WIKA cpd8000-g, cpd8000-a User Manual
Digital Pressure Standard
Model CPD8000
Applications
High level Digital Primary standard.
Reference instrument for testing, adjusting and
calibrating pressure measuring instruments in
factories and calibration laboratories.
Unique working principle.
Self-contained, complete system also suitable for
on-site measurements/calibrations
Special Features
Absolute & gauge
Resolution down to 1 ppm
Several ranges up to 5 MPa
Accuracy down to 20 ppm of reading
Perfect for automatic calibration system.
Description
A unique concept
The CPD8000 measuring principle lies on the principle of
the pressure balances and is based on the fundamental
equation which defines pressure: P = F/A with P as a
pressure, F a force and A an effective area.
CPD8000 is a worldwide exclusivity combining two high
level technologies:
• Best available piston cylinder assemblies; whose
effective area A is perfectly known
• High accuracy force cell which measure the force F.
CPD8000 is defined as a digital pressure balance and is a
high accuracy pressure measurer.
Primary principle
As a result, the CPD8000 measuring principle is a
primary principle; it associates the measurement
accuracy and reliability of fundamental pressure
standards with the ease of use of automatic digital
instruments.
Easy of use
Model CPD8000 offers same high accuracy as a high
end pressure primary standard with the benefits of:
• No weights manipulation
• Built-in reference mass for auto-calibration
• Displaying of full corrected pressure
Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
Calibration Technology
CPD8000-A fitted with low pressure head
Page 1 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
The working principle
• The pressure is applied on the piston, and turns it
linearly into a perfectly proportional force that is
transferred to the measuring force cell.
• A microprocessor calculates the force corresponding
to the pressure, corrects it for all the environmental
influences and finally transfers the pressure value to
the display and to the communication interface.
• The measuring force cell permanently measures and
interpolates the pressure-generated force.
Absolute and gauge mode
Two models of CPD8000 are available according to your
needs :
CPD8000-G: Gauge mode only
Dedicated to gauge measurements, the force cell is let at
the atmospheric pressure.
CPD8000-A: Absolute and gauge mode
Versatile measurer, the force cell is placed in reference
chamber which can be at the atmospheric pressure for
gauge measurement or vacuum for absolute measurement.
The measurer is placed under a reference vacuum
chamber:
• Absolute pressure measurement is a simple and fast solution,
it allows to measure in continue an absolute pressure
without to have to break the vacuum between each
pressure point as it is necessary with the classical pressure
balances.
• The vacuum realised on the measuring block and in
the reference chamber is around 2 Pa.
CPD8000 basic principle
P
F
A
=
CPD8000-G
CPD8000-A
Page 2 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
General Assembly
CPD8000’s measurement quality and long-term performance are based on 5 main subsets.
1 – The Piston-Cylinder Assembly: The Corner Stone
The role of the piston-cylinder assembly consists in turning
perfectly the pressure into force. The quality of this
transformation mainly depends on an excellent geometry,
but also on a very low sensitivity to external influences.
The Desgranges & Huot’s piston-cylinder assemblies are
manufactured in a special grade of tungsten carbide,
according to techniques which have been permanently
refined for more than 50 years. The manufacturing
tolerances are typically below 0.1 micrometer as far as
straightness, roundness and parallelism are concerned,
which gives them sensitivity, linearity and a repeatability no
other manufacturer in the world can offer. The assemblies
which equip the CPD8000 are absolutely identical to those
used to develop the highest-performance pressure
standards.
Tungsten carbide has the advantage of not being very
easily distorted under temperature and pressure.
Therefore, the piston keeps its metrological qualities
regardless the operating conditions.
A large choice of pressure ranges
DH manufactures 21 piston-cylinder assemblies of different
area (6 for the CPD8000-A, 15 for the CPD8000-G) , each
of them offering a different measuring range.
In order to increase the ease of use, each nominal areas
has been designed in order that the piston-cylinder
assembly has a simple conversion coefficient of pressure
into mass called Kn, so that a Kn bar pressure is converted
in 1 kg.
2 – The Measuring Head: An Essential Role
The measuring head is aimed at containing, operating and
protecting the piston-cylinder assembly.
It is fitted with the new motorised rotating system which
ensures the centring by rotation of the piston in its cylinder
so that the force transmitted to the measuring force cell by
the pressure is perfectly and fully vertical then without
alteration. It has been created to make sure that the
rotating noises be less important than the sensitivity of both
the piston and measuring cell.
It is equipped with a 4-wire platinum resistance
thermometer allowing the most accurate measurement of
the piston-cylinder assembly temperature.
The measuring head is coupled with the measuring force
cell by 3 screws and can be dismantled in a few seconds.
It is possible to combine a measuring force cell with several
measuring heads, each of which being fitted with a pistoncylinder assembly of different Kn to meet various
application fields.
3 – The Measuring Cell: A Force Transferring Function
The electronic measuring force cell has been developed for
the high accurate manufacturing of mass comparators.
It uses the MONOBLOC technology manufactured by
electro erosion; this technology reflects latest innovations
realised in mechanics, electronic, computer science and
opto-electronic.
The concept of MONOBLOC eliminates all the complicated
mechanical links fit in a force sensor, due to the
substitution of the 90 assembly spares found in a traditional
load cell by only one part.
The measuring force cell is associated with an Auto
Calibrating Function (see further) which enables to apply to
it, easily and whenever it is necessary, a reference force
that is equivalent to the product of the mass multiplied by
the local acceleration of the gravity (F = M x g) in order to
recalibrate it.
Consequently, the measuring cell is not used as a force
measuring instrument but as a comparator between the
reference force created by the mass when the calibration
takes place and the force which is exerted by the piston
during the pressure measurements. The measuring force
cell is thus exclusively used for its short-term repeatability.
Page 3 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
Measuring
force cell
and
vacuum
chamber
Measuring
block
Coupling
device
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