Humboldt H-3250 Length Comparators - Manual (Page 3)

Introduction:
Length comparators measure length changes of hardened cement paste, mortar
and concrete prismatic specimens. Indicators are mounted on a sturdy upright
support attached to a solid triangular base. All units include an invar reference
bar and stationary and movable anvils designed to fit H-3260 gauge studs,
which are cast into test specimens. Humboldt Length Comparators comply with
ASTM C151, C157, C227, C311, C341, C342, C452, C490, C596; AASHTO
M210, T107, T160. Custom length comparators are also available, contact
us for details.
Length Comparators consist of three main components:
• A base with an upright frame, which includes an adjustable terminal and
collar on the base.
• A dial or digital indicator with an adjustable terminal and collar.
• A reference bar for calibration. An lnvar Test Bar is included for this
purpose. A 10" effective-length bar is included with the H-3250 and a
16" effective-length bar is included with the H-3248.
Note: ASTM C806 and C878 require specimens to be measured while under
restraint. For those using these specifications different collars are required for
the Length Comparator. For ASTM C806 order H-3251 collars and for ASTM
C878 order H-3257.5 collars.
Humboldt Length Comparators can also be used to measure length changes of
prismatic specimens over an effective gauge length of 5". To accomplish this, it
is necessary to use our 5" adapter, H-3250.8 and a 5" Reference Bar, H-3249.1.
Unpacking
Your equipment was thoroughly inspected before it was shipped and should be
ready to operate as soon as you have completed the set-up procedure. Notify
Humboldt Mfg. Co. or your local agent and file a claim with any carriers involved
if you find any damage to the machine. Unpack all of the equipment carefully to
prevent loss of small items or manuals.
Assembly & Set-up
Place the comparator frame on a stable surface with sufficient space to work. If
using digital models, a receptacle to power the digital indicator may be desired.
It is recommended the instrument be checked and adjusted when received
using the Standard lnvar Test Bar as follows (dial-type indicator example):