Humboldt H-3220A Benkelman Beam - Manual (Page 3)

General
The H-3220A Benkelman Beam Apparatus is a convenient and accurate device
used for measuring the deflection of flexible pavements under moving wheel
loads.
Operating on a simple lever arm principal, the device consists of a reference
beam body, two-part probe beam, and rear zero adjustment assembly. The
dial indicator is not included and must be purchased separately.
The Benkelman Beam has the following key features:
• Lightweight aluminum construction for easy transport to test site locations.
• Telescoping design for easy set up and reduced storage space requirements.
• Easy-reading dial indicators for fast and accurate deflection measurements.
• Built-in vibration system for improved dial indicator accuracy and repeatability.
These operating procedures do not contain all of the required information
on the complete test procedures used to measure the deflection of flexible
pavements under moving wheel loads. Please refer to the American Association
of State Highway and Transportation Officials (AASHTO) test method T256 for
more information.
Installation
Assembly and Preliminary Setup
1. Carefully unpack the unit and inspect it for any evident damage.
Report any damage or defects to Humboldt’s Customer Service
Department immediately and save original packaging.
Indicator Installation
The following instructions cover preliminary adjustments of the digital indicator;
final adjustments for individual operating techniques and field conditions can
be made in the field.
1. Place the Benkelman Beam on a sturdy workbench or table. Loosen the
lock nut (Fig. 1, #39) and the stop screw (#34). This stop screw acts as a
mechanical stop, preventing the dial indicator from bottoming out when
the unit is moved with the beams extended. Later adjust the screw correctly
to eliminate the possibility of repeated bottoming, which can cause severe
damage to the dial indicator.
2. Deflect the spring clip and extend the center and end beams (Fig. 1, #16 &
#22) out about two feet. Remove the locking studs (#15 & #14) from their
storage holes and place them aside for later installation. 3. Gently install
the indicator into the indicator collet (Fig. 1, #7), loosening the collet nut,
if necessary. By placing a finger through the hole on the side of the inner
frame beam, move the beam through its extreme up and down range.
Watch the indicator as you move it. (If you are using a dial indicator,
count the number of pointer revolutions your dial indicator makes from
one extreme to the other, and record this number for future reference.)