# Pressurebased flowmeter calculations

## Instrumentation and Process Control

• #### Question 1

A Pitot tube measuring the flow of glycerin (78.6 lb/ft$^{3}$) produces a differential pressure of 35 inches W.C. at a mass flow rate of 450 pounds per minute.

Calculate the differential pressure produced by this same Pitot tube at a flow rate of 310 lb/min.

Calculate the mass flow rate at a differential pressure of 12.6 “WC.

If the glycerin density happens to change from 78.6 lb/ft$^{3}$ to 75.1 lb/ft$^{3}$, calculate the mass flow rate at a differential pressure of 24.8 “WC.

• #### Question 2

A pneumatic DP transmitter measures the flow of gasoline through a an orifice plate, using a separate square root extractor relay to characterize the signal so that it may be displayed linearly on the receiver gauge (FI-20):

Based on other flow-measuring devices in this process, operations personnel have determined the actual flow rate through this pipe is 158 gallons per minute. FI-20, however, registers a flow of 142 gallons per minute. Based on the data you see in this illustration, determine the location of the calibration error.

• #### Question 3

A pneumatic DP transmitter measures the flow of gasoline through a an orifice plate, using a separate square root extractor relay to characterize the signal so that it may be displayed linearly on the receiver gauge (FI-20):

Based on other flow-measuring devices in this process, operations personnel have determined the actual flow rate through this pipe is 171 gallons per minute. FI-20, however, registers a flow of 184 gallons per minute. Based on the data you see in this illustration, determine the location of the calibration error.

• #### Question 4

A smart’’ DP transmitter with built-in square root characterization is used to measure flow through a pipe. The orifice plate range is 0 to 125 inches WC at 0 to 277 gallons per minute:

A technician removes the transmitter from service and tests it by applying several air pressures to the H’’ port while leaving the L’’ port vented. Here are the As-Found results:

$$\begin{array} {|l|l|} \hline Applied Pressure (“WC) & Current signal (mA) \\ \hline 0 & 4.020 \\ \hline 31.25 & 12.060 \\ \hline 62.5 & 15.390 \\ \hline 93.75 & 17.946 \\ \hline 125 & 20.100 \\ \hline \end{array}$$

• #### Question 5

A smart’’ DP transmitter with built-in square root characterization is used to measure flow through a pipe. The orifice plate range is 0 to 125 inches WC at 0 to 277 gallons per minute:

A technician removes the transmitter from service and tests it by applying several air pressures to the H’’ port while leaving the L’’ port vented. Here are the As-Found results:

$$\begin{array} {|l|l|} \hline Applied Pressure (“WC) & Current signal (mA) \\ \hline 0 & 5.431 \\ \hline 31.25 & 12.127 \\ \hline 62.5 & 15.404 \\ \hline 93.75 & 16.128 \\ \hline 125 & 20.064 \\ \hline \end{array}$$

• #### Question 6

A smart’’ DP transmitter with built-in square root characterization is used to measure flow through a pipe. The orifice plate range is 0 to 150 inches WC at 0 to 480 gallons per minute:

Operations personnel have strong reason to believe that the actual flow rate through this pipe is 160 GPM, yet the DCS registers a flow rate of 182.4 GPM. Based on this information, determine the likely source of calibration error in this system. Also determine whether this transmitter has square-root characterization enabled or not.

Additionally, suggest a good next step’’ to perform to either pinpoint the location of this problem or correct it.

• #### Question 7

A smart’’ DP transmitter and orifice plate were recently installed to measure flow through a pipe. The orifice plate range is 0 to 150 inches WC at 0 to 1000 gallons per minute:

Operations personnel register a flow rate of 699 gallons per minute on the display of their DCS, which they believe to be too much. Based on what you see here, do you think there is a problem, or is this new system working as it should?