Siemens SITRANS FC410 Operating Instructions Manual page 72

Functions
7.2 Zero point adjustment
Automatic zero point adjustment
The device measures and calculates the correct zero point automatically.
The automatic zero point adjustment of the flowmeter is set by the following parameters:
● Duration (Modbus address 2135)
● Start Zero Point Adjustment (Modbus address 2180)
When zero adjust is initiated by selecting Start Zero Point Adjustment, the massflow values
are acquired and totalized for the configured period (Duration). The default zero point
adjustment period (30 s.) is normally sufficient for a stable zero point measurement.
Note
Extremely low flow quantity
If the flow quantity is extremely small, extremely precise measurement is necessary. In this
case, a long zero point adjustment period can be selected for improved zero point
adjustment.
Zero point calculation
During zero point adjustment, an average value is automatically calculated using the
following formula:
Zero Point Offset Value
Average of N flow values
The offset value must be within the determined Zero Point Offset Limit (Modbus address
2140).
Note
Exceeded zero point offset limit
If the offset value is greater than the configured limit, proceed as follows:
• Check that the tube is completely filled and that the flowrate is absolute zero.
• Check the validity of the configured zero point offset limit.
• Repeat the zero point adjustment.
70
x is an instantaneous flow value sampled in
i
the time domain
N = Number of samples during zero point
adjustment
Operating Instructions, 02/2016, A5E33120874-AC
FC410 with Modbus