Fluke Calibration P3025, P3015, P3031, P3011, P3022 Data Sheet

Deadweight tester

selection guide

The deadweight tester (DWT) is a
very robust and flexible pressure
measurement standard. This guide
is intended to simplify the process of
selecting the right deadweight tester
for your application. The following
considerations will help you get started:

• Pressure range

• Pressure media

• Pressure generation options

• Weight increments

• Accuracy

• Adapters

• Available models

Bestselling pneumatic
deadweight testers*

P3025 3.5 MPa (500 psi)
P3015 3.5 MPa (500 psi)
P3031 7 MPa (1000 psi)
P3011 100 kPa (30 mmHg)
P3022 100 kPa (400 inH2O)
P3014 1 MPa (150 psi)
P3023 200 kPa (800 inH2O)
P3012 100 kPa (400 inH2O)

*For details about these and other models,
see the table starting on page 4.

Bestselling hydraulic
deadweight testers*

P3123 35 MPa (5000 psi)
P3125 110 MPa (16000 psi)
P3223 35 MPa (5000 psi)
P3224 70 MPa (10000 psi)
P3124 70 MPa (10000 psi)
P3116 140 MPa (20000 psi)
P3114 70 MPa (10000 psi)
P3112 14 MPa (2000 psi)
P3113 35 MPa (5000 psi)
P3213 35 MPa (5000 psi)

*For details about these and other models,
see the tables starting on page 6.

Things to consider when
selecting a deadweight tester

Range

The first thing to consider is
the pressure range. One of the
advantages of a DWT is the wide
range of instruments that it can
cover. The DWT is an inher­ent percent-of-reading device,
meaning that its performance
actually improves as it is used at
pressures below full scale. There
is a lower breakpoint, normally
10 % of full scale, where the
specification ceases to be per­cent of reading.

When selecting the range of
a deadweight tester, first con­sider the highest pressure that
needs to be generated. The
full scale needs to be greater
than this. Since the accuracy
is a percent of reading speci­fication, it is okay to consider
possible future expansion and
select a DWT that has a higher
full scale than what is cur­rently needed.

The next step is to confirm
that the unit can generate
the lowest pressure that is
required. As stated, the perfor­mance is less than ideal when
the pressure being generated
is below 10 % of the full scale.
Applications that require both
low and high hydraulic pres­sures can be handled using
dual piston units. These units
are provided with both a low
range and high range piston/
cylinder. Switching between
the low range and high range
on a Fluke Calibration DWT
is as simple as removing the
masses from one piston and
placing them on the other. No
valves need to be switched.

Many pneumatic devices
also support measuring gauge
mode pressures that are below
atmospheric pressure. This
is often referred to as nega­tive gauge or vacuum mode.
To support the calibration
of these devices, a DWT can
be provided with a vacuum
piston, where the piston is

suspended with the weights
below it. A partial vacuum
is then generated above the
piston to float the piston. The
Fluke Calibration P3000 is
available in configurations of
vacuum only, positive pressure
only, or combined vacuum and
pressure. Due to the relatively
low additional cost of having
a combined pressure/vacuum
system, they are normally
preferable.

Media

The next thing to consider when
selecting a DWT is the medium
to be used. Often the choice of
the medium is dependent upon
the pressure range required.
Pneumatic, or gas, instruments
are ideal for lower pressure
ranges. Gas is preferred when­ever cleanliness is required.
In addition, using gas reduces
the impact of head height cor­rections. However, at higher
pressures it is necessary to use
water or oil.

The usefulness of gas as a
medium is limited to approxi­mately 2000 psi. There are
two reasons for this. First,
there is more risk of explosion
at high gas pressures, and that
is a safety concern. Second,
generating high gas pressure
will require expensive inten­sifiers or gas boosters. Using
oil or water eliminates these
issues. Since water is not a
very good lubricant, oil is pref­erable when allowed.

One advantage of liquids is
they are incompressible. This
allows a small change in the
volume of the system (through
a screw pump) to result in
large changes in pressure.
The most common approach
is to use a mineral oil as the
medium. This is ideal in that it
assists in lubricating the piston
and cylinder. The downside to
using oil as a medium is it now
introduces the device under
test to possible contamination.

If a device under test cannot
be exposed to oil, then there
are a couple of options avail­able. First, in certain devices
you can use water instead.
Another option is to use a
liquid-to-liquid separator.
The separator allows you to
use one liquid in the device
under test and another in the
DWT. Second, certain ranges
are available with water as
the media. This allows for
the device under test to be
connected straight to the
deadweight tester without oil
contamination.

Pressure generation

A DWT is a complete solution
that encompasses both
the ability to measure the
pressure as well as generate
the pressure.

To increase pressure in a
hydraulic deadweight tester, a
priming pump is used. Fluke
Calibration P3100 and P3200
Series Deadweight Testers
have a priming pump included
standard in the device. The
priming pump can also be
used to remove gas from the
system.

For low gas pressures, the
pressure is generated using a
hand pump. Higher gas pres­sures (more than 2 MPa or
300 psi) require the use of
an external source, such as
a nitrogen bottle. Even when
pumps are rated to higher
pressures, users will normally
find them difficult to use
because of the forces involved.

Generation of negative
gauge, or vacuum, is similar in
concept to positive pressure.
For lower vacuum pressures
with small volumes a built in
hand pump will be sufficient.
For larger volumes or higher
vacuums, an external vacuum
pump may be desirable.

2 Fluke Calibration Deadweight tester selection guide

Weight sets

Deadweight testers use a preci­sion piston-gauge system con­sisting of a vertically mounted,
piston and cylinder assembly,
and accurately calibrated weight
masses that are loaded onto the
piston. Weight sets are available
in a variety of units of measure
such as psi, inH₂O or MPa, and
are calibrated to match a specific
deadweight tester. If more than
one unit of measure is desired
then, additional weight sets
called conversion weight sets,
can be purchased in the desired
units and calibrated to match
the same deadweight tester.

On certain deadweight
testers, a fine increment weight
set is also available. This is
useful when calibrating a wide
range of devices by allowing
for more discrete pressure set
points. These smaller weights
supplement the larger weights
to produce fine incremental
pressures. For more information
on the standard weight sets
provided as well as the fine
increment weight sets, please
see document 4090591, “Pres­surements Deadweight Tester’s
Weight Increments.”

Accuracy

Like most measurement systems
there are many factors that af­fect your accuracy. Potentially,
the largest factor affecting ac­curacy in a deadweight tester
is local gravity. Gravity varies
slightly from one location to
another (see map). This has an
impact on the nominal pressure
increments of a deadweight
tester. To overcome this issue, at

the time of
manufac­ture Fluke
Calibration
trims the
weights to
produce
the correct
nominal
pressures
at your
location.
This is

3 Fluke Calibration Deadweight tester selection guide

an advantage of buying a new
deadweight tester and hav­ing the manufacturer trim the
weights for you.

Deadweight testers are
available in the marketplace
at varying accuracy classes.
When comparing accuracy
specifications it is important
to realize that those values
can only be realized under the
right conditions. Better accura­cies may require the users to
make additional corrections
not mentioned on the data
sheet. For example, an accu­racy of 0.006 % may only be
valid if you correct for temper­ature and use a more accurate
value for local gravity in your
calculations.

Each Fluke Calibration DWT
is available with standard
accuracy or an improved accu­racy option. Instruments with
the improved accuracy option
come standard with software
to assist in the calculation of
the generated pressure.

For better accuracies, a
piston gauge may be appropri­ate. A piston gauge works on
the same principle as a DWT
but is designed, built, and
operated in such a way to pro­vide improved uncertainties.

Adapters

A DWT will include a test port
to allow for the connection of
the unit under test. Since one of
the inherent features of a DWT
is its flexibility, it is important
that the test port connection be
adaptable to multiple types of
pressure devices.

The test port on a Fluke Cal­ibration DWT is available with
adaptors for various sizes and
types, 1/8, 1/4, 3/8, and 1/2
NPT and BSP as well as M20
x 1.5 and M14 x 15 included
standard. Due to the unique
design of the Fluke Calibra­tion test port, all of the above
adapters are capable of provid­ing leak tight seals to 140 MPa
(20,000 psi) without the use of
wrenches or PTFEtape.

Calibration

The measurements that you
make with your deadweight
tester are very important, and
often influence decisions that
have a big financial impact on
your company. It is important
to ensure that you have the
highest quality calibration data
backing up the measurements
that you make. Fluke Calibra­tion automatically provides an
ISO 17025 accredited calibra­tion for each DWT. With an ISO
17025 accredited calibration,
you know that the calibration
laboratory has been assessed
by third party calibration
experts to ensure that the
technician training, environ­ment, procedures, measurement
uncertainty, equipment used
and measurement traceability
associated with the calibration
all are performed to stringent
requirements. Having your
DWT accompanied with an
ISO 17025 accredited calibra­tion also reduces total cost to
your company by reducing, or
in some cases eliminating, the
need for supplier audits, with a
potential savings of hundreds
or even thousands of dollars.

Some customers may require
you to demonstrate that the
calibration of your DWT is
traceable to the International
System of Units (SI), usually
through a national metrology
institute like NIST. When your
DWT comes with an accred­ited calibration, this has been
internationally recognized to
provide sufficient demonstra­tion of traceabilty. You won’t
have to spend the additional
time calling your calibration
supplier and requesting addi­tional documentation in order
to prove that your measure­ments are traceable.

When your work is impor­tant, and your measurements
matter, an accredited calibra­tion is a great way to provide
additional confidence in your
measurement results and to
demonstrate to your custom­ers that you meet their quality
requirements.