Description:
The DD-4 seismic displacement recorder is a
self contained data acquisition system that provides up to
five time histories of structural distortion during an earthquake.
A very small environmentally sealed computer system captures
data from a reel type potentiometer that has an output signal
of zero to five volts d.c.
This signal is captured by an A/D converter within the computer and converted
to a series of 14 bit digital words. A non-volatile memory in the computer stores
two minutes of data every time an earthquake triggers the system. The displacement
level that triggers the recorder can be adjusted by the user. The suggested value
is 5% of the maximum displacement, as this level is unlikely to be exceeded during
microseisms, traffic and other transients, or wind excitation.
The end result is a two minute history of displacement vs.
time for each event. Sampling interval is .010 seconds which
is more than adequate as the minimum expected structure period
is .50 seconds. Maximum error is .15% of the full stroke
range.
When installed inside a building this instrument provides
a full time history of interstory drift during each seismic
event. It can provide similar measurements for a bridge,
or for a structure on base isolators. These applications
would require a greater range of motion and as much as +/-125
inches is available.
When installed across a viscous damper or other energy absorbing
element this instrument will provide a complete stroke/time
history.
The basic version of the Displacement Recorder has USB output
and a battery power supply. Many options are available, like
a recharging cable which taps into a local power line, dial-up
or modem interrogation and wireless download.
Both the computer and the reel type potentiometer are environmentally
sealed and can withstand any expected range of temperature
as well as other weather conditions that could be expected. |
