Siemens SITRANS FC330 Operating Instructions Manual page 193

Incorrect installation of the sensor
● Has the sensor been correctly installed, that is fastened to the floor / wall or frame with good
mounting brackets as shown in the instructions?
Especially for low flowrates, that is flowrates less than 10% of the maximum capacity of the
flowmeter, it is important that the sensor is correctly and stably installed.
If the sensor is not correctly fixed in place, the zero point of the sensor will change, leading to
measuring errors.
Try to tighten up the sensor brackets to see whether the flow instability is reduced.
Vibrations and cross talk
Vibrations in the pipe system are normally generated by pumps.
Typically, cross talk is generated by two sensors of identical size and positioned in close
proximity in the same pipe, or installed on the same rail or frame.
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.
SITRANS FC330
Operating Instructions, 01/2019, A5E44030648-AB
Diagnostics and troubleshooting
10.3 Operation troubleshooting
193