Siemens SITRANS FC410 Operating Instructions Manual page 89

Calculating the measurement error
Given the Zero Point Standard Deviation, the error expected for different flow rates can be
calculated, without performing time-consuming measurements. So using this formula, one
can assess if the application can be used as–is, or whether to use more time improving the
installation.
E
Where:
E
Z
Qm =
Example 1: Low flow application
● DN 15 sensor. The sensor's nominal flowrate is specified to 3700 kg/h
● Zero point error (Zero Point Standard Deviation) value is specified as 0.2 kg/h
● Flow: Min. 10 kg/h - Max. 100 kg/h
After the zero point adjustment, the Zero Point Standard Deviation value 'Z' is read as 1 kg/h,
that is 5 times greater than that specified for the sensor.
The error for a flowrate of 10 kg/h is estimated as:
● E = 1 kg/h x 100% / 10 kg/h = 10%.
For a flowrate of 100 kg/h the error is estimated as:
● E = 1 kg/h x 100% / 100 kg/h = 1%
For this application it is necessary to investigate more closely what the cause of the relatively
high Zero Point Standard Deviation value is, in order to establish what needs to be done to
improve the measurement accuracy.
Example 2: High flow application
DN 15 sensor. The sensor flowrate is specified as max. 3700 kg/h
● The zero point error/ Zero Point Standard Deviation value is specified as 0.2 kg/h
● Flowrate: Min. 1000 kg/h - Max. 3000 kg/h
After the zero point adjustment, the Zero Point Standard Deviation value 'Z' is read as 1 kg/h,
that is 5 times greater than specified for the sensor !
The error at a flowrate of 1000 kg/h is estimated as:
● E = 1 kg/h x 100% / 1000 kg/h = 0.1%
At a flowrate of 3000 kg/h the error is estimated to be:
● E = 1 kg/h x 100% / 3000 kg/h = 0.03%
In all of the above examples, the linearity error of ±0.1% must be added to the calculated
error.
FC410 with Modbus
Operating Instructions, 02/2016, A5E33120874-AC
= Z x 100 % / Qm
= measurement error in % of flowrate
= zero point standard deviation value in kg/h
current flowrate in (kg/h)
Troubleshooting/FAQs
10.2 Troubleshooting
87