Fox Thermal Blog

Thermal Mass Flow

Other technologies

Flow measurement of gases

Direct mass flow measurement of air and gases in standard volumetric units (ie SCFM or NM3/H) or mass units (ie LBS/M or KG/H). Each meter has the option for the user to select a variety of flow units (see model data sheets for specific flow units available).

Other technologies require multiple instruments to determine the volumetric flow rate at reference conditions.

Pressure or temperature compensation

No additional pressure or temperature compensation is required. This is a time and cost saving measure. No additional calculations or equipment are needed to calculate flow because the meter measures the mass flow rate. Some models offer a second 4-20mA output that can be programmed to measure temperature or flow.

Differential pressure flow meters require pressure and temperature compensation.

Turndown

Repeatability and exceptionally broad measurement range: up to 1000:1 (100:1 typical). Whether the flow is at a very high or low velocity, thermal mass flow meters can measure it.

Vortex meters are only suitable for very high flow rates.

DP meters do not have good turndown.

Pressure Drop

Low pressure drop. The pressure drop of a thermal mass flow meter is negligible.

If a DP meter is used to measure low velocity flow, a very small orifice is required resulting in high pressure drop. 

Moving Parts

No moving parts.

A meter with moving parts, like a Turbine meter, will need regular maintenance.

Price

Cost effective. Thermal mass flow meters offer a low cost alternative.

Ultrasonic meters are especially expensive.

Installation

Easy to install. Insertion (all Fox models) and inline (FT2A/FT3 models only) configurations. Insertion meters are easy to install, inline meters come equipped with flow conditioners to help reduce the straight run requirements. Communication options available and intrinsic to meter electronics.

Some meter technologies are complicated and difficult to install, require additional equipment, or long straight pipe run requirements.

Operation

Microprocessor based, field rangeable electronics. Fox pioneered the use of microprocessors in thermal mass flow meters and continues to create innovative solutions to measurement needs across many industries and applications. Gas-SelectX, available in some Fox models, allows the user to change the gas selection in the field. Displays with configuration panels and free software allow users to interact and program the meter in the field. Using the online Product Configurator, the customer can enter process data into the system for an instant Fox Product recommendation: no need to search a list of meters for the one that’s right for you!

Most manufacturers build meters for a single purpose, gas calibration, or application.  The customer must sift through pages of specs to find the right meter for their application. This is time consuming and ineffective.