ABB FSM4000 Series, Руководство по эксплуатации

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100 FSM4000 ELECTROMAGNETIC FLOWMETER | OI/FSM4000-EN REV. E
… 8 Operation
… Additional information regarding use of enhanced diagnostic functions
Determining the signal-to-noise ratio
1
Signal from the sensor
2
Filtered signal
Illustration58:
Detect changes in the measuring medium, e.g., gas bubbles,
increased/reduced solid content.
To determine the signal-to-noise ratio (SNR), the electrode AC
voltage - raw signal for the sensor is set in relation to the
digitally filtered signal.
SNR =
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑣𝑣𝑣𝑣𝑣𝑣 𝑀𝑀𝐺𝐺𝐺𝐺𝐺𝐺𝑀𝑀𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝑀𝑀𝐺𝐺𝐺𝐺𝐺𝐺ℎ𝑣𝑣𝐺𝐺𝐺𝐺
The SNR is measured without impairing the flow measurement
in any way. To perform this calculation, you need to power-up
one of the relevant errors or a warning in the submenu
Diagnostics / Alarm Settings (see
Alarm Settings on page 85).
Determining the magnetic linearity
Figure 59
ML =
1 R 2
2 R 1
U I
U I
∗
∗
Detect magnetic field interference. This can affect the accuracy
of the measurement.
When measuring magnetic linearity (ML), the coil current I
1
is
measured at current reference voltage U
R1
and coil current I
2
at
approximately half the reference voltage U
R2
.
The operating time at half the reference voltage is approx. 1 sec.
During this period, the most recently acquired value is retained.
To perform this test, you need to power-up one of the relevant
errors or warnings in the submenu ‘Diagnostics / Alarm Settings’
(see
Alarm Settings on page 85).
Determining the maximum DAC value
Driver
Figure 60
For detecting changes in the coil circuit.
To compensate the set reference voltage U
ref
, the level of the
digital/analog converter (DAC) value is manipulated in the
transmitter driver circuit to vary the excitation signal of the coil.
The amplitude of this value then serves as an indicator of the
level of the excitation signal.
The DAC value is measured without affecting the flow
measurement in any way.
To perform this measurement, you need to power-up one of the
relevant errors or a warning in the submenu ‘Diagnostics / Alarm
Settings’ (see
Alarm Settings
on page 85).