Fluke Calibration 721 is a precise dual-sensor pressure calibrator developed especially for gas custody transfer, flow measurement and process calibration applications. Two isolated stainless-steel pressure sensors allow static and differential pressure to be measured simultaneously with a single handheld instrument. The calibrator also measures 4–20 mA signals, DC voltage and temperature via an optional Pt100 probe and provides an internal 24 V loop power supply for transmitters. Fluke

The Fluke Calibration 721 is particularly useful in natural-gas metering and custody-transfer systems where both the static line pressure and a relatively small differential pressure across a primary flow element must be measured accurately. The user can select a low-pressure sensor with either 16 psi / 1.1 bar or 36 psi / 2.48 bar range and combine it with one of seven higher-pressure ranges from 100 psi up to 5,000 psi / 345 bar. Fluke

For most pressure ranges, Fluke specifies an accuracy of 0.025% of full scale. The 5,000 psi high-pressure sensor is specified at 0.035% FS. This combination of two independent pressure measurements in one portable calibrator can substantially simplify calibration work on gas flow computers, pressure transmitters and related process instrumentation. Fluke

At europascal, the Fluke Calibration 721 can be combined with suitable pressure sources, pressure modules and calibration accessories for professional pressure measurement applications. For regular metrological traceability, use the europascal Calibration Service.

Your Benefits at a Glance

• Dual isolated stainless-steel pressure sensors
• Simultaneous static and differential pressure measurement
• Designed especially for gas custody transfer applications
• Low-pressure sensor available with 16 psi or 36 psi range
• Seven selectable high-pressure ranges up to 5,000 psi / 345 bar
• Pressure accuracy down to 0.025% FS
• 0 to 24 mA measurement
• Integrated 24 V loop power
• 0 to 30 V DC measurement
• Pt100 RTD input for temperature measurement
• Optional Fluke 720RTD temperature probe
• Temperature measurement from -40 °C to 150 °C
• Support for external Fluke 750P pressure modules
• Large backlit graphic display
• Up to three measurement values displayed simultaneously
• Five instrument setups can be stored
• Numerous selectable pressure units
• More than 35 hours typical battery life
• Four standard AA batteries
• Compact handheld construction
• Suitable for field and laboratory calibration
• Traceable calibration certificate supplied with current listed configurations

Dual Pressure Sensors for Gas Custody Transfer

The defining feature of the Fluke Calibration 721 is its combination of two isolated pressure sensors in one instrument.

In gas custody-transfer applications, it is often necessary to measure a relatively small differential pressure while simultaneously monitoring a much higher static line pressure. The 721 is specifically designed for this task. Fluke describes it as a precision pressure calibrator for gas flow and custody-transfer applications, with simultaneous static and differential pressure measurement. Fluke

This arrangement reduces the need for multiple separate pressure instruments and makes the calibrator particularly useful for servicing flow-computer installations and differential-pressure-based gas flow systems.

The 721 itself should not be confused with a flow standard: it measures the pressure, electrical and optional temperature quantities required during calibration and verification of the associated instrumentation.

Selectable Low-Pressure Range

The low-pressure sensor can be selected in one of two configurations:

16 psi version: approximately -0.97 to +1.1 bar

36 psi version: approximately -0.97 to +2.48 bar.

Both versions offer a fine pressure resolution of 0.001 psi / 0.0001 bar and a specified accuracy of 0.025% FS. Fluke

The low-pressure channel is especially valuable when measuring relatively small pressure differences in gas flow applications.

High-Pressure Sensor up to 345 bar

In addition to the low-pressure channel, the Fluke Calibration 721 can be configured with one of seven higher-pressure sensors.

Available nominal high-pressure ranges are:

Fluke’s international product information confirms the choice of seven high-pressure ranges up to 5,000 psi / 345 bar. Fluke

This broad range selection allows the Fluke Calibration 721 to be configured for different gas transmission, process and industrial pressure applications.

Pressure Accuracy down to 0.025% FS

Pressure measurement accuracy is a central specification for any pressure calibrator.

For the low-pressure sensors and most high-pressure versions, Fluke specifies:

0.025% of full scale.

For the highest 5,000 psi / 345 bar sensor, the one-year specification is:

0.035% of full scale. Fluke

Selecting an appropriately sized pressure range is therefore important when the 721 is used as a calibration reference.

4–20 mA Measurement

Many pressure and differential-pressure transmitters used in process plants provide a standardized 4–20 mA output signal.

The Fluke Calibration 721 measures:

0 to 24 mA

with a resolution of:

0.001 mA.

Fluke specifies the one-year mA accuracy as ±0.015% of reading ±0.002 mA. Fluke

This allows the user to compare the measured pressure directly with the electrical output of a pressure transmitter.

The capability is particularly useful for calibrating differential-pressure and static-pressure transmitters used as inputs to flow computers.

Integrated 24 V Loop Power

The Fluke Calibration 721 incorporates a 24 V loop power supply capable of supplying a transmitter under test.

Fluke specifies the loop supply as:

24 V at 24 mA. Fluke

A separate loop supply is therefore unnecessary for many common transmitter calibration tasks.

Together, the 721 can measure pressure, power the transmitter and measure its current output, significantly simplifying a portable calibration setup.

DC Voltage Measurement

The Fluke Calibration 721 also measures DC voltage up to:

30 V DC.

Resolution is:

0.001 V

and the specified accuracy is ±0.015% of reading ±0.002 V. Fluke

This capability can be used for checking loop supplies and other process signals encountered during calibration and troubleshooting.

Pt100 Temperature Measurement

Pressure and temperature are closely related in gas measurement applications. The 721 therefore incorporates an input for a Pt100 RTD.

With the optional Fluke 720RTD probe, temperature measurements can be integrated directly into the calibration procedure. Fluke specifies a temperature measurement range from:

-40 °C to 150 °C

with a resolution of:

0.01 °C. Fluke

When used with the optional 720RTD probe, Fluke specifies a combined uncertainty of approximately ±0.25 °C. Fluke

This additional measurement channel is particularly useful when pressure and temperature values must be evaluated together during gas custody-transfer calibration.

Three Measurements on One Display

The Fluke Calibration 721 has a large backlit graphic display capable of showing up to three measurement inputs simultaneously. Fluke

For example, an operator can monitor:

Low pressure + high pressure + temperature

or combine pressure information with the electrical signal from a transmitter.

This makes it easier to observe how several process variables interact without repeatedly changing display modes.

Store Five Instrument Setups

The Fluke Calibration 721 can store five instrument configurations for later recall. Fluke

This is particularly practical when the same types of instruments or flow-computer installations are serviced regularly.

Frequently used configurations can be recalled instead of setting up every measurement parameter from scratch.

The instrument also recalls the last-used configuration after power-up.

External Fluke 750P Pressure Modules

The internal dual sensors cover a wide range of pressure applications, but the flexibility of the Fluke Calibration 721 can be expanded further.

The calibrator supports external Fluke 750P Series pressure modules. Fluke currently lists approximately 50 module ranges for the 750P family. Fluke

An external module can be useful when:

• another pressure range is required,
• another pressure type is needed,
• an additional reference range is desirable,
• or the application extends beyond the installed internal sensors.

The measurement capability depends on the pressure module selected.

Pressure Engineering Units

The Fluke Calibration 721 supports numerous pressure engineering units, including psi, bar, mbar, kPa, kg/cm² and several water- and mercury-column units. Fluke

This is useful when calibrating equipment from different manufacturers or working with installations that use different unit conventions.

Direct unit selection also reduces the need for manual pressure conversions during field calibration.

Compact Handheld Design

Despite its dual pressure sensors and electrical and temperature measurement functions, the Fluke Calibration 721 remains a compact portable instrument.

Fluke specifies dimensions of approximately:

20 × 11 × 5.8 cm

and a weight of approximately:

0.54 kg. Fluke

The compact dimensions make the calibrator suitable for field service, while its integrated measurement functions reduce the number of separate instruments required.

Long Battery Life

The Fluke Calibration 721 operates from:

4 standard AA batteries.

Typical battery life is specified as:

more than 35 hours. Fluke

This makes the instrument well suited to mobile calibration work where a mains supply may not be readily available.

Standard AA cells also simplify battery replacement during field use.

Environmental Specifications

The operating temperature range is:

-10 °C to +50 °C.

Storage temperature without batteries is:

-20 °C to +60 °C.

Maximum specified altitude is:

2,000 m.

The housing is rated:

IP40. Fluke

These specifications support the intended use of the 721 as a portable process calibration instrument.

Technical Data

The specifications above are based on the current official Fluke product information. Fluke

Ideal for Gas Custody Transfer

The Fluke Calibration 721 was developed with gas custody-transfer applications in mind. Custody-transfer measurement systems often rely on accurate measurement of differential pressure, static pressure and temperature.

By combining two isolated pressure sensors and an optional Pt100 temperature channel, the 721 allows several important variables to be checked with one handheld instrument. Fluke

This makes it particularly suitable for calibration and verification work involving:

• Gas flow computers
• Differential-pressure transmitters
• Static-pressure transmitters
• Orifice-based gas flow measurement systems
• Natural-gas metering stations
• Process pressure instrumentation
• 4–20 mA pressure transmitters
• Pressure sensors
• Field calibration
• Laboratory calibration

Scope of Delivery

Fluke currently lists the following items with the available 721 model configurations:

Soft carrying case, four AA batteries, manual, traceable calibration certificate and test leads. Fluke

The optional Fluke 720RTD Pt100 probe is required when temperature measurements are to be made with the calibrator.

Compatible pressure pumps, hose kits and Fluke 750P pressure modules are also available separately. Fluke

Calibration by europascal

Professional pressure calibration requires reliable metrological traceability. The Fluke Calibration 721 combines several measurement quantities in a single instrument, making regular calibration particularly important when it is used as reference equipment for field verification.

europascal offers professional calibration services for pressure measurement equipment and can also support customers with suitable pressure-generation and calibration solutions.

For more information, visit the europascal Calibration Service.

Further pressure calibration equipment is available in the europascal pressure technology section. europascal currently lists a broad portfolio of pressure controllers, calibrators, modules, gauges and pressure-generation equipment. europascal.de

Why Choose the Fluke Calibration 721?

The Fluke Calibration 721 is an especially strong solution when several process variables must be measured during one calibration task.

Its two isolated pressure sensors allow low differential pressure and high static pressure to be monitored simultaneously. Depending on configuration, the instrument covers high-pressure measurement up to 345 bar, while most sensor ranges provide 0.025% FS accuracy.

The additional 0–24 mA measurement, 24 V loop power and 0–30 V DC measurement functions make it possible to test common industrial pressure transmitters without carrying several additional electrical instruments.

For gas flow applications, the optional Pt100 input adds temperature measurement from -40 °C to 150 °C. The large backlit display can show up to three inputs at once, while five stored setups speed up recurring calibration work.

With its compact handheld format, more than 35 hours of typical battery operation and compatibility with Fluke 750P modules, the Fluke Calibration 721 is a flexible solution for field service, process calibration and gas custody-transfer applications.

Further products from Fluke Calibration can be found here.

Manufacturer information about the Fluke Calibration 721 can be found on the official Fluke website.

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