| The frequency
of any periodic signal is mathematically related to each of the amplitude
units: displacement, velocity and acceleration - if you know any two of
these variables, you can mathematically calculate the other two. For instance,
if you know:
1. How far
a bearing is moving back and forth (the displacement amplitude), and
2. How much
time it takes to complete the trip (the 'cycle', from which the frequency
is derived) |
Then armed
with the proper mathematical formula, you can calculate the peak velocity
reached during that trip. For instance:
-
A bearing vibrates
10 mils (254 microns) in 0.1 seconds. We know two of the variables:
-
The pk-pk displacement
is 10 mils.
-
The period is
0.1 seconds (time required for 1 cycle).
|
| Frequency
is represented as the number of cycles during a certain period - a second
or a minute. The bearing will make 10 of these trips in one second. Since
the total distance travelled in one second is 100 mils, your average
speed is 100 mils/sec (0.1 inches per second or 2.5 mm/sec). Of course,
that is the average speed. Since you are constantly speeding up
or slowing down, your peak speed would be about twice that average
speed (0.2 in/sec or 5 mm/sec). |
| Let's look
more closely at the relationship between these 4 variables. |
