Siemens SITRANS F Series Operating Instructions Manual page 96

Diagnostics and troubleshooting
9.4 Inspect the application (A2)
Application inspection examples
The following examples, possible causes and suggestions for corrective action may give the
answer to why the flow measurement is inaccurate, unstable or not possible.
Installation problem
Sensors installed too close to a pipe el‐
bow, Tee fitting, expansion, throttling
valve or partially open ball or butterfly
valve.
Excessive use of ultrasonic couplant on
small pipes.
Operation under conditions involving
elevated fluid temperature or suddenly
changing temperature.
Ungrounded transmitter enclosure
96
Possible impact
There will likely be a significant impact
on the measurement accuracy. In ex‐
treme cases, flow measurement will not
be possible due to the extreme turbu‐
lence. Flow instability is likely to occur
with poor upstream pipe conditions.
Poor SNR (signal to noise ratio) may re‐
sult to excessive use of couplant, espe‐
cially on small pipes with relatively thick
walls.
Unstable or intermittent operation due to
poor SNR and high amplifier gain may
result from a large temperature gradient
inside the sensor.
Increased susceptibility to external elec‐
tronic EMC noise may result in unstable
flow measurement.
Remedy
● Install the sensors in a different
location with sufficient straight run
conditions, especially upstream.
● Install sensors in the preferred
reflect "V" configuration, if at all
possible.
● Install 2 paths to minimize the impact
on accuracy.
● For pipes <DN50, use only a thin
layer of couplant (< 1mm),
especially when the pipe surface is
very smooth.
● Evaluate the Rx signal and SNR first
with a moderate layer of couplant.
Remove couplant to see if the signal
improves.
● Consider applying insulation over
the pipe / sensor installation to
reduce the temperature gradient
inside the sensor.
● Consider the use of FS200 High
Temperature sensors.
● Ensure that the transmitter housing
is properly grounded using the
earthing clamp.
SITRANS FST030 (Modbus)
Operating Instructions, 08/2018, A5E37367739-AD