already in place, there also was limited straight run of pipe
available, which could create irregular fluid flow dynamics
(swirl) within the piping where the new flow meters were to be
After learning the flow meter performance and installation requirements, the FCI applications group recommended the ST98 Air/Gas Thermal Mass Flow Meter (Figure
1) with remote electronics. The plant team agreed, and the
vortex meters were removed from the two CUP buildings.
FCI then installed 16 new thermal flow meters on the 16
gas lines (eight in each building supporting 16 boilers total). A three-inch [75 mm] Vortab VIS flow conditioner was
also installed on each line to ensure optimum flow measurement under the limited straight-run conditions and to avoid
the high cost of relocating any equipment or piping.
Each thermal meter’s insertion probe was inserted directly in the natural gas line downstream from the flow conditioner (Figure 2). The team appreciated the meter’s simple
insertion probe type design for its low cost of installation.
With their no-moving parts design, the thermal mass flow
sensors are unaffected by the continuous vibration within
the pipes and require virtually no maintenance. Each me-
about 15 feet
away from the
the local dis-
plays would be
easy to view
by the plant
team and fur-
dispersion sensing technology, which provides accurate mass
flow measurement under difficult mechanical conditions.
Other volumetric based air/gas flow sensor technologies gen-
erally would have required additional separate temperature
and pressure sensors for the same mass flow measurement
with increased installed cost, maintenance requirements and
The FCI thermal dispersion sensing technology provides
direct mass flow measurement, using two thermowell-pro-
tected platinum RTD temperature sensors inserted directly
in the process stream (Figure 3). One RTD is heated while
the other RTD senses the actual process temperature. The
temperature differential between these two sensors generates
a voltage output signal, which is proportional to the media
cooling effect and is used to indicate the mass flow rate.
The FCI thermal dispersion technology meter also includes
built-in temperature compensation to ensure repeatable and
reliable measurement even with large changes in process
temperatures. The FCI constant current temperature compensation technology, adjusts automatically for accurate flow
measurement with changes in process temperatures including effects from seasonal changes, such as cold winters, hot
The plant team was satisfied with the meter’s accuracy of
± 1 percent of reading, ±0.5 percent of full scale, with repeatability of ±0.5 percent of reading. The meter includes a rugged, NEMA 4X/IP66-rated enclosure and is agency-approved
for installation in hazardous gas (Ex) locations including
combustible natural gas or biogases.
With the installation of the 16 new thermal dispersion meters on the gas lines feeding each boiler at the two CUP’s on
campus, the plant team was able to confirm the actual natural
gas flow rates were within its permitted usage levels. There
would be no discrepancy in reporting to the various governmental agencies that monitor the plant’s energy consumption
and environmental impact.
The plant team found the thermal dispersion meters provided accurate and reliable measurement within the industrial environment where high vibration was present inside
the CUP’s. The insertion style configuration combined with
the VORTAB flow conditioners made them easy to install on
the existing piping and required no retrofitting of equipment,
while also avoiding any accuracy problems that might have
been caused by the limited pipe straight runs in the CUP’s.
After more than a year, the plant team reports that the thermal dispersion meters continue to operate without any issues.
The plant team is considering thermal dispersion meters for
future air and special gas applications based on its experience with the meter’s direct mass flow technology.
Carl Wilmarth is senior engineer at La Tech Equipment.
Steve Cox is senior applications manager for Fluid Components International.
Fig 2. Installed ST98 and Vortab Flow Conditioner
Fig 3. Theory of Thermal Dispersion