Mass flow meters and controllers measure flow rate in units of mass or volume per units of time (e.g., pounds per minute). They contain integral electronics are designed for use with gases, liquids, steams, or slurries. In processing applications, accurate and reliable mass flow measurement is an important part of material balance determinations and recipe formulations. When selecting flow metering products, buyers need to specify the type, media, and pipe diameter as well as performance criteria and features.

Product Types

The Engineering360 SpecSearch database provides information about two main types of mass flow meters and controllers: thermal meters and Coriolis meters.

• Thermal meters use a heated sensing element isolated from the fluid flow path. The flow stream conducts heat from the sensing element. The conducted heat is directly proportional to the mass flow rate.

• Coriolis meters pass fluid through a small vibrating flow tube. The resulting deflection of the tube is proportional to the mass flow rate of material.

Suppliers may also designate products as ultrasonic, magnetic, ultrapure, or hygienic.

Specifications

The performance of a mass flow meters and controllers is a function of turndown ratio, the device's effective dynamic or operating range. For example, a 500-SCCM flow rate device with a turndown ratio of 50:1 will operate effectively and resolve flow down to 10 SCCM. Devices with a turndown of 100:1 will resolve effectively to 5 SCCM.

When comparing products, buyers should also note the operating temperature, operating pressure, and media temperature. Depending upon the media measured, gas volumetric or liquid volumetric flow rate may apply. Both are measured in volume/time. With solid, the rate of flow is measured in mass/time.

Mounting Types and End Fittings

Mass flow meters and controllers have three different mounting styles and use various end fittings.

• In-line devices are installed directly in the process line. They have a variety of end fittings, including flanges, threads, and compression devices.Typically, in-line flow metersrequire a straight run of pipe for installation.
• Insertion devices areinserted perpendicular to flow path. They usually require a threaded hole in the process pipe or another means of access.
• Non-invasive flow meters do not require mounting directly in the process flow, and can be used in closed piping systems. Ultrasonic flow meters such as Doppler devices may use this type ofmounting to read the flow through the pipe.

In addition to the end fittings mentioned above, devices may use clamps, tube ends or hose nipples, and VCO® or VCR® connections (Swagelok).

Features and Interface Options

Some mass flow meters and controllers can measure density, levels, or temperature. Product features also include audible or visual alarms, flow rate averaging, and recorder or totalizer functions. Typically, programmable devices have a built-in microprocessor. For medical, pharmaceutical, and food processing application, buyers should choose mass flow meters that are designed for use in sanitary environments.

In terms of interface options, mass flow meters can provide signal outputs in serial, parallel, Ethernet and other network formats. Supplier datasheets typically indicate whether industrial Fieldbus protocols such as CANbus are supported.

References

Flow and Level Measurement - Mass Flowmeters

Coriolis Mass Flowmeters

Image credit:

Brooks Instrument