When using a large UUT, a minimum of four control accelerometers should be mounted to the fixture. Use the multi-point averaging mode provided with the shaker controller when using multiple control accelerometers.
It is also a good practice to attach an accelerometer to the shaker head for monitoring overall vibration levels. This extra monitoring channel is not to be used for control, but is an inexpensive check to protect the shaker's armature from potential damage.