Home » Flow Standards
Flow Measurement

Flow Standards

Most forms of continuous flow measurement are inferential; that is, we measure flow indirectly by measuring some other variable (such as pressure, voltage, or frequency) directly. With this in mind, we may usually achieve reasonable calibration accuracy simply by calibrating the primary sensor and replacing the flow element (if inspection proves necessary).

In the case of an orifice plate used to measure fluid flow rate, this would mean calibrating the differential pressure transmitter to measure pressure accurately and replacing the orifice plate if it shows signs of wear.

In some cases, though, direct validation of flow measurement accuracy is needed. Most techniques of flow rate validation take the form of measuring accumulated fluid volume over time. This may prove to be complicated, especially if the fluids in question are hazardous in any way, and/or the flow rates are large, and/or the fluid is a gas or vapor.

For simple validation of liquid flow rates, the flow may be diverted from its normal path in the process and into a container where either accumulated volume or accumulated weight may be measured over time. If the rate of flow into this container is constant, the accumulated volume (or weight) should increase linearly over time.

The actual flow rate may then be calculated by dividing the change in volume (ΔV ) by the time period over which the change in volume was measured (Δt). The resulting quotient is the average flow rate between those two points in time, which is an approximation of instantaneous flow rate:

liquid flow rates

If a suitable vessel exists in the process with level-measuring capability (e.g. a liquid storage vessel equipped with a level transmitter), you may apply the same mathematical technique: use that vessel as an accumulator for the flow in question, tracking the accumulated (or lost) volume over time and then calculating ΔV/Δt .

The accuracy of this technique rests on some additional factors, though:

  • The accuracy of the level transmitter (as a volume measuring instrument!)
  • The ability to ensure only one flow path in or out of that vessel

The first condition listed here places significant limitations on the flow calibration accuracy one can achieve with this method. In essence, you are using the level instrument as the “test gauge” for the flow instrument, so it needs to be high-accuracy in order to achieve even reasonable accuracy for the flowmeter being calibrated.

A more sophisticated approach for direct flow validation is the use of a device called a flow prover. A “flow prover” is a precision piston-and-cylinder mechanism used to precisely measure a quantity of liquid over time.

Process flow is diverted through the prover, moving the piston over time. Sensors on the prover mechanism detect when the piston has reached certain positions, and time measurements taken at those different positions enable the calculation of average flow (ΔV/Δt ).

Articles You May Like :

What is Orifice Flow Meter ?

Flow meter Turndown Ratio

V Cone Flow Meter Principle

Oval Gear Flow Meters

Intrusive & Non-intrusive

Related Articles

Basics of Ultrasonic Flow meters & Factors Affecting its Performance

S Bharadwaj Reddy

Impeller Flow Sensor Working Principle Animation

S Bharadwaj Reddy

Wedge Flow Meter Principle

S Bharadwaj Reddy

Coriolis Mass Flow meter as a Multi Variable Transmitter

S Bharadwaj Reddy

Magnetic Flow Meter Animation

S Bharadwaj Reddy

What is Differential Pressure Flow meter?

S Bharadwaj Reddy

Leave a Comment

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

Flow Standards

Send this to a friend