Siemens SITRANS FC410 Operating Instructions Manual page 91

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.
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.
If solid particles are present in the liquid, they must be homogeneously distributed and have
similar density as the liquid. Otherwise they can cause relatively large measurement errors.
It is important that the sensor is installed such that solid particles can easily run out of the
sensor.
1. Ensure that the sensor is installed vertically with an upwards flow.
2. Check if solid particles are present in the liquid:
Take a sample of the liquid, fill a glass and see if the solids precipitate.
FC410 with Modbus
Operating Instructions, 02/2016, A5E33120874-AC
Troubleshooting/FAQs
10.2 Troubleshooting
89