Fluke Calibration molbox2 is a precise flow terminal for professional gas flow measurement and calibration using Fluke Calibration molbloc flow elements. Combined with molbloc-L laminar flow elements or molbloc-S sonic nozzle flow elements, the molbox2 creates a highly accurate and flexible gas flow calibration system covering flow rates from less than 1 sccm to more than 5000 slm.
Designed as the central measurement and processing unit of the molbloc/molbox system, the Fluke Calibration molbox2 measures the pressure and temperature conditions at the connected molbloc and calculates the corresponding gas mass flow in real time. This modular concept allows different molbloc elements to be connected to the same molbox2 terminal, enabling a single system to cover an exceptionally wide range of gas flow calibration applications.
With Premium molbloc calibration, the system can achieve flow measurement uncertainty as low as ±0.125% of reading, making it suitable for demanding calibration laboratories, research facilities and industrial applications requiring high-level traceability and measurement performance.
The molbox2 is designed for calibrating flow meters, mass flow meters, thermal mass flow controllers (MFCs), rotameters, turbine gas meters, bubble flow meters and other gas flow measurement devices.
At europascal, the Fluke Calibration molbox2 complements a comprehensive range of professional calibration equipment for flow, pressure, temperature and other measurement quantities. For information about professional calibration and metrological traceability, visit the europascal Calibration Service.
Your Benefits at a Glance
The Fluke Calibration molbox2 combines high-accuracy pressure and temperature measurement with intelligent gas property calculations to create a powerful gas flow calibration system.
Key advantages include:
- Gas flow measurement from less than 1 sccm to more than 5000 slm depending on molbloc configuration
- Flow measurement uncertainty down to ±0.125% of reading with Premium calibration
- Compatible with molbloc-L laminar flow elements
- Compatible with molbloc-S sonic nozzle flow elements
- Real-time gas flow measurement
- No moving parts in the molbloc flow elements
- Q-RPT quartz reference pressure transducer technology
- Integrated molbloc PRT temperature measurement
- Support for numerous gases
- Gas property calculations based on NIST REFPROP10 data
- Multiple calibration levels available
- Three times faster flow response than previous molbox generations
- 340 ms flow measurement rate
- Optional MFC control
- Optional valve driver
- RS-232 interfaces
- IEEE-488.2 interface
- Compatible with COMPASS for Flow calibration software
- Suitable for automated calibration systems
- Broad industrial and laboratory application range
Gas Flow Measurement from <1 sccm to >5000 slm
The Fluke Calibration molbox2 provides an exceptionally wide flow measurement capability when combined with suitable molbloc elements.
The complete molbloc/molbox2 system can cover flow rates from:
less than 1 sccm
to:
more than 5000 slm.
The actual usable flow range depends on the selected molbloc element, calibration type, gas, operating pressure and system configuration.
This modular design enables users to select the molbloc that best matches the required flow range instead of using one fixed flow sensor for all applications.
Several molbloc elements can therefore be used with one molbox2 terminal to create a comprehensive gas flow calibration system.
molbox2 and molbloc – How the System Works
The Fluke Calibration molbox2 should not be considered as the primary flow element on its own.
The complete system consists of:
molbox2 Flow Terminal + molbloc Flow Element + Gas Supply + Device Under Test
The molbloc provides the characterized flow element.
The molbox2 measures the pressure and temperature conditions required to determine the gas flow through that element.
The instrument then calculates and displays the corresponding flow value.
This separation between flow terminal and interchangeable flow element is one of the key advantages of the molbloc/molbox concept.
Different molbloc elements can be connected according to the required flow range and application.
molbloc-L Laminar Flow Elements
The Fluke Calibration molbox2 can be combined with molbloc-L laminar flow elements.
A molbloc-L determines gas flow using the relationship between pressure drop and flow through a precisely characterized laminar flow element.
The molbox2 measures the differential pressure across the molbloc-L together with the relevant absolute pressure and temperature.
Using the stored calibration data and gas properties, the system calculates the actual gas mass flow.
The molbloc-L concept is particularly suitable for applications requiring broad rangeability and high measurement accuracy.
molbloc-S Sonic Nozzle Flow Elements
The molbox2 system can also be used with molbloc-S sonic nozzle flow elements.
These elements operate according to the principle of critical or choked gas flow.
When the required pressure ratio across the nozzle is achieved, gas velocity reaches sonic conditions at the nozzle throat.
Under these conditions, the mass flow is primarily determined by upstream pressure, gas temperature, nozzle geometry and gas properties.
Fluke specifies molbloc-S flow measurement over 10% to 100% of the molbloc full-scale range.
With Premium calibration, measurement uncertainty can reach:
±0.125% of reading.
Premium Flow Measurement Uncertainty
One of the major advantages of the Fluke Calibration molbox2 system is its low measurement uncertainty.
With molbloc-L elements and Premium calibration, Fluke specifies measurement uncertainty of:
±0.125% of reading
or:
±0.0125% of molbloc full scale below 10% FS.
With molbloc-S sonic nozzle elements and Premium calibration, the specified measurement uncertainty is:
±0.125% of reading.
These specifications apply when the molbloc is calibrated for the gas being used.
This high measurement performance makes the molbox2 particularly suitable for professional calibration laboratories and demanding industrial flow calibration applications.
Standard and Premium molbloc Calibration
Fluke offers different calibration levels for molbloc elements.
With Standard calibration, the specified flow measurement uncertainty for a calibrated gas is typically:
±0.2% of reading
and for molbloc-L:
±0.02% FS below 10% FS.
Premium calibration improves the measurement uncertainty to:
±0.125% of reading
and for molbloc-L:
±0.0125% FS below 10% FS.
The appropriate calibration level can therefore be selected according to the required measurement uncertainty and calibration application.
Q-RPT Quartz Reference Pressure Transducers
The Fluke Calibration molbox2 uses Fluke Calibration’s Q-RPT technology for pressure measurement.
Q-RPT stands for:
Quartz Reference Pressure Transducer.
These characterized reference pressure transducers use an oscillating quartz crystal combined with a mechanical bellows.
The same fundamental Q-RPT technology is used in Fluke Calibration pressure transfer standards.
Depending on the molbox2 configuration, different pressure ranges are available.
These include:
A350K: 0 to 300 kPa absolute
A700K: 0 to 600 kPa absolute
and for molbox2-S configurations:
A1.4M: 0 to 1.2 MPa absolute
A2M: 0 to 2 MPa absolute.
The pressure measurements provide essential input quantities for calculating the flow through the connected molbloc.
Precise Temperature Measurement
Gas temperature is another essential parameter in accurate gas flow measurement.
The molbox2 measures the PRT integrated into the connected molbloc.
The specified temperature measurement range is:
0 °C to 40 °C.
Temperature resolution is:
0.01 °C.
The molbloc PRT precision is specified as:
±0.02 °C from 15 °C to 30 °C.
The molbox2 uses an integrated resistance measurement system to determine the temperature of the molbloc and incorporate it into the flow calculation.
Support for Numerous Gases
The Fluke Calibration molbox2 supports a broad selection of gases.
These include:
- Nitrogen
- Air
- Argon
- Helium
- Oxygen
- Carbon dioxide
- Hydrogen
- Methane
- Propane
- Ethane
- Ethylene
- Nitrous oxide
- Sulfur hexafluoride
- Xenon
- Neon
- Krypton
- Acetylene
- Natural gas
and numerous additional gases.
The availability of multiple gas calibrations and gas property modeling enables the molbox2 system to be adapted to many different industrial and laboratory applications.
NIST REFPROP10 Gas Property Data
Gas properties play an important role in accurate mass flow measurement.
The Fluke Calibration molbox2 system uses gas property data from:
NIST REFPROP10.
REFPROP is the NIST Reference Fluid Thermodynamic and Transport Properties Database.
Using high-quality gas property data enables the molbox2 to calculate flow for different gases based on their thermodynamic and transport properties.
Fluke also provides traceable uncertainty specifications for selected gases even when the connected molbloc has not been individually calibrated using the actual gas.
This can significantly reduce the need for separate actual-gas calibrations in applications involving multiple gases.
Fast Flow Measurement
The Fluke Calibration molbox2 has a specified flow measurement rate of:
340 milliseconds.
Fluke states that the molbox2 provides approximately three times faster flow response compared with previous molbox generations.
Fast measurement response is particularly useful when calibrating mass flow controllers or when several calibration points must be evaluated efficiently.
It also improves productivity in automated calibration systems.
Calibration of Mass Flow Controllers
One of the primary applications of the Fluke Calibration molbox2 is calibration of thermal mass flow controllers.
A typical calibration system consists of:
Gas Supply → molbloc → Mass Flow Controller Under Test → Flow Control/Back Pressure System
with the molbox2 connected to the molbloc for pressure, temperature and flow determination.
Depending on the configuration, the device under test can also be positioned upstream of the molbloc.
The molbox2 provides the reference flow value, which is compared with the indicated or commanded flow of the MFC.
Optional MFC Control
The molbox2 is available with an optional MFC control function.
This provides analog input and output capabilities for controlling and measuring mass flow controllers.
The nominal voltage ranges include:
0 to 6 V DC input
and:
0 to 5 V DC output.
The nominal current range is:
4 to 20 mA.
Fluke specifies MFC control accuracy of:
±0.1% FS for setting
and:
±0.05% FS for measurement.
This option allows the molbox2 to become a more integrated MFC calibration platform.
Optional Valve Driver
An optional valve driver is also available.
It provides:
eight 12 V outputs.
Each output can sink up to:
500 mA at 12 V
with a maximum total current of:
1 A.
This enables external valves and flow system components to be integrated into automated gas flow calibration setups.
molbox2-S for Sonic Nozzle Applications
The molbox2-S is a special configuration optimized for molbloc-S sonic nozzle elements.
It provides higher upstream pressure measurement capability than standard molbox2 configurations.
The A2M version provides absolute pressure measurement up to:
2 MPa / 290 psia.
This enables molbloc-S elements to operate over a wider flow range when positioned upstream of a device under test operating near atmospheric pressure.
For some applications, this eliminates the need for a vacuum pump.
It can also reduce the number of molbloc-S elements required to cover a broad flow range.
10:1 Rangeability with molbloc-S
Using molbox2-S with appropriate high-pressure molbloc-S calibration can significantly increase the usable range of a sonic nozzle.
Fluke describes a typical:
10:1 range turndown.
For example, a molbloc-S element that covers a limited range in a conventional low-pressure configuration can provide a substantially wider flow range when operated at higher upstream pressure.
This can simplify calibration system configuration and reduce hardware requirements.
Real-Time Flow Measurement
Unlike gravimetric or volumetric primary flow measurement methods that may require flow collection over a defined time interval, the molbloc/molbox2 system provides real-time flow measurement.
This makes it particularly useful for calibrating devices whose output changes dynamically with flow.
The user can directly observe the response of the device under test while changing the flow.
This is especially valuable for:
- Mass flow controllers
- Flow meters
- Variable-area flow meters
- Process flow instruments
- Research applications
No Moving Parts in the molbloc
The molbloc flow elements contain no moving parts.
This design provides several advantages:
- High repeatability
- Low mechanical wear
- Excellent long-term stability
- Reduced maintenance
- Predictable calibration behavior
For professional calibration laboratories, long-term stability is particularly important because it directly affects recalibration intervals and measurement uncertainty.
COMPASS for Flow Software
The Fluke Calibration molbox2 can be integrated with Fluke Calibration’s:
COMPASS for Flow
calibration software.
COMPASS for Flow supports automation of gas flow calibration systems.
Depending on the system configuration, automated calibration can include:
- Flow point generation
- Device-under-test control
- Reference measurement
- Data acquisition
- Calibration sequence execution
- Result calculation
- Calibration data management
This makes the molbox2 suitable for both manual calibration benches and sophisticated automated flow calibration systems.
Communication Interfaces
The Fluke Calibration molbox2 provides several interfaces for integration into calibration systems.
Standard communication ports include:
- RS-232 COM1
- RS-232 COM2
- IEEE-488.2
These interfaces enable remote operation and integration with calibration software and automated test systems.
Technical Highlights
| Feature | Fluke Calibration molbox2 |
|---|---|
| Device type | Gas flow terminal |
| Flow principle | Used with molbloc-L or molbloc-S |
| System flow range | <1 sccm to >5000 slm |
| Premium uncertainty | Down to ±0.125% of reading |
| Standard uncertainty | Down to ±0.2% of reading |
| Flow measurement rate | 340 ms |
| Pressure sensors | Q-RPT quartz reference pressure transducers |
| Temperature measurement | molbloc PRT |
| Temperature range | 0 °C to 40 °C |
| Temperature resolution | 0.01 °C |
| molbloc PRT precision | ±0.02 °C from 15 °C to 30 °C |
| Communication | 2 × RS-232, IEEE-488.2 |
| MFC control | Optional |
| Valve driver | Optional |
| Software | COMPASS for Flow |
| Operating temperature | 15 °C to 30 °C |
| Storage temperature | -20 °C to 70 °C |
| Power | 85 to 264 V AC, 47 to 440 Hz |
| Maximum power consumption | 18 VA |
| Dimensions | Approx. 32 × 12 × 30 cm |
| Weight | Max. 6.8 kg |
molbox2 with molbloc-L vs. molbloc-S
The Fluke Calibration molbox2 supports two fundamentally different molbloc flow element technologies.
molbloc-L is a laminar flow element.
It determines flow based on the relationship between gas flow and differential pressure across a characterized laminar flow path.
It can operate over:
0 to 100% of the molbloc full-scale range.
molbloc-S uses a sonic nozzle.
It operates with critical gas flow and is specified over:
10 to 100% of the molbloc full-scale range.
Both technologies can achieve measurement uncertainty down to:
±0.125% of reading
when used with Premium calibration.
The appropriate technology depends on the flow range, gas, pressure conditions, required rangeability and calibration application.
Applications of the Fluke Calibration molbox2
The Fluke Calibration molbox2 is suitable for calibration of:
- Mass flow meters
- Thermal mass flow controllers
- Mass flow sensors
- Rotameters
- Variable-area flow meters
- Turbine gas meters
- Bubble flow meters
- Process flow meters
- Gas flow controllers
- Laboratory flow instruments
Typical industries include:
- Calibration laboratories
- Semiconductor manufacturing
- Pharmaceutical production
- Aerospace
- Environmental monitoring
- Energy production
- Reference gas preparation
- Research laboratories
- National and industrial metrology laboratories
Why Choose the Fluke Calibration molbox2?
The Fluke Calibration molbox2 provides a flexible and highly accurate platform for professional gas flow calibration.
Rather than using a fixed internal flow sensor, the system combines the molbox2 flow terminal with interchangeable molbloc-L or molbloc-S flow elements.
This modular concept allows a single molbox2 terminal to cover flow rates from less than 1 sccm to more than 5000 slm, depending on the selected molbloc configuration.
With Premium molbloc calibration, measurement uncertainty can be as low as ±0.125% of reading.
Q-RPT quartz reference pressure transducers provide precise pressure measurements, while integrated molbloc PRT measurement provides the temperature information required for accurate gas flow determination.
Support for numerous gases and NIST REFPROP10 gas property data further increases the flexibility of the system.
Optional MFC control, valve driver outputs and COMPASS for Flow software enable the molbox2 to be integrated into automated calibration systems.
The result is a scalable gas flow calibration platform suitable for demanding industrial, research and calibration laboratory applications.
At europascal, we provide Fluke Calibration flow, pressure, temperature and electrical calibration technology for professional laboratory and industrial applications.
For professional calibration and metrological traceability, visit the europascal Calibration Service.
Further products from Fluke Calibration are available from europascal.
Manufacturer information about the Fluke Calibration molbox2 is available on the official Fluke Calibration website.
