“F” IS FOR FLOWRATE!

Do you know what I mean?Do you know, know what I mean?

("Do You Know What I Mean," Lee Michaels, 1971)

F IS FOR FLOWRATE! ... HOW THE PV FLOWRATE IS SHOWN ON P&IDs and PFDs

Brilliant PTOA Readers and Students ... meaning those who are reading the PTOA Segments in the intended, sequential order ... just learned the definition of Flowrate in PTOA Segment #233.

"Flowrate" identifies how fast a fluid flows through the Piping Network in a processing facility.

Way back in PTOA Segment #11, PTOA Readers and Students were introduced to ISA symbols which appear on Process Flow Diagrams (PFDs) and Piping and Instrumentation Diagrams (P&IDs).

Thus, brilliant PTOA Readers and Students already know that PV Temperature-related control hardware is delineated with a "T" and PV Pressure-related control hardware is delineated with a "P."

Ergo, no PTOA Reader or Student will be surprised to learn that PV Flowrate-related control hardware is delineated with an "F"!

"Flow" does not tell the whole story. "Flowrate" defines how fast a gas, liquid, or multi-phase flow is moving through a distance of pipe. The Flow-Through Area of a Pipe is the same as the Area of a Circle with an internal Pipe Diameter=D (and thus Radius = D/2).

Yep, "F is for "Flowrate!"

Be aware: "Flowrate" is often erroneously truncated to just the word "Flow." Most commonly, "Flowrate Meters" are truncated to "Flowmeters."

"Flow" without "rate" does not inform the Process Operator how fast the volume or mass of fluid is moving through the pipes in a unit of time and thus predicting when the fluid will arrive at its intended destination. The PV Flowrate is the only Process Variable that is divided by a unit of time.

The nearby chart depicts ISA Tag symbols for a variety of hardware used in process monitoring and control.

At the bottom of the chart is the ISA symbol for FIC 55 (Flow Indicating Controller for Flow Control Loop #55). The leading "F" indicates the Process Variable of interest is Flowrate.

The function of the device is revealed by the middle letter of the Tag Name, I = Indicating.

The third and final letter of the instrument Tag Name identifies the type of instrument. In this case C=Controller.

The solid line drawn across the bubble at the mid-point reveals that FIC 55 is board-mounted and can be found in a control panel/DCS in the Control Room.

An ISA symbol "FT" might be representing the Foxboro 13A dp cell Transmitter shown in the photo.

Note that the top part of the chart has three vertical columns of ISA symbols.

The middle column contains the following Field Mounted PV Flowrate ISA symbols:

FI, a Flowrate Indicator
FT, a Flowrate Transmitter
FR, a Flowrate Recorder
FC, a Flowrate Controller

The nearby photo of a Foxboro 13A pneumatic Delta P Transmitter is a Real Word example of what an "FT" in a blank bubble (no line) on a P&ID would look like. This PV Flowrate Transmitter is not located in the Control Room but rather with the pumps and pipes out in the processing area.

In a real P&ID, the blank bubble would have a number indicating which Flow Loop the FT belongs to.

FT = Flowrate Transmitter. FC=Flowrate Controller. FY=Flowrate Transducer. FV=Flowrate Control Valve.

Many thanks to Instrumentation Tools for use of their Liquid Flowrate Control Loop schematic. This nearby schematic features a PV Flowrate Control Loop drawn according to ISA nomenclature.

PTOA Readers and Students were introduced to the modes of automatic control signal transmission way back in PTOA Segment #14.

The nearby Line Symbols chart illustrates the ISA symbols used for control signal transmission.

Prior to decoding the PV Flowrate Control Loop in the diagram, PTOA Readers and Students should also review the difference between "transduction" and "conversion" which was recently featured in PTOA Segment #230.

Decoding the nearby PV Flowrate Control Loop yields the following information:

The 4-20 mA signal (or voltage) appears as a dashed line on a P&ID. The 3-15 psi pneumatic signals is a line with evenly spaced double hash marks on it.

Liquid is discharged from a Centrifugal Pump and flows into a (turbine-style) PV Flowrate Detection/Measurement Device. Older versions of a P&ID would label the turbine-style Flowrate Detection/Measurement device as "FE" for "Flow Element" in a clear bubble.
The output from the Flowrate Detector/Measurement Device is transduced by the Flow Transmitter (FT) into an output 4-20 mA signal.
The FT's 4-20 mA Output Signal is transmitted to a Board-Mounted Flow Controller (FC) located in the Control Room. Note: The Output Signal from the FT is the Input Signal to the FC.
The function of the FC is to compare a pre-set PV Flowrate Set Point value to the 4-20 mA input signal. The 4-20 mA Output Signal from the FC will be whatever is needed to adjust the Detected/Measured Flowrate to the PV Flowrate Setpoint value.
A Flow Transducer (FY) transduces the 4-20 mA Flowrate Controller Output Signal into a pneumatic 3-15 psi signal.
The Flowrate Control Valve (FCV) is incompletely labelled in the graphic as FC. This Valve IS NOT an on-off Valve; the FCV will open up a little more or close down a little more depending upon what the transduced Output Signal from the FC has determined is needed to attain the PV Flowrate Setpoint.

Guess what?

The components and functions of a simple Automatic PV Flowrate Control Loop were just described.

The upcoming PTOA Focus Study featuring the Detection, Measurement and Transmission of the PV Flowrate will more thoroughly explore the automatic instrumentation technology used to control industrial processes.

TAKE HOME MESSAGES: F is for Flowrate! P&IDs and Process Flow Diagrams will delineate automatic instrumentation used for the PV Flowrate with the leading letter "F."

PTOA Readers and Students were introduced to the functions of the hardware used in a simple Flowrate Control Loop.

PTOA PV FLOWRATE FOCUS STUDY AREA
PV FLOWRATE FUNDAMENTALS

You need to login or register to bookmark/favorite this content.