Siemens SITRANS FC430 Operating Instructions Manual page 226

Diagnosing and troubleshooting
10.3 Operation troubleshooting
Vibrations / cross talk have a greater or lesser effect upon the zero point stability and therefore
also the measurement accuracy.
1. Check whether there are vibrations.
Turn off the pump and check whether the zero point stability improves, that is if the flowrate
fluctuation in kg/h is reduced.
If the sensor is disturbed by vibration from the pump or by pressure pulsations, the
installation should be improved or the pump should be exchanged, for example to another
type.
2. Check for cross talk.
Turn off the power to the other flow meter(s) and wait approximately 2 minutes, so the
vibrating tubes in the sensor have stopped vibrating. Then check if the zero point stability
has improved, that is that the fluctuation in kg/h has been reduced. If this is the case, the
sensors disturb one another and the installation should be improved.
Air in the liquid
When air is present in the liquid, the zero point becomes unstable, which leads to a poor
measurement accuracy.
Checking for air:
● Check the Driver Current (View → Device Diagnostics → Advanced Diagnostic)
● Check if the Driver Current varies more than ±1 mA. If this is the case, it is usually due to
the presence of air or gas bubbles in the liquid.
● Increase the pressure in the sensor, creating a large back pressure upon the sensor by
reducing the opening of the outlet valve or by increasing the pump pressure. Thereby the
size of air bubbles inside the sensor will be minimized. If the Driver Current value increases
and/or the stability of the Driver Current decreases, it is proof that the liquid contains air or
gas bubbles.
Typical causes of air in the liquid
● The entry pipe and sensor have not been properly filled with liquid.
● The pump cavitates, the rotary speed of the pump is too high in relation to the supply of
liquid to the pump.
● The flow rate in the pipe is too high, so components sitting in front of the flowmeter can
cause cavitation.
● If there is a filter installed before the flowmeter, it may be close to blocking, which also can
cause cavitation.
● Liquid flashes to vapor bubbles while passing through partially open valves or orifices.
● The piping on the pump suction side, pump gaskets or the pump itself is not tight. Air gets
sucked into the system due to a low pressure on the pump suction side.
● The piping on the pump suction side, pump gaskets or the pump itself is not tight. Air gets
sucked into the system due to a low pressure on the pump suction side.
Solid particles in the liquid
If the solid particles in a liquid have a density higher than that of the liquid, they can precipitate
inside the sensor and cause instability which leads to a measurement error.
226
FC430 (From firmware 4.0)
Operating Instructions, 06/2017, A5E39789392-AA