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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
Page 2
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
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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
Page 4
4 – The Autocalibrating Function (ACF)
The CPD8000 measuring force cell response to the force,
which is applied to it, may drift with time. In addition to this
drift which is due to the ageing of the measuring force cell,
a low short-term drift may appear: this is an evolution of the
measuring force cell response according to the change of
the environmental parameters, above all ambient
temperature and relative humidity.
To curb these drifts, the CPD8000 is fitted with an Auto
Calibrating Function (ACF) coupled with an
Environment Monitoring Module (EMM).
The use of the ACF enables the measuring force cell to
easily free from this drift by readjusting its deviation
according to the new environmental conditions, even when
the measuring head is fitted.
The ACF consists in an automatic loading of an internal
standard mass which can be easily loaded by pressing a
key located on the front panel, or from a remote computer.
By applying the standard mass, you readjust the deviation
of the measuring force cell according to two points: zero
and the mass generated force value (i.e. the full scale
value).
You can optionally use a set of external standard masses
in order to check the measuring force cell linearity over 5
points. These masses can also be used to run an external
calibration.
5 – The Environment Monitoring Module (EMM)
In order to determine whether it is worthy to use the ACF,
the CPD8000 is equipped with an Environment Monitoring
Module which consists in 3 sensors for ambient
temperature, relative humidity and barometric
pressure, and their electronic components.
After the calibration, the EMM keeps on monitoring the
evolution of the ambient conditions in real time.
If these conditions vary in proportions that might noticeably
alter the measuring performance, the CPD8000 displays a
warning flag to advise the user to command the ACF in
order to readjust the dynamometer to the new operating
conditions. The warning flag is also sent to the command
software if the CPD8000 is operated from a remote
computer.
When the ACF is in use, the environment conditions, for
which the measurements carried out by the measuring
force cell are valid, are measured by the EMM and stored
in the internal memory
Therefore, the EMM monitors the difference between the
conditions stored during the calibration, at t0, and the
conditions measured when the operation took place, at t+1
.
The sensors with which the EMM is fitted are not used for
their accuracy and long-term stability, but for their short
term repeatability.
Measuring force cell
Computer
connection
Internal standard mass
EMM sensors
Page 4 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
Page 5
Displayed Pressure Calculation
The pressure displayed by the CPD8000 is calculated according to the following formula
( )( ) ( )( )
PvactP
g
g
N
N
KnP
man
mac
PCPC
n
l
k
+
−
−
×−×−××−×××=
ρρ
ρρ
αλ
2011
where:
− Kn is the specific coefficient of the piston-cylinder
assembly
− N is the indication of the measuring force cell in count
− Nk is the sensitivity of the measuring force cell
− gl is the local gravity in m.s-2
− gn is the normal gravity in m.s-2
− λλλλPC is the pressure distortion coefficient of the piston-
cylinder assembly
− ααααPC is the thermal dilation coefficient of the piston-
cylinder assembly
− t is the temperature of the piston-cylinder assembly in
°C
- ρρρρ
ac
is the air density during the adjustment of the
measuring force cell in en kg.m-3. This parameter is
null when the CPD8000-A operates in absolute mode.
- ρ
m
is the density of the adjustment mass in kg.m-3
- ρ
an
is the normal air density in kg.m-3
-
P
Vac
is the residual vacuum in the reference chamber.
Constant Parameters
The constant parameters entering in the computing of
pressure are stored in the non-volatile memory of the
CPD8000:
• Kn of the piston-cylinder assembly,
• Sensitivity of the measuring force cell (Nk),
• Normal gravity (gn),
• Local gravity (gl),
• Pressure distortion coefficient of the piston-cylinder
assembly (λPC),
• Thermal dilation coefficient of the piston-cylinder
assembly (αPC),
• Density of the calibration mass (ρm),
• Normal air density (ρan).
Some of these parameters are specific to each pistoncylinder assembly and are determined during the
calibration. You can easily modify them if necessary and
the internal memory allow to save the parameter of three
different piston-cylinder assemblies
Variable Parameters
The variable parameters affecting the calculation of the
pressure are automatically measured and integrated in the
expression of the pressure :
• temperature of the piston-cylinder assembly (t),
• ambient temperature ,
• humidity,
• atmospheric pressure.
• residual vacuum (P
Vide
)
The pressure is automatically converted into any of the
common pressure units and the user has the possibility to
configure the system to special units.
This rigorous metrology enables an ease of use as well as
a speed of measurement operation.
Defining the air density
during the calibration
(
ρ
ac
)
Page 5 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
Page 6
Technical Specifications
Measuring Ranges
The CPD8000’s pressure measuring ranges depend on
the specific Kn coefficient of the piston-cylinder assembly
with which the measuring head is equipped.
Various measuring heads can be used with a same
CPD8000 in order to adapt the standard to several
applications.
They are interchangeable in a few seconds and the
CPD8000’s internal memory has the ability to save the
metrological coefficients for 3 different piston cylinder
assemblies.
Designation Pressure Ranges Resolution PCA Kn Operating fluid
A01 0.1 Pa ... 100 kPa 0,1 Pa 0,1 bar/kg Pure gas
A02 0.2 Pa ... 200 kPa 0,2 Pa 0,2 bar/kg Pure gas
A03 0.5 Pa ... 500 kPa 0,5 Pa 0,5 bar/kg Pure gas
A04 1 Pa ... 1 MPa 1 Pa 1 bar/kg Pure gas
A05 2 Pa ... 2 MPa 2 Pa 2 bar/kg Pure gas
A06 5 Pa ... 5 MPa 5 Pa 5 bar/kg Pure gas
G01 0.1 Pa ... 100 kPa 0,1 Pa 0,1 bar/kg Pure gas
G02 0.2 Pa ... 200 kPa 0,2 Pa 0,2 bar/kg Pure gas
G03 0.5 Pa ... 500 kPa 0,5 Pa 0,5 bar/kg Pure gas
G04 1 Pa ... 1 MPa 1 Pa 1 bar/kg Lubricated gas
G05 2 Pa ... 2 MPa 2 Pa 2 bar/kg Lubricated gas
G06 5 Pa ... 5 MPa 5 Pa 5 bar/kg Lubricated gas
G07 10 Pa ... 10 MPa 10 Pa 10 bar/kg Lubricated gas
G08 20 Pa ... 20 MPa 20 Pa 20 bar/kg Lubricated gas
G09 50 Pa ... 50 MPa 50 Pa 50 bar/kg Lubricated gas
G20 2E
-
4
... 200 Psi 2E
-
4
Psi 20 Psi/kg Lubricated gas
G21 5E
-
4
... 500 Psi 5E
-
4
Psi 50 Psi/kg Lubricated gas
G22 1E
-
3
... 1000 Psi 1E
-
3
Psi 100 Psi/kg Lubricated gas
G23 2.5E
-
3
... 2500 Psi 2.5E
-
3
Psi 250 Psi/kg Lubricated gas
G24 3E
-
3
... 3000 Psi 2E
-
3
Psi 200 Psi/kg Lubricated gas
G25 5E
-
3
... 5000 Psi 5E
-
3
Psi 500 Psi/kg Lubricated gas
The measuring blocks highlighted in green are “standard products”, available in shorter delivery time.
Page 6 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
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Technical Specifications (Continuation)
Piston-Cylinder Assemblies Standard Masses
Material: tungsten carbide
Poisson’s ratio: 0,218
Young’s modulus: 6 10
11
N/m
Typical geometry researched:
Straightness (typical manufacturing tolerance): 0,1 µm
Roundness (typical manufacturing tolerance): 0,1 µm
Parallelism (typical manufacturing tolerance) : 0,1 µm
Clearance between the piston and the cylinder: 0,2 to 0,4
µm according to the model
Stability of the effective area: ≤ 1 ppm / an
Internal mass
Material: nickel chromium steel
Mass density: 7900 kg/m3 ± 10%
External optional calibration masses
Material: 304L steel
Mass density: 7920 kg/m3± 10%
Composition of the set: 5 x 2 kg
Adjusting tolerance to the nominal value: ±1E
-6
M
Calibration Uncertainty: ± 2,4E
-6
M
EMM Environmental Measuring Module
Sensors Type Accuracy Alarm setting
Ambient temperature: 4-wire PT100
± 0,2°C ± 2°C
Relative humidity: Capacitive sensor
± 5 % ± 20%
Atmospheric pressure: Strain gauge
± 2 mbar ± 10 mbar
PCA temperature: A DIN 43760 4-wire PT100 ± 0,1 °C N/A
Metrological Specifications
Researched metrological specifications
Linearity: 2E-6 FS
Hysteresis: 2E-6 FS
Bias: 7E-6 FS
Repeatability: ≤ 5E-6 FS
Temperature effect: full compensation
Precision* : ≤ 11E-6 FS (Combination of repeatability, hysteresis, linearity and 3-year stability)
Typical uncertainty researched for a 200 kPa range (k=2) : U=0.8 Pa + 1.E-5 P
Dimension (L x W x H): 530 x 400 x 320 mm Measurement fluid: Dry and non corrosive clean gas
Maximum overpressure: 110 % FS Operating temperature: 10 to 30 ° C
Sampling rate: 250 ms Operating humidity: 15 to 85 % HR
Computer interface: RS232C Power supply: 110 - 240 VAC, 50-60 Hz
Residual vacuum : Pirani gauge ≥ 1Pa ±1E-4 Power consumption: 20 VA
Weight 20 kg
Summary of the Functions
The CPD8000 has a great variety of functions aimed at facilitating its use and assuring the quality of its long-term
operation:
Menus in English, French, German and Spanish
Saving of the metrological characteristics for 3 pressure
ranges
Large LCD back-lighting graphic screen with contrast adjustment
Mechanical protection against overpressure up to 110%
Overpressure visual and sound warning
Calibration visual warning when the calibration is
necessary
Pressure display in 12 pressure units, and a user unit User adjustable pressure stability criterion
Front panel tarring key Front panel ACF running key
Choice between internal/external calibration EMM parameters display
Piston-cylinder assembly temperature measuring circuit
with auto-calibration by resistance of integrated reference
Permanent display of the residual vacuum
Summary of the Functions (Continuation)
Page 7 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
Page 8
Remote Control
Maintenance
All the CPD8000 functions, even the ACF running
command, can be executed from an external computer
through serial communication (RS232C), which enables it
to be integrated in an automatic calibrating system.
A programming example is given in the user’s manual.
The CPD8000 is delivered with all the operating
instructions, consumables and tools allowing its general
maintenance. No other maintenance is necessary if the
standard is used in accordance with the routine
instructions described in the manual. Usual recalibrations
need only take place every 3 years.
Calibration CE Compatibility
All the CPD8000 standards are delivered with a gauge
calibration certificate issued as standard by the COFRAC
accredited Degranges & Huot’s laboratory (accreditations
2-1033 and 2-1129), which assures the user that the
presented calibration results are unbiased.
The COFRAC calibration guarantees the traceability of the
measurements done by the CPD8000 to the National and
International Standards.
The calibration is operated in accordance with the RM
aero 802.22 recommendation and takes into account:
- The Kn specific coefficient determination
- The ACF calibration control
The uncertainty calculation presented in the certificate
respects the ISO TAG4 and EAL recommendations and
shows the enlarged uncertainty of the CPD8000 with a
coefficient k = 2.
It takes into account the CPD8000’s intrinsic measurement
errors, the uncertainty of the reference means as well as
the influence of the environment conditions, the pressure
control of the CPD8000’s metrological performances and
the calculation of its measurement uncertainty by
comparison with a reference standard.
The CPD8000 complies with the following European
directives and norms:
- n° 89/336/CEE Electromagnetic Compatibility Directive
dated May 3th, 1989 modified by the n° 92/31/CEE
directive dated May 12th, 1992 and the n° 93/68/CEE
directive dated July 22th, 1993
- n° 73/23/CEE Low Tension Directive dated February
19th, 1973 modified by the n° 93/68/CEE directive
dated July 22 th, 1993
- EN 50082-1 Ed.92 norm (Emission with the
89/336/CEE directive)
- EN 55022 B Class Ed. 87 norm (Immunity with the
89/336/CEE directive), EN 61010 norm (Safety rules
for the use of measuring, regulating and laboratory
electric instruments with the 73/23/CEE directive)
Option
By using a special adaptation kit, it is possible to use the
gauge head model of the CPD8000-G(Head model 110,
111, 410 and 710) with the CPD8000-A. Those heads can
be used to works only in gauge mode but allows extending
the range capability of the CPD8000-A up to 50 MPa.
Conclusion
Due to its design and its performances, the CPD8000
primary digital standard is unique in the world. The
operations with the balance do not necessitate a bell to
make the vacuum and masses to load.
Associated to an automatic controller, the CPD8000 allows
performing fast calibrations, without having to break the
vacuum between each pressure point, with a high
metrological reliability.
This instruments is used by our more faithful customer
who are National Laboratories, Meteorology, the R&D
laboratories, sensor manufacturers, airway companies …
Desgranges & Huot
56 Rue des Ecoles
93303 Aubervilliers – France
Tel : +33 1 4839 8300
Fax: +33 1 4833 6590
E-Mail :
dhonline@dh-budenberg.com
www.dh-budenberg.com
Page 8 of 8 Desgranges & Huot WIKA Data Sheet CPD8000 04/2012
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