X90 mobile modules
252
X90 mobile system User's manual V 1.20 - Translation of the original manual
Displacement, velocity and acceleration
Sensors can record oscillation acceleration, oscillation velocity or oscillation displacement. Regardless of the phys-
ical value that the sensor records, the oscillation can be represented as a combination of acceleration, velocity
or displacement since:
s = vdt = dt , or
= =
ʃ
ʃʃ
ɑ
2
ɑ
d s
2
dv
dt
d
t
2
Legend:
•
s - Oscillation path
•
v - Oscillation velocity
•
ɑ - Oscillation acceleration
•
t - Time
Since oscillation velocity is calculated through integration from the oscillation acceleration and oscillation displace-
ment is calculated through integration from the oscillation velocity, it is possible to convert the sensor value when-
ever necessary.
Acceleration is proportional to the force. In contrast, the velocity is an indication of the energy.
What is significant from a practical standpoint is that, when one physical value is converted to another, the frequency
is included. For a sinusoidal oscillation, the following applies:
s =
ɑ
(2 ·
ƒ)
π ·
2
v =
ɑ
2 ·
ƒ
π ·
The frequency is in the denominator. As a result, high-frequency signal portions are underestimated when using
oscillation velocity in comparison with oscillation acceleration. This effect is squared with the application of oscil-
lation displacement.
5.4.1.6.2.3 Determining limits and alarm limits
A general statement about the health of a machine can be made by comparing the measured characteristic values
with limit values defined by standards (e.g. ISO 10816) or by the manufacturer of the machine.
Characteristic values are calculated from the measured signals, which are representative of the status of the system
at the given measurement point.
Norms can be used in part to determine alarm limits. In addition, limits can be set based on the machine's history
and the experience of the operator.
Comparison with references and norms
For certain machines and systems, limits are fixed by norms. With the exception of ISO 10816, these give little
information for assessing the actual status of the machine.
Manufacturer's limits
A few machine manufacturers give limits for permissible oscillations and other relevant factors for assessing the
status of the machine. These are based partly on calculations as well as the manufacturer's own knowledge and
experience.
Whenever possible, these are the limits that should be used for assessing condition.
