13
The Force Sensor of the WDSS
The WDSS includes a general-purpose load cell for measuring pushing and pulling
forces. It can be used as a replacement for a hand-held spring scale, mounted on a
dynamics cart to study collisions, or on a ring stand. Many of the experiments that
can be done with the WDSS force sensor are explained later in this manual.
Forces as small as 0.01 N and as large as 50 N can be measured by the WDSS. There
are actually two force sensing systems inside the WDSS. One is for smaller forces
and the other is for forces over 10 newtons. The sensor automatically switches
ranges depending on the forces applied. To a user, it seems that as if there is only
one force sensor.
How the Force Sensor Works
The WDSS uses a dual-beam aluminum
load cell
. A load cell is an electro-
mechanical device with strain gages in a Wheatstone bridge configuration used to
convert a force into a differential electrical signal. The load cell provides very
accurate measurements of the force with little movement of the force sensor arm. It
has good dynamic response and minimal “ringing” (vibration back and forth) when
the force is taken away.
As mentioned above, the WDSS force sensor actually reports force in two different
ranges, ±10 N and ±50 N. If the force is between ±10 N, then Logger
Pro
will read
in the force data from the more sensitive, ±10 N channel. If the force is outside the
range of ±10 N, then Logger
Pro
will read the force data from the less sensitive,
±50 N channel. This transition between ranges should not be noticeable.
The load cell is built with internal stops to reduce, but not eliminate, the possibility
of damage from excessive force being applied. Do not apply more than 75 newtons
(17 pounds) of push or pull to the force sensor. If you do, you may permanently
damage the sensor. You may need to re-zero the force sensor if a force greater than
50 newtons is applied to it.
Using the Force Sensor
Start Logger
Pro
software and make sure the WDSS is connected. Normally the
force sensor of the WDSS will be on and you will see force readings displayed on
the toolbar of Logger
Pro
. If the force sensor is off, click on the WDSS icon at the
left of the toolbar and turn on the force sensor.
14
Hooks or Bumpers
The end of the WDSS farthest from the On/Off switch has an aluminum extension
with a threaded hole. This is the connection to the force sensor, and it can be used for
mounting various bumpers and hooks for force measurement. It has a standard (US)
#6-32 threaded hole. All hooks and bumpers that thread into the Vernier Dual-Range
Force Sensor (DFS-BTA) will work with the WDSS force sensor. The WDSS comes
with two different accessories for connection here:
Wire hook with plastic lock nut–The hook is used to measure pulling forces (or
pushes).
The hook connected to the force sensor
Rubber bumper with 1/2" 6-32 aluminum extension–The Bumper is used mostly for
collision experiments or any time you want to measure pushing forces.
The WDSS on a dynamics track with a bumper
Important:
If the aluminum extension on the force sensor ever comes out, do not
thread anything directly into the #6-32 hole in the load cell that could extend farther
than 0.5 cm (3/16 inch) into the load cell. This could damage the load cell hardware.
Force Sensor Calibration
The calibration stored on the WDSS is usually adequate for most force
measurements. You usually do not need to perform a new calibration when using the
force sensor.
