FAM3200
| CI/FAM3200-EN Rev. B 11
6.2.5
Heat tracing
Trace heating may be used under the following conditions:
— The heat tracing must be installed in a way that ensures
there is no temperature increase in the indicator housing.
— The maximum permitted temperature of the heat tracing
must not exceed the permitted measuring medium
temperature.
— When using electrical heat tracing, attention must be paid
to potential functional impairment by electromagnetic
fields.
6.3
Operating conditions
A variable area flowmeter is specified for a defined set of
operating conditions of the measuring medium. For liquids and
gases, these are pressure and temperature-related properties
(density and viscosity) under operating conditions.
For gases, in particular, this means operating at a specific
operating pressure and operating temperature. The specified
accuracy of the device always refers to the operating
conditions underlying the specification.
6.3.1
Pressure loss
The available operating pressure at the measuring point must
be higher than the pressure loss listed for the flowmeter in the
specifications.
It is important to also consider the pressure loss downstream
from the flowmeter due to losses in the piping and other
fittings.
For information on pressure loss, see chapter "Measuring
range table" on page 17.
6.3.2
Prevention of compression oscillations when
measuring gases
With low flow amounts and low operating pressure, so-called
compression oscillations of the float can occur.
If the maximum upstream pressure listed in the specifications
is not reached, the flowmeter can optionally be equipped with
a mechanical float damper.
Damping is available for the device types FAM3225 and
FAM3255 with a process connection size > 1/4".
To prevent self-generated compression oscillations, note the
following information from VDI / VDE 3513 Sheet 3:
— Select a flowmeter with the lowest possible pressure loss.
— Minimize the piping length between the flowmeter and the
closest up or downstream throttling location.
— Restrict the usual measuring range from the usual
10 … 100 % to 25 … 100 %.
— When setting the flow rate value, always start assuming
larger values.
— Increase the operating pressure and consider its effect on
the flow rate values due to the change in gas density at
the new operating conditions.
— Minimize
non-throttled,
free volumes upstream and
downstream of the device.
6.3.3
Pressure shocks
Especially when measuring gases, it is possible that pressure
or shock waves can occur when fast opening solenoid valves
are employed and the piping cross-sections are not throttled,
or if there are gas bubbles in liquids.
As a result of the sudden expansion of the gas in the piping,
the float is forcibly driven against the upper floatstop.
Under certain conditions, this can lead to destruction of the
device.
The mechanical float damping is not suitable for the
compensation of pressure shocks!
