Molbox 1 Plus
Molbox1 plus Flow Terminal

± 0.125 % of reading uncertainty on mass flow measurements with molbloc-L and molbloc-S elements with premium calibrations
– molbox1+S configuration gives extra rangeability with molbloc-S elements without requiring vacuum
– Now use any molbloc element for both high and low pressure applications in the same gas
– Even more robust internal pneumatic design
– Full suite of software automation products and hardware accessories to create a complete gas flow calibration system?including new COMPASS? for Flow calibration assistance software.


The molbox1+ flow terminal from Fluke Calibration represents a significant update to the molbloc/molbox gas flow calibration system. molbox1+ combined with molbloc flow elements enables you to achieve the lowest uncertainty available for gas flow meter and controller calibrations. A special configuration, molbox1+S, allows you to use molbloc-S sonic nozzle flow elements at higher pressures than were previously possible, greatly extending their usable flow range.
A molbloc/molbox1+ gas flow calibration system is the ideal solution for calibrating flow meters, thermal mass flow controllers (MFCs), rotameters, turbine meters, bubble meters, and other flow measurement devices.
With real-time measurements, no moving parts and supported by traceable calibration in several different gases and operating pressures, molbloc/molbox can handle virtually any calibration application without compromise. molbloc/molbox systems are widely used in many industries, including pharmaceuticals, semiconductors, aerospace, environmental monitoring, energy production, reference gas blending, and research and standards laboratories.utomation products and hardware accessories to create a complete gas flow calibration system?including new COMPASS? for Flow calibration assistance software.

Unparalleled uncertainty specifications

molbox1+ innovations enable the molbloc/ molbox1+ system to achieve the lowest gas flow measurement uncertainties in the industry. The lower uncertainty is made possible by several key improvements, including:

– Use of Fluke Calibration’s exclusive quartz reference pressure transducer (Q-RPT) technology to precisely measure both absolute and differential pressure. molbox1+ Q-RPTs are specially characterized sensors benefitting from the same technology used in Fluke Calibration?s pressure transfer standards.
– Premium molbloc calibrations linearize molbloc flow output to better capitalize on existing precision and repeatability.
– Expanded molbloc modelization enables improved performance of molbloc-L laminar flow elements across their range of operating pressures.
– Reduced uncertainty on gas properties utilizing data from NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP).
– Continued improvements in Fluke Calibration?s molbloc calibration chain, based on fundamental massand time-based mass flow measurements using Fluke Calibration?s own dynamic Gravimetric Flow Standard.
Two levels of molbloc flow element calibration are now available to let you balance uncertainty and cost:
– Premium: ? 0.125 % of reading flow measurement uncertainty (with molbox1+)
– Standard: ? 0.2 % of reading flow measurement uncertainty (with molbox1 or molbox1+)

New molblocs are eligible for either calibration type. Existing molblocs are compatible with molbox1+ at ? 0.2 % of reading uncertainty with no changes required. See below for details on upgrade service to existing molblocs to allow premium calibration and measurement specifications.

The molbloc/molbox system has stood the test of time for flow meter calibration since the early 1990?s, used in many demanding calibration laboratories, intercomparisons and government organizations worldwide. Fluke Calibration?s uncertainty specifications are conservative and backed by a thorough uncertainty analysis and metrology support. Fluke Calibration?s innovation and design is continually aimed at making sure our products deliver specifications that can be realized by the user, not under best case conditions but in your real-world application.

molbox1+S sonic nozzle calibration device expands rangeability?without vacuum pumps molbox1+S is a special configuration of molbox 1+ that enables you to cover a wide range (10:1 range turndown) with molbloc-S sonic nozzle flow elements, without requiring costly vacuum pumps. molbox1+S sonic nozzle calibration device is available with upstream Q-RPT pressure range up to 2 MPa (300 psia) to allow molbloc-S elements to be conveniently used over a wide flow range upstream of flow meters being tested at atmospheric pressure, a common application. This extra rangeability makes it simple to configure a calibration system using fewer molbloc elements and minimal accessories. It also greatly extends the range of your existing molbloc-S elements when a high pressure molbloc calibration is added.

molbloc-S range example with device under test at atmospheric pressure

Molbloc-S elementUsable range with SP calibration and molbox1 A700KUsable range with HP calibration and molbox1+S A2M
1E2-S15 to 50 slm*20 to 200 slm
5E2-S67 to 250 slm*100 to 1000 slm

*Minimum usable flow of molbloc-S elements with SP calibrations are limited by back pressure requirements for sonic flow when used upstream of a device at atmospheric pressure. Flow values are in standard liters per minute referenced to 0 ?C.
molbox1+S is designed for use with molbloc-S sonic nozzle calibration devices and therefore is configured for absolute pressure measurement only, reducing its cost. It also reduces flow system complexity and overall cost, as well as ongoing recalibration costs.

Use the same molbloc in multiple applications
Multiple molbloc calibrations are now supported for each gas. This means that you can now have a molbloc calibrated separately for use both at high pressure (upstream of the device under test) and low pressure (downstream of the device under test) to support different applications instead of requiring two molblocs or manually loading separate molbloc calibration files. All calibrations are stored on the molbloc EEPROM and the user simply selects the calibration type from the molbox1+ front panel or via molbox1+ remote interface.

General specifications
Power requirements85 V ac to 264 V ac, 47 Hz to 440 Hz, 18 VA max consumption
Normal operating temperature range15 °C to 30 °C (59 °F to 86 °F)
Storage temperature range-20 °C to 70 °C (-4 °F to 158 °F)
VibrationMeets MIL-T-28800D
Weight6.8 kg (15 lb) max
Dimensions (WxHxD)32 cm x 12 cm x 30 cm (12.6 in x 4.7 in x 11.8 in) approx.
Communication portsRS-232 (COM1), RS-232 (COM2), IEEE-488.2
Pressure connections (molbox1+ and molbloc)Quick connectors equivalent to Swagelok® QM Series (SS-QM2-B200)
Flow ranges5000 slm

See separate molbloc-L and molbloc-S range tables

Flow measurement rate1 second
Gases supported
(Consult your sales representative for a current list of gases available for factory molbloc calibration.)
Nitrogen (N2), Air, Argon (Ar), Carbon Monoxide (CO), Helium (He), Oxygen (O2), Carbon Dioxide (CO2), Carbon Tetrafluoride (CF4), Ethane (C2H6), Ethylene (C2H4), Fluoroform (CHF3), Hexafluoroethane (C2F6), Hydrogen (H2), Methane (CH4), Nitrous Oxide (N2O), Propane (C3H8), Sulfur Hexafluoride (SF6), Butane (C4H10), Octafluorocyclobutane (C4F8), Xenon (Xe)
Valve driver option(8) 12 V outputs

Each output can sink 500 mA at 12 V, max 1 Amp total

MFC control option (analog input/output)Nominal voltage range:

0 V dc to 6 V dc input

0 V dc to 5 V dc output


Nominal current range:

4 mA to 20 mA input

4.01 mA to 20 mA output


± 0.1 % FS (set), ± 0.05 % FS (measure)


Pressure measurement
TypeQ-RPT Characterized Quartz Reference Pressure Transducers –Oscillating quartz crystal with mechanical bellows
Calibrated pressure range (full scale)A700K: 0 to 600 kPa absolute (0 to 87 psia)
A350K: 0 to 300 kPa absolute (0 to 44 psia)
S A1.4M (molbloc-S only): 0 to 1.2 MPa absolute (0 to 174 psia)
S A2M (molbloc-S only): 0 to 2 MPa absolute (0 to 290 psia)
Measurement uncertainty (one-year)Absolute pressure4
± (0.01 % of reading or 0.003 % Q-RPT span, whichever is greater)Differential pressure (A700K with Tare)
± (8.4 Pa (0.0012 psi) or 0.032 % ΔP, whichever is greater)Differential pressure (A350K with Tare)


Temperature measurement
Typemolbloc PRTs with molbox1+ Ohmic Measurement System
Range (FS)0 to 40 °C
Resolution0.01 °C
molbloc PRT precision± 0.02 °C (15 to 30 C)
On-boardReference resistor
100 and 110 Ω ± 0.01 %, stability < 25 ppm/yearOhmic measurement
± 0.02 % of reading (15 °C to 30 °C)


Flow measurement
With molbloc-L laminar flow elements
Standard molbloc calibrationPremium molbloc calibration
Range0 to 100 % molbloc full scale0 to 100 % molbloc full scale
Resolution0.0015 % FS0.0015 % FS
Precision1± 0.07 % of reading,
± 0.007 % FS under 10 % FS
± 0.07 % of reading,
± 0.007 % FS under 10 % FS
Stability (one-year)2± 0.09 % of reading,
± 0.009 % FS under 10 % FS
± 0.03 % of reading,
± 0.003 % FS under 10 % FS
Measurement uncertainty3
(For any gas for which the molbloc in use is calibrated)
± 0.2 % of reading,
± 0.02 % FS under 10 % FS
± 0.125 % of reading,
± 0.0125 % FS under 10 % FS
With molbloc-S sonic nozzle flow elements
Standard molbloc calibrationPremium molbloc calibration
Range10 % to 100 % molbloc full scale10 % to 100 % molbloc full scale
Resolution0.0015 % FS0.0015 % FS
Precision1± 0.06 % of reading± 0.06 % of reading
Stability (one-year)2± 0.05 % of reading± 0.03 % of reading
Measurement uncertainty3
(For any gas for which the
molbloc in use is calibrated)
± 0.2 % of reading± 0.125 % of rea


1 Precision: Combined linearity, hysteresis, repeatability.2 Stability: Maximum change in zero and span over specified time period for typical molbox and molbloc used under typical conditions. As stability can only be predicted, stability for a specific molbox and molbloc should be established from experience.
3 Measurement uncertainty: Maximum deviation of the molbox1+ flow indication from the true value of the flow through the molbloc including precision, stability and Fluke Calibration. For a complete description of uncertainties see technical note 2011TN06B UNCERTAINTY ANALYSIS FOR FLOW MEASURED BY molbloc-L AND molbloc-S MASS FLOW TRANSFER STANDARDS.
4 With regular use of Autozero. Add 0.005 % of Q-RPT span for one year without use of AutoZero, (translates to 0.005 % FS for molbloc-S, does not significantly affect molbloc-S standard calibration or molbloc-L uncertainty.)
All uncertainty specifications reported at k=2