Flowmeter Selection

Overview

Engineering reference data for Flowmeter Selection in process control.

Key Formulas

PID Controller

$u(t) = K_p e(t) + K_i \int e(t)dt + K_d \frac{de}{dt}$

Proportional-Integral-Derivative control.

Transfer Function

$G(s) = \frac{K}{\tau s + 1}$

First-order system.

Variables

Symbol	Description	Unit
$K_p$	Proportional gain	—
$K_i$	Integral gain	1/s
$K_d$	Derivative gain	s
$\tau$	Time constant	s

Flowmeter Comparison

The following table provides a detailed comparison of common industrial flowmeter types, highlighting their operating principles, best-use scenarios, and performance characteristics.

Key Selection Criteria

Fluid Properties:

• Conductivity: Required for electromagnetic meters.
• Cleanliness/Presence of Solids: Dictates choice between intrusive (turbine, orifice) and non-intrusive (ultrasonic) types.
• Viscosity: Affects differential pressure (DP) meters (orifice, wedge) and turbine meters significantly.
• Phase: Most meters are for liquids; some (vortex, turbine, thermal mass) also handle gases and steam.

Performance Requirements:

• Accuracy: Mass flow meters (Coriolis) offer the highest accuracy. DP meters (orifice) have lower accuracy but are robust and inexpensive.
• Rangeability (Turndown): Electromagnetic and turbine meters offer the widest operating ranges.
• Permanent Pressure Loss: DP meters (orifice) inherently cause a pressure drop. Non-intrusive meters (electromagnetic, ultrasonic) have minimal loss.

Installation & Cost:

• Upstream Straight Pipe: Critical for DP and turbine meters to ensure a stable flow profile. Not required for Coriolis or thermal mass meters.
• Relative Cost: Electromagnetic and Coriolis meters are high-cost but high-performance. Orifice plates are low-cost but require more maintenance and calibration.

References

• Original Source