Introduction
The Model 2485 hydraulic piston gauge is a
high precision standard that provides unsurpassed
performance in the field of hydraulic
piston pressure gauge metrology. The Model
2485 continues the Fluke Calibration standard
of excellence, building on over 50 years of
piston gauge manufacturing expertise. This
instrument can be used to calibrate virtually
any pressure device including other industrial or
portable piston gauges, transducers, transmitters,
gauges, or pressure switches. Available
in dioctyl sebacate (DOS) oil, the Model 2485
can also be used in multiple media systems
to facilitate calibrations of the wide variety of
instrumentation in use today.
Each Model 2485 system includes a calibration
report traceable to the U.S. National Institute
of Standards and Technology (NIST). Traceability
to other national or international standards
organizations is also available.
A compact, space-saving design
The Model 2485 is designed for easy use and for
the space limitations of today’s calibration environment.
The entire bench top system requires
less than two square feet of bench space. The
main pressure housing secures the piston/cylinder assembly and provides support
for the
mass load. Two adjustable support legs and a
permanently attached, sensitive level indicator
facilitate precise alignment of the piston axis.
A fixed support leg directly underneath the
main pressure housing supports the load and
eliminates platform distortion so that continuous
level adjustments are not needed. An auxiliary
pressure housing, fluid reservoir, valves and
positive displacement pump are enclosed by a
simple cover that is easily removed for servicing
internal components. The auxiliary housing
also provides a convenient location to connect
a device under test. A rapid fill pump is used
to quickly purge hydraulic lines of air prior to
starting the calibration procedure.
Other design features include a valve for
connecting to an external reservoir (useful
for applications where a reservoir larger than
250 mL (8.5 oz) is needed), and a liquid-in glass
thermometer to aid in compensating for
temperature effects. Reservoir and system isolation
valves allow for pump recharging when returning the system to atmosphere.
The drive
motor can be used to provide consistent relative
motion between the piston and cylinder when
the inertia of a small mass load is insufficient to
maintain adequate free rotation time.
Piston/cylinder Assemblies
The Model 2485 piston/cylinder assemblies
are simple in configuration and there are no
mounting flanges or other geometric irregularities
that can result in complicated stresses in
the cylinder. This design minimizes stress due
to mounting and sealing, and allows quick and
easy change out of all ranges without special
tools.
The effective area of each Model 2485 piston/cylinder assembly is adjusted
so that a given
load in kilogram denominations will generate
nominal pressure increments in either English
(psi) or SI units (bar). All assemblies are identified
with a pressure unit/increment designator
and serial number.
Mass sets
The mass set for the Model 2485 includes:
•
A hanger or sleeve mass, used to keep the
center of mass below the piston
•
Nineteen 5 kg platters
•
Mass platters in incremental denominations
[down to 200 g (7 oz)] for a total of 100 kg
(3.5 oz)
Each mass is adjusted to within 50 ppm of the
nominal mass denomination and calibrated to
5 ppm. Each mass is marked with the serial
number of the set, a sequence number and the
nominal mass denomination. The mass set is
supplemented with a laboratory-style trim mass
set, with denominations to 5 mg (0.0002 oz),
to generate any pressure within the range and
resolution of the instrument.
Quality materials, quality
manufacturing
All piston/cylinder assemblies are manufactured
from cemented tungsten carbide, offering superior
strength and proven durability for:
•
Low distortion
•
Virtually undetectable hysteresis
•
Excellent long-term stability
•
A very low thermal coefficient
The manufacturing techniques used for the
Model 2485 piston/cylinder assemblies ensure undetectable pressure change
due to speed
or direction of rotation, resolution better than
1 ppm, a sink rate typically less than 0.25 mm
(0.01 in) per minute at maximum pressure and
a useable pressure range down to 1 % of full
scale (FS).
Protecting your investment
The Model 2485 features the PistonSafe system,
a unique non-rigid system that results in automatic
centering of the mass load and protection
of the piston/cylinder assembly from forces
induced by loading and unloading masses. The
system minimizes lateral forces, maintains the
vertical force along the piston axis, reduces friction,
and promotes a higher level of performance
than with rigidly mounted load. The piston and
cylinder components are fully protected should
the pressure be released while under load, or
the load removed while at full pressure. Installation
or change of piston/cylinder ranges is quick
and easy and can be completed in minutes
without special tools.
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