RFM Reference Flow Monitor

RFM Reference Flow Monitor

Molbox RFM Flow Monitors are support units for making mass flow measurements using molbloc-L laminar and molbloc-S sonic flow elements.

molbloc flow elements are connected to molbox RFM Flow Monitors with two pressure connections and one data line. molbox RFM Flow Monitors read calibration data off the molbloc EEPROM and measures molbloc upstream and downstream pressure with a built-in high accuracy Reference Pressure Transducers (RPTs). An ohmic measurement system reads the resistance of the molbloc platinum resistance thermometers from which molbloc temperature is calculated. Using the molbloc calibration data, pressures, temperature and gas properties stored in molbox RFM memory, the flow rate of the gas flowing through the molbloc is calculated. For molbloc-L flow elements, a microrange option is available to increase flow measurement resolution and accuracy under 10 % FS of the flow range.

Compact presentation

  • Covers the flow range of 1 sccm to 100 slm with molbloc-L, and up to 5000 slm with molbloc-S
  • Select from 20 different gases
  • Accredited measurement uncertainty of ± 0.5 % of reading with up to 100:1 rangeability
  • Internal valving for on-board purge, leak test and tare support
  • Includes advanced measurement functions such as totalize, average, hi/lo and deviation
  • Complete front panel control and RS232 and IEEE-488 remote communications
  • Measures mass and volume flow with user setable reference pressure and temperature conditions

Flow Measurement Specifications

molbox RFM measures the flow through molbloc flow elements. The flow range, usable operating pressure, and differential pressure for molbloc-L, or the flow range and absolute pressure range for molbloc-S, depend on the molbloc element used and its calibration options. See the molbloc-L and molbloc-S range sheets for calibration and range details.

For molbloc-L ranges up to 3E4, the resolution and accuracy under 10% FS are improved by the microrange option. For the 1E5-L molbloc, the microrange option is necessary to achieve the specification.

molbox RFM Reference Flow Monitors

molbloc-L (ranges 1E1-L thru 3E4-L)

molbloc-S (all ranges)

Measurement update rate

1 second

1 second

Range

to molbloc full scale depending on gas and molbloc pressure

dependent calibration type (see molbloc-L range sheet)

The flow related to 20 kPa to 200 kPa absolute (3 psia to 30 psia) or 50 kPa to 500 kPa absolute (7 psia to 70 psia) upstream

(see molbloc-S range sheet)

Resolution

0.01 % FS

± 0.01 % of reading

Linearity

± 0.23 % of reading from 10 % to 100 % FS,

± 0.023 % FS under 10 % FS

± 0.25 % of reading

Repeatability

± 0.1% of reading from 10 % to 100 % FS,

± 0.01% FS under 10 % FS

± 0.1 % of reading

Precision1

± 0.25 % of reading from 10 % to 100 % FS,

± 0.025 % FS under 10 % FS

± 0.3 % of reading

Predicted stability2
(one year)

± 0.15 % of reading from 10 % to 100 % FS,

± 0.015 % FS under 10 % FS

± 0.2 % of reading

Measurement uncertainty3

± 0.5 % of reading from 10 % to 100 % FS,

± 0.05 % FS under 10 % FS

± 0.5 % of reading from 50 kPa to 500 kPa, ± 0.5 % of the flow @

50 kPa from 20 kPa to 50 kPa

molbox RFM with Microrange option

molbloc-L (ranges 1E1-L thru 3E4-L)

molbloc-L (ranges 1E5 only)

Measurement update rate

1 second

1 second

Range

0 to molbloc full scale depending on gas and molbloc pressure

dependent calibration type (see molbloc-L tables)

0 to molbloc full scale depending on gas and molbloc pressure

dependent calibration type (see molbloc-L tables)

Resolution

0.01 % FS, 0.001 % FS under

10 % FS

0.01 % FS

Linearity

± 0.23 % of reading from 1 % to 100 % FS, ± 0.0023 % FS under 1 % FS

± 0.25 % of reading from 5 % to 100 % FS,

± 0.0125 % FS under 5 % FS

Repeatability

± 0.1 % of reading from 1 % to 100 % FS,

± 0.001 % FS under 1 % FS

± 0.2 % of reading from 5 % to 100 % FS,

± 0.01 % FS under 5% FS

Precision1

± 0.25 % of reading from 1 % to 100 % FS,

± 0.0025 % FS under 1% FS

± 0.32 % of reading from 5 % to 100 % FS,

± 0.016 % FS under 5 % FS

Predicted stability2
(one year)

± 0.15 % of reading from 1 % to 100 % FS,

± 0.0015 % FS under 1 % FS

± 0.2 % of reading from 5 % to 100 % FS,

± 0.01 % FS under 5 % FS

Measurement uncertainty3

± 0.5 % of reading from 1 % to 100 % FS,

± 0.005 % FS under 1 % FS

± 0.5 % of reading from 5 % to 100 % FS,

± 0.025 % FS under 5 % FS

molbloc-S (all ranges)

Specifications are the same as a molbox RFM without Microrange. The Microrange transducer is disabled whenever the molbox RFM is connected to a molbloc-S.

1 Precision: Combined linearity, hysteresis, repeatability.

2 Predicted Stability: Maximum change in zero and span over one year for typical molbox RFM and molbloc used under typical conditions. As stability can only be predicted, stability for a specific molbox RFM should be established from experience.

3 Measurement Uncertainty: Maximum deviation of the molbox RFM flow indication from the true value of the flow through the molbloc including precision, stability and DHI calibration standard uncertainty. Measurement uncertainty specifications for molblocs are valid only for gases with which the molbloc has been calibrated. All molblocs are calibrated for N2. Calibrations with other gases are optional. DHI calibration capability is not maintained at all times for all gases on all molbloc designations. Check for availability before ordering.