Improved Accuracy Specifications on Mass Flow Meters and Controllers

Alicat’s latest product release introduces an unprecedented new level of flow accuracy for mass flow meters and controllers. Through improved temperature and pressure compensation our flow measurements are even more resistant to the effects of changing temperature and pressure, and a fully redesigned circuit board has increased our signal to noise ratio and enabled higher resolution for raw sensor data sampling. These augmentations have transformed the already-outstanding Alicat mass flow instruments into one of the most accurate differential pressure-based flow measurement systems on the market.

The Old and The New

Alicat mass flow instruments’ old flow accuracy specifications of ±(0.8% of reading + 0.2% of full scale) for standard calibration and ±(0.4 % of reading + 0.2% of full scale) for high accuracy calibration have been dropped to ±0.6% of reading or ±0.1% of full scale, whichever is greater (with the high accuracy calibration specification dropping to ±0.5% of reading or ±0.1% of full scale).

In addition, compensation refinements have increased the flow resolution specifications by a factor of ten. Not only are Alicat devices more accurate, they also maintain that accuracy to a significantly lower level than before.








Example Calculations

To calculate Alicat’s accuracy using the new specification, you’ll need to know the full scale of a flow instrument and its reading. Let’s assume an M-series mass flow meter with a standard calibration has a full scale of 10 SLPM and it is reading 5 SLPM of flow. For standard accuracy, if the reading is ≤ 16.7% of full scale then the full scale dependent accuracy spec is used. Otherwise the accuracy only depends on the reading. Since the flow reading is above 16.7% of the full scale, the accuracy calculation is based on the flow reading:


Accuracy = ±0.6% of Reading = (0.005)(5 SLPM) = ±0.03 SLPM


If the flow reading on the mass flow meter is below 16.7% of full scale, e.g. 0.5 SLPM, then the accuracy calculation would look like this:


Accuracy = ±0.1% of Full Scale = (0.01)(10 SLPM) = ±0.1 SLPM


For high accuracy calibrations, the error dominance transitions between reading and full scale at 20% of full scale. With the same full scale and readings as the previous example, the calculations would be as follows:


Accuracy = ±0.5% of Reading = (0.005)(5 SLPM) = ±0.025 SLPM


Accuracy = ±0.1% of Full Scale = (0.01)(10 SLPM) = ±0.1 SLPM

The Benefits of Switching

  1. The usable range is significantly higher than comparable products; therefore, you may be able to use one MFC in your system where two were needed because of the flow range limitations of your current MFCs. For example, if you need to control the flow of O2 between 100 SLPM and 100 SCCM, one Alicat MFC can provide accurate, repeatable control over the entire range.  Most thermal based MFCs would require you to have two or more MFCs to complete this same task. This ability leads to:
    1. A lower overall build cost
    2. Lower cost of operation
    3. Less money tied up in inventory for spares/back up units. The ability to select over 98 gases also contributes to fewer number of spares required.
    4. Less complicated setup
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