REO REOVIB MFS 368 - 9.3 Acceleration and Vibration Amplitude; 9.4 Determining Resonant Frequency; Manual Vibration Frequency Setting

REOVIB MFS 368
Operating instructions
21
9.3 Correlation between acceleration and vibration amplitude
The sensor measures the feeder's instantaneous acceleration. This results in a sinusoidal output voltage
of the sensor. The acceleration increases with increasing vibrating frequency. Therefore, the sensor
output signal can be larger at high frequencies and small vibration amplitude than at low frequencies and
larger vibration amplitude.
Acceleration
Since, in practice, the acceleration is referred to the gravity
acceleration, and the effective vibration amplitude is measured in
mm, the following rule of thumb applies:
[ ]
[
]
[
]
[
]
[
]
49710281,9
2
2
2
3
2
222
mmsHzf
mmsHzf
ga
n
n
=
⋅
=
π
a[g] = acceleration (referred to gravity acceleration 9.81 m/s
2
)
Sn
[mm] = effective vibration amplitude
Put into practice, where 497 ~ 500 results in,
for example:
1.
Vibrating frequency 50 Hz, vibration amplitude
3 mm
or
2.
Vibrating frequency 33 Hz, vibration amplitude
5 mm
ga 89,10
500
533
2
=
≈
⋅
=
With a sensor output voltage of 0.3 V/g, the sensor produces a peak voltage of 4.5 V at a peak
acceleration of 15 g (example 1), which corresponds to an RMS value of 3.18 V.
Example 1: => 15 g => 4.5 V => 3.18 Vrms.
Example 2: => 11 g => 3.3 V => 2.33 Vrms.
Therefore, the widely differing acceleration values of the various feeders may result in large differences in
the feedback signals, which makes it necessary to adjust the control unit to the maximum value.
9.4 Determining the resonant frequency
Caution!
When operating at resonance frequency, small setpoints can cause very large vibration
amplitudes.
Manual vibration frequency setting
(operation without accelerometer)
It is essential that the output frequency is set at a low value, as a large vibration amplitude can be
generated even with a low output voltage at the resonant frequency. To determine the resonant
frequency, an RMS current meter must be connected on the output cable. Please adjust a low setpoint.
Then change the frequency and observe the current and the vibration amplitude. The resonant
frequency is reached at maximum vibration amplitude and minimum output current. For stable
feeder operation, it is recommended to offset the value by approx. 1...2 Hz, depending on the
requirements, below or above the determined resonant frequency. This frequency offset must be
determined by the user, as different conditions prevail with different feeders.
!
f
π
ω
2
=
sa
2
ω =
ga 15
500
350
2
=
≈
⋅
=
where
by