low transmitters vary in terms of operating conditions, flow range parameters, performance measurements, and optional features. Operating conditions include maximum operating pressure, fluid temperature range, and operating temperature.
Measured in pounds per square inch (psi), operating pressure is the maximum head pressure that flow transmitters can withstand.
Fluid temperature range, a function of construction and liner materials, is usually measured in degrees Fahrenheit; however, metric devices are commonly available. Flow range parameters for flow transmitters include velocity flow rate range, volumetric flow rate range, and mass flow rate range.
- Mass flow rate is the range of flow in mass/time. The specification applies to mass flow sensors and meters.
- Velocity flow rate range is the range of flow in distance/time. This specification applies to velocity flow sensors and meters.
- Gas volumetric flow rate range is the range of flow in volume/time. This specification applies to volumetric flow sensors and meters for gases.
Performance measurements include the maximum pressure drop for media traveling through the device. A meter’s performance can be determined by its turndown ratio. Turndown ratio is the effective dynamic or operating range of the flow meter. For example, if a 500 SCCM flow rate device has a turndown ratio of 50:1; it will operate effectively and resolve flow down to 10 SCCM. If the same device has a turndown of 100:1, then it will resolve effectively to 5 SCCM.
Generally, the type of flow meter determines available features. Some flow transmitters can measure temperature or density. Others measure fluid levels.