The fourth channel (A) of the VM31 in combination with a uniaxial accelerometer
can be used to determine SEAT values. Metra recommends the TEDS accelerometer
KS78.100 for this purpose. It is connected via a sensor cable VM31-A to the left
socket (see 1). The fourth channel is named “A” on the display. The sensitivity of
the KS78.100 will be automatically detected. With a non-TEDS sensor it needs to
be entered manually (see section 4.2).
Select “Whole-body ISO 2631” / “Unweighted” for channels X/Y/Z. Channel A
does not have frequency weightings. Its frequency range (-3 dB) is 0.8 to 250 Hz.
The RMS or VDV of channel A is displayed below channels X/Y/Z (Figure 23).
5. General Vibration Measurement
In addition to human vibration the VM31 measures:
•
Vibration acceleration from 0.2 to 1500 Hz and 1 to
1000 Hz,
•
Vibration velocity from 1 to 100 Hz, 2 to1000 Hz and
10 to 1000 Hz (for machine vibration to ISO 10816),
•
Vibration displacement from 5 to 200 Hz.
Press F3 to open the menu, select “Measuring mode” and
use the keys ▲▼ to select the vibration range.
You can switch the measuring screen from RMS to peak
display by pressing the key ◄. Please note that the RMS
and peak values in the general vibration ranges are mea-
sured over the last display cycle (not over a long period).
A display cycle can be between 1 and 4 seconds, depend-
ing on the frequency range.
RMS or peak values are shown for each channel in addi-
tion to combined sum or maximum values (Figure 24). If
these combined values are not needed you can switch to a
mode which only shows the channel values in large char-
acters by pressing key ◄ repeatedly (Figure 25).
There will also be an RMS or peak value for channel A if
you have connected a sensor to this input. Channel A al-
ways measures acceleration. Its frequency range depends
on the mode selected for X/Y/Z (Table 3).
If only an uniaxial accelerometer is connected to channel
X (sensor cable with 4 pin connector needed) the VM31
displays the results in large numbers (Figure 26).
Mode X/Y/Z Range X/Y/Z
Range A (acceler.)
Acceleration
0.2 to 1500 Hz 0.2 to 1500 Hz
Acceleration
1 to 1000 Hz
3 to 1000 Hz
Velocity
1 to 100 Hz
1 to 250 Hz
Velocity
2 to 1000 Hz
2.5 to 750 Hz
Velocity
10 to 1000 Hz
2.5 to 750 Hz
Displacement 5 to 200 Hz
1 to 250 Hz
Table 3: Frequency ranges of channels X/YZ A
19
Figure 24: 4 channels
and combined values
Figure 25: 4 channels
in large characters
Figure 26: Indication
of 1 channel (X)