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Pump
Close
valves
Close
valves
720TRD
RTD Probe
Fluid
stream
Fluid
stream
7.21psi
30V
24mA
MAX
V
mA
COM
F1
F2
F3
ZERO
PRESSURE
CALIBRATOR
721
To get started, isolate the flow computer from the pipeline. It is normally in-
stalled with a 5 valve manifold. If so, closing the valves on the pipeline side
of the manifold should isolate it. Be sure to follow local policy and safety
procedures when performing this isolation step. Set the P1 sensor of the
721 to measure inH20 and the P2 sensor to measure PSI and the tempera-
ture sensor to measure degrees Celsius or Fahrenheit as needed.
Low pressure differential pressure calibration
is performed using
atmospheric pressure as a low side reference. Vent the low connection
of the flow computer or pressure transmitter and connect the high pressure
connection of the flow computer or transmitter to the low pressure port (P1)
on the calibrator.
Connect the computer (PC) to the flow computer serial or USB port. The PC
will instruct the user to apply one or more test pressures to the flow com-
puter or transmitter. For example, 0, 100 and 200 inH20. Squeeze the pump
to get close to the test pressure and use the vernier or fine pressure adjust
to dial in.
Static pressure calibration
will normally be applied to either the same
high pressure port of the flow computer or both the high and low pressure
ports. Refer to the manufacturer’s instructions for details. Connect the high
pressure sensor input (P2) to the appropriate port on the flow computer or
transmitter and to the high pressure test source. The PC will instruct the
pressures for the user to apply from the pressure source.
Temperature calibration
of the temperature measurement on the flow
computer is done with a single temperature point at the pipeline operating
temperature. Insert the RTD probe into the test thermowell and allow time
for the measurement to stabilize.
The PC will prompt the user to enter the temperature measured by the
calibrator. Remove the RTD from the test thermowell and the calibration is
complete.
Flow Computers with 4 to 20 mA inputs:
Many flow computers utilize a
low pressure, static and temperature transmitter to convert the measured
parameters into 4 to 20 mA signals. In this instance these transmitters may
need individual calibration if the test results are not satisfactory (see HART
Transmitter Calibration application note or video for more details). Anoth-
er source for errors in this configuration is the input A/D cards of the flow
computer. These can be independently tested using a mA signal source
from a loop calibrator.
STEP
1
STEP
2
STEP
3
STEP
4
To perform the test:
•
Always center the vernier
of your hand pump before
starting any pressure
calibration. This will allow
you to increase or decrease
the pressure when making
fine adjustments.
•
Store the temperature
probe in a protective
case such as the built in
slot of the 721 soft case.
Exposing the RTD probe
to mechanical stress can
reduce the measurement
accuracy of the probe.
• Be careful to not connect
the P1 low pressure
side of the calibrator
when doing high
pressure calibrations
or measurement or the
sensor will be damaged
and possibly rupture
creating a dangerous
condition.
•
Inserting the RTD probe
prior to the pressure
calibrations typically
allows sufficient time to
reach a stable temperature
measurement.
Additional resources
For more in depth information
about this application check out
these videos and application notes
from Fluke.
HART pressure and HART
smart RTD transmitter
754 videos
Custody Transfer calibration
application note
HART transmitter calibration
TECH
TIPS
35
Pressure Applications