Siemens SITRANS FC430 Operating Instructions Manual page 192

Troubleshooting/FAQs
12.2 Troubleshooting sensor-related problems
As can be seen, in this case it is not so important that the standard deviation is 1 kg/h. The error
due to the zero point is only 0.1% for a flowrate of 1000 kg/h, and even less for a higher flowrate.
So for this installation with the given flowrate and zero point error (Zero Point Standard
Deviation value), you should typically choose not to spend more time finding ways to
improve the application.
Step 4: Improving the application
In the following it is described how to find the causes of a high Zero Point Standard Deviation
and how to improve the installation.
Setting Low Flow Cut-Off
In order to see if the zero point becomes more stable when making changes / adjustments,
the Low Mass Flow Cut-Off (MassFlowCutOff) must be set to 0.0 kg/s.
When Low Flow Cut-Off has been set, it is possible to see the instability directly from the
massflow in the online window ("View → Process variables")
This information can be used to troubleshoot. For example, tightening the brackets which
hold the sensor, or turning off the pump to check if vibrations from the pump are disturbing
the sensor, etc.
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
flow meter, 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.
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Operating Instructions, 05/2015, A5E03361511-AF
FC430 with HART