A practical approach to bump test, learn why and how to perform bump test, when machine is off or if machine is running, equipment used for this session is CSI 2130 and CSI 2140, these are the universal setting and can be used for any of vibration analyzers such as SKF, SPM, Timken, Pruif Technique or any data acquisition unit having the option of bump test.

1. Bump Test
HOW AND WHY

2. What is Natural Frequency?

3. What is Machine Natural Frequency (MNF)?

4. What is Resonance?

5. What is Bump Test?
The Bump Test is a simple method to excite and measure the natural
frequencies for modal response of a machine or structure.
when impacted, a machine or structure produces a broad frequency band of
excitation components.

6. When to Perform Bump Test?
To identify a resonance
To understand a change in mass
To understand a change in stiffness
To understand a change in damping

7. Bump Test Example

8. Methods of Bump Test
Bump Test Equipment off:
When machine is not running (Preferable)
Window = Rectangle / Uniform window will be use
F Max = 10X of running speed
Resolution = 1Hz to 1.5 Hz low resolution is recommended (400 to 800 LOR)
Averages = 6 to 10 no overlap and peak hold option to use (Avoid double hit)
Bump Test Equipment Running:
When unable to stop machine
Window = Hanning window will be use
F Max = 10X of running speed
Resolution = 0.5Hz to 1.0 Hz good resolution is recommended (800 to 1600 LOR)
Averages = 10 to 15, 50% overlap and negative averaging to use (One hit at least / Avg.)

9. Tips and Trick
Trigger Setting
Pre Trigger

10. Trigger Setting
AmplitudeinG’s
0
+2.0
-2.0
+1.8
0 1.0
Trigger Level
Gain (Trigger Level) = Depends on stiffness of structure and have to adjust manually
Use free run (Live monitoring) of time wave form to check the response of bumping hammer
Check the peak level of G’s to select the trigger level

11. Pre Trigger Setting
10% Pre. Trigger
0
+2.0
-2.0
+1.8
0 1.1
Pre trigger data should not be more than 20 % , preferable is 10%, even 0% pre trigger is fine
AmplitudeinG’s

12. Result of Bump Test (Machine Natural Frequency)

13. Thank You
Taqi Ud Din Haider
Sr. Manager Technical Services
Sumico Technologies, Pakistan
Email: t.haider@Sumico.com.pk