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Follow these instructions to set up the FRF test apparatus.
1. Fit the correct tip to a modally tuned hammer.
The hammer is used to create the force that is to be measured in the FRF.
TIP
2. Connect the modally tuned hammer to Connector A of the instrument.
3. Support the object being tested, allowing free movement, for example, on a
foam support.
4. Select an accelerometer of the correct mass and connect it to Connector B
of the instrument.
TIP
5. Connect the accelerometer to one of the sides of the object you are
measuring.
Avoid Bad Data
An FRF measurement involves placing an accelerometer onto the measurement
position and pressing Enter the Dynamix 2500 data collector. Be aware of these
items before placing the accelerometer:
• The magnet should be firmly screwed onto the accelerometer. Any
looseness between the magnet and accelerometer will corrupt the
measurement.
• Gently slide the accelerometer onto the measurement position. Using too
much force while placing the transducer onto the machine may cause data
overload.
• The magnet should be in firm contact with machine's surface. Any
movement of the magnet will be falsely recorded as vibration data. Try
sliding or rotating the magnet until a firm seating is achieved.
• Avoid knocking or disturbing the accelerometer while taking the
measurement.
Rockwell Automation Publication 1441-UM003A-EN-P - May 2011
FRF Frequency Response Function Extension Module
Use a harder tip for higher frequency and a softer tip for lower
frequency measurements.
The accelerometer is used to measure the response to the
hammer input of the FRF. The accelerometer mass should be low
in relation to the test piece, that is, less than 10%.
Chapter 2
17
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