OPTIONAL SENSORS
:
STU IMPACT DETECTION
Overview
The STU/I is equipped with a 35G accelerometer and is programmed with a 10Hz and 100Hz level
filter.
Standard impact thresholds are:
1G 10Hz
5G 100Hz
5DV (delta velocity)
These thresholds can be changed over the air via the Lat-Lon website (see the Website Manual for
more information)
Below is a chart of a high G force, short interval impact. The force measured at 100Hz was 18.0G’s
and the force measured at 10Hz was 1.5G’s. Because of the short interval the 10Hz filtering (1/10 of
a second) averages out the large spike of data. The difference between the two filters will be large
during this type of impact.
Delta-Velocity (or DV) is the sum of the accelerations during the impact event. More technically, it
is the integral of the acceleration over time. The DV measures the net change in speed associated
with the impact event. For a railcar coupling to another railcar, the DV will be approximately the
approach speed between the two cars. This becomes less true if the car being hit moves after being
hit. In this case the change in speed is less than the approach speed because the approaching car did
not come to a stop, but only slowed down during the impact.
High-G, short interval impact
100Hz and 10Hz G's vastly different
-10
-5
0
5
10
15
20
25
0
0.05
0.1
0.15
0.2
0.25
Time (sec)
A
c
c
e
l
(G
)
a
n
d
D
e
lt
a
-V
(
M
P
H
)
Impact event data
18.0 G's (100Hz)
1.50 G's (10Hz)
1.2 MPH Delta-V
Delta-V
10Hz G
Actual and
100Hz G
